Nonsurgical endodontics is the only dental discipline where the dentist cannot simultaneously see and do treatment.

The mechanics of endodontics are performed in a dark and often lonely space. This unknowingness of “drilling into a patient’s head” is nerve-racking, unsettling, fearful, and one of dentistry’s biggest stressors. However, according to the Greek philosopher Heraclitus, “The only constant in life is change,” and today, innovative change is aiding dentists in reducing the anxiety of doing endodontics. This article reviews 9 recent-past, present, and future innovations that are transforming endodontics to be easier and more predictable. What this means to us as dentists is more confidence, consistency, and control during the endodontic experience. When this is all added up, endodontics begins to change from fear to fun!

WHAT IF?

“Humans are the only animals that build machines.”¹ 

By doing so, we expand our capacities beyond our biological limits. Tools turn our hands into more versatile appendages. Innovations are indirectly and directly enabling dentists to have proof that we have successfully cleaned, shaped, and obturated the root canal system. Mechanical endodontic shaping systems now create specific radicular preparations with extreme accuracy even though we cannot directly inspect the preparation itself. Microscopes and 2D and 3D digital imaging currently permit dentists to see the previously unseen. Every day, new devices intended to improve 3D irrigation, agitation, and cleaning flood the endodontic market with a “mine is better than yours” mantra. New innovations may tell the 3D cleaning truth. Soon, we will be able to detect tooth cracks and restorative micromovements previously invisible through visual or symptom-duplicating tests. This breakthrough innovation alone would provide early detection and immediately reduce potential catastrophic restorative consequences.  

Since endodontics was recognized by the ADA as a specialty in 1964, endodontists, engineers, inventors, and dental companies have been innovating to improve root canal system cleaning; preparing a solid root canal system replacement; and, in effect, produce an impervious endodontic seal.²

The oral cavity has an astonishing 40 billion bacterial inhabitants. It could only take a few million of them to feed and flourish off of nutrient-latent diseased endodontic anatomy contents to enable them to emanate from uncleaned and/or underfilled root canal system portals of exit (POEs) and cause an endodontic failure.

The purpose of this article is to examine what is in the near-past, present, and future horizon of humans building machines for inventing safer, easier, and more predictable endodontics. My disclaimer is the observations of these innovations are my own. As I have said to my audiences in the past, “The best education in the world is your own.” I invite the reader to thoroughly test and research my innovation evaluations and see if they fit for you. We are all different. All of us have a different mix of patients, different skill levels, practice different styles, and are at a different stage of our practice life.

1. What if detecting cracks in teeth or micromovement of existing tooth restorations without directly seeing them was possible?  

Every dentist has experienced the challenge of diagnosing breakdowns in teeth and implants. For example, a major reason clinicians have trouble diagnosing cracks in teeth and the elusive “cracked tooth syndrome” is having to rely on visual and clinical assessments, which simply do not pinpoint the diagnosis. Identifying cracks early in the “crack or restoratively damaged cycle” has been evasive as root cracks and restorative gaps most often begin as microns of separation and are not visible on radiographs, digital scans, CBCT, photographs, or clinical examination until later. Often, it is too late in the “crack or gap cycle” to restore the tooth. In addition, and most significantly, current diagnostic aides provide data about a tooth during a static moment in time when teeth are at rest vs dynamic movement. 

InnerView, a new diagnostic aide that is getting close to being released by Perimetrics, Inc, takes an engineering approach to evaluating the structural stability of teeth and implants. Using quantitative percussion diagnostics (QPD), gentle tapping on the facial side of a tooth allows a rod sensor to measure the amount of energy returned to the sensor with each tap. The information indicates if there are any oscillations in the tooth as measured by a sensor in the testing rod during the light impact. The more oscillations, the less structurally sound the tooth and the greater the probability that there is a crack in the tooth or breakdown in existing restorations. QPD testing simulates what happens when the patient is using his or her teeth during chewing or other parafunctional habits.³

Perimetrics has one of the largest databases in the world of damaged (cracked) teeth. Cracks are referred to as microgap defects (MGDs) and have more than 28 peer-reviewed publications about this revolutionary technology in dental, engineering, and science journals. It takes only 3 minutes to test an entire mouth and collect immediate results and only 3 seconds to test an individual tooth. 

We will be using our teeth longer than ever needed before in human history. Therefore, the requirement for this type of diagnostic instrument is growing exponentially. Humans are living longer, and we want our teeth in order to look good, smell good, feel good, and be successful. The rough estimate is that humans have 1 million significant teeth loading repetitions per year.⁴ This means that, for a 60-year-old “pounding” on permanent teeth for 50 years, his or her teeth have experienced 50 million impacts to date! It is no surprise teeth break and crack. Stay tuned to the InnerView System of locating MGD’s from cracks and failing restorations. This invention promises to change the way we see dentistry for years to come (Figure 1).

Figure 1. (a) InnerView device (Perimetrics) in clinical use. (b) Cordless handheld

2. What if, seeing chairside evidence, your cleaned, shaped, and conefit root canal system preparation is 3D cleaned of any pulp, nerve tissue, apical fluid, blood, and/or bacteria?  

The purpose of endodontics is to prevent or heal lesions of endodontic origin (LEOs). The rationale of endodontics is that nature has the capacity to prevent or heal these LEOs 100% of the time if the root canal system has been eliminated as a source of endodontic disease.^4,5 For several years, there has been a raging debate that “My instrument cleans root canal systems better than yours.”  In the past, there has been little comparative proof for these claims. A soon-to-be-released chairside device called the Endocator  claims to quantify in 10 seconds how clean the root canal system is and give chairside feedback about the effectiveness of your shaping system, disinfection protocol, and activation.⁶ The device promises to tell the accuracy of the patient’s root canal cleanliness (cellular debris). Operating on a multi-biomarker detection mechanism, the most pivotal of which is adenosine triphosphate (ATP), the Endocator boasts universal applicability. ATP’s ubiquity in every living organism renders this instrument suitable for vital, nonvital, and retreatment endodontic patients (Figure 2). 

Figure 2. Endocator chairside biomarker.

3. What if seeing proximal caries 20% more accurately with RVG sensors and minimizing metal artifacts in CBCT scans were both already available?

Diagnosing interproximal caries at the earliest possible stage is key to taking advantage of minimally invasive restorative techniques. Radiographs, whether they are analog or digital, typically do not accurately show interproximal caries until the caries penetrate 30% to 40% of the enamel. Carestream Dental offers Logicon caries detector software used with RVG intraoral sensors to aid dentists in accurately predicting interproximal caries in enamel and dentin.^7,8 We are now also seeing a new wave of products that are using artificial intelligence (AI) technology to help us read radiographs. All of these products will surely revolutionize our diagnostic capabilities.

Metal in CBCT scans can cause scatter, which can make it difficult to identify and diagnose pathology or the restorative foundation status. In endodontic retreatment, metal scatter often makes it impossible to unravel if the metal is a post, silver cone, or even the outline of a crown. Carestream Dental provides a novel innovation to solve this situation. It is called the Metal Artifact Reduction (MAR) algorithm—CS MAR—and is available with its CBCT systems, such as the CS 9600, CS 8200 3D, and CS 8100 3D, which assists practitioners in applying the algorithm before or after taking the scan. Carestream Dental’s software allows the user to toggle between the CBCT scan and the CS MAR filter while reducing the risk of missing filtered-out structures (Figure 3). 

Figure 3a.

Figure 3b.

Figure 3c.

Figure 3d — Figure 3. (a) Carestream Dental 9600. (b) Bite-wing of a maxillary right first molar without Logicon (Carestream Dental). Note, distal caries is vaguely perceived. There is no radio- graphic evidence of mesial caries. (c) The Logicon closeup (red markings), however, clearly outlines easily missed distal caries as well as previously unperceived mesial caries. (d) Left image metal scatter camouflages the mesial incisal fracture and discriminating anatomy around the post of this lateral incisor. The right image reveals improved Metal Artifact Reduction clarity.

4. What if we were able to capture and see 3D imaging at chairside? 

Three-dimensional chairside imaging units now give dentists more data than 2D ones without the patient leaving the operatory. Seeing 3D images at chairside could be like having superhero eyes. 

The innovative product Portray Xray has become a significant positive change for any practice looking to improve its imaging diagnostics over current, traditional 2D imaging. This imaging device utilizes a technology called 3D intraoral tomosynthesis, which integrates improved hardware and intuitive software with minimal radiation and no change in workflow.⁹ The imaging head has 7 imaging units vs a traditional single unit. The software divides the volume into 0.5-mm slices, providing a virtual dissection of each tooth, and the Synthetic 2D mode gives the clinician the ability to rotate the image to see into interproximal spaces. The Portray system was specifically designed to allow dentists to see more caries, fractures, and root structures that may not be visible in a standard x-ray (Figure 4). 

Figure 4. Portray chairside 3D Imaging. The left image of a mandibular left molar is unremarkable. The right chairside 3D image, however, divulges obvious mesial root resorption. While Portray is not designed to replace CBCT, it may indeed someday replace 2D chairside imaging.

5. What if “feeling vs seeing” clinical microgaps and extremely narrow endodontic orifi was significantly improved for the endodontic clinician and endo/perio probings were more accurate and comfortable for the patient? 

In endodontics, smaller is better. The English proverb, “Necessity is the mother of invention,” inspired me to think everything in endodontics needs to be smaller. Micro explorers and periodontal probes have been an essential part of our private endodontic practice for several years but only recently have been perfected. The JW 17 Standard and Signature Series Micro Explorer and Micro Endo/Perio probe (DoWell Dental Products) are valuable for every endodontic clinician. At half the size of the standard DG 16, the explorers are really “feelers” in identifying tiny orifi, and the JW microprobe allows for accurately identifying vertical fractures compared to the wider periodontist’s favorite Marquis probe (Figure 5). 

Figure 5a.

Figure 5b.

Figure 5c — Figure 5. (a) The arrow points to Mueller bur (Brasseler USA) compressed hydroxyapatite (endodontic clinicians call this the “white spot”) into a calcified central incisor canal and identifying the canal’s entrance. (b) Graphic comparison of DG 16 further blocking the canal vs the narrower JW Micro 17 piercing the compacted hydroxyapatite. (c) From left to right: JW Signature Micro Explorer, JW Standard Micro Explorer, and JW Micro Endo/Perio probe.

6. What if an endodontic rotary system required no hand files 50% to 80% of the time, produced a simultaneous “slender body” and “deep shape” with only 3 files, and had a successful conefit 100% of the time? 

Dentsply Sirona’s ProTaper Ultimate Shaping System and Conform Conefit precision machine-made gutta-percha cones have achieved the shaping technology to produce a “deep shape,” providing 3D cleaning and 3D obturation while maintaining minimally invasive, appropriate body preparations.¹⁰ Sounds too good to be true? Well, it is too good, and it’s true! (For 100% conefit, root canal preparations must be cleaned of any obstructive debris.)

The technique is as easy as 1, 2, 3: one Slider; one Shaper; and, in many cases, one Finisher. This innovation, which took 2 years to develop, is especially beneficial in longer, thinner, and more curved canals. It is critical to note that when a slider does not follow to length easily, a manual Glidepath (Slidepath) is a prerequisite. Always read DFUs first!

As one of the designers, our biggest challenge was to continue the illustrious legacy of ProTaper by simultaneously breaking new ground while always maintaining being true to ProTaper values. Design is so much more than just simply designing a system that produces predictable shapes. It is about maintaining a brand of optimal performance (Figure 6). 

Figure 6a.

Figure 6b.

Figure 6c — Figure 6. (a) Dentsply Sirona ProTaper Ultimate Shaping System and Conform Fit gutta-percha cone. The image compares ProTaper Gold Finisher 1 vs the narrower body ProTaper Ultimate Finisher 1 while maintaining essential “deep shape” for 3D Cleaning and 3D Obturation. (b) Illustration of a maxillary molar DB canal demonstrating precision-machined Conform Conefit, which occurs 100% of the time if the funnel form radicular preparation is thoroughly clean of any debris. (Image courtesy of Advanced Endodontics, Santa Barbara, Calif.) (c) Typical ProTaper Ultimate radiographic “look” with “narrow body” and “deep shape.” (Image courtesy of Dr. Reid Pullen, Brea, Calif.)

7. What if you could see down a root canal system and identify anatomy such as blocks, ledges, transportations, perforations, lateral POEs, broken instruments, and retreatment conditions?

Introducing the future Endoscope, which is early in its development stages. As an endodontist, one of my most significant stressors is doing endodontics in the dark. My fantasy has always been to visually see deep inside a canal and determine what obstacles are present, such as broken files, blocks, ledges, transportations, or failing obturation materials and where they are. I call this the Small Space Race and invite the reader to join in! Eric J. Seibel, PhD, research professor, mechanical engineering and director of the Human Photonics Laboratory at the University of Washington, is explorating the use of the technology for viewing the root canal system. Contact him at eseibel@uw.edu. 

The imaging of adult root canal systems before and after shaping has been limited by the sub-millimeter inner diameter size. Commercial ultrathin endoscopes based on coherent fiber bundles do exist, such as the 0.5-mm-diameter Fujikura FIGH-10-350S, but their low number of imaging pixels, fragility, and semi-rigid shafts have limited their use in healthcare.^11,12 Two new scanning flexible endoscope designs under development for sub-millimeter-diameter clinical products are rotating a single optical fiber that produces a line of pixels with an optical grating at the fiber tip, called a spectral-encoded endoscope,¹³ and vibrating a single optical fiber with a microscanner at the tip, called a scanning fiber endoscope.¹⁴ Alternative new designs from academia use sophisticated computer algorithms to generate images through a single multimodal optical fiber (<0.5-mm diameter) without scanning, which is called various names depending on the academic lab developing the technology, such as spatial-frequency tracking adaptive beacon light-field encoded endoscope and sense.¹⁵

Futuristic designs from academia that use sophisticated computer algorithms to generate images through a single multimodal optical fiber (<0.5-mm diameter) may sooner than later allow us to see what has never been seen before (Figure 7). 

Figure 7. (a) Micro Endoscope seeing a lateral portal of exit (POE) several millimeters from the apical POE. (b) The Pilot Endoscope set up in its early development.

8. What if a simple addition to your microscope improved the clinical team’s diagnostic treatment mechanics and raised the level of enjoyment during treatment? 

In 1683, Dutch researcher Anton van Leeuwenhoek ushered in a new age of science when he peered through a hand-ground lens and, for the first time, described a living cell.¹⁶ Approaching 3.5 centuries later, dentistry is still discovering the microscope as a means of coaxial magnification (common light and visual axis), which eliminates disturbing shadows, no longer tethers the dentist to a headset, and grants the patient co-observation and understanding of the clinical diagnosis and treatment.¹⁷

Doing endodontics can be a lonely experience. The clinician is frequently the only person who is aware of how his or her endodontics are progressing during the actual endodontic treatment. The assistant is often excused because there is no presumed need for participation. The dentist is the only one who can see and do the treatment. In addition, just sitting chairside with an occasional request for saliva aspiration makes for a long and boring day.

The microscope-trained clinical team is literally seeing the patient’s endodontic tooth with 4 eyes! The assistant anticipates what is technically next more accurately, gives honest guidance, and adds enormous energy and encouragement, such as “We can do this,” because they can see the situation. This is all authentic. But for me, the trained assistant’s intimate endodontic presence and the awareness that the Global Surgical Co-Observation System Microscope brings is crucial to experiencing a joyful, energizing, and fun day. Lastly, by seeing what we are doing together, we have a unique way to hold each other accountable for the practice’s level of performance (Figure 8). 

Figure 8. The Global Surgical Co-Observation System Microscope enables the dentist and clinical assistant to see the same image at the same time.

9. What if there were a “magic juice” that could more effectively remove the fatal flaw (dentin mud and collagen) of endodontics?

If this were true, the marquis skill of endodontics, “following” from orifice to radiographic terminus in order to prepare the Glidepath (Slidepath) would be easier. There has not been a novel endodontic irrigant introduced for a number of years. Cleaning the root canal system is challenging because anatomical crypts are complex, and the complete elimination of pulp tissue, microbial pathogens, calcifications, and miscellaneous debris is often a real clinical test.  

Endodontist Dr. Terry Pannkuk has explored the use of a trichloroacetic acid (TCA)-based irrigant to have enhanced benefits while performing endodontic treatment of external root resorption from an internal root approach. In his patented TCA-based solution, Terry has also observed an increase in the number of POEs radiographically visibly filled. These properties are currently being researched, and human clinical trials are being performed.

In addition, the following claims and benefits are being studied at the university level: hemostasis, calcific debris removal, smear layer removal, dehydration of the pulp, and facilitating digestion with sodium hypochlorite. 

These properties appear to reduce treatment time because of the efficient dissolving action. Small files are reportedly able to slip and slide into tight, narrow canals without early blockage, and apical preparations can be better cleared and dried before obturation, resulting in void-free, controlled flow (Figure 9). 

Figure 9. (a) This radiographic example demonstrates the power of cleanliness and 3D resistant form funnel-shaped canals. From left to right is the maxillary left second premolar pretreatment, downpack (note multiple POEs visibly filled), and finish images using trichloroacetic acid (TCA) as an adjunct irrigant agitated with the SmartLite Pro EndoActivator (Dentsply Sirona) and vertical compaction of warm gutta-percha obturation. (Image courtesy of Dr. Terry Pannkuk, Santa Barbara, Calif.) (b) Graphic of TCA delivery device.

CLOSING COMMENTS

The purpose of this article is to review 9 recent-past, present, and future innovations designed to enable the endodontic clinician to see direct and indirect information that brings us closer to the truth of endodontic diagnostic and treatment accuracy.

I have been an educator and have been called an endodontic clinical visionary for most of my professional career. However, I am just like you. I am compensated for my level of performance one patient at a time. For each of these patients, we have the knowledge, skills, and tools to be successful. The difference is our willingness.

This article introduces a small window into our innovativeness. The question, however, is always the same: “Will we show up?” Will we be present for this next patient’s treatment? Do we care? I care, and I believe that since you have read my article to this point, this is ample evidence that you care too. Together, we can and will impact our level of endo-
dontic mastery and craftsmanship. 

There will be more innovations in years to come. Some will be disruptive. The ultimate benefactor of our improved endodontic performance is the one that will never read this article and the one that matters the most: our patient. 

As endodontists, what’s in it for us is that our level of performance becomes even more predictable; easier; and, quite frankly, more fun!

REFERENCES

1. Domingos P. Artificial intelligence will serve humans, not enslave them. Scientific American. 2021;30(4):100–3.  

2. West JD. The relationship between the three-dimensional endodontic seal and endodontic failures. Master’s Thesis. Boston University; 1975.

3. Sheets CG, Quan DA, Wu JC, et al. An evaluation of quantitative percussion diagnostics for determining the probability of a microgap defect in restored and unrestored teeth: A prospective clinical study. J Prosthet Dent. 2023:S0022-3913(23)00272-X. doi:10.1016/j.prosdent.2023.04.016 

4. Schilder H. Vertical compaction of warm gutta percha. In: Gerstein H, ed. Techniques in Clinical Endodontics. W.B. Saunders; 1983:84-90.

5. Schilder H. Cleaning and shaping the root canal. Dent Clin North Am. 1974;18(2):269–96.

6. Tan KS, Yu VS, Quah SY, et al. Rapid method for the detection of root canal bacteria in endo-
dontic therapy. J Endod. 2015;41(4):447–50. doi:10.1016/j.joen.2014.11.025 

7. Gakenheimer DC. The efficacy of a computerized caries detector in intraoral digital radiography. J Am Dent Assoc. 2002;133(7):883–90. doi:10.14219/jada.archive.2002.0303

8. Tracy KD, Dykstra BA, Gakenheimer DC, et al. Utility and effectiveness of computer-aided diagnosis of dental caries. Gen Dent. 2011;59(2):136–44. 

9. Mauriello SM, Broome AM, Platin E, et al. The role of stationary intraoral tomosynthesis in reducing proximal overlap in bitewing radiography. Dentomaxillofac Radiol. 2020;49(8):20190504. doi:10.1259/dmfr.20190504

10. Machtou P, West J, Ruddle CJ. Deep shape in endodontics: significance, rationale, and benefit. Dent Today. 2022;41(1):74–7.

11. Orth A, Ploschner M, Wilson ER, et al. Optical fiber bundles: Ultra-slim light field imaging probes. Sci Adv. 2019;5(4):eaav1555. doi:10.1126/sciadv.aav1555 

12. Lee CM, Engelbrecht CJ, Soper TD, et al. Scanning fiber endoscopy with highly flexible, 1 mm catheterscopes for wide-field, full-color imaging. J Biophotonics. 2010;3(5-6):385-407. doi:10.1002/jbio.200900087

13. Zeidan A, Do D, Kang D, et al. High-resolution, wide-field, forward-viewing spectrally encoded endoscope. Lasers Surg Med. 2019;51(9):808–14. doi:10.1002/lsm.23102 

14. Wen Z, Dong Z, Deng Q, et al. Single multimode fibre for in vivo light-field-encoded endoscopic imaging. Nat Photon. 2023;17:679–87. doi:10.1038/s41566-023-01240-x

15. Xie N, Tanguy QAA, Fröch JE, et al. Spectrally-encoded non-scanning imaging through a fiber. arXiv Phys. 2023. doi:10.48550/arXiv.2305.17113

16. West JD. The role of the microscope in 21st-century endodontics: visions of a new frontier. Dent Today. 2000;19(12):62–4, 66–9.  

17. van As GA. Digital documentation and the dental operating microscope. Oral Health. 2001;91(12):19-30. 

ABOUT THE AUTHOR

Dr. West received his DDS degree from the University of Washington, where he is an affiliate professor, and his MSD degree in endo-
dontics from Boston University, where he was honored with the Distinguished Alumni Award. Dr. West is founder and director of the West Center for Endodontics in Tacoma, Wash, where he is in private practice with his 2 sons, Jason and Jordan. He can be reached at (253) 473-0101 or via email at johnwest@centerforendodontics.com.

Disclosure: Dr. West is co-inventor of ProTaper and WaveOne and the inventor of JW17 Microexplorers and Micro Endo/Perio probes. He also serves on the clinical advisory board of Perimetrics, Inc.

NOTE ABOUT UPCOMING WEBINAR

Dr. John West will be leading a FREE CE webinar on March 27 at 1 PM (EST) that expands on the topic of this article.

In this FREE CE webinar, the esteemed Dr. John West will describe new and exciting endodontic technologies in combination with tools from the past and how these are used today in his everyday practice. Techniques and carefully documented protocols are shared in a fun and playful way.

Click HERE to register now.

Endodontic mastery at its essence comes down to achieving high-quality, reproducible results without reliance on a particular instrument system (matching instruments, motor presets, matching paper and gutta-percha points, etc). Rather, endodontic mastery is derived from reliance on basic principles that can be applied to virtually any system of instruments or materials. In practical terms, this means adherence to literature-based and time-proven concepts. This clinical article was written to provide the general dentist with a set of guiding endodontic principles that can be implemented using any shaping and obturation system for the types of root canal procedures that will be commonly treated by general dentists performing endodontic therapy.  

GUIDING PRINCIPLE 1: CASE SELECTION AND PREPARATION FOR TREATMENT

As a starting place, it is essential that the clinician perform a thorough endodontic examination and provide a pulpal and periapical diagnosis for every case prior to making access. This examination requires adequate radiographic assessment (possible CBCT and adequate diagnostic, 2D periapical radiographs); thermal testing as required; and assessment of percussion, palpation, mobility, and probings, all relative to controls.  

Accompanying the aforementioned diagnosis, the clinician should obtain written informed consent. Ideally, this consent requires that the procedure be reviewed personally with the patient, risks discussed, questions answered, and alternatives given. Coincident to obtaining a pulpal and periapical diagnosis, the clinician should assess the iatrogenic risks of treatment (file separation in severely curved and calcified canals, extrusion of irrigants and filling materials in lower second molar apices that lie near the mandibular canal, and perforation in calcified canals, among many potential sources of risk). Prior to starting the case, profound local anesthesia must be assured. The rubber dam is the legal and ethical standard of care. 

GUIDING PRINCIPLE 2: PREPARE AN ACCESS THAT PRESERVES TOOTH STRUCTURE AND PROVIDES VISUAL AND TACTILE CONTROL 

The astute clinician takes a CBCT scan as indicated (in the presence of complex anatomy, vital anatomic structures, severe curvature, possible resorption, retreatment cases, etc). The CBCT scan can inform the clinician of the location of canal orifices, given the preoperative measurement tools embedded in the software. Adequate 2D periapical images prior to treatment can also help the clinician mentally imagine orifice locations. Preservation of tooth structure in access and canal locations is accentuated by using safe-ended burs under a surgical operating microscope (SOM) (EndoGuard [Komet], EX-24 [Mani], and others). Safe-ended burs allow removal of tooth structure on axial walls without gouging the pulpal floor (Figure 1). 

Figure 1. EndoGuard (Komet). This safe-ended bur is used to plane axial access walls without gouging the pulp floor and unnecessarily removing tooth structure.

In relatively simple cases, opening into the chamber is straightforward. Severely calcified cases present challenges in canal location, providing an indication for CBCT. Attempting access into severely calcified pulp chambers and/or crowned teeth with obscured pulp chambers is highly problematic. Tipped and/or rotated teeth also present the clinician with perforation risk. Without significant experience and advanced visualization, ie, the SOM and CBCT, these teeth are best referred.  

It is axiomatic that the clinician attempts to save as much tooth structure as possible during access and canal preparation to minimize the long-term risk of crown and root fracture. Specifically, it is critical to preserve pericervical dentin (4 mm coronal and apical to crestal bone). Caries may ultimately dictate how much tooth structure is removed, but the ideal access should be made first and followed by careful caries removal (often with a slow-speed CA round bur of an appropriate diameter). The use of a caries indicator is helpful to ensure complete caries removal. Assurance of straight-line access is optimal prior to entering files into a canal orifice, shaping the coronal third, and/or taking length measurements. 

Canal location is generally straightforward in non-calcified cases, but in the daily practice of an endodontist, many non-vital cases are moderately to severely calcified, hence the need for specialty burs (EndoTracer [Komet], 1,500 to 20,000 rpm; 34-mm #2 CA burs [Mani]), which allow the clinician far greater precision in tooth structure removal during canal location relative to their short shank options (Figure 2). 

Figure 2. EndoTracer (Komet). These extended round burs are very help- ful in selectively removing tooth structure while attempting to locate calcified canals. Alternatively, ultrasonics would be another option for this purpose.

Alternatively, specialty ultrasonic units and tips can be used for this purpose. Ultrasonics are beyond the scope of this article, but if appropriate care is undertaken to avoid heat generation during their use, ultrasonics are a precise method for canal location in addition to exacting tooth structure removal. The Varios 970 (NSK) is the author’s preferred ultrasonic unit in combination with NSK tips. The unit features its own irrigant reservoirs, and the variation in power between the lowest and highest powers is notable. Alternative tips and units include those manufactured by Dentsply Sirona and Bonart, among many other manufacturers.  

GUIDING PRINCIPLE 3: REMOVE RESTRICTIVE DENTIN AT THE ORIFICE AND IN THE CORONAL THIRD BEFORE MOVING APICALLY 

Be it with the use of small Gates Glidden drills (#1 or #2) and/or NiTi orifice openers, opening the orifice, removing restrictive dentin, clearing the chamber, and providing clear and unmistakable orifices for file insertion has immense value. Orifice openers come in many forms, sizes, and tapers and include rotary, reciprocating, and Gates Glidden drill varieties. All of these have the same purpose, which is to define the orifice and provide files and irrigants unrestricted access to the more apical portions of the canal. Coincident with the steps above, it is critical to clear the chamber with sodium hypochlorite and water rinsing to avoid debris from apical movement. 

Endodontics is a sequential process. Profound local anesthesia precedes access. Conservative access and unroofing the pulp chamber precede canal entry. Shaping the coronal third and defining the orifice precedes placing instruments into the middle canal third. 

When shaping multi-rooted teeth, it’s immensely helpful (especially with novice clinicians) to do so sequentially because it aids in conceptualizing protocol. In practical terms, this means resisting the urge to place orifice openers and glidepath files into the apical third before the coronal third is shaped and irrigated. It is easy to lose track of where one is in the cleaning and shaping process if different files are taken to different canal levels in multirooted teeth simultaneously. Lack of flowing taper and canal transportation can easily result if the clinician loses sight of where he or she is in the preparation process and/or does not have a clear vision of the final desired shape. 

GUIDING PRINCIPLE 4: NEGOTIATE THE CANAL TO THE APEX AND OBTAIN A TRUE WORKING LENGTH 

Canal negotiation with hand files informs the clinician of the true calcification, curvature, apex size, 3D nature of the apex and canal, canal length, and exact position of the minor constriction. It is the authors’ preference to always precurve hand files and always start canal negotiation with a #6 hand K-file. In addition, hand files are inserted into a canal once and then discarded as they rapidly lose their sharpness. Hand files come in a bewildering array of cross-sectional designs, materials, and clinical attributes. As a result, making generic recommendations about which hand files to use for a specific clinical indication is challenging due to the ability to achieve a particular task with many different hand files. This said, for the vast majority of canals, the standard K-file (.02 tapered hand K-File [Komet], K-Files [Mani]) will provide the average general practitioner the ability to negotiate canals, prepare a glide path, and obtain a true working length with an apex locator (Root ZX [J. Morita], EndoPilot [Komet], ProMark [Dentsply Sirona], and more). 

The above notwithstanding, the single greatest variety of hand files (designs, lengths, tapers) available commercially is represented by the line of instruments marketed by Mani Dental of Japan. The clinician is directed to Mani’s catalog of safe-ended hand files, stiff hand files for canal negotiation in calcified cases (D Finders), and tapered hand files, among many other hand file options.  

Once precurved, in the presence of irrigant, the hand file should slide to the estimated working length, and the apex locator should read 0.0 (the position of the minor constriction), which is the most natural place to end shaping, irrigation, and obturation procedures. More specifically, instrumentation, irrigation, and obturation should end at the exit of the canal from the tooth with careful attention paid to the avoidance of extrusion of foreign materials beyond the constriction. Apex locator measurements are most accurately made in a dry canal (despite the manufacturer’s assurances to the contrary) with the largest file possible, taking care not to touch the file to metal during measurement. 

GUIDING PRINCIPLE 5: CREATE THE GLIDE PATH

Glide paths can be created with K-files, with rotary NiTi instruments, and through the reciprocation of hand K-files, among other methods. Common glidepath instruments include PathGlider for FQ (Komet), PathGlider for ProcQ (Komet), ProGlider (Dentsply Sirona), and PathFile (Dentsply Sirona), among many others. A properly created glide path significantly reduces the possibility of NiTi file breakage and ensures a time savings in that shaping files should move easily to the true working length. The glide path should be made to the true working length with frequent recapitulation using hand K-files to ensure that the canal path remains open and negotiable. Recapitulation should be accompanied by frequent irrigation and canal flushing to maximize debris removal, allowing the master cone to fit to true working length. 

Should a canal become non-negotiable where it was once negotiable, in all likelihood, either a ledge has begun or the canal is blocked with debris. Rather than forcing additional files apically, the clinician should stop, go back to smaller precurved hand files, and attempt to regain the canal path and/or irrigate the debris coronally. File separation, canal transportation, and a wide variety of iatrogenic events have as their origin an impatience to reach the apex, especially in the presence of a blockage. The use of a viscous EDTA gel, such as ProLube (Dentsply Sirona) or File-Eze (Ultradent Products), may be valuable in bypassing a ledge or negotiating around debris and facilitating removal. 

Once a #15 hand file can spin freely at the TWL, the glide path is prepared, and the canal is ready for shaping. Many mechanized glidepath instruments are .03/15 in dimension. Once they are taken to the TWL, the glide path is prepared.  

GUIDING PRINCIPLE 6: SHAPE AND DISINFECT THE CANAL

Given the steps taken above, if performed correctly, shaping should be a formality. The shaping file utilized should move to the apex with minimal pressure in the presence of an adequate glide path. Knowing the endpoint of shaping and the desired goal of irrigation provides strong clues as to when the clinician is done and the canal is ready for obturation. 

Ideally, the canal is prepared when the canal can be adequately disinfected and obturated. The advent of laser disinfection (Waterlase [BIOLASE], LightWalker [Fotona]) and multisonic negative/neutral pressure systems (GentleWave [Sonendo]) have all allowed the disinfection of smaller prepared canal spaces relative to traditional methods (passive ultrasonic irrigation, sonic irrigation, mechanical agitation, negative pressure systems [EndoVac]). While an absolute superiority of any given irrigation method has not been shown in the literature, and no single regimen or system has been able to demonstrate absolute sterility in canals, it is fair to say that we are closer to this objective than ever before. 

In the context of shaping, if irrigation is ideal and adequate with regard to volume, placement, activation, refreshment, and solution type, it is clear that irrigation is performing the disinfection step in the endodontic procedure and that removal of tooth structure is of secondary value in cleaning. Stated differently, removal of tooth structure allows for irrigants to enter canal spaces and perform removal of the smear layer, dissolution of tissue, and/or antibacterial functions. Traditional irrigation solutions have included sodium hypochlorite, 17% EDTA, and 2% chlorhexidine. Newer “2-in-1” irrigation solutions have emerged in the marketplace, such as Triton (Brasseler USA), which are stated to disinfect canals while simultaneously removing the smear layer.  

Methods to shape the canal generally fall into 2 categories: rotary- and reciprocation-powered NiTi files. There are dozens of commercially available NiTi systems. The cases shown were prepared with both the Procodile Q heat-treated system (reciprocation) or the FQ system (rotary), both powered by the EndoPilot motor (Komet). One significant advantage of the EndoPilot motor relative to others is the optional setting for user control of forward and backward degrees of reciprocation. The unit also features a heat source and an apex locator built in, and added features include a gutta-percha extruder and ultrasonic capability (Figures 3 and 4). 

Figure 3. (a to e) Cases shaped using either the Procodile Q heat treated system (reciprocation) or the FQ system (rotary), both by powered by the EndoPilot motor (Komet). (f) Procodile Q (Komet).

Figure 4. The ProMark endodontic motor (Dentsply Sirona) reciprocates and provides a rotary function with presets. The forward degree and reverse degrees of reciprocation cannot be user-modified as they can on the EndoPilot motor. ProMark motors typically are used with the WaveOne reciprocating system (Dentsply Sirona).

Figure 5. Dia-Root Bio Sealer (DiaDent) is a calcium silicate-based bioceramic sealer in the same general class as BioSeal (Komet) and EndoSequence BC Sealer (Brasseler USA).

In summary, preparing a canal space with narrowing cross-sectional diameters requires respecting the unique anatomy of the tooth. Maintaining the canal’s initial position, keeping the minor constriction at its original position and size, and appropriately sizing/preparing a canal space that can be predictably irrigated and obturated are the goals of canal shaping, regardless of the system used. In guitar terms, some players like Fender, some players like Gibson, and there is a universe of players who like other models. Which system is best is a matter of personal preference. What is critical is that the clinician knows his or her system, its attributes and limitations, and how to use it comprehensively from orifice to apex. 

GUIDING PRINCIPLE 7: OBTURATION 

Once the chosen irrigation/disinfection protocol has been achieved, the clinician should be able to dry the canal with paper points, fit a cone with a modest amount of sealer on it (ideally a calcium silicate sealer, such as BioSeal [Komet] or Dia-Root Bio Sealer [DiaDent], among many), and take a trial cone radiograph to assure that the master cone is in the correct position relative to the apex before obturation is concluded. All of the major instrumentation systems available at this time have matching paper points and gutta-percha points, whereby the master apical file (the largest file used at the apex) has a matching paper point and gutta-percha point. The cases illustrated using both Procodile Q and FQ (Komet) were obturated with this convenience (Figure 5). 

It is beyond the scope of this article to discuss obturation. This stated, if the clinician is going to perform endodontics, it is essential to have a heat source and a source of extruded gutta-percha readily at hand. Reliable systems with these features include the Dia-Duo (DiaDent), Calamus Unit (Dentsply Sirona), and the optional attachments to the EndoPilot (Figures 6 and 7). 

Figure 6. (a) Dia-Duo (DiaDent) is a cost-effective heat source with a smaller footprint relative to some other market options and a gutta-percha extrusion option. (b) The Calamus Unit (Dentsply Sirona) is a proven alternative to the Dia-Duo, but with a slightly larger footprint.

Figure 7. The EndoPilot motor has expanded capabilities to provide a heat source, an apex locator, gutta-percha obturation, and ultrasonics.

SUMMARY

This article has provided the reader a road map of steps on the road to endodontic mastery. Guiding principles that are independent of the material used have been presented. These principles include the critical importance of irrigation, removal of restrictive dentin in the coronal third, and achieving apical patency, among other key concepts. We welcome your feedback.

ABOUT THE AUTHORS

Dr. Neal earned his DMD degree from Roseman Dental School in 2023 and currently attends the GPR at Ohio State University. He can be reached at tylerhneal@gmail.com. 

Dr. Mounce earned his DDS degree from Northwestern Dental School and received his endodontics certificate from Oregon Health Sciences University. He practices endodontics in Eagle River, Alaska. He is widely published in trade magazines and has lectured globally. He can be reached via email at
richardmounce@mounceendo.com. 

Disclosure: The authors report no disclosures. 

Generally, an endodontic article with the above title would be one about making rotary endodontics safer, reducing the possibility of instrument separation with, perhaps, a secondary effort to discuss ways to improve the 3D cleaning and debriding of canal systems. What would not be addressed is rotary’s potential to induce microcracks in canal walls.^1-4 It would be a given that the overriding advantage of rotary NiTi is the increased ability to shape curved canals with far less distortion than the use of stainless steel K-files.^5,6 It would also be a given that an engine-driven system is likely to reduce the procedural time necessary to accomplish its tasks while also lowering the amount of hand fatigue the dentist will encounter. In short, the thrust of most articles of this nature is to emphasize the superiority of rotary NiTi instrumentation while ignoring negative impacts such as dentinal microcracks or declaring that they are artifacts of experimental protocols that don’t reflect clinical reality. Also, with a set of simple precautions, separation can be drastically reduced without compromising the goals of instrumentation—namely 3D cleansing and debridement and the introduction of ever newer versions of heat-treated NiTi instruments, reinforcing their already accepted use as an ongoing paradigm improvement over anything that came before it. 

This article is different. It discusses the impact of the precautions necessary to maintain the integrity of rotary NiTi instruments. It then offers alternative methods of instrumentation that virtually eliminate the need for implementing those precautionary steps, giving the dentist the freedom to more thoroughly cleanse the canals three-dimensionally, rapidly, and without distortion. Let’s start with some of the more strongly suggested precautions.

STAYING CENTERED 

The idea behind this precaution is to minimize the amount of flexural stress the rotary NiTi instruments are subjected to. Rotating NiTi instruments that are negotiating canals of increasing and more abrupt curvatures will unavoidably encounter flexural stresses, subjecting them to repetitive bouts of tension and compression that can lead to cyclic fatigue and instrument separation, even if they stay centered.^7-9 In canals that are oval, typically having a wider dimension buccolingually than mesiodistally, one can only reach the tissue in the buccal and lingual extensions if the instruments are applied to those locations. Straight canals give the dentist some latitude in veering off center to reach these extended spaces, but an oval canal that is already curved mesiodistally subjects the rotary instruments to far greater flexural stresses if they are also applied buccolingually to remove that tissue. Experienced clinicians, as well as informed manufacturers, are aware of these stresses that have led to the implementation of the precaution to stay centered.

This precaution does not exist in a vacuum. Non-application of the instruments buccolingually leads to inadequate cleansing of oval canals and thin isthmuses, as has been demonstrated in numerous research articles over the past decades.^10-12 The improvements in NiTi metallurgy have not eliminated the need to keep applying this precaution. Perhaps of greater significance is the redirection of the goals of instrumentation. It is supposed to be about 3D cleansing, but as the precaution of staying centered so clearly demonstrates, it increasingly appears that maintaining the integrity of the instruments has become more important than the cleansing of the canal. Those advocates of rotary NiTi would disagree, showing endless beautifully shaped and obturated highly curved canals mesiodistally. What is missing is any information on the quality of instrumentation and obturation in the buccolingual plane, something that we know exists because of the myriad of articles discussing this shortcoming.

From a practical point of view, despite articles saying that rotary NiTi can be used with a light brushing motion against all canal walls, anyone employing these instruments in canals significantly curved in the mesiodistal plane is unlikely to extend their use buccolingually, knowing intuitively that leaving a separated instrument glaringly visible on radiographs is simply less appealing than shaping a canal that looks great on a radiograph even though it may be inadequately prepared buccolingually (Figure 1). And we can always rationalize that the canals are probably round in cross section along their entire length. There is no evidence present to contradict this conclusion when all information is confined to the mesiodistal plane.

Figure 1. Radiograph of a separated instrument, which is rotary’s main concern.

Other precautions include routine inspection of the instruments, noting any detectable defects of unwinding or overwinding of the flutes that demand immediate discarding of the instruments. The instruments should be used with a light pecking motion to minimize torsional stresses. Single usage is highly recommended, and the motors driving the instruments should be set to a low torque setting so the engine can kick into auto-reverse, if exceeded. It goes without saying that a well-defined glide path is essential before contemplating rotary usage, particularly where canal anatomy is becoming more complex. It is important to note that the implementation of these precautions takes on greater importance as the canal anatomy becomes more challenging. The inverse of this insight is that rotary can be done relatively safely where canal anatomy is simple, namely straight canals, fairly wide in the mesiodistal plane, and again discounting the possibilities that the canal may be wider in the buccolingual plane.

The state of canal anatomy has a profound impact on the stresses that the rotary NiTi instruments are subject to, and it is imperative that dentists routinely make these distinctions. What is easily possible in a straight, fairly wide canal is likely a far greater challenge in narrow, curved, oval canals.^13,14 What I have been describing up to this point are the limitations of rotary NiTi and the compromises they must make to reduce the incidence of instrument separation. This goal is so embedded in their usage that it is reasonable to say that the prevention of separation takes precedence over their cleansing action. Indeed, in recent years, we have seen the introduction of minimally prepared canals as an evolutionary step in their safe usage, defined as a lower incidence of instrument separation. More conservative instrumentation subjects the instruments to less flexural and torsional stresses because they simply encounter less resistance on the way to the apex. They reduce the number of instruments required, lowering the costs of armamentarium to the dentists. Procedural times are reduced—all pluses for the dentists. What is not considered is the exacerbation of inadequate cleaning, in general, and oval canals, in particular, in the buccolingual dimension.¹⁵ That lack of concern is consistent, however, with what is now most important to those employing rotary instrumentation, which is keeping the instruments intact.

Given this critical review of the compromises inherent in the use of rotary NiTi, what alternatives exist that do not compromise the cleansing of canals and, at the same time, don’t induce instrument separation? The answer lies in the use of stainless steel, relieved, twisted reamers employed in a 30° handpiece oscillating at 3,000 to 4,000 cycles per minute, or about 60 cycles per second (Figure 2).¹⁶ To appreciate the positive collective impact of the instruments and the handpiece, we must get into the details of their action.

Figure 2. Illustration showing the 30° oscillating handpiece utilizing the relieved reamers.

We use reamers rather than K-files because the flutes on a reamer are twice as vertically oriented as those on a K-file. Why is that important? Dentin is only shaved away from the canal walls when the flutes of the instrument are more or less at right angles to the plane of motion. A K-file with predominantly horizontal flutes is in the same plane as the motion of an oscillating handpiece. Consequently, its function under these circumstances is to embed or screw into the dentin, penetrating the canal wall without removing any dentin up to this point, only to unscrew and repeat the process in the next cycle. Dentin is only removed when the pull motion is applied. Since the handpiece is oscillating horizontally at 3,000 to 4,000 cycles per minute, the implementation of a file design is grossly inefficient. If we substitute a reamer, its predominantly vertical flute orientation starts to shave dentin away with the first clockwise stroke. Now, admittedly, the 30° short arc of motion removes very little dentin per stroke, but at a frequency of 3,000 to 4,000 cycles per minute, or about 60 cycles per second, this automated use of a reamer is very efficient at shaping and cleansing the canals.

We further improve the mechanics by incorporating a flat along the length of the reamers, reducing their engagement with the canal walls, resulting in reduced resistance and more rapid negotiation to the apex. These instruments employed in the oscillating handpiece are used with a pecking motion—but not one concerned with exceeding the torsional limits of the metal. The 30° arc of motion is so small that it reduces the torsional stresses to which the instruments are subjected to the level of insignificance, eliminating any chances of instrument separation under these conditions. The same can be said for flexural stresses when negotiating around a curve. The repetitive, high amounts of tension and compression that a rotary instrument undergoes when negotiating significantly curved canals are reduced to insignificant amounts when the arc of motion is limited to 30°, despite the high frequency.

The most significant difference between rotary NiTi instrumentation and the 30° oscillation of relieved, stainless steel, twisted reamers is that the latter is virtually immune to separation. That fact alone stands in stark contrast to rotary instruments, where the goal of avoiding instrument separation has become the number one priority in their usage. With instrument separation a non-issue, 30° oscillating instruments are not confined to centered shaping. Limited to very rapid, short arcs of motion, the oscillating instruments can be applied aggressively buccolingually in oval canals while simultaneously negotiating highly curved canals mesiodistally (Figure 3). Their resistance to instrument separation has been verified in research studies as well as in clinical usage over many years.¹⁷

Figure 3. Photograph of the 3D cleansing that is possible with 30° oscillating reamers.

Other advantages are to be considered: Since aggressive usage does not lead to instrument separation, they may be used multiple times. It is unlikely any instrument will show signs of unwinding or overwinding when used in this manner. Confining the instruments to short arcs of motion is not only beneficial to them; it is also beneficial to maintaining the integrity of canal walls. Newton’s Third Law of Motion states that 2 interactive bodies have an equal and opposite effect on each other. We know that when confined to short arcs of motion, the impact of the canal walls on the instruments does not result in instrument separation. In like manner, the impact of the instruments on the canal walls, in accordance with Newton’s Third Law of Motion, should not result in dentinal defects. This is in stark contrast to the use of rotary NiTi instruments, which not only results in instrument separation but also in well-documented data demonstrating their production of dentinal defects at the same location where maximum stresses are produced. Ignoring these facts does not make the problem go away.

Even if a rotary NiTi enthusiast were to concede that 30° oscillating, stainless steel, relieved, twisted reamers are virtually immune to instrument separation, he or she would still argue that it is a moot point because stainless steel stiffer than NiTi is going to produce distortions to the canal walls that imperil successful endodontic instrumentation. One goal of instrumentation is to avoid the transportation of canals that can produce blunderbuss anatomy, something that is extremely difficult to obturate. The claim to superior non-distorted shaping is the final defense of rotary users, and that would be true if stainless steel were used with full rotations. However, when confined to short arcs of motion, they have been shown to remain true to canal anatomy. How can an instrument significantly stiffer than NiTi remain true no matter how short the arc of motion?

To understand this concept, we must go back in time to 1985, when Dr. James Roane published a paper describing what he called the balanced force technique using K-files.^18,19 These files, however, were not used with a filing-up-and-down motion. Instead, they were employed first with a short clockwise stroke, followed by a short counterclockwise stroke, while at the same time applying an apical force to prevent the instrument from simply unscrewing. He describes employing the K-files with a reamer (horizontal) action. The counterclockwise motion cleaves off the dentin that was engaged in the initial clockwise motion. The secret to non-distortion lies in the fact that, confined to short arcs of motion, the resistance of the canal walls to deformation is greater than the tip of the stainless steel instruments. When the tip of the instrument contacts the canal walls in a curved canal, it is the instrument that is being deflected into the pathway of least resistance, which is the patent canal pathway. The same instrument used in full rotation would likely cause a ledge and lead to the distortions that are to be avoided. The reamers being relieved with the flat side along their entire working lengths are more flexible, further improving their adaptability to any canal curvatures they encounter.

So, what do we have up until this point as an alternative to rotary NiTi? We have a method of instrumentation that virtually avoids separation, and because we no longer have separation as a cause of concern, we have a method that can be vigorously applied to all the canal walls, including oval canals and thin isthmuses. We have a system that is fully automated from the first instrument that enters the canal to the last, essentially eliminating all hand fatigue, including the creation of the glide path. It is a system that is far less likely to produce dentinal defects. The instruments can be used multiple times with significant cost savings. From my perspective, the elimination of instrument separation takes away the greatest source of anxiety and lets us address what should truly be our main goal: the improved ability to thoroughly cleanse the canals in 3 dimensions without distortion.

Practical Application

This alternative method of instrumenting canals sounds good, but how does it work in practice? Let’s take a typical mandibular molar to see how we apply the mechanics from start to finish. After giving the appropriate anesthesia—in my case, 2 mandibular blocks, the first with carbocaine, followed by xylocaine 1/100m, and then augmented with intraligamentary injections using articaine—I apply the rubber dam over a #4 clamp. I then gain access under the microscope to the pulp chamber, generally using a long-shank, high-speed #4 round bur. If I am lucky, a non-calcified pulp chamber is present, and I quickly debride it of pulp tissue using slow-speed #3 and #2 Munce Discovery Burs (CJM Engineering). Once I detect the canal orifices, I generally apply 6% NaOCl if the case is non-vital or 17% EDTA if it is vital or at least partially vital. At this point, I generally take a 25-mm 06/02 stainless steel reamer into the MB canal and negotiate it manually to the length of the canal using the apex locator as my measuring device. This reamer is so thin and flexible that it generally negotiates to the apex with minimal resistance. If the canals are somewhat calcified and I meet significant resistance to deeper penetration, I will always then apply 17% EDTA and place the 06/02 reamer in the oscillating handpiece. This greatly facilitates negotiating the instrument to the apex. I then confirm the correct length via the apex locator. In this manner, I gain the lengths of the canals that are present—typically 3, sometimes 4—and generally use the MB cusp as my reference point for length.

Once I have negotiated to length via the 30° oscillating handpiece, I work the instrument vigorously against the buccal and lingual walls of all the canals. If any of the canals are oval in nature or an isthmus is present, the shaving of dentin in these wider dimensions will be visually apparent after about 5 seconds of application. Interestingly, a canal that is tight and offers resistance to a 06/02 stainless steel twisted reamer always encounters less resistance when I skip to the 10/02 to further widen the canals, clearly demonstrating the effectiveness of the initial instrument having the ability to effectively shave dentin away from the canal walls. Its thin dimensions give it the freedom of greater penetration, and the 30° oscillations, combined with its high frequency of use, make it a perfect instrument for what I call “internal routing,” the enlargement of the canal space beyond the dimensions of the instrument being used to shape the canals. In this manner, I tend to enlarge the canal spaces typically to a 35/02, always flooding the canals with irrigant, be it NaOCl, EDTA, or Irritrol, a combination of EDTA and CHX that efficiently kills any bacteria that may be remaining in the canals. The combination of irrigant and physical contact of the canal walls tends to remove adherent biofilms that would be resistant to irrigants alone.

Not all canals are opened to 35/02. In particularly long, tortuous canals that are extremely narrow to start with, I may elect to limit enlargement to a 30/02. If that is the case, it still does not prevent me from working the instruments aggressively buccolingually for improved debridement. In either case, I am not quite done with the instrumentation. As much as I am wary of rotary NiTi, it has 2 advantages of which I take advantage: (1) It smoothes the canal walls in the mesio-distal plane, and (2) it sizes the canal at least mesiodistally for the appropriate gutta-percha point. If opened to a 35/02, I follow up with a 30/04 rotary, and if limited to a 30/02 preparation, I will then take a 30/02 rotary and negotiate to the apex.

However, it should be clearly understood that when I apply rotary NiTi, I have already cleansed the canals, possibly oval with thin isthmuses, with the oscillating, stainless steel, relieved reamers. If I encounter anything that I interpret as excessive resistance when using the rotary system, I will further enlarge the canals with the stainless steel, oscillating reamers to the point where the resistance is minimal. In that way, I have not separated a rotary instrument in years. I should add that we developed helically relieved rotary NiTi instruments that, because of the relief, encounter less resistance when negotiating to the apex. These particular relieved NiTi reamers minimize the possibility that the canals will require further enlargement before they can safely reach the apex.

That pretty much takes care of the mechanics prior to obturation. Figures 4 to 9 illustrate a number of cases that I have treated, showing the adaptability that this approach offers the dentist in achieving results that would entail more risk if they were done predominantly with rotary NiTi.

Figures 4 to 9. Examples of canal instrumentation and obturation following 30° oscillation with no more than one final rotary instrument smoothing the walls and preparing the canal, at least mesiodistally, for the appropriate gutta-percha point.

CONCLUSION

The marketing of rotary NiTi instrumentation has been so ubiquitous that it has been accepted as the norm, with any deviation from that approach ridiculed as retrogressive. Yet, devotion to this approach is intimately tied to compromises that have been thoroughly diagnosed and documented in the endodontic literature and, in my opinion, needlessly inhibit the implementation of techniques readily available to the dentist and specialist alike. Alternate engine-driven non-rotary systems will tend to eliminate the stresses and uncertainty that are ever present with the extensive reliance on rotary instrumentation.

REFERENCES

1. Adorno CG, Yoshioka T, Suda H. The effect of root preparation technique and instrumentation length on the development of apical root cracks. J Endod. 2009;35(3):389–92. doi:10.1016/j.joen.2008.12.008  

2. Adorno CG, Yoshioka T, Suda H. Crack initiation on the apical root surface caused by three different nickel-titanium rotary files at different working lengths. J Endod. 2011;37(4):522–5. doi:10.1016/j.joen.2010.12.002 

3. Bier CA, Shemesh H, Tanomaru-Filho M, et al. The ability of different nickel-titanium rotary instruments to induce dentinal damage during canal preparation. J Endod. 2009;35(2):236–8. doi:10.1016/j.joen.2008.10.021 

4. Bürklein S, Tsotsis P, Schäfer E. Incidence of dentinal defects after root canal preparation: reciprocating versus rotary instrumentation. J Endod. 2013;39(4):501–4. doi:10.1016/j.joen.2012.11.045

5. Cheung GS, Liu CS. A retrospective study of endodontic treatment outcome between nickel-titanium rotary and stainless steel hand filing techniques. J Endod. 2009;35(7):938–43. doi:10.1016/j.joen.2009.04.016

6. Pettiette MT, Delano EO, Trope M. Evaluation of success rate of endodontic treatment performed by students with stainless-steel K-files and nickel-titanium hand files. J Endod. 2001;27(2):124–7. doi:10.1097/00004770-200102000-00017 

7. Bahcall JK, Carp S, Miner M, et al. The causes, prevention, and clinical management of broken endodontic rotary files. Dent Today. 2005;24(11):74, 76, 78-80; quiz 80.

8. Bahcall JK. Remedying and preventing endodontic rotary nickel-titanium (NiTi) file breakage. Compend Contin Educ Dent. 2013;34(5):324–7; quiz 328. 

9. Madarati AA, Watts DC, Qualtrough AJ. Factors contributing to the separation of endodontic files. Br Dent J. 2008;204(5):241–5. doi:10.1038/bdj.2008.152

10. Peters OA, Schönenberger K, Laib A. Effects of four Ni-Ti preparation techniques on root canal geometry assessed by micro computed tomography. Int Endod J. 2001;34(3):221–30. doi:10.1046/j.1365-2591.2001.00373.x 

11. Versiani MA, Leoni GB, Steier L, et al. Micro-computed tomography study of oval-shaped canals prepared with the self-adjusting file, Reciproc, WaveOne, and ProTaper universal systems. J Endod. 2013;39(8):1060–6. doi:10.1016/j.joen.2013.04.009 

12. Cheung LH, Cheung GS. Evaluation of a rotary instrumentation method for C-shaped canals with micro-computed tomography. J Endod. 2008;34(10):1233–8. doi:10.1016/j.joen.2008.07.015  

13. Iqbal MK, Kohli MR, Kim JS. A retrospective clinical study of incidence of root canal instrument separation in an endodontics graduate program: a PennEndo database study. J Endod. 2006;32(11):1048–52. doi:10.1016/j.joen.2006.03.001  

14. Martín B, Zelada G, Varela P, et al. Factors influencing the fracture of nickel-titanium rotary instruments. Int Endod J. 2003;36(4):262–6. doi:10.1046/j.1365-2591.2003.00630.x 

15. Shabbir J, Zehra T, Najmi N, et al. Access cavity preparations: classification and literature review of traditional and minimally invasive endodontic access cavity designs. J Endod. 2021;47(8):1229–44. doi:10.1016/j.joen.2021.05.007  

16. Wan J, Rasimick BJ, Musikant BL, et al. Cutting efficiency of 3 different instrument designs used in reciprocation. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2010;109(5):e82-5. doi:10.1016/j.tripleo.2009.12.037

17. Wan J, Rasimick BJ, Musikant BL, et al. A comparison of cyclic fatigue resistance in reciprocating and rotary nickel-titanium instruments. Aust Endod J. 2011;37(3):122–7. doi:10.1111/j.1747-4477.2010.00222.x

18. Kyomen SM, Caputo AA, White SN. Critical analysis of the balanced force technique in endodontics. J Endod. 1994l;20(7):332–7. doi:10.1016/S0099-2399(06)80095-6

19. Charles TJ, Charles JE. The ‘balanced force’ concept for instrumentation of curved canals revisited. Int Endod J. 1998;31(3):166–72. doi: 10.1046/j.1365-2591.1998.00137.x

ABOUT THE AUTHOR

Dr. Musikant has lectured worldwide in more than 150 locations and has coauthored more than 300 dental articles published in major dental journals. As a partner in a New York City endodontic practice, his 40-plus years of clinical experience have crafted him into one of the top authorities in endodontics.  He can be reached at (888) 542-6376, via email at info@essentialseminars.org, or via the website essentialseminars.org.

Disclosure: Dr. Musikant is director and co-founder of Essential Dental Systems. 

Do you ever stop to reflect that, as dentists, we are living in a truly amazing time? We have incredible technology at our fingertips, and patients are fortunate to have unprecedented access to dental care.

But no matter how much shiny, state-of-the-art technology is available, if dentists believe that a tooth can’t be saved, it automatically becomes impossible to save it. We were all taught to cultivate certain beliefs in dental school. However, have you ever thought, “I wonder if that tooth would respond to treatment?” Remembering your training, though, you decided the safest bet was to extract.

Over the years as a practicing endodontist, I’ve been privileged to witness so many “unsavable” teeth be saved that I knew I had to re-examine my own beliefs.

Today, I view myself as a tooth saver, and I’d like to encourage all of us to open ourselves up to new beliefs about which teeth can be saved. This way, we can serve our patients at an even higher level.

Teeth are so incredibly important, but since we treat them day in and day out, we sometimes lose sight of the bigger picture.

What if our beliefs were the most important piece of technology that we really needed to upgrade? Take a moment, step back, and think about it. I view our teeth as tiny little temples within our mouths—the gateway to our bodies. Our teeth help nourish and hydrate our bodies, and they give us confidence when we smile. Teeth are precious, and we were born with them for many reasons.

Right now, I believe we are being called to make a shift in our beliefs around saving vs extracting these precious pearls that Mother Nature gave each of us. That way, we can wholeheartedly help our patients.

We can each trust ourselves to save teeth, and we can trust the incredible power of the human body to heal when given proper treatment. Believe in your healing power as a dentist. 

I’m not asking you to shift your beliefs without evidence, though. So I’m going to use real tooth stories from my own practice to explore some of the biggest and most common dental beliefs about “unsavable” teeth. Once we shift these beliefs into the new, upgraded beliefs I will propose, we can make a long-lasting, positive impact on the patients we touch. Walk with me down Tooth Story Lane, and I hope you will feel inspired, empowered, and ready to make an upgrade to your beliefs.

COMMON BELIEF NO. 1: BIG LESIONS DON’T HEAL 

How do you feel when you encounter a big lesion? If you’re thinking, “It’s hopeless; let’s extract it,” you aren’t alone, my friend. Across the community of dental professionals, there are different views on whether these teeth should be extracted or saved.

It’s easy to be concerned about the amount of bone loss around the tooth. The general teaching in dentistry is that the tooth will not respond to treatment, especially when there is a loss of the buccal cortical plate. In this situation, it’s not uncommon for us, as dentists, to believe the treatment won’t work.

But there is a shining beacon of hope. We can actually see healing in this scenario when we shift our thinking. 

Understanding the pulpal diagnosis of the tooth—and furthermore, understanding the fact that when a patient has a necrotic pulp, it will create bone loss—is an essential part of this discussion.

Sometimes that bone loss is little, and sometimes it’s monstrously big. It will vary per case and per patient, so I encourage us not to be so quick to judge these situations with a blanket statement. If we solely look at the radiograph and treat it based on the size of that lesion without doing any endodontic diagnostic testing, we are making a diagnosis based on the limiting beliefs that have been imprinted on so many of us from our previous teachers. And that means that, despite our very best intentions and aspirations, we may be doing our patients a disservice.

It’s time to truly understand the disease process and step into our superhero roles as dentists to save teeth.  

A Tooth Story About a Giant Periapical Radiolucency

Take, for example, a 46-year-old woman who presented to my office after her dentist found a periapical radiolucency around tooth No. 31. She was asymptomatic, and there was a significant amount of circumferential bone loss.

I performed my endodontic diagnostic tests and found that the tooth had no response to cold, had no pain upon percussion, and had no mobility, believe it or not. Additionally, there was a 9-mm mid-buccal probing (all other areas of the tooth probed normally). I diagnosed the tooth as necrotic pulp and chronic apical abscess on No. 31 (Figures 1a and 1b).

Figure 1a. Preoperative periapical radiograph of tooth No. 31.

Figure 1b. Pre-op bite-wing radiograph of tooth No. 31.

Most of the time, when I present this case in my lectures, I ask the audience, “What would your treatment plan be?” The answer I most often get is “Extraction.” This is because we, as dentists, have been taught to believe that lesions of this size are incapable of healing.

Instead, what’s important to understand is that the endodontic diagnosis (not lesion size) is what will guide you to the right treatment plan.

Remember, necrotic pulps create bone loss, and sometimes that bone loss can be massive. That just happens to be what is natural for that particular patient, including the one I’m sharing with you here.

As an endodontist, I have learned to reframe the beliefs that I learned in dental school and to trust my diagnosis. So, in this case, I did the root canal (Figure 1c).

Figure 1c. Immediate final post-operative obturation radiograph of tooth No. 31.

Now, it’s just a matter of giving the body the time that it needs to regenerate that bone. This is the importance of following up with your patients when it comes to endodontics. One year later, I witnessed her great recovery. Some may call it a miracle, but it’s not. It’s simply the superpower that exists within all of us: the ability to regrow our own bone back (Figure 1d).

Figure 1d. One-year recall radiograph of tooth No. 31.

And at 2 years postoperatively, there was even more bone deposition and maturation (Figure 1e). 

Figure 1e. Two-year recall radiograph of tooth No. 31.

All of this occurred with root canal therapy only. There was no other dental intervention.  

This is not a one-off success story. It can happen time and time again in any practice—so long as we relax into what our bodies are capable of, like regrowing bone, given enough time and healing.

In sharing this case, I intend for us to understand and trust our diagnosis to save teeth. When we understand the etiology of the disease process, we can make a more effective and meaningful treatment plan that we can be confident will serve our patients.

But if we were taught that big lesions don’t heal, and we impose that belief on our patients, it may lead them in the wrong direction. So many other dentists would have extracted this tooth. 

I believe that when we, the providers, can reframe our dental beliefs to trust that lesions can heal with endodontic treatment—no matter their size—we can serve our patients to the fullest extent possible.

Tooth-saving belief No. 1: Lesions can heal with endodontic treatment, no matter their size.

COMMON BELIEF NO. 2: THE J-SHAPED RADIOLUCENCY MEANS THE TOOTH IS FRACTURED

The J-shaped radiolucency most certainly gets a bad reputation when making an endodontic diagnosis. And despite having more than a decade of endodontic experience as a specialist, it still makes me second-guess my own diagnoses when I see them.

However, we now know and accept that the human body will look for the pathway of least resistance to drain an infection, and this may just happen to look like a J-shaped radiolucency, meaning that the tooth is not cracked at all.

If there is one thing I could change about endodontic education within dental school, it would be to emphasize the fact that J-shaped radiolucencies are not synonymous with root fractures. 

If you are questioning the probing on the mid-buccal because you, like me, were taught that a probing equates to a root fracture—and, therefore, a non-restorable tooth—I want to address your concern. It is also not true that an area that probes is always associated with a root fracture. A probing can simply mean that the body found the pathway of least resistance to drain the infection and created a sinus tract (hence the diagnosis of a chronic apical abscess). 

This sinus tract can drain through the sulcus and does not need to look like a pimple on the gingiva. Unfortunately, this sinus tract clinically looks just like a probing that is associated with a root fracture, so it most definitely complicates the endodontic diagnosis and creates a layer of uncertainty.

Let’s explore an example to illustrate this point.

A J-Shaped Radiolucency Tooth Story

A 38-year-old woman had a previous root canal that appeared to be failing. When I looked at her preoperative radiographs, I could see that notorious J-shaped radiolucency around the mesial root and even some bone loss around the distal root (Figures 2a and 2b).

Figure 2a. Pre-op periapical radiograph of tooth No. 30.

Figure 2b. Pre-op bite-wing radiograph of tooth No. 30.

My diagnostic tests showed that there was some moderate tenderness to percussion and obviously no response to cold. All other findings were within normal limits, except that there was a 9-mm mid-buccal probing. The diagnosis was a previously treated and chronic apical abscess on No. 30.

I also obtained a pre-op cone beam, which more clearly delineated the classic J-shaped radiolucency (Figures 2c to 2f).

Figure 2c. Pre-op sagittal CBCT view of tooth No. 30.

Figure 2d. Pre-op axial CBCT view of tooth No. 30.

Figure 2e. Pre-op coronal CBCT view of the mesial root of tooth No. 30.

Figure 2f. Pre-op coronal CBCT view of the distal root of tooth No. 30.

I had a long discussion with the patient to present all of her treatment options, including endodontic re-treatment vs extraction. This is because I always want to empower my patients with knowledge so that they can make the best choices for their health.

We decided together that we both felt comfortable attempting the re-treatment to see if we could save the tooth. I told her that if I located an internal fracture under magnification, I would have to refer her for the extraction. 

The patient, however, wanted to do whatever it took to save her tooth, which meant giving treatment a try. I was on board with this plan because, over the years, giving teeth a chance has allowed me to see what magic our bodies are truly capable of.

Upon removing the gutta-percha and carefully inspecting the internal walls of the tooth, I didn’t see any sign of a fracture, so I continued to obturate the tooth (Figures 2g and 2h).  

Figure 2g. Immediate post-op radiograph of tooth No. 30.

Figure 2h. Immediate post-op off-angle radiograph of tooth No. 30.

As stated earlier, followup is the key to understanding the healing process in endodontics. I saw her back in my chair at her one-year post-op. She had almost completely regenerated all of her bone (Figure 2i).  

Figure 2i. One-year recall radiograph.

This patient does have a bit more healing to do, but this will continue to happen with more time. She has made remarkable progress for a lesion of this size, which extended into the furcal area. All that means is that it may take a bit longer to heal. Bone is slow to grow, so when you see a lesion of this magnitude and shape, it may take a few years to fully reconstitute with bone. “Bone can grow” is another empowering belief that I encourage each of us to embody in our practices in order to fully serve our patients.

Tooth-saving belief No. 2: J-shaped radiolucencies may be restorable.

COMMON BELIEF NO. 3: WHEN A CANAL CAN’T BE SEEN ON a CBCT, IT MEANS IT’S NOT THERE 

It is generally accepted that the MB2 canal of a maxillary first molar is one of the hardest canals to find and treat in the world of endodontics. Cone-beam technology has no doubt been a game-changer for me with respect to this canal. But it can also be a trap if we are not prepared to read the scans correctly.

Finding the proper support in reading these scans can also be a challenge after we have invested in CBCT technology, so I want to share a few secrets that I have learned, hoping you will have an easier time succeeding.

An MB2 Canal Tooth Story

This 42-year-old male patient was in need of a root canal due to a high level of pain. His pre-op radiographs showed a deep composite restoration on tooth No. 2 (Figures 3a and 3b). His endodontic diagnostic tests revealed that he had lingering pain to cold and tenderness to percussion. All other testing was within normal limits. I diagnosed tooth No. 2 with symptomatic irreversible pulpitis and symptomatic apical periodontitis.

Figure 3a. Pre-op periapical radiograph of tooth No. 2.

Figure 3b. Pre-op bite-wing radiograph of tooth No. 2.

Before I start any root canal, I always like to understand the internal canal anatomy of a tooth prior to the procedure. Therefore, I took a cone-beam scan (Figures 3c to 3e).  

Figure 3c. Pre-op sagittal CBCT view of tooth No. 2.

Figure 3d. Pre-op axial CBCT view of tooth No. 2.

Figure 3e. Pre-op coronal CBCT view of tooth No. 2.

The axial view of the CBCT scan is where a dentist could easily get stumped (Figure 3d). When looking at tooth No. 2, it appears as if there are only 3 canals: the MB, DB, and  P canals. However, when we look at the connecting root of the MB canal to the P canal, there is definitely more space that could house a teeny, tiny canal—even though you can’t actually see a fourth canal on the scan.  

It is really important to look at your cone-beam scan in all of its planes. In these situations, I particularly like to look at the tooth in the coronal view (Figure 3e).

Imagine a line going through the MB orifice and the P orifice (from the axial slice). This creates the coronal slice that you are seeing (Figure 3e). And now we can see that there is an MB2 canal that could not be seen as clearly in the axial view (Figure 3d). 

What did this tell me about this case, even before I accessed the tooth? It told me that this MB2 was going to be a tough one to find.

If we look at the axial view alone, it would be so easy to believe that there is no MB2 at all in this case. Unfortunately, that would have resulted in a root canal failure in the future, which neither the dentist nor the patient would want to happen! That’s why the thought that canals that can’t be seen on a CBCT scan simply aren’t there is ultimately a false belief that each of us needs to examine.

Remember the 2 cardinal rules of root canals: Root canals only work when we (1) find all the canals and (2) get to the end of every canal.

As a side note, this may be a great way to perform a risk assessment and see if this is a case that you want to take on in your practice or refer to a specialist. In my opinion, this type of canal configuration is one of the hardest to treat.

I am incredibly grateful that, thanks to my CBCT scanner, I can understand the difficulty level of the canal’s anatomy before I even get inside. This allows me to have a more meaningful conversation with my patients, and it also manages their expectations throughout the process of their treatment. 

With all of this additional information and guidance from my cone-beam scan, I was able to take this case to completion with confidence that I was addressing the entire tooth (Figures 3f to 3h). 

Figure 3f. Conefit radiograph of tooth No. 2.

Figure 3g. Backfill radiograph of tooth No. 2.

Figure 3h. Immediate post-op radiograph of tooth No. 2.

I hope that we’ll collectively adopt a new empowering belief that can lead to saved teeth: that the MB2 canal is almost always there, even if it isn’t easy to see. It’s better to assume it is than to risk a failed root canal and re-treatment.

Tooth-saving belief No. 3: The MB2 canal is almost always there, even if it isn’t easy to see.

COMMON BELIEF NO. 4: WHEN A TOOTH IS STILL SYMPTOMATIC AFTER ROOT CANAL THERAPY, THE TOOTH MUST BE CRACKED 

One of the most frustrating aspects of being an endodontist is when you complete a picture-perfect root canal and that tooth still bothers the patient afterward. It doesn’t happen very often, but when it does, it can feel so defeating. 

The uncertainty as to why that tooth is still giving our patients some pain can be frustrating. The typical explanation I have heard dentists give patients is that the tooth is cracked and now needs to be extracted.

But if we really think about it, this determination doesn’t ultimately serve our patients. Most of the time in these scenarios, the tooth is not cracked, but rather there is still some bacterial contamination in the tooth. So, my recommendation is to re-treat the root canal before we condemn the tooth. Consider this—would you extract your own tooth or your child’s tooth, or would you give it another chance?

This same clinical scenario has happened to me in my own practice, and my first instinct is to redo my own work. When the patient still feels something when he or she taps on that tooth, I always offer to try again to see if re-disinfecting the tooth’s canals helps the patient. Happily, it works about 80% of the time and the patient feels better.

The key is not to give up on your patient’s tooth when it’s savable. It’s totally okay to try again. Re-treating my own root canals has taught me many lessons, has changed my tooth beliefs permanently through years of evidence, and has made me a better clinician. I now understand root canal anatomy better than ever before, and I appreciate that the internal anatomy can really limit what we can do with traditional root canal therapy.

This has encouraged me to invest in additional technology, such as the GentleWave System (Sonendo), which can elevate my current root canal experiences and outcomes. 

Examples of Root Canal Re-treatment Success Stories

Figure 4 shows a few post-op radiographs of tooth stories that demonstrate what I mean about root canal anatomy.

Figure 4a. Post-op radiograph of tooth No. 21 (the smaller canal was not instru- mented with a rotary file, only activated irrigation via the GentleWave System [Sonendo]).

Figure 4b. Immediate post-op radiograph of tooth No. 15 (the smaller MB2 canal was not instrumented with a rotary file, only activated irrigation via the GentleWave System).

Figure 4c. Immediate post-op radiograph of tooth No. 19 (the smaller middle mesial canal was not instrumented with a rotary file, only activated irrigation via the GentleWave System).

These teeny tiny canals are areas where no rotary file can go—and they didn’t in these cases—which makes mechanical instrumentation difficult.

I treated all of these cases with GentleWave technology. This has solidified my belief that irrigation is instrumentation, and that makes it a crucial part of the endodontic future. It’s a huge paradigm shift, and it’s time to believe in it.

So, when we are in this situation, remember the new belief that teeth that are symptomatic after a root canal may not be cracked but just need re-treatment. That is because there could be a tiny canal somewhere that is still harboring a little bit of bacteria. 

It’s okay if you don’t have the same technology at your disposal, but my purpose is to bring awareness into your life so you know where to turn to take the next step to help your patients. Maybe this means you treat the tooth, or maybe this means you refer to a specialist with that technology for re-treatment before you extract the tooth. Remember, it’s all about saving the tooth, and that only happens if we give it a chance.

Tooth-saving belief No. 4: Symptomatic teeth after root canals may not be cracked and may need re-treatment.

OLD BELIEFS GIVE WAY TO NEW, EMPOWERING, TOOTH-SAVING BELIEFS

My intention with these tooth stories has been to bring all of us hope that we can save more teeth and to inspire us to think and evaluate carefully before we extract. 

I encourage us to think twice before taking a tooth out and to embrace my motto in life, which is #GiveTeethAChance. 

When we do, we’ll find that:

• “Big lesions don’t heal” becomes “lesion size is not a determinant of healing ability.”
• “The J-shaped radiolucency means the tooth is fractured and needs to be extracted” becomes “the J-shaped radiolucency is not synonymous with a root fracture.”
• “A probing equates to a root fracture and, therefore, a non-restorable tooth” becomes “a probing can simply mean that the body has found the pathway of least resistance, and that tooth can be saved.”
• “Bone doesn’t grow back” becomes “bone can regrow, but it is slow, so have patience.”
• “When a canal can’t be seen on a CBCT scan, it’s not there” becomes “look at your cone-beam scan in all of its planes, and assume that the MB2 is almost always there.”
• “When a tooth is still symptomatic after root canal therapy, it must be cracked” becomes “when a tooth is still symptomatic after root canal therapy, some of the infection may have been missed, and a re-treatment will lead to a good outcome.”

These are not the only situations where teeth that are typically extracted can be saved. I’ve shared specific situations because they’re very common and because I also want us to start seeing a pattern. If there’s one message I hope dentists take away from this article, it’s this final tooth-saving belief: You are a tooth saver and a tooth healer if you allow yourself to be. You have the ability to save teeth, even in scenarios in which you didn’t think it was possible. It only requires your belief.

I hope you are feeling excited and that you are already starting to believe in the ability of teeth to be saved. Most of all, I hope you are ready to take on the identity of a tooth saver.

I promise that the more we start to cultivate these new, empowering, tooth-saving beliefs and truly understand the power of our human bodies to heal, the more we can create better outcomes that lead to better lives for patients around the world.

ABOUT THE AUTHOR  

Dr. Chopra is a board-certified endodontist, TEDx speaker, Forbes contributor, author, endodontic instructor, and founder of Ballantyne Endodontics in Charlotte, NC. Through her award-winning endodontic CE course, E-School, she teaches tangible lessons to make root canals simple. She can be reached at soniachopradds.com or soniachopradds.com/e-school, or via the Instagram handle
@soniachopradds.

Disclosure: Dr. Chopra is a KOL for Sonendo. She did not receive compensation for writing this article.  

With the arrival of NiTi engine-driven files and mechanized instrumentation systems, root canal instrumentation became exponentially faster and somehow more predictable compared to manual instrumentation techniques. However, with the popularization of these files in recent decades, a breach between speedy preparation and infection control becomes evident, especially regarding the time and volume of irrigating fluid during the operation. Nevertheless, it is undeniable that the technical advance arising from NiTi engine-driven files has benefited the endodontic technique. The question is what is more important, speed or infection control? Naturally, the answer lies in infection control efficiency, without which the repair process will be impossible.

Rapid canal shaping impairs the quality of cleaning and disinfection processes based on the sodium hypochlorite (NaOCl) action principle. It does not provide the time necessary to accomplish either and gives even less time to guarantee the volume and renewal of the irrigating liquid, which can compromise the main objective of the treatment.¹ This realization has triggered a change in the primary goal of root canal preparation. Mechanical instrumentation currently provides access to the apical morphology of the canal. It allows irrigants to flow, which is expected to accomplish most of the cleaning and disinfection. Therefore, the focus gradually shifted from types of irrigants to delivery methods and ways to enhance their effectiveness within the intricate root canal system.

The ideal mechanical preparation should uniformly debride and enlarge the entire perimeter of the root canal. However, micro-CT-based studies show inadequate canal preparation with engine-driven files (Figure 1) despite their design or kinematics (rotation or asymmetric reciprocation movements). As a result, microorganisms that remain on unprepared dentin walls may have the opportunity to recolonize the canal system, compromising the treatment outcome.^2,3

Another critical point to be considered is to clean the canal space while preserving the maximum sound structure of the tooth. As already noted, current endodontic instruments have not evolved sufficiently to the point of adapting perfectly to the anatomy of the root canal during their use. Thus, the unnecessary removal of sound dentin tissue results from any preparation protocol currently available because of the need to reach all the root canal walls. Even performing more minor dentin-cutting maneuvers with small instruments—the minimally invasive preparation—does not seem to reduce unnecessary dentin removal significantly⁴ and can compromise proper cleaning and root canal disinfection.⁵

A side effect of mechanical preparation is hard-tissue debris accumulation,⁶ which carries the likelihood of being more clinically relevant than the smear layer. Engine-driven shaping produces and packs dentin debris into irregular areas of the canal space, with a sizable accumulation of debris in fins, isthmuses, and irregularities with ramifications of the complex canal network. In addition, non-removed debris could easily harbor bacteria biofilm from the disinfection procedures and reduce the antiseptic activity of the irrigating solution.^7-9

THE QUINTESSENTIAL IMPORTANCE OF IRRIGATION

From a didactic point of view, the endodontic technique is divided into separate steps or phases so that the student can understand and practice systematically; from a clinical standpoint, the process is quite different. Cleaning and shaping should be seen as one single procedure. Mechanical instrumentation opens the way for the action of chemical disinfection through the use of irrigating solutions and intracanal medicaments. The initial cleaning of root canals is commonly performed by mechanical instrumentation, which removes the large bulk of the pulp tissue, the necrotic debris, bacterial biofilms, and/or a previous root filling. Unless this bulk material is first removed, no further cleaning is possible. Nevertheless, it is prudent to state that final intracanal disinfection mainly depends on the physicochemical activity of irrigation. Reaching areas not touched during the mechanical preparation with NaOCl solution is necessary to dissolve the biofilm and remaining necrotic tissues. When instruments fail to prepare the canal walls in complex canal systems, such as in molars or even oval canals, the chemical action of sodium hypochlorite is the last opportunity to gain control of the infectious contingent within the root canal system.

Recent histological and micro-CT analysis studies have determined that the instrumentation leaves around 40% of the walls untouched.^10,11 Furthermore, the conventional irrigation technique with a syringe and an open-ended cannula does not solve the problem. There is conclusive evidence in the literature that more effective irrigation techniques related to accessing irrigation fluids in critical areas—for instance, the last apical millimeters and isthmuses and irregularities—should be used instead of the conventional irrigation technique.^12,13

It seems paradoxical that, on the one hand, instrumentation techniques have undergone an extraordinary evolution with NiTi instruments capable of cutting significant amounts of dentin in short periods, yet on the other hand, the NaOCl solution requires a more extended time than that required by mechanical instrumentation to reach its full potential.^14-16 The result is that the root canal is shaped but not properly cleaned and disinfected.

In the syringe-cannula classic irrigation method, irrigants are delivered deeply into the canal space using positive pressure irrigation through a cannula connected to a syringe via applying finger pressure on the syringe plunger, which pushes the irrigant solution through the cannula into the canal space by directly injecting the solution. In contrast, the suction cannula simultaneously aspirates it. The high flow rate used to introduce the irrigant into the canal results in technique-related factors that increase irrigant pressure at the apical portion of the canal when open-ended cannulas are used. This can sometimes extrude the solution periapically, resulting in tissue damage and postoperative pain. The proper frequency of such accidents is unknown as many of them may not be reported. Minor extrusion incidents might even remain undetected due to the absence of severe symptoms. A 2008 survey of endodontists in the United States indicated that nearly half of the respondents (42%) had experienced at least one NaOCl accident during their practice careers.¹⁷ The extrusion accident, and its consequences, explain why most clinicians often avoid a closer approach to the working length while irrigating with NaOCl solution. Regarding its efficacy, conventional syringes and open-ended cannula irrigation leave a large amount of debris clogged in the irregularities of the root canal system and do not efficiently deliver the irrigant solution into the apical third of the canal.¹⁸

Figure 1. (a) Representation of a micro-CT cross section of a ribbon-shaped canal space. (b) Engine-driven file action after instrumentation, leaving non-touched areas.

Figure 2. Representation of different end types of cannulas: (a) open-ended; (b) notched-ended; and (c) side vented, close-ended.

Figure 3. Vapor lock or blockage in a 0.50-mm (ID) capillary glass tube.

Modifications in the distal end of the irrigation cannulas were carried out to minimize the problem of accidental NaOCl extrusion. This allowed the use of these closed-ended cannulas in a position closer to the working length, resulting in the development of lower liquid pressure at the apical foramen compared to open-ended cannulas. The modification directly affects the irrigant flow rate, the most frequently reported technique-related factor in extrusion accident case reports. Closed-ended, open-side cannulas (Figure 2, right) vary in diameter, length, and tip design. Because of its lateral laminar flow (and not contiguous along the long axis of the cannula), safety is improved. However, it has a negative impact on the effectiveness of irrigation in some areas of the canal, predominantly in the last apical millimeters.

Additionally, it is well documented that a “dead water” or stagnation zone is produced between the tip of the closed-end cannula and the apex, where no flow of irrigation occurs,^19-21 resulting in the accumulation of debris in this region.²² This phenomenon, known as the “vapor lock effect or blockage” (Figure 3), has been confirmed in both in vitro and in vivo studies.^23,24 Its origin is attributed to the interaction between the trapping of air bubbles caused by the irrigation distribution (positive pressure) and the gas production created by the chemical reaction of NaOCl with organic tissues. As a result, a vapor lock could theoretically block the irrigant from flowing toward the apical third. The phenomenon is described as the difficulty of irrigant solution dispersion in a narrowed space such as the root canal.

APICAL NEGATIVE PRESSURE IRRIGATION 

There is substantial evidence showing that the apical negative pressure irrigation (ANPI) method can improve the cleaning and disinfection process and the overall safety of the irrigation procedure.^25-30 ANPI efficiency depends on the suction cannula’s positioning at the canal’s apical region, which aspirates the irrigating solution supplied in the pulp chamber. The first commercial irrigation system using ANPI (EndoVac [Kerr]) became available in 2007. The irrigating solution circulates through the canal by creating a negative apical pressure in the working length and generating a rapid apical-oriented fluid stream that allows the use of a greater volume of the solution than conventional irrigation and better control of the apical extrusion. Despite the efficacy shown, the EndoVac included design drawbacks severely limiting its clinical practice use. One of the features is the micro-cannula end, which consists of 12 micro-ports within the first 1 mm near the distal end with a diameter of 0.10 mm (Figure 4). The port’s diameter is minimal and frequently clogs due to dental pulp fragments and cut dentin debris being sucked into the ports during use.³¹

Figure 4. Representation of the EndoVac (Kerr) end cannula.

SONIC AND ULTRASONIC IRRIGANT ACTIVATION

The effectiveness of irrigation relies on both the mechanical flushing action and the chemical ability of irrigants to dissolve the tissue and control the infection. Sonic and ultrasonic activation/irrigation techniques are designed to create acoustic microstreaming and transient cavitation that push the irrigant laterally into the irregularities of the canal. Acoustic microstreaming is defined as a rapid movement of fluid in a vortex motion, generating shear stresses that enhance debridement. Transient cavitation causes bubbles that, when collapsing, produce radiating shockwaves and a rise in temperature, increasing efficiency.^32-35 In addition, studies reported that both sonic and ultrasonic devices might remove the smear layer^36,37 and have better disinfection ability^38,39 compared to conventional irrigation. One of the most used techniques is passive ultrasonic irrigation (PUI). “Passive” refers to the noncutting action of the tip or ultrasonic insert used in the procedure. PUI uses a K-file type insert or a smooth file attached to a connector and an ultrasonic handpiece in through which vibration is supplied. 

After the completion of mechanical preparation, PUI can be used in either intermittent or continuous mode. In the intermittent option, the canal is first filled with the chemical solution using a syringe and cannula. Next, an ultrasonic insert is activated in the canal up to 2 mm from the working length. The tip is moved passively with an in-and-out motion to avoid binding with the root canal walls. Although sonic or ultrasonic activation performs better than conventional irrigation, some limitations, such as not reaching the last apical millimeters and only moving the residues inside the canal and not removing them, are still controversial points in this technique. 

Continuous ultrasonic passive irrigation is achieved by simultaneously and continuously delivering irrigation during ultrasonic activation through the irrigation insert (Figure 5), in contrast to intermittent PUI, which needs manual (syringe and cannula) replacement of the liquid inside the canal. The chemical solution (NaOCl or EDTA) is housed in a reservoir or in attached irrigant bottles placed on the ultrasonic unit. The irrigant will be continuously dispensed, providing a fresh reactant for the irrigation’s chemical reaction. By constantly using a new reactant, the chemical reaction will always favor tissue dissolution, keeping a high concentration of chlorine (in the case of NaOCl) and a high concentration of chelating action (in the case of EDTA) in the canal.^40,41

Figure 5. Continuous ultrasonic passive irrigation with the Sonus Polysonic irrigation/activation tip (Medidenta).

PUTTING EVERYTHING TOGETHER FOR A NEW APPROACH

The iVac System (Pac-Dent) (Figure 6)⁴² brings a new approach to some limitations of the irrigation/activation systems previously discussed. The method continuously delivers the irrigation liquid to the entire working length without apical pressure, alongside concomitant ultrasonic activation and a safe evacuation via negative pressure (Figure 7). The iVac system consists of a non-tapered 0.35- or 0.50-mm-diameter polymer cannula (Figure 8) self-threaded to a piezo ultrasonic connector (iVac S or iVac E [Pac-Dent]). The connector will be coupled to a piezoelectric ultrasonic handpiece, providing vibrations to the iVac cannula and delivering concomitant irrigation from the reservoir (Figure 9). The vibration will help carry the irrigation fluid throughout the canal extension, alongside the external cannula surface, and be recollected via the apical opening. The iVac piezo ultrasonic connector has a passageway that provides a continuous flow path for delivering fluid to the pulp chamber and root canal, projecting the liquid at the polymer cannula’s external surface through an opening near the threading housing (Figure 10a, red arrow). The other end of the iVac cannula will be connected to the evacuation tubing (Figure 10a, green arrow), creating negative pressure powered by the standard evacuation equipment. Additional evacuation is necessary since the volume of liquid during irrigation will be bigger than the negative pressure suction capacity (Figure 10b).

Figure 6. The iVac system (Pac-Dent) includes (a) 0.35- mm cannulas (green), (b) 0.50-mm cannulas (yellow), (c) rings, (d) S-type insert, (e) low-vac and high-vac con- nectors, (f) angled capillary tips, (g) small tubes, and (h) a long tube.

Figure 7. (a) An iVac tip connected to a piezoelectric ultrasonic handpiece. The irrigation solution will come from the connector (blue arrows). The 0.35- or 0.50-mm cannula will vibrate and collect the liquid via negative pressure (red arrows). (b) Sequential action of the iVac in a capillary glass tube showing the negative pressure aspiration of the content (golden phosphorescent particles) with simultaneous activation/irrigation.

Figure 8. The 0.35-mm (green) iVac cannula.

Figure 9. The iVac piezoelectric unit (Pac-Dent).

Figure 10. (a) Connector irrigant exit port (red arrow) and evacuation tubing connected to the distal end of the iVac cannula (green arrow). (b) An additional evacuation cannula (yellow arrow) and the iVac in action.

There are some unique aspects regarding the iVac system. First, the polymer cannula has a single continuous evacuation path that creates negative pressure, allowing a large volume of irrigation fluid to reach the working length without being extruded. Second, the configuration of the cannula assembly transfers ultrasonic vibrations, which provide a microstreaming effect and proper activation of the irrigation liquid. Third, the connection with the piezoelectric handpiece provides continuous automated irrigation flow that doesn’t require secondary assembly with a syringe or an irrigation pump (Figure 11). Finally, the iVac polymer cannula is disposable, and the iVac ultrasonic connector can be cleaned, appropriately sterilized, and reused. The iVac system can be used with the majority of piezo ultrasonic units on the market. 

Figure 11. (a) The iVac in action. Note the activation of sodium hypochlorite (foaming effect) inside the pulp chamber/root canal (red arrow). (b) Optionally, the irrigation can be done using a syringe-cannula dripping irrigant inside the pulp chamber (green arrow).

Aiming to solve the clogging problem encountered by the previously cited EndoVac (Kerr) system, the iVac features an aspiration cannula with an outer diameter of 0.35 mm and an inner diameter of 0.15 mm. The latter offers superior suction capacity compared to EndoVac, with the advantage of being less likely to clog. In addition, the simultaneous ultrasonic vibration helps move debris and fluid removed from the canal inside the cannula.

The system features continuous flush irrigation, providing an uninterrupted supply of fresh solution during the procedure, reducing the time required for final irrigation compared to PUI, and achieving better results in removing debris from the apical third.⁴³ The iVac cannula provides the same level of ultrasonic vibration as the metal tips used in the PUI. However, they are more flexible and do not break during use. In addition, metallic inserts for PUI are usually designed using a K-file as a base, showing unintentional dentin removal. Furthermore, by using a polymer cannula, the chances of separating the cannula within the canal are low, if any.

CLOSING COMMENTS

The perceived importance of irrigation on the outcome of root canal treatment has grown considerably over the last decade. It seems paradoxical that mechanical instrumentation creates more debris during the action of the instruments and doesn’t reach areas of the canal due to the anatomy of the root canal system. Effective cleaning comes from the irrigation liquids, which must be appropriately used by respecting appropriate volume, time of action, and concentration. In addition, the full extension of the canal to the apical foramen must be achieved, especially with NaOCl. Even the best irrigating solution would be pointless if it could not reach its targets in the root canal system in sufficient amounts.⁴⁴

REFERENCES

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7. Haapasalo M, Shen Y, Wang Z, et al. Irrigation in endodontics. Br Dent J. 2014;216:299-303. doi:10.1038/sj.bdj.2014.204

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9. Portenier I, Haapasalo H, Rye A, et al. Inactivation of root canal medicaments by dentine, hydroxylapatite and bovine serum albumin. Int Endod J. 2001;34:184–8. doi:10.1046/j.1365-2591.2001.00366.x

10. Paqué F, Balmer M, Attin T, et al. Preparation of oval-shaped root canals in mandibular molars using nickel-titanium rotary instruments: a micro-computed tomography study. J Endod. 2010;36:703–7.  doi:10.1016/j.joen.2009.12.020

11. Paqué F, Peters OA. Micro-computed tomography evaluation of the preparation of long oval root canals in mandibular molars with the self-adjusting file. J Endod. 2011;37:517–21. doi:10.1016/j.joen.2010.12.011

12. Jena A, Sahoo SK, Govind S. Root canal irrigants: a review of their interactions, benefits, and limitations. Compend Contin Educ Dent. 2015;36(4):256–64. 

13. Boutsioukis C, Gutierrez Nova P. Syringe irrigation in minimally shaped root canals using 3 endodontic needles: a computational fluid dynamics study. J Endod. 2021;47(9):1487–95.  doi:10.1016/j.joen.2021.06.001

14. Teixeira CS, Felippe MC, Felippe WT. The effect of application time of EDTA and NaOCI on intracanal smear layer removal: an SEM analysis. Int Endod J. 2005;38(5):285–90. doi:10.1111/j.1365-2591.2005.00930.x

15. McDonnell G, Russell AD. Antiseptics and disinfectants: activity, action, and resistance. Clin Microbiol Rev. 1999;12(1):147–79. doi:10.1128/CMR.12.1.147

16. Naenni N, Thoma K, Zehnder M. Soft tissue dissolution capacity of currently used and potential endodontic irrigants. J Endod. 2004;30(ll):785–7. doi:10.1097/00004770-200411000-00009

17. Kleier DJ, Averbach RE, Mehdipour O. The sodium hypochlorite accident: experience of diplomates of the American Board of Endodontics. J Endod. 2008;34:1346–50. doi:10.1016/j.joen.2008.07.021

18. Waltimo T, Trope M, Haapasalo M, et al. Clinical efficacy of treatment procedures in endodontic infection control and one-year follow-up of periapical healing. J Endod. 2005;31:863–6. doi:10.1097/01.don.0000164856.27920.85

19. Fernandez Rivas D, Verhaagen B, Seddon JR, et al. Localized removal of layers of metal, polymer, or biomaterial by ultrasound cavitation bubbles. Biomicrofluidics. 2012;6:34114. doi:10.1063/1.4747166

20. van der Sluis LW, Versluis M, Wu MK, et al. Passive ultrasonic irrigation of the root canal: a review of the literature. Int Endod J. 2007;40:415–26. doi:10.1111/j.1365-2591.2007.01243.x

21. Shankar PN, Deshpande MD. Fluid mechanics in the driven cavity. Annu Rev Fluid Mech. 2000;32:93–136. doi:10.1146/annurev.fluid.32.1.93

22. Tay FR, Gu LS, Schoeffel GJ, et al. Effect of vapor lock on root canal debridement by using a side-vented needle for positive-pressure irrigant delivery. J Endod. 2010;36:745–50. doi:10.1016/j.joen.2009.11.022

23. Agarwal A, Deore RB, Rudagi K, et al. Evaluation of apical vapor lock formation and comparative evaluation of its elimination using three different techniques: an in vitro study. J Contemp Dent Pract. 2017;18:790–4. doi:10.5005/jp-journals-10024-2128

24. Vera J, Arias A, Romero M. Effect of maintaining apical patency on irrigant penetration into the apical third of root canals when using passive ultrasonic irrigation: an in vivo study. J Endod. 2011;37:1276–8. doi:10.1016/j.joen.2011.05.042

25. Abarajithan M, Dham S, Velmurugan N, et al. Comparison of Endovac irrigation system with conventional irrigation for removal of intracanal smear layer: an in vitro study. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2011;112:407–11. doi:10.1016/j.tripleo.2011.02.024

26. Buldur B, Kapdan A. Comparison of the EndoVac system and conventional needle irrigation on removal of the smear layer in primary molar root canals. Niger J Clin Pract. 2017;20:1168–74 .doi:10.4103/1119-3077.181351

27. Buldur B, Kapdan A. Comparison of the antimicrobial Efficacy of the EndoVac system and conventional needle irrigation in primary molar root canals. J Clin Pediatr Dent. 2017;41:284–8. doi:10.17796/1053-4628-41.4.284

28. de Miranda RG, Gusman HD, Colombo AP. Antimicrobial efficacy of the EndoVac system plus PDT against intracanal Candida albicans: an ex vivo study. Braz Oral Res. 2015;29:S1806–83242015000100308. doi:10.1590/1807-3107BOR-2015.vol29.0129

29. Nielsen B, Craig Baumgartner J. Comparison of the EndoVac system to needle irrigation of root canals. J Endod. 2007;33:611–5. doi:10.1016/j.joen.2007.01.020

30. Parente JM, Loushine RJ, Susin L, et al. Root canal debridement using manual dynamic agitation or the EndoVac for final irrigation in a closed system and an open system. Int Endod J. 2010;43:1001–12. doi:10.1111/j.1365-2591.2010.01755.x

31. Mitchell RP, Yang SE, Baumgartner JC. Comparison of apical extrusion of NaOCl using the EndoVac or needle irrigation of root canals. J Endod. 2010;36:338–41. doi:10.1016/j.joen.2009.10.003

32. Căpută PE, Retsas A, Kuijk L, et al. Ultrasonic irrigant activation during root canal treatment: a systematic review. J Endod. 2019;45:31-44. E13. doi:10.1016/j.joen.2018.09.010

33. Dioguardi M, Gioia GD, Illuzzi G, et al. Endodontic irrigants: different methods to improve efficacy and related problems. Eur J Dent. 2018;12:459–66. doi:10.4103/ejd.ejd_56_18

34. Plotino G, Cortese T, Grande NM, et al. New technologies to improve root canal disinfection. Braz Dent J. 2016;27:3–8. doi:10.1590/0103-6440201600726

35. Silva E, Rover G, Belladonna FG, et al. Effectiveness of passive ultrasonic irrigation on periapical healing and root canal disinfection: a systematic review. Br Dent J. 2019;227:228–34. doi:10.1038/s41415-019-0532-z

36. Rius L, Arias A, Aranguren JM, et al. Analysis of the smear layer generated by different activation systems: an in vitro study. Clin Oral Investig. 2021;25:45-51. doi:10.1007/s00784-020-03355-9

37. Urban K, Donnermeyer D, Schäfer E, et al. Canal cleanliness using different irrigation activation systems: a SEM evaluation. Clin Oral Investig. 2017;21:2681–7. doi:10.1007/s00784-017-2070-x

38. Ma JZ, Shen Y, Al-Ashaw AJ, et al. Micro-computed tomography evaluation of the removal of calcium hydroxide medicament from C-shaped root canals of mandibular second molars. Int Endod J. 2015;48:333–41. doi:10.1111/iej.12319

39. Neuhaus KW, Liebi M, Stauffacher S, et al. Antibacterial efficacy of a new sonic irrigation device for root canal disinfection. J Endod. 2016;42:1799–803. doi:10.1016/j.joen.2016.08.024

40. Layton G, Wu WI, Selvaganapathy PR, et al. Fluid Dynamics and Biofilm Removal Generated by Syringe-delivered and 2 Ultrasonic-assisted Irrigation Methods: A Novel Experimental Approach. J Endod. 2015;41(6):884–9. doi:10.1016/j.joen.2015.01.027

41. Plotino G, Colangeli M, Özyürek T, et al. Evaluation of smear layer and debris removal by stepwise intraoperative activation (SIA) of sodium hypochlorite. Clin Oral Investig. 2021;25(1):237–45. doi:10.1007/s00784-020-03358-6

42. Ramos CAS. Ultrasonic negative pressure irrigation and evacuation high-performance polymer micro-capillary cannula (U.S. Patent No. 63221851). U.S. Patent and Trademark Office, 2021.

43. Bueno CRE, Cury MTS, Vasques AMV, et al. Cyclic fatigue resistance of novel Genius and Edgefile nickel-titanium reciprocating instruments. Braz Oral Res. 2019;33:e028. doi:10.1590/1807-3107bor-2019.vol33.0028

44. Boutsioukis C. Root canal irrigation: beyond the tsunami. ENDO EPT. 2019;13(2):87–8. 

ABOUT THE AUTHOR

Dr. Ramos graduated with a degree in dentistry from the State University of Londrina in Brazil (1987). He has a PhD in endodontics and is a former head of the endodontics department at the State University of Londrina. He can be reached at spironelli05@gmail.com.

Disclosure: Dr. Ramos reports no disclosures.

It has been well-documented that the “triad” for success in endodontics includes instrumentation, irrigation, and obturation. Without proper instrumentation, effective irrigation and obturation become nearly impossible, as it is the instrumentation that facilitates adequate disinfection and then obturation. A delicate balance must be struck when instrumenting a canal. On the one hand, we must create sufficient space in the canal to accommodate irrigants and medicaments for proper disinfection. On the other hand, we must preserve radicular dentin to maintain the tooth’s structural integrity and its resistance to future fracturing. The goal of endodontics is not only to eliminate infection but also to ensure the tooth survives long-term. Proper instrumentation is essential in achieving these goals.

There has clearly been a revolution in the realm of instrumentation. The time is gone when one might spend countless visits hand instrumenting a root canal. Today, we have the most efficient systems, utilizing nickel titanium (NiTi) rotary files that allow for a relatively quick and seamless canal preparation compared to instrumentation with stainless steel hand files.¹ As the saying goes, “with great power comes great responsibility,” and instrumentation with NiTi rotary systems is no exception. The dreaded file separation is something that anyone who has ever performed root canal therapy has experienced. The question is not how to deal with file separation but rather how to avoid it in the first place. 

NiTi is a “superelastic” metallic alloy that, when flexed, undergoes an austenitic-martensitic transformation from its original structure, making it extremely flexible.^2-5 This transformation usually happens when the metal is stressed, such as during the instrumentation of the root canal. If, however, the NiTi file is stressed beyond its elastic limit, it will break. One of the unique characteristics of NiTi is its “shape memory,” allowing it to be deformed during usage and then return to its original shape if it is not stressed beyond its elastic envelope.⁵ NiTi files also have high elastic flexibility in bending and torsion compared to stainless steel files. Flexibility is the hallmark of NiTi rotary files, and it is this feature that allows it to overcome one of the greatest challenges of root canal instrumentation, namely following the sharp and unexpected curves contained in most canals without causing iatrogenic damage, such as canal transportation—in essence, “respecting” canal anatomy (RCA) (Figures 1 and 2). Unfortunately, stainless steel files, in larger sizes, do not provide this same benefit. It is often forgotten that most canals have some curvature, whether in the mesiodistal dimension (noted radiographically) or buccolingually (not seen in 2D radiographs).⁶ When NiTi rotary files are used correctly, they are significantly faster and more efficient than stainless steel hand files.^7-10 

Figure 1. Altered apical anatomy: canal anatomy was not maintained due to increased dentin removal at the outer aspect of the curve caused by stiff files that often seek to return to their original shapes.

Figure 2. Cases that demonstrate “respecting root anatomy” via consistently maintaining canal curvatures.

Another unique feature of NiTi files is their tip design. When we think of a file, we think of an instrument that cuts along its entire length. Not so with most NiTi files, which have non-cutting tips that guide the instrument to the apical portion of the root canal. There is ample evidence that this feature makes NiTi superior in maintaining the original canal curvature, preserving the apical constriction, and avoiding canal transportation.¹¹ When instrumenting a canal, one of 2 things will likely happen: You will accommodate the canal by following its complex and tortuous anatomy, or the canal will accommodate you by straightening itself out to accommodate your aggressive instrumentation. The process of instrumenting a canal will only be a successful endeavor when one learns to accommodate the canal and not vice versa.

During root canal preparation, our goal is to maintain the original canal anatomy and to avoid iatrogenic canal transportation. What follows are some tips to help navigate calcified and curved canals while avoiding the unfortunate file separation and/or iatrogenic damage to root structure. Avoiding these errors and “respecting” apical anatomy will lead to greater outcomes in our endodontic treatment.

TIP NO. 1: HAND FILES FIRST!

There was a time when instrumenting a canal was accomplished completely with hand files, which could take many visits. The pendulum has swung, and now with NiTi rotary instrumentation, endodontic treatment can be carried out more seamlessly in less time. There is the misconception, however, that rotary files have replaced hand files completely. This couldn’t be further from the truth. Many practitioners will try incorrectly to jump straight to rotary. It is important to remember that without first obtaining a smooth glide path to the apex with hand files, rotaries will be stressed beyond their elastic limits, leading to needless file separations. Hand filing a canal, as opposed to rotary instrumentation, provides tactile sensation, which allows one to better gauge the level of curvature and calcification. As a general rule, rotary files should never be placed in a canal before the canal has been properly “scouted” with hand files. If you can’t get a hand file to length in a canal, rest assured that if you then try to force a rotary into that same canal, the chances of separation and/or transportation are high.  

TIP NO. 2: CORONAL FLARE

NiTi rotary instrument fractures can be greatly reduced by creating a proper coronal flare.^12-14 This allows the unobstructed penetration by the hand file and then later the rotary file all the way to the working length. This is done by preflaring the canal orifice with a NiTi orifice opener, which is placed only in the coronal third of the canal. Most rotary systems will contain an orifice opener (Figure 3a). The benefit of this file is its short length and wider taper. This is also one of the goals of the “crown-down” instrumentation technique. By removing coronal interferences and restrictive dentin from the coronal third of the canal, one will have a much easier time placing both hand files and rotary files into the canal and then down to length. The orifice opener eliminates the “triangle of dentin,” which obstructs the orifice (Figure 4). You may successfully leave this triangle of dentin and negotiate around it, but this puts tension on the file at the occlusal end, making it more likely to separate should it find additional tension when negotiating an apical curve. The ProTaper S1 file (Dentsply Sirona Endodontics) (Figure 3b) is another great favorite of many endodontists for flaring the coronal and middle thirds of the root canal.

Figure 3. (a) Orifice openers and (b) shaping file.

Figure 4. (a) “Triangle of dentin” obstructing entry into the root canal—the file is strained from navigating 2 curves instead of one. (b) The triangle of dentin is removed once the canal is coronally flared. (c) Unobstructed penetration of the file into the canal orifice and then the entire root canal system.

This file has the benefit of having a very narrow tip with a taper that allows for proper shaping of the coronal and middle thirds of the canal. It is prudent to remember that these rotary files should only be used after the canal has first been scouted with hand files. It is always important to stress moderation, as “over-flaring” a canal can weaken the tooth by removing too much dentin in critical zones, so while flaring is beneficial for many reasons, it should be done as conservatively as possible to avoid removing too much dentin, thereby weakening the root. The TruNatomy orifice opener (Dentsply Sirona Endodontics) (Figure 3a) is a great example of a file that appropriately flares the canal orifice without excessively removing dentin from the critical zones. One of the most important components for long-term tooth survival is maintaining as much dentin as possible, specifically pericervical dentin (PCD), which is the dentin near the alveolar crest (Figure 5). Preserving the dentin above and below the canal orifice/alveolar crest is crucial for long-term survival of the tooth.^15,16

TIP NO. 3: GLIDE PATH 

Another important component in proper instrumentation is establishing a glide path, which is the creation of a predictable path so that the rotary file can reach all the way to the working length unencumbered. The first step in creating this glide path is by hand filing the canal to at least a size  15 hand (K-) file. Although it is possible to skip the size 15 in loose canals, a tight canal will not accept a rotary file well before it has been opened to at least a size 15 K-file. Before one ever places a rotary file to length in a canal, he or she should first instrument the canal comfortably with an 8, a 10, and a 15 hand file to help remove the restrictive dentin and allow for a more predictable glide path. The orifice opener or ProTaper S1 can also help to establish this glide path. While most endodontists use K-files for hand instrumentation, a much stiffer C or C+ file can also help to loosen up a tight canal, as smaller size K-files will often buckle when encountering a tight canal. The use of these hand files will, in essence, pave the pathway for the first rotary instrument to length and reduce the chance of separation of the rotary files. Establishing the glide path also causes less canal transportation (“ledging”) as compared to preparations done without a glide path. To quote Dr. Cliff Ruddle, “Whoever owns the glide path wins the shaping game of endodontics.” 

TIP NO. 4: SEQUENCE MATTERS! 

Don’t skip around. If you start with a size 8 file, don’t skip to a size 15 as your next file in the canal. While this might be okay in a looser canal, developing healthy habits while instrumenting is important. It is tempting to cut corners, especially when hand filing a canal, as this can be quite tedious. This will place more stress on the larger size files and increase the odds of instrumentation errors, such as canal blockage and/or ledging (Figure 1). 

TIP NO. 5: RECAPITULATION

After each use of a rotary file, make sure to re-enter the canal with a smaller hand file. Rotary instrumentation creates a significant amount of debris, which can clog up the canal, negatively affecting the ever-important glide path. What occasionally happens is that, at some point during the instrumentation process, your file no longer reaches the working length. This is because either the canal has been ledged or, more commonly, dentinal debris has clogged a portion of the canal. Re-entering with smaller files throughout the instrumentation process to break up this debris allows for maintenance of the glide path. Putting a slight bend on the tip of the hand file can also help work around a blockage. Trying to penetrate this blockage with a rotary file will inevitably lead to file separation. Without the glide path, we end up stressing (pushing too hard on) the NiTi files, ultimately leading to fracture. 

TIP NO. 6: REUSE OF NICKEL TITANIUM FILES

How many times is too many? File fatigue will depend on several variables, including instrument properties, canal morphology, and operator skills.¹⁷ For example, working one calcified canal will stress a file more than working multiple “loose” canals. Forcing a file in a tight or curved canal will fatigue it more than placing a file in a relatively straight and loose canal. Thus, there is no magic number of times a file can be used. It is prudent to often examine the cutting edges for wear and strains. 

TIP NO. 7: ROTARY MOVEMENTS

Stopping the rotary file midway down a canal will put more pressure and stress on the file, predisposing it to fracturing because of cyclic fatigue. Constant movement of the rotary file within the canal will better distribute the forces and prevent breakage. The rotary file should be in motion as it is removed from the canal. Stopping the motor while the file is in the canal can potentially cause the file to get locked into a tight spot and separate.^18-25 A rotary file should be used in an “in-and-out” (pecking) motion with light apical pressure. Never force a rotary file into a canal, and never place heavy apical pressure as this will cause the file to lock into the canal and separate. When NiTi files fracture, it is due to cyclic fatigue or torsional strain. Torsional fracture is when the tip of the instrument locks in a canal while the shaft continues to rotate. Excessive force on the file during instrumentation causes the tip of the file to lock in a “tight spot.” Larger-sized files tend to be more resistant to these torsional fractures as they don’t bind as easily. Cyclic fatigue occurs after the repeated bending of instruments in curved canals, causing the metal to fatigue and fracture. Obviously, the more curved a canal is, the higher the probability of the file separating due to cyclic fatigue.

Figure 5. Preserving the dentin above and below the canal orifice/alveolar crest is crucial for long-term survival of the tooth.

TIP NO. 8: FILE INSPECTION

One of the indicators that a file has been fatigued and is on the cusp of breakage is when the flutes of that file begin to unwind. It should be a habit to always inspect the file for this unwinding, and when you see it, toss it (Figure 6). File inspection should also include wiping the file of debris before re-entering the canal. This can be done with wet cotton gauze. 

Figure 6. Note file deformation (unwinding of file flutes). This is an indicator that the file is on the cusp of breakage and should be discarded.

TIP NO. 9: IRRIGATION AND LUBRICATION  

Never file a dry canal as this will create excessive debris in the canal, which ultimately will lead to canal blockage. In trying to force your way through a blockage, the chances of file separation are significantly increased. Irrigation serves the purpose of disinfection and flushing of debris from the canal. Some commonly used lubricants/irrigants are RC prep (Premier Dental), EDTA, sodium hypochlorite, Triton (Brasseler USA), QMix (Dentsply Sirona), and MTAD.

TIP NO. 10: STRAIGHT-LINE ACCESS 

Straight-line access into the pulp chamber as well as the root canal is crucial to help avoid coronal tension on the file.²⁶ There are 2 components to straight-line access: the initial access into the pulp chamber and the access into the root canal. Managing both well puts less stress on the file and will ultimately prevent needless file separation. This also aids in glide path maintenance. It is prudent to point out that while straight-line access into both the pulp chamber and root canal is important, we must also strive to preserve as much dentin as possible to avoid weakening the tooth. Many have the motto “You can’t do what you can’t see,” but with more experience, skill, magnification, and image guidance, one can create smaller access preparations and still avoid iatrogenic damage while locating and treating all the complexities of the root canal system. The great benefit to conservative access is preserving the very valuable PCD (Figure 5). 

TIP NO. 11: BITE BLOCK

Having the patient use a bite block during treatment is another great way to avoid file separation. When the patient’s range of opening is compromised, your access to the posterior teeth may be limited. A sudden closure, even slight, by the patient during instrumentation can lead to file fracture. 

TIP NO. 12: PRE-BEND!

Obtaining access into a canal with hand or rotary files can be difficult, especially in an MB canal of a maxillary molar or a mesial canal of a lower molar. The angulation and location of the canal can make it challenging, especially with longer-length rotary files. A good piece of advice is to use shorter length files in these situations (21-mm length as opposed to 25-mm or 31-mm). One of the benefits of NiTi files is that they can be pre-bent to obtain the proper angulation. Putting a curve on the file can simplify this complexity (Figures 7a and 7b). Coronal flaring with shorter length files also helps obtain better access and prevents the dreaded “snap” of the file when it’s improperly placed in the canal. Pre-bending the tip of a small hand file also helps to navigate the curvatures within the canal itself and can help work around a blockage or ledge (Figure 7c).

Figure 7. Pre-bending the tip of a small hand file can help to navigate curvatures within the canal itself and help work around a blockage or ledge.

TIP NO. 13: BE PREPARED! 

Thoroughly inspect the radiograph before starting a case. CBCT can also help to evaluate subtle canal curvatures. Extra care in rotary file usage will be needed in cases that have calcified or curved roots. Never rush! Never blame the file! Never cut corners! With proper technique, patience, and experience, separating files will become a rare occurrence, and navigating curved and calcified canals will become less stressful and easier to manage.

ACKNOWLEDGMENTS

The author wishes to thank Drs. Charles Solomon, Leslie Elfenbein, and Eric Wachs for their valuable input and guidance.

REFERENCES

1. Short JA, Morgan LA, Baumgartner JC. A comparison of canal centering ability of four instrumentation techniques. J Endod. 1997;23(8):503–7. doi:10.1016/S0099-2399(97)80310-X 

2. Peters OA, Paque F. Current developments in rotary root canal instrument technology and clinical use: a review. Quintessence Int. 2010;41(6):479–88. 

3. Viana AC, Chaves Craveiro de Melo M, Guiomar de Azevedo Bahia M, et al. Relationship between flexibility and physical, chemical, and geometric characteristics of rotary nickel-titanium instruments. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2010;110(4):527–33. doi:10.1016/j.tripleo.2010.05.006

4. Peters OA, Gluskin AK, Weiss RA, et al. An in vitro assessment of the physical properties of novel Hyflex nickel-titanium rotary instruments. Int Endod J. 2012;45(11):1027–34. doi:10.1111/j.1365-2591.2012.02067.x

5. Shen Y, Zhou HM, Zheng YF, et al. Metallurgical characterization of controlled memory wire nickel-titanium rotary instruments. J Endod. 2011;37(11):1566–71. doi:10.1016/j.joen.2011.08.005 

6. Cunningham CJ, Senia ES. A three-dimensional study of canal curvatures in the mesial roots of mandibular molars. J Endod. 1992;18(6):294-300. doi:10.1016/s0099-2399(06)80957-x 

7. Kazemi RB, Stenman E, Spångberg LS. A comparison of stainless steel and nickel-titanium H-type instruments of identical design: torsional and bending tests. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2000;90(4):500–6. doi:10.1067/moe.2000.108959

8. Schäfer E, Tepel J, Hoppe W. Properties of endodontic hand instruments used in rotary motion. Part 2. Instrumentation of curved canals. J Endod. 1995;21(10):493–7. doi:10.1016/s0099-2399(06)80519-4 

9. Tepel J, Schäfer E, Hoppe W. Properties of endodontic hand instruments used in rotary motion. Part 3. Resistance to bending and fracture. J Endod. 1997;23(3):141–5. doi:10.1016/S0099-2399(97)80262-2 

10. Tepel J, Schäfer E. Endodontic hand instruments: cutting efficiency, instrumentation of curved canals, bending and torsional properties. Endod Dent Traumatol. 1997;13(5):201-10. doi:10.1111/j.1600-9657.1997.tb00041.x

11. Kuhn WG, Carnes DL Jr, Clement DJ, et al. Effect of tip design of nickel-titanium and stainless steel files on root canal preparation. J Endod. 1997;23(12):735–8. doi:10.1016/S0099-2399(97)80345-7 

12. Hartmann RC, Peters OA, de Figueiredo JAP, et al. Association of manual or engine-driven glide path preparation with canal centring and apical transportation: a systematic review. Int Endod J. 2018;51(11):1239–52. doi:10.1111/iej.12943 

13. Kwak SW, Ha JH, Cheung GS, et al. Effect of the glide path establishment on the torque generation to the files during instrumentation: an in vitro measurement. J Endod. 2018;44(3):496-500. doi:10.1016/j.joen.2017.09.016 

14. Patiño PV, Biedma BM, Liébana CR, et al. The influence of a manual glide path on the separation rate of NiTi rotary instruments. J Endod. 2005;31(2):114–6. doi:10.1097/01.don.0000136209.28647.13 

15. Clark D, Khademi J. Modern molar endodontic access and directed dentin conservation. Dent Clin North Am. 2010;54(2):249–73. doi:10.1016/j.cden.2010.01.001 

16. Clark D, Khademi JA. Case studies in modern molar endodontic access and directed dentin conservation. Dent Clin North Am. 2010;54(2):275–89. doi:10.1016/j.cden.2010.01.003 

17. Yared G, Kulkarni GK. An in vitro study of the torsional properties of new and used rotary nickel-titanium files in plastic blocks. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2003;96(4):466–71. doi:10.1016/s1079-2104(02)91706-3

18. Miyai K, Ebihara A, Hayashi Y, et al. Influence of phase transformation on the torsional and bending properties of nickel-titanium rotary endodontic instruments. Int Endod J. 2006;39(2):119–26. doi:10.1111/j.1365-2591.2006.01055.x 

19. Wolcott J, Himel VT. Torsional properties of nickel-titanium versus stainless steel endodontic files. J Endod. 1997;23(4):217–20. doi:10.1016/S0099-2399(97)80049-0 

20. Walia HM, Brantley WA, Gerstein H. An initial investigation of the bending and torsional properties of Nitinol root canal files. J Endod. 1988;14(7):346–51. doi:10.1016/s0099-2399(88)80196-1 

21. Parashos P, Messer HH. Rotary NiTi instrument fracture and its consequences. J Endod. 2006;32(11):1031–43. doi:10.1016/j.joen.2006.06.008 

22. Plotino G, Grande NM, Cordaro M, et al. A review of cyclic fatigue testing of nickel-titanium rotary instruments. J Endod. 2009;35(11):1469–76. doi:10.1016/j.joen.2009.06.015 

23. Bergmans L, Van Cleynenbreugel J, Wevers M, et al. Mechanical root canal preparation with NiTi rotary instruments: rationale, performance and safety. Status report for the American Journal of Dentistry. Am J Dent. 2001;14(5):324–33.

24. Sattapan B, Nervo GJ, Palamara JE, et al. Defects in rotary nickel-titanium files after clinical use. J Endod. 2000;26(3):161–5. doi:10.1097/00004770-200003000-00008 

25. Pruett JP, Clement DJ, Carnes DL Jr. Cyclic fatigue testing of nickel-titanium endodontic instruments. J Endod. 1997;23(2):77-85. doi:10.1016/S0099-2399(97)80250-6 

26. Patel S, Rhodes J. A practical guide to endodontic access cavity preparation in molar teeth. Br Dent J. 2007;203(3):133–40. doi:10.1038/bdj.2007.682 

ABOUT THE AUTHOR

Dr. Stern is a Diplomate of the American Board of Endodontics. He is the director of endodontics at the Touro College of Dental Medicine and frequently lectures on the subject of clinical endodontics. He has lectured at many local county dental societies, at the New Jersey Dental Association Annual Session in May 2019, and at the Greater New York Dental Meeting in 2020. He maintains a private practice, Clifton Endodontics, in Clifton, NJ.

He can be reached at jstern5819@gmail.com or via the Instagram handle @the_barbed_broach1.

Disclosure: Dr. Stern reports no disclosures.  

It is globally accepted that 3D cleaning and disinfection are central to endodontic success and that bacteria are ubiquitous in endodontically failing teeth. Yet, there is ongoing controversy regarding the very clinical methods used that directly influence eliminating these microbial invaders. The role of bacteria in the pathogenesis of endodontic disease is well established, and therefore, it is critical to eradicate these pathogens by employing the highest level of presently developed standards.¹

The goals of contemporary endodontics are directed toward shaping canals, 3D cleaning, and filling root canal systems—often referred to as the 3 pillars of the endodontic trifecta or triad. It is appreciated that each pillar, individually and in combination, serves to influence the biological objectives for predictably successful endodontics (Figure 1).

Figure 1. This radiographic image demonstrates that shaping canals facilitate the 3D cleaning and filling of root canal systems.

Some proponents of minimally invasive endodontics are advocating minimal instrumentation of a canal or no instrumentation at all. Yet, the question remains, can a minimally prepared canal and its related root canal system be predictably cleaned and filled? From a biological point of view, the apical one-third is a critical zone because it is the most difficult portion to clean and disinfect.² As such, root-appropriate shaping is directed toward preparing a canal with a conservative body and deep shape.

Deep shape shortens the length of the lateral anatomy, increases the volume of an irrigant, and facilitates the exchange of irrigant into all aspects of the root canal system (Figure 2).³

Figure 2. This collage of post-treatment images demonstrates the significance, rationale, and benefit of endodontic deep shape.

The absence of adequate shaping places an almost fanatical emphasis on utilizing controversial disinfection technologies and unproven obturation methods.

There are only a few 3D disinfection technologies in the marketplace that claim to not require canal preparation as traditionally advocated. The Lightwalker Er:YAG laser (Fotona) and GentleWave (Sonendo) are examples of technologies designed to clean more minimally instrumented canals prepared to a size 15/04 or 20/02.⁴ However, in the case of GentleWave, a recent scientific article reported an abundance of remaining micro-organisms in canals minimally prepared to a size 20/02 and “cleaned” with the GentleWave system.⁵

Further, do the frequent reports of unintended consequences following the disinfection cycle and the high costs associated with using this technology fulfill the value proposition? 

This article will describe the sonic advantage, focus on a system-integrated technology that may be utilized for 3D cleaning in root-appropriate shapes, and provide the clinical protocol. 

THREE-DIMENSIONAL DISINFECTION IN APPROPRIATELY SHAPED CANALS 

Experience suggests most dentists performing endodontics strongly desire a seamless workflow that is directed toward root-appropriate shaping that enables the utilization of 3D cleaning and filling methods that are evidence-based, easy to use, and readily affordable.

The EndoActivator (Dentsply Sirona) is such a technology; has been utilized widely in the marketplace since 2007; and has been featured in more than 50 scientific, peer-reviewed published papers. That’s the good news; the better news is the new SmartLite Pro (SLP) EndoActivator builds on that cleaning and disinfection technology and can advantageously be utilized to perform other procedures as well (Figure 3).

Figure 3. This image compares the original EndoActivator to the SmartLite Pro (SLP) EndoActivator (Dentsply Sirona), which provides twice the frequency and a multi-directional tip movement.

Let’s now examine the sonic advantage for 3D cleaning.

THE SONIC ADVANTAGE 

Sonic technology produces frequencies in the range of 10,000 to 20,000 cpm and, importantly, has been shown to be superior to ultrasonic technology when utilized for 3D disinfection.⁶ It is important to know the mechanical variables that most influence 3D cleaning. The streaming velocity of an irrigant prognosticates cleaning potential, and the variables include frequency (f); amplitude (a); and the radius (r), or the cross-sectional dimensions, of a tip. This concept is best appreciated by the mathematical formula: streaming velocity (v) = 2πfa²/r. 

This formula identifies the variables that most influence the hydrodynamic phenomenon, which results when a vibrating tip generates fluid activation and intracanal waves. Random waves fracture, resulting in the formation of bubbles that oscillate within any given reagent. These bubbles are unstable due to heat and pressure, expand, and then collapse and implode. Each implosion generates up to 30,000 shockwaves that serve to powerfully penetrate, break up potential biofilms, and wipe surfaces clean.⁷ 

Frequency and Amplitude 

The frequency is the interval of time it takes a vibrating tip to move through one back-and-forth displacement cycle. Upon activation, a sinusoidal wave of energy travels over the length of the insert tip. For 3D disinfection, clinicians have traditionally used ultrasonic technology to drive metal insert tips at a frequency of approximately 40,000 cps. However, an ultra-high frequency requires a super-low amplitude to mitigate tip breakage. Ultrasonically driven metal insert tips contribute to many iatrogenic events in both straighter and more curved canals.

Amplitude is the maximum back-and-forth displacement value of a vibrating tip. Advantageously, sonic technology produces a super-high tip amplitude that is about 50 times greater than ultrasonic technology (Figure 4).

Figure 4a. Ultrasonic energy delivers an ultra-high frequency with an ultra-low amplitude to drive a metal insert tip.

Figure 4b. Sonic energy delivers an ultra-low frequency with an ultra-high amplitude to safely drive a polymer snap-on tip.

In accordance with the above formula, a high amplitude value exponentially impacts streaming velocity. Fortuitously, sonic energy drives highly flexible, strong, polymer tips that will not break when utilized with a large amplitude value. Amplitude is the single most important factor to maximize 3D disinfection.^4,6,8,9

Noncutting

Sonic technology drives highly flexible, noncutting, polymer tips that absolutely maintain the anatomical integrity of the final preparation.^8,9 On the contrary, all ultrasonically driven instruments are manufactured from metal alloys and are either active and have cutting edges or are nonactive in that their cutting edges have been reduced or eliminated.

Regardless, any ultrasonically activated metal tip that contacts dentin will cut dentin and generate its own smear layer. Vibrating any metal tip, even pre-curved, around a canal curvature invites internal ledges, apical transportations, lateral perforations, or broken instruments (Figure 5).¹⁰

Figure 5a. In this plastic S-block, note the danger of using a metal insert tip around root curvatures, which has resulted in both internal and external transportations.

Figure 5b. In this plastic S-block, note the advantages of a noncutting, flexible polymer tip for 3D disinfection.

Continuous Movement

It should be understood that, even in well-shaped canals, any vibrating tip will certainly contact dentin. Research has shown that when a sonically activated polymer tip is constrained against a dentinal wall, the entire length of the tip advantageously continues to display a large displacement amplitude.¹¹

To validate this sonic phenomenon, purposefully constrain a vibrating sonic tip at any level and note that, apical to the constrainment, the tip will continue to vigorously move!

On the contrary, constrain an activated ultrasonic insert tip and note the tip movement will be sharply reduced or the tip will not move at all; this reduces the exchange of any irrigant and potential to clean. 

EVOLUTION OF THE TECHNOLOGY

Since 2007, the EndoActivator system has been available as a cordless, battery-operated handpiece that utilizes sonic energy to drive snap-on polymer tips.

Now, as a result of technological advancements, this system has evolved into a newly designed and considerably improved EndoActivator that is now a component part of the SmartLite Pro (SLP) multi-functional platform. Let’s look at this new system. 

Platform System   

The SLP platform is a unique, modular design, and multi-functional platform composed of a cordless, pen-style handpiece and 3 interchangeable, quick-connect attachments. Of the 3 attachments, one provides a curing light, a second is for transillumination, and the third is a sonically powered SLP EndoActivator attachment.

This latter attachment is designed to drive new and improved snap-on polymer tips, which, in turn, serve to activate and exchange an irrigant (Figure 6).

Figure 6. The SLP is a battery-powered system that provides 3 attachments. The EndoActivator attachment drives highly flexible, noncutting polymer tips.

Lastly, the SLP platform provides 2 latest-generation lithium iron phosphate batteries to power the handpiece and any given attachment. The platform is designed to organize and simplify the clinical workflow, but the clinician has a choice and can acquire any attachment, as desired. Let’s look at the SLP EndoActivator’s mode of action and the new polymer tips.

Handpiece and Disinfection Attachment 

The SLP handpiece and EndoActivator attachment (SLP EndoActivator) operates at a frequency of 18,000 cpm. Importantly, the SLP EndoActivator drives newly designed polymer tips in a novel, random elliptical motion, whereas the first-generation EndoActivator utilized a back-and-forth linear motion.

Research shows that, beyond producing the hydrodynamic phenomenon, this multi-directional motion mechanically hits more internal canal walls, synergistically increasing the cleaning action (Figure 7). For infection control, a custom protective barrier sleeve easily slides over the entire SLP EndoActivator.

Figure 7. The SLP EndoActivator advantageously drives newly designed polymer tips in a novel, random, and elliptical motion.

After the disinfection cycle, the SLP handpiece and EndoActivator attachment are simply wiped clean with a mild disinfectant.

Tips and Selection

The SLP EndoActivator tips have a new paddle-like, parallelogram-shaped cross-sectional design to improve fluid exchange and cleaning potential (Figure 8).

Figure 8. The newly designed polymer tips provide a paddle-shaped cross section to improve the exchange of an irrigant into the uninstrumentable anatomy.

These new-generation tips are color-coded yellow and red to approximately correspond to file sizes 20/02 and 25/04, respectively.

The tips are made from a noncutting, medical-grade polymer; are strong and flexible; and have orientational depth gauge rings positioned at 18, 19, and 20 mm. The yellow tip is available in a 22-mm length, while the red tip is available in 22-mm and 28-mm lengths. The EndoActivator tips are single-use devices that should not be autoclaved or placed in any sterilizing solution, as this reduces elasticity, which in turn decreases tip amplitude and performance. 

The protocol is to select a tip that fits loosely to within 2 mm of working length. Tip placement is easy in root-appropriate shapes, such as those cut by the ProTaper Ultimate F1 (20/07) or F2 (25/08) regressively tapered Finishing files. Moving an activated polymer tip in short 2- to 3-mm vertical strokes during the disinfection cycle synergistically produces a powerful hydrodynamic phenomenon (Figure 9).

Figure 9a. This video animation image demonstrates the importance of dynamic irrigation to exchange irrigant into the uninstrumentable anatomy.

Figure 9b. This video animation image reveals how bubbles expand, collapse, and implode to generate shockwaves, which serve to wipe surfaces clean.

Figure 9c. Note that dynamic irrigation exchanges irrigant into all aspects of this simulated root canal system.

Scientific evidence supports that this specific technology debrides tissue remnants, eliminates the smear layer, and disrupts biofilms (Figure 10).^6,8,9 

Figure 10. Three SEM images provide evidence that the EndoActivator system can clean root canal systems (Courtesy of Dr. Grégory Caron, Paris).

CLINICAL PROTOCOL 

Following the shaping procedure, the root canal space is flushed with a 6% solution of NaOCl, then suctioned and removed. The pulp chamber is then flooded with a 17% solution of EDTA, as this reagent removes the smear layer, which serves to open up the uninstrumentable anatomy for more effective lateral exchange and deep cleaning.

The selected tip is placed over the protective barrier sleeve and utilized in a crown-down manner to agitate this solution of EDTA for 60 seconds per canal.

“Crown-down” means agitating this reagent for 5 seconds starting in the coronal one-third, then another 5 seconds in the middle one-third, and finally moving deeper to within 2 mm of working length to finish the 60-second disinfection cycle (Figure 11). 

Figure 11. This clinical image shows the SLP EndoActivator in use. Note the powerful activation of fluid and appreciate the suborifice potential for 3D cleaning.

This crown-down method creates a powerful vortex where, upon activation, the fluid flow around the axis of the activated tip has microscale shape characteristics similar to a macroscale tornado. This disinfection process should be repeated for each canal or until the fluid in the pulp chamber is clinically observed to be visually clear.

After agitating 17% EDTA for 1 minute per canal, remove this reagent by vacuum. The root canal space is voluminously flushed with a 6% solution of NaOCl, and then this solution is activated for 30 seconds per canal to encourage deep penetration, circulation, and 3D cleaning (Figure 12).

Figure 12. (Left) An SEM image demonstrates that both the instrumented and uninstrumented surfaces are free of organic material. Note the deep lateral cleaning into the dentinal tubules. (Right) A stained axial cross section demonstrates the depth of exchange of silver ions deep into the dentinal tubules after using the SLP EndoActivator (Courtesy of Dr. Roberta Pileggi, Gainesville, Fla).

When the clinical procedure has been completed, the single-use activator tip and barrier sleeve are discarded. 

ADJUNCTIVE USES

We have discussed the SLP EndoActivator in terms of 3D disinfection, but this technology is frequently used to perform other clinical procedures as well. For example, the SLP EndoActivator may be utilized to adapt and remove calcium hydroxide, or to move and adapt MTA into a wide-open canal or root defect, or to agitate an intracanal solvent.¹²

The latter serves to remove residual obturation remnants more effectively in the retreatment situation. In these clinical situations, the on/off switch on the SLP handpiece is quickly pressed twice to lower the frequency from 18,000 cpm to 3,000 cpm to best perform these adjunctive procedures.

To learn more about the various clinical uses of the SLP EndoActivator, go to endoruddle.com.

CLOSING COMMENTS

The goal of global endodontics should be to provide the greatest number of international patients with a 3D disinfection method that is safe, effective, and readily affordable. Importantly, the 3D disinfection method selected should be easy to use and fit seamlessly into a workflow that takes into consideration each pillar of the endodontic triad and its role in endodontic success. If you have the desire to treat root canal systems and are looking for predictability, possibility, and practicality, look no further than the SmartLite Pro EndoActivator.

REFERENCES

1. Schilder H. Cleaning and shaping the root canal. Dent Clin North Am. 1974;18(2):269–96. 

2. Zehnder M. Root canal irrigants. J Endod. 2006;32(5):389–98. doi:10.1016/j.joen.2005.09.014 

3. Machtou P, West JD, Ruddle CJ. Deep shape in endodontics: significance, rationale, and benefit. Dent Today. 2022;41(1):4-77.

4. Ruddle CJ. Endodontic Triad for Success: The Role of Minimally Invasive Technology. Dent Today. 2015;34(5):76, 78-80. 

5. Ordinola-Zapata R, Mansour D, Saavedra F, et al. In vitro efficacy of a non-instrumentation technique to remove intracanal multispecies biofilm. Int Endod J. 2022. doi:10.1111/iej.13706 

6. Kanter V, Weldon E, Nair U, et al. A quantitative and qualitative analysis of ultrasonic versus sonic endodontic systems on canal cleanliness and obturation. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2011;112(6):809–13. doi:10.1016/j.tripleo.2011.06.002

7. Gutarts R, Nusstein J, Reader A, et al. In vivo debridement efficacy of ultrasonic irrigation following hand-rotary instrumentation in human mandibular molars. J Endod. 2005;31(3):166–70. doi:10.1097/01.don.0000137651.01496.48 

8. Ruddle CJ. Endodontic disinfection: tsunami irrigation. Endodontic Practice. 2008;11(1):7-15.

9. Caron G, Nham K, Bronnec F, et al. Effectiveness of different final irrigant activation protocols on smear layer removal in curved canals. J Endod. 2010;36(8):1361–6. doi:10.1016/j.joen.2010.03.037

10. Ruddle CJ. Chapter 25: Nonsurgical endodontic retreatment. In: Cohen S, Burns RC, eds. Pathways of the Pulp. Mosby; 2002:875-929.

11. Walmsley AD, Lumley PJ, Laird WR. Oscillatory pattern of sonically powered endodontic files. Int Endod J. 1989;22(3):125–32. doi:10.1111/j.1365-2591.1989.tb00910.x 

12. Ruddle CJ. Endodontic advancements: game-changing technologies. Dent Today. 2009;28(11):82, 84. 

ABOUT THE AUTHOR

Dr. Ruddle is founder and director of Advanced Endodontics, an international educational source, in Santa Barbara, Calif.

Further, he is the creator of The Ruddle Show.

There are 5 important questions to consider prior to treating a traumatic pulpal exposure (see Table 1): 

Question 1: How long has the exposure been present?

Short answer: The longer the exposure has been present, the higher the likelihood for bacterial contamination of the pulp. However, as long as the pulp is still vital and the patient’s symptoms don’t necessitate root canal therapy, vital pulpal treatments can be utilized. 

Question 2: Is the patient symptomatic? What are the pulpal and periapical diagnoses?

Short answer: The pulpal and periapical diagnoses will dictate treatment. For example, if the pulpal diagnosis is necrosis or irreversible pulpitis (spontaneous or lingering pain), then pulpectomy (root canal therapy) is usually indicated rather than a vital pulpal treatment, such as a pulp cap or partial pulpotomy. A tooth with periapical pathology is obviously not a good candidate for vital pulpal treatments. A proper diagnosis must be reached before deciding to perform vital pulpal treatments. Vital pulpal treatments will usually not work if the pulp is severely inflamed or infected. 

Question 3: Is there a concomitant luxation injury or root fracture?

Short answer: A concomitant luxation injury (see Tables 1 to 3) or root fracture might further complicate pulpal circulation and thereby necessitate a full root canal rather than vital pulpal treatment.

Question 4: Are the roots fully developed?

Short answer: As a general rule, we make every effort to preserve the pulp vitality of an immature tooth to allow for continued root growth (apexogenesis). It is important to remember that although vital pulpal treatments are usually the treatment of choice for immature permanent teeth, they can be performed for both mature and immature permanent teeth.

Question 5: How large is the fracture/exposure?

Short answer: There are different levels of vital pulpal therapy, ranging from a direct pulp cap to a full pulpotomy. The size of the exposure will play a role in dictating which vital pulpal treatment is best. There are times when a fracture might compromise significant tooth structure, necessitating a post (for retention of a core). In this case, endodontic treatment is indicated even when the pulp is vital and the exposure is relatively small.

DEFINITION

Vital pulp therapy (VPT) techniques are means of preserving the vitality and function of the dental pulp after injury resulting from trauma, caries, or restorative procedures. VPT procedures have traditionally included indirect or direct pulp capping and partial or complete pulpotomy¹ (Figure 1). VPT includes the removal of part of the pulp, allowing the rest of it to remain vital and functional. We assume that by removing a small portion of the superficial inflamed pulp, the remaining pulp remains healthy.

Figure 1. Level of pulp treatment.

When the pulp is exposed, bacterial invasion can be resisted by both the patient’s immune system present within the pulp and the bathing of the area by the patient’s saliva, which prevents impaction of contaminated debris/bacteria. While the pulp is a low-compliant environment, making it more vulnerable to injury, it also has the ability to heal itself. Vital pulpal therapy is built upon this very important principle. Overall, VPT has been shown to have a very high success rate.²

OBJECTIVES

There are 2 essential objectives for the treatment of the vital pulp that make the level of pulpal amputation important: A wound dressing should be placed on non-inflamed tissue, and the loss of tooth structure should be kept to a minimum. In crown-fractured teeth showing vital pulp tissue after exposure, not more than 2 mm of the pulp beneath the exposure needs to be removed³ (Figures 1 and 2).

Figure 2. (a) Traumatic (or carious) pulpal exposure. (b) A high-speed round bur was used to remove 2 mm of the pulp tissue below the exposure. (c) A calcium silicate cement (CSC) was placed in direct contact with the pulp tissue at a minimum thickness of 2 to 3 mm. The tooth was then restored. If available, the tooth segment can be rebonded.

CVEK PULPOTOMY

With children and young adults, most teeth that have the pulp exposed by a crown fracture can be treated successfully by partial pulpotomy, also known as a Cvek pulpotomy, in which a small portion of the pulp tissue (usually 2 mm) is removed beneath an exposure⁴ (Figure 2 and Table 2). The major benefit to maintaining vital pulp in immature teeth is that it allows for continued root growth (apexogenesis). The exposure size amenable to partial pulpotomy will usually range from 0.5 to 4 mm in size.⁵

This treatment can also be performed on mature permanent teeth, not just children’s.^4,6 Some studies show a higher success rate with VPTs on an immature permanent tooth when compared to a mature permanent tooth with a closed apex.⁷ The reason is that, in older patients, the pulp is more fibrotic, is less cellular with a reduced blood supply, and has a diminished healing capacity.^8,9 It is also impractical to do vital pulpal treatment on a fully mature tooth that you anticipate will end up needing full root canal treatment, as future entry into the root canal will be made more difficult once vital pulpal therapy is done. Cvek,⁵ in a clinical report of partial pulpotomies carried out on 60 young teeth, found a success rate of 96.7%, with the majority of these teeth being treated within 4 days of traumatic exposure. In another classic study by Cvek,⁴ partial pulpotomies were performed on 178 teeth with traumatic pulpal exposures. Patients were followed for 3 to 15 years, both clinically and radiographically. Healing with hard-tissue barriers and the maintaining of pulp vitality were seen in 95% of the cases. A majority of these cases were treated within 3 days of the trauma. 

PARTIAL PULPOTOMY VS DIRECT PULP CAP

The advantage of partial pulpotomy (removing 2 mm of coronal pulp) compared to pulp capping lies in better control of the surgical wound and retention of the sealing material. Capping of the pulp is recommended only when the exposure is small (less than 1 mm in size) and when it can be treated shortly after the accident.¹⁰ These indications apply to only a limited number of teeth, and in the majority of cases, a partial pulpotomy is therefore performed.⁵ It is also noteworthy that most studies find a much higher success rate with partial pulpotomy compared to pulp capping after a traumatic pulpal exposure^11-13 due to the better control of superficial inflammation below the exposure. It has been clearly shown that as time elapses (from one hour to 7 days) after injury, the success of pulp capping significantly decreases (from 93% to 56%).¹⁴ Vital pulpal treatments can be used as a permanent treatment modality for mature and immature permanent teeth with complicated crown fractures, and re-entering of the pulp at a later time is not necessary as long as the pulp remains vital.^7,15

HEMOSTASIS

Sodium hypochlorite is an antimicrobial solution that provides hemostasis, disinfection of the dentin pulp interface, biofilm removal, chemical removal of the blood clot and fibrin, and clearance of dentinal chips along with damaged cells at the mechanical exposure site. Therefore, sodium hypochlorite can be used to disinfect the exposure site during a pulpotomy prior to restoring the pulpal wound (saline or chlorhexidine can be used as well).¹⁶ A cotton-soaked pellet is placed on the pulpal wound with pressure for this purpose.

The examination of pulp tissues after exposure is a critical step in pulp assessment. Controlled bleeding (complete hemostasis) is needed for a successful partial pulpotomy. If hemostasis cannot be achieved, this is an indicator that the pulp is inflamed and should not be “capped”. On occasion, more pulp tissue needs to be removed to achieve hemostasis, and what was initially planned as a partial pulpotomy might turn into a full pulpotomy. A pulpal diagnosis of necrosis (non-vital pulp) or the inability to achieve hemostasis would obviously preclude vital pulpal treatments such as a pulp cap or pulpotomy (partial or full) (Figure 3).¹⁷ 

Figure 3. (a) A preoperative radiograph of a complicated crown fracture. An 8-year-old patient presented after a recent trauma in which teeth Nos. 8 and 9 suffered complicated crown fractures. The patient was asymptomatic on both teeth. Tooth No. 8 tested vital and was planned for a Cvek pulpotomy. Tooth No. 9 had a more extensive fracture and was testing non-vital. This tooth was planned for full endodontic treatment. (b) Hemostasis was achieved after a surgical length carbide #2 bur was used to remove the coronal 2 mm of the pulp. (c) Bioceramic putty (a CSC) was placed directly on the pulpal wound. (d) A postoperative radiograph of tooth No. 8 after completion of a Cvek pulpotomy and a composite restoration. Note that tooth No. 9 had calcium hydroxide in the canal as an inter-visit medicament prior to completion of endodontic treatment.

CALCIUM SILICATE CEMENTS

There have been few materials as groundbreaking in endodontics as mineral trioxide aggregate (MTA). This material, developed in 1993, was the first of the calcium silicate cements (CSCs) and was initially introduced for the purpose of sealing root perforations. Over time, they were found to be so biocompatible and successful in their applications that they have become mainstreamed for the use of apexogenesis, apexification, apicoectomies, and to seal root perforations (see Table 4).^18-20

Table 4.

CSCs are a class of materials that include tricalcium silicates, dicalcium silicates, hydraulic calcium silicate cements, and “bioceramics” (MTA [Angelus], TheraCal [BISCO Dental Products], EndoSequence BC RRM [Brasseler USA], EndoSequence BC sealer [Brasseler USA], and Biodentine [Septodont] are some examples). CSCs have become more commonplace for use in VPT procedures. These materials are placed directly on the pulpal wound (Figure 4). While calcium hydroxide (CH) has classically been used for vital pulpal treatments, most current studies clearly demonstrate that CSCs are superior in terms of healing and success rates and are the preferred materials to place on a pulpal exposure (once hemostasis is achieved).^4,21-24 MTA was the first of these materials introduced for this purpose, but newer materials have recently flooded the market. One of the advantages of the newer materials is that they don’t cause significant tooth discoloration, which can be beneficial, especially when used in the aesthetic zone. 

Figure 4. EndoSequence BC RRM (Brasseler USA) is an example of a CSC placed directly on the pulpal wound to a level of 2 to 3 mm.

The mechanism by which CH works is by eliciting the formation of a dentinal bridge right below the capping material. These materials cause superficial coagulation necrosis (1 to 1.5 mm in depth), which induces a low-grade irritation that leads to differentiation of the undifferentiated cells of the pulp. These cells then synthesize predentin, which is subsequently mineralized, while the coagulated tissue is calcified. Finally, predentin is transformed into dentin by further mineralization. In essence, it is the low-grade irritation from coagulation necrosis that causes the hard-tissue barrier to form right below the capping material. This low-grade irritation is not strong enough to damage the pulp. Still, it is sufficient to elicit an immune response that triggers the formation of a dentin bridge, which protects the underlying pulp. CSCs such as MTA benefit from forming a stronger dentin bridge without the disadvantage of triggering a zone of necrosis, like in the case with CH. Pitt Ford et al²³ compared CH and MTA and found that the majority of pulps that were capped with MTA were free of inflammation, and all of them showed calcified bridge formations after 5 months. In contrast, the pulp of teeth that were capped with CH showed the presence of inflammation and significantly less calcified bridge formation. Tziafas et al²⁵ found that during the first 2 weeks, osteodentin matrix formation takes place right below the MTA, and after 3 weeks, a complete layer of reparative dentin (tertiary dentin) is formed at the capping site. Therefore, the placement of MTA on pulp tissue causes proliferation, migration, and differentiation of odontoblast-like cells that produce a collagen matrix, which then mineralizes and produces osteodentin. This is then replaced with a tertiary dentinal bridge a few weeks after pulp capping.^18,23,25-33 

CSCs offer many advantages as agents for use in pulpotomies. They are biocompatible, provide excellent resistance to microleakage, allow an opportunity for dentin bridging at the site of pulp exposure, are dimensionally stable over time, and appear to be associated with very positive clinical outcomes. The main difference between CSCs and CH may be that CSCs provide a good protective barrier against microleakage and do not break down, requiring replacement, as is the case with CH. CSCs form a much higher quality dentin bridge than CH. If microleakage occurs in the case of CH, bacteria can reach the dentin bridge, which usually has numerous tunneling defects, allowing for potential bacterial leakage directly into the pulp.^3,34 This is not significant when CSCs are used as the dentin bridge formed does not have tunneling defects.^23,35

CONCLUSION

When treatment planned correctly, vital pulpal treatments, such as a partial pulpotomy, can be a valuable option with a high success rate. They can be successfully utilized not only for traumatic pulpal exposures but for carious pulpal exposures as well.^36-38 The key to this high success rate is proper diagnosis and a well-sealed restoration above the capping material. Bacterial leakage ultimately can cause any vital pulpal treatment to fail.^{5,26,27,39,40} 

A successful followup to VPT would be dentin bridge formation, continued root development, positive response to pulp vitality testing, no symptoms, and no radiographic development of apical periodontitis or root resorption (see Table 5).

Click here to read Table 6, which summarizes a few classic studies associated with treating pulpal exposures.

ACNOWLEDGEMENTS 

The author wishes to thank Drs. Charles Solomon, Leslie Elfenbein, and Eric Wachs for their valuable input and guidance.

REFERENCES

1. AAE Position Statement on Vital Pulp Therapy. J Endod. 2021;47(9):1340–44. doi:10.1016/j.joen.2021.07.015 

2. Sabeti M, Huang Y, Chung YJ, et al. Prognosis of vital pulp therapy on permanent dentition: a systematic review and meta-analysis of randomized controlled trials. J Endod. 2021;47(11):1683–95. doi:10.1016/j.joen.2021.08.008

3. Cvek M, Cleaton-Jones PE, Austin JC, et al. Pulp reactions to exposure after experimental crown fractures or grinding in adult monkeys. J Endod. 1982;8(9):391–7. doi:10.1016/S0099-2399(82)80092-7

4. Cvek M. Partial pulpotomy in crown fractured incisors: results 3 to 15 years after treatment. Acta Stomatol Croat. 1993;27:167–73.

5. Cvek M. A clinical report on partial pulpotomy and capping with calcium hydroxide in permanent incisors with complicated crown fracture. J Endod. 1978;4(8):232–7. doi:10.1016/S0099-2399(78)80153-8

6. Lin LM, Ricucci D, Saoud TM, et al. Vital pulp therapy of mature permanent teeth with irreversible pulpitis from the perspective of pulp biology. Aust Endod J. 2020;46(1):154-166. doi:10.1111/aej.12392

7. Bimstein E, Rotstein I. Cvek pulpotomy—revisited. Dent Traumatol. 2016;32(6):438-442. doi:10.1111/edt.12297 

8. Fong CD, Davis MJ. Partial pulpotomy for immature permanent teeth, its present and future. Pediatr Dent. 2002;24(1):29-32.  

9. Massler M. Therapy conductive to healing of the human pulp. Oral Surg Oral Med Oral Pathol. 1972;34(1):122–30. doi:10.1016/0030-4220(72)90281-2

10. Heide S, Kerekes K. Delayed direct pulp capping in permanent incisors of monkeys. Int Endod J. 1987;20(2):65-74. doi:10.1111/j.1365-2591.1987.tb00591.x 

11. Fuks AB, Bielak S, Chosak A. Clinical and radiographic assessment of direct pulp capping and pulpotomy in young permanent teeth. Pediatr Dent. 1982;4(3):240–4. 

12. Barthel CR, Rosenkranz B, Leuenberg A, et al. Pulp capping of carious exposures: treatment outcome after 5 and 10 years: a retrospective study. J Endod. 2000;26(9):525–8. doi:10.1097/00004770-200009000-00010 

13. Dammaschke T, Leidinger J, Schäfer E. Long-term evaluation of direct pulp capping–treatment outcomes over an average period of 6.1 years. Clin Oral Investig. 2010;14(5):559–67. doi:10.1007/s00784-009-0326-9

14. Cox CF, Bergenholtz G, Fitzgerald M, et al. Capping of the dental pulp mechanically exposed to the oral microflora—a 5-week observation of wound healing in the monkey. J Oral Pathol. 1982;11(4):327–39. doi:10.1111/j.1600-0714.1982.tb00173.x 

15. Cvek M, Lundberg M. Histological appearance of pulps after exposure by a crown fracture, partial pulpotomy, and clinical diagnosis of healing. J Endod. 1983;9(1):8-11. doi:10.1016/S0099-2399(83)80005-3 

16. Hafez AA, Cox CF, Tarim B, et al. An in vivo evaluation of hemorrhage control using sodium hypochlorite and direct capping with a one- or two-component adhesive system in exposed nonhuman primate pulps. Quintessence Int. 2002;33(4):26–72. 

17. Cho SY, Seo DG, Lee SJ, et al. Prognostic factors for clinical outcomes according to time after direct pulp capping. J Endod. 2013;39(3):327–31. doi:10.1016/j.joen.2012.11.034 

18. Parirokh M, Torabinejad M. Mineral trioxide aggregate: a comprehensive literature review—Part III: Clinical applications, drawbacks, and mechanism of action. J Endod. 2010;36(3):400–13. doi:10.1016/j.joen.2009.09.009 

19. Parirokh M, Torabinejad M. Mineral trioxide aggregate: a comprehensive literature review—Part I: chemical, physical, and antibacterial properties. J Endod. 2010;36(1):16-27. doi:10.1016/j.joen.2009.09.006 

20. Torabinejad M, Parirokh M. Mineral trioxide aggregate: a comprehensive literature review—part II: leakage and biocompatibility investigations. J Endod. 2010;36(2):190-202. doi:10.1016/j.joen.2009.09.010 

21. Bakland LK, Andreasen JO. Will mineral trioxide aggregate replace calcium hydroxide in treating pulpal and periodontal healing complications subsequent to dental trauma? A review. Dent Traumatol. 2012;28(1):25-32. doi:10.1111/j.1600-9657.2011.01049.x 

22. Mente J, Geletneky B, Ohle M, et al. Mineral trioxide aggregate or calcium hydroxide direct pulp capping: an analysis of the clinical treatment outcome. J Endod. 2010;36(5):806–13. doi:10.1016/j.joen.2010.02.024 

23. Pitt Ford TR, Torabinejad M, Abedi HR, et al. Using mineral trioxide aggregate as a pulp-capping material. J Am Dent Assoc. 1996;127(10):1491–4. doi:10.14219/jada.archive.1996.0058

24. Faraco IM Jr, Holland R. Response of the pulp of dogs to capping with mineral trioxide aggregate or a calcium hydroxide cement. Dent Traumatol. 2001;17(4):163–6. doi:10.1034/j.1600-9657.2001.170405.x

25. Tziafas D, Pantelidou O, Alvanou A, et al. The dentinogenic effect of mineral trioxide aggregate (MTA) in short-term capping experiments. Int Endod J. 2002;35(3):245–54. doi:10.1046/j.1365-2591.2002.00471.x

26. Fuks AB, Cosack A, Klein H, et al. Partial pulpotomy as a treatment alternative for exposed pulps in crown-fractured permanent incisors. Endod Dent Traumatol. 1987;3(3):100–2. doi:10.1111/j.1600-9657.1987.tb00610.x 

27. de Blanco LP. Treatment of crown fractures with pulp exposure. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 1996;82(5):564–8. doi:10.1016/s1079-2104(96)80204-6 

28. Foreman PC, Barnes IE. Review of calcium hydroxide. Int Endod J. 1990;23(6):283–97. doi:10.1111/j.1365-2591.1990.tb00108.x 

29. Olsburgh S, Jacoby T, Krejci I. Crown fractures in the permanent dentition: pulpal and restorative considerations. Dent Traumatol. 2002;18(3):103–15. doi:10.1034/j.1600-9657.2002.00004.x 

30. Schröder U, Granath LE. Early reaction of intact human teeth to calcium hydroxide following experimental pulpotomy and its significance to the development of hard tissue barrier. Odontol Revy. 1971;22(4):379–95. 

31. Schröder U. Reaction of human dental pulp to experimental pulpotomy and capping with calcium hydroxide. Odontol Revy. 1973;24:(Suppl 25):1–97.

32. Cvek M, Granath L, Cleaton-Jones P, et al. Hard tissue barrier formation in pulpotomized monkey teeth capped with cyanoacrylate or calcium hydroxide for 10 and 60 minutes. J Dent Res. 1987;66(6):1166–74. doi:10.1177/00220345870660061501 

33. Kuratate M, Yoshiba K, Shigetani Y, et al. Immunohistochemical analysis of nestin, osteopontin, and proliferating cells in the reparative process of exposed dental pulp capped with mineral trioxide aggregate. J Endod. 2008;34(8):970–4. doi:10.1016/j.joen.2008.03.021

34. Cox CF, Sübay RK, Ostro E, et al. Tunnel defects in dentin bridges: their formation following direct pulp capping. Oper Dent. 1996;21(1):4-11. 

35. Nair PN, Duncan HF, Pitt Ford TR, et al. Histological, ultrastructural and quantitative investigations on the response of healthy human pulps to experimental capping with mineral trioxide aggregate: a randomized controlled trial. Int Endod J. 2008;41(2):128–50. doi:10.1111/j.1365-2591.2007.01329.x

36. Elmsmari F, Ruiz XF, Miró Q, et al. Outcome of partial pulpotomy in cariously exposed posterior permanent teeth: a systematic review and meta-analysis. J Endod. 2019;45(11):1296-1306.e3. doi:10.1016/j.joen.2019.07.005 

37. Li Z, Cao L, Fan M, et al. Direct pulp capping with calcium hydroxide or mineral trioxide aggregate: a meta-analysis. J Endod. 2015;41(9):1412–7. doi:10.1016/j.joen.2015.04.012

38. Mejàre I, Cvek M. Partial pulpotomy in young permanent teeth with deep carious lesions. Endod Dent Traumatol. 1993;9(6):238–42. doi:10.1111/j.1600-9657.1993.tb00279.x

39. Fuks AB, Gavra S, Chosack A. Long-term follow-up of traumatized incisors treated by partial pulpotomy. Pediatr Dent. 1993;15(5):334–6. 

40. Parirokh M, Torabinejad M, Dummer PMH. Mineral trioxide aggregate and other bioactive endodontic cements: an updated overview—part I: vital pulp therapy. Int Endod J. 2018;51(2):177-205. doi:10.1111/iej.12841

ABOUT THE AUTHOR

Dr. Stern is a Diplomate of the American Board of Endodontics. He is the director of endodontics at the Touro College of Dental Medicine and frequently lectures on clinical endodontics. He has lectured at local county dental societies, the New Jersey Dental Association Annual Session, and the Greater New York Dental Meeting. He maintains a private practice, Clifton Endodontics, in Clifton, NJ. He can be reached at jstern5819@gmail.com or via the Instagram handle @the_barbed_broach1.

Disclosure: Dr. Stern reports no disclosures.

In the early 1990s, the use of nickel-titanium (NiTi) alloy to manufacture engine-driven instruments for shaping root canals moved endodontics to a different level. Practitioners, universities, and companies started unprecedented cooperation to understand the countless advantages that adopting this unique metal alloy could provide for the evolution of the instrumentation technique.

As a result, the last 3 decades have seen an explosion in the development of NiTi endodontic file systems, and tremendous progress has been made. Improvements in metallurgical technology allowed the development of various new instruments with innovative designs, blade geometries, and alloy thermomechanical treatments, resulting in improved efficiency.^1-7

NiTi rotary instruments for the mechanized preparation of root canals were developed by John McSpadden and Ben Johnson in 1990. The first-generation NiTi rotary files were characterized by instruments having passive cutting radial land (Figure 1), constant taper, and a neutral or negative rake angle. Examples of the first generation are McXim File (NT Company), GT system (Dentsply Sirona), LightSpeed (LightSpeed Technology), Pow-R (Moyco), ProFile (Dentsply Sirona), and Quantec (Tycom). The primary deficiencies of the systems in this group were the number of instruments required to achieve the complete canal preparation and the rather complex protocols needed.

Figure 1. Blade of a first-generation engine-driven file. The double arrow shows the radial land.

The second generation of NiTi engine-driven files appeared at the end of the 1990s. Instruments were manufactured with changes in their helical angles, tapers, and cutting angles. As a result, this generation’s engine-driven files had active cutting edges (Figure 2), improving their efficiency, and most of them were without radial land.

Figure 2. Second-generation file showing modifications on the cutting surface.

These enhancements led to fewer instruments required to accomplish complete canal preparation. In addition, some manufacturers applied a supplemental treatment on the file surface called electropolishing (EP). EP removes surface irregularities, cracks, and residual stress caused by the previous grinding process.⁸ However, only one study found that EP significantly reduces the resistance to cyclic fatigue while increasing the angle of deflection at failure.⁹

Examples of the second generation are EndoSequence (Brasseler), K3 (Sybron), ProTaper Universal (Dentsply Sirona), and Genius (Medidenta). Despite requiring fewer instruments, fractures were still a significant concern, and preliminary clinical guidelines were recommended, such as glide path and coronal preflaring, which reduced the occurrence of file separations.

In 2007, post-grinding thermomechanical procedures began to be used by the leading manufacturers initiating the third generation of instruments. Each company developed a different heat treatment method. Following the implementation of these technologies, the engine-driven files became safer, with enhanced performance in shaping ability, especially in the preparation of anatomical challenges, such as curved canals. At the same time, clinical studies reported lower fracture rates using these heat-treated files.^10,11

Examples of the latest generation are HyFlex CM (Coltène), K3XF (SybronEndo), ProFile Vortex Blue (Dentsply Sirona), ProTaper Ultimate (Dentsply Sirona), ZenFlex (Kerr), EdgeTaper Platinum (EdgeEndo), and Genius Proflex (Medidenta).  

THE RATIONALE FOR HEAT-TREATED NITI FILES

Originally, NiTi alloy was developed by the Naval Ordnance Laboratory (White Oak, Md) and named Nitinol, an acronym for nickel (Ni), titanium (Ti), and Naval Ordnance Laboratory (NOL). NiTi alloy used in endodontic instruments contains approximately 56 wt% nickel and 44 wt% titanium, resulting in a nearly one-to-one atomic ratio (equiatomic).¹²

This equiatomic NiTi alloy can exist in 2 different strain- and temperature-dependent crystal structures (Figure 3) called austenitic (cubic B2 crystal structure) and martensitic (monoclinic B19 crystal structure) phases.¹³  

Figure 3. NiTi alloy phase expressions (austenitic, transitional R-phase, and martensitic) with representations of the different atomic crystal structures.

Heat treatment is one of the fundamental approaches to adjust the crystalline transition phase of a metal alloy and improve its fatigue resistance. This modification is essential because several properties of each alloy phase expression are notably different. For example, the proportions of the austenitic phase (more rigid and with the spring-back effect) and martensitic phase (more flexible with permanent plastic deformation) determine different instrument performances.

The file is soft when the alloy is in its martensitic phase, and it can easily be permanently bent (also defined as controlled memory). In contrast, the austenitic phase is firm and returns to the original straight condition when the load is removed (spring-back effect, see Figure 4). From a practical point of view, martensitic instruments are recommended to be used in curved canals once they are supposed to provide better maintenance of the original canal path.^14-17

Figure 4. Representation of the spring-back effect. The applied load will deform the file temporally. However, the file returns to its original, straight position once the load is removed.

The major limitation of controlled memory (CM) instruments is that the martensitic alloy phase expression requires less load for deformation, meaning that the unwinding of CM files can be experienced more often, particularly in the initial prospection phase of instrumentation with small-diameter files.

In addition, predominant martensitic alloy phase expression under torsion has a high angular deflection to sustain great rotation before fracture (Figure 5); however, the torque needed to deform and fracture these instruments is lower than with austenitic instruments.^18-22

Figure 5. Representation of torsional load without separation on a martensite file. (a) The file tip locks inside the canal’s narrowest segment, (b) but the motor continues the clockwise file rotation. (c) The martensitic characteristic of high angular deflection allows [SC: for?]unwinding, visible deformation without separation.

Therefore, instruments whose alloys are mainly in the martensitic phase have more flexibility to deal with curvatures, but they tend to have more significant distortion in the face of forces contrary to their progress in the apical direction. It is concluded that the martensitic phase would be more attractive in instruments of a higher caliber, above 25 (ISO 25), for example.

In these instruments, the greater metallic mass factor influences flexibility negatively yet, in the meantime, collaborates with their resistance to harmful torsional fatigue. The martensitic alloy phase expression given by the heat treatment can help flexibility without decreasing the torsional strength. 

Different factors regarding torsional stress generation during root canal preparation have been identified in the literature. These include the type of canal curvature, instrument design and cutting efficiency, instrument size and canal size, contact area, preparation technique, preparation time, insertion depth and the number of insertions, correlation with displacement, motor source, kinematics, operative motion type, rotational speed and pecking speed, lubricant, experience, and alloy phase expression.²³

NiTi rotary files with high expression of the austenitic alloy phase will have more torsional fatigue resistance.²⁴ The alloy in a predominant austenitic phase expression is more suitable for thinner instruments, with a 20 (ISO 20) diameter or lower. Moreover, these instruments have lower metallic mass, leading to a natural flexibility that is given to the small diameter.

An interesting consequence of the various heat treatments in a NiTi alloy is the deposition of titanium oxide layers on the external surface of the instrument blade. Differences in the thicknesses of these layers are responsible for changing the exterior color of the instrument blade (Figure 6), which can be presented with different hues of violet, blue, or gold.²⁵

Some heat treatment formulas do not necessarily lead to the formation of a titanium oxide layer relevant enough to change the instrument’s color, such as M-Wire (Dentsply Sirona). 

Figure 6. Gold, blue, and violet blade colors due to different heat treatments that were applied (Genius Proflex [Medidenta]).

PURSUING THE RIGHT BALANCE BETWEEN FLEXIBILITY AND RESISTANCE: THE CUSTOMIZED HEAT TREATMENT

Instruments whose alloys are entirely in the austenitic phase have limited indications. For example, an instrument that is less prone to torsional fatigue may be desired in cases of retreatment, where the force exerted against the filling material to be removed results in a more significant torsional load on the instrument. However, these instruments, also known as super elastic (SE), have less flexibility and are more susceptible to cyclic fatigue fracture.

In addition, a slight deformation in the face of torsional forces is welcome, showing the operator that the force applied to the instrument’s progression is too great and there is an imminent danger of fracture. For instance, suppose the instrument locks within the canal walls and continues to rotate at a high torque.

In that case, it will inevitably reach its elastic resistance limit, and a torsional fracture will occur.

Therefore, it would be fair to say that the operator should choose an instrument alloy phase expression that is more austenitic for files during the initial apical approach, such as glide path instruments or smaller diameter instruments, as flexibility would be present due to the design and metallic mass. In contrast, these instruments need a performance surplus due to torsional fatigue resistance by a higher angular deflection.

On the contrary, files of greater caliber should present their alloy phase expressions in a more martensitic phase given their greater volume in mass and lesser flexibility. It is worth remembering that fully austenitic instruments must be relegated to specific functions, such as retreatment. If the same heat treatment is performed for all sizes, some will benefit from the accomplished metallurgical changes while others will be harmed. Therefore, one method doesn’t equally satisfy the needs for all sizes.

Until mid-2020, the scenario was that if the operator wanted to get the most out of heat treatment in endodontic instruments, he or she would have to mix and match different systems. However, considering that “other systems” implies a different protocol sequence and that no consensus or research is showing the results of this mix of instruments, evaluating the quality and safety of this mix-and-match option seems to be entirely empirical and only based on individual experiences.

Genius files were established in 2015 with a design that allowed rotary and asymmetrical reciprocal motion use. The improved generation of Genius files, Genius Proflex (Medidenta), was launched in 2020 as the first system to adopt customized heat treatments (Figure 7) to balance torsional strength and high flexibility in different sizes of files.

Figure 7. Genius Proflex file examples of the 3 different heat treatments applied. Small-diameter files (purple) received a more austenitic heat treatment, intermediate files (blue) received a more martensitic treatment, and larger files (gold) received the higher martensitic heat treatment.

With new instruments in the series and 3 tailored heat treatments, Genius Proflex showed a better balance between torsional resistance (more austenitic in the smaller caliber files) and higher flexibility (more martensitic in the larger caliber files) (Figure 8). 

Figure 8. As a result of the customized heat treatments applied for different diameters of files, Genius Proflex large files present a more martensitic alloy expression phase showing the same flexibility as the small-diameter files, which naturally offer more flexibility due to less metallic mass.

The thinner (ISO 13 .03, 17 .05, and 25 .04) instruments received a heat treatment with a more dominant austenitic phase, which led to a violet stain. The more martensitic, larger files (ISO 40 .04, 50 .04, and 60 .04) resulted in a golden color. There are also 2 intermediate instruments (ISO 30 .04 and 35 .04) whose heat treatment resulted in a bluish hue.

This mix of heat treatments leads to a differentiated performance of each instrument in the series, increasing resistance to the 2 biggest challenges presented during instrumentation (torsional and cyclic fatigue) at different stages of treatment. 

It seems that there is a trend toward customized heat treatments based on the metallic mass of the instrument. Since the launch of Genius Proflex in 2020, other manufacturers have presented systems with a differentiated heat treatment in the sequence, corroborating the original idea that the same heat treatment should not merely be applied to different file sizes.

One example is an instrument ISO 15 .04 whose alloy is in the martensitic phase. Indeed, the operator will have a lot of difficulties advancing apically given the high degree of distortion and ineffectiveness of the cut of this instrument.

Clinically, the instrument has an angular deflection angle up to the fracture that is so high that the instrument distorts, even before the dentin walls are cut, and the canal widens.

CLOSING COMMENTS

Instrument separation during shaping procedures with rotary NiTi systems is an undesired event that can lead to complex resolutions. The wide range of fracture rates reported in the literature (from 1.98% to 26%) highlights the unpredictability of this phenomenon in clinical practice. It could certainly be related to multiple factors, such as instrument design, number of uses, motor kinematics, root canal anatomy, or operator experience.

Extensive clinical and scientific knowledge was created about the benefits of file heat treatments and the predominant phases acquired. It is essential to know that different heat treatments lead to various instrument performances, helping to overcome the separation of instruments in different stages of instrumentation.

REFERENCES

1. Gavini G, Santos MD, Caldeira CL, et al. Nickel-titanium instruments in endodontics: a concise review of the state of the art. Braz Oral Res. 2018;32(suppl 1):e67. doi:10.1590/1807-3107bor-2018.vol32.0067 

2. Haapasalo M, Shen Y. Evolution of nickel-titanium instruments: from past to future. Endod Topics. 2013;29:3–17. doi:10.1111/etp.12049

3. Peters OA. Current challenges and concepts in the preparation of root canal systems: a review. J Endod. 2004;30(8):559–67. doi:10.1097/01.don.0000129039.59003.9d

4. Shen Y, Coil JM, Zhou H, et al. HyFlex nickel-titanium rotary instruments after clinical use: metallurgical properties. Int Endod J. 2013;46(8):720–9. doi:10.1111/iej.12049

5. Shen Y, Zhou HM, Zheng YF, et al. Current challenges and concepts of the thermomechanical treatment of nickel-titanium instruments. J Endod. 2013;39(2):163–72. doi:10.1016/j.joen.2012.11.005 

6. Zhou H, Peng B, Zheng YF. An overview of the mechanical properties of nickel-titanium endodontic instruments. Endod Topics. 2013;29:42–54. doi:10.1111/etp.12045

7. Zupanc J, Vahdat-Pajouh N, Schäfer E. New thermomechanically treated NiTi alloys – a review. Int Endod J. 2018;51(10):1088-1103. doi:10.1111/iej.12924

8. Kuhn G, Tavernier B, Jordan L. Influence of structure on nickel-titanium endodontic instruments failure. J Endod. 2001;27(8):516–20. doi:10.1097/00004770-200108000-00005 

9. Bui TB, Mitchell JC, Baumgartner JC. Effect of electropolishing ProFile nickel-titanium rotary instruments on cyclic fatigue resistance, torsional resistance, and cutting efficiency. J Endod. 2008;34(2):190–3. doi:10.1016/j.joen.2007.10.007

10. Shen Y, Zhou HM, Zheng YF, et al. Current challenges and concepts of the thermomechanical treatment of nickel-titanium instruments. J Endod. 2013;39(2):163–72. doi:10.1016/j.joen.2012.11.005 

11. Gambarini G, Piasecki L, Di Nardo D, et al. Incidence of deformation and fracture of twisted file adaptive instruments after repeated clinical use. J Oral Maxillofac Res. 2016;7(4):e5. doi:10.5037/jomr.2016.7405

12. Thompson SA. An overview of nickel-titanium alloys used in dentistry. Int Endod J. 2000;33(4):297-310. doi:10.1046/j.1365-2591.2000.00339.x 

13. Buehler W, Gilfrich J, Wiley RC. Effects of low-temperature phase changes on the mechanical properties of alloys near composition TiNi. Int J Appl Phys. 1963;34:1475–7.  doi:10.1063/1.1729603 

14. Sousa-Neto MD, Silva-Sousa YC, Mazzi-Chaves JF, et al. Root canal preparation using micro-computed tomography analysis: a literature review. Braz Oral Res. 2018;32(suppl 1):e66. doi:10.1590/1807-3107bor-2018.vol32.0066

15. Arslan H, Yildiz ED, Gunduz HA, et al. Comparative study of ProTaper gold, reciproc, and ProTaper universal for root canal preparation in severely curved root canals. J Conserv Dent. 2017;20(4):222–4. doi:10.4103/JCD.JCD_94_17

16. Bürklein S, Hinschitza K, Dammaschke T, et al. Shaping ability and cleaning effectiveness of two single-file systems in severely curved root canals of extracted teeth: Reciproc and WaveOne versus Mtwo and ProTaper. Int Endod J. 2012;45(5):449–61. doi:10.1111/j.1365-2591.2011.01996.x

17. Plotino G, Ahmed HM, Grande NM, et al. Current assessment of reciprocation in endodontic preparation: a comprehensive review–part II: properties and effectiveness. J Endod. 2015;41(12):1939–50. doi:10.1016/j.joen.2015.08.018

18. Silva EJNL, Vieira VTL, Belladonna FG, et al. Cyclic and torsional fatigue resistance of XP-endo shaper and TRUShape instruments. J Endod. 2018;44(1):168–72. doi:10.1016/j.joen.2017.08.033 

19. Silva EJNL, Giraldes JFN, de Lima CO, et al. Influence of heat treatment on torsional resistance and surface roughness of nickel-titanium instruments. Int Endod J. 2019;52(11):1645–51. doi:10.1111/iej.13164 

20. Silva EJNL, Hecksher F, Antunes HDS, et al. Torsional fatigue resistance of blue-treated reciprocating instruments. J Endod. 2018;44(6):1038–41. doi:10.1016/j.joen.2018.03.005

21. Silva EJNL, Vieira VTL, Hecksher F, et al. Cyclic fatigue using severely curved canals and torsional resistance of thermally treated reciprocating instruments. Clin Oral Investig. 2018;22(7):2633–38. doi:10.1007/s00784-018-2362-9 

22. Pedullà E, Lo Savio F, Boninelli S, et al. Torsional and cyclic fatigue resistance of a new nickel-titanium instrument manufactured by electrical discharge machining. J Endod. 2016;42(1):156–9. doi:10.1016/j.joen.2015.10.004

23.Thu M, Ebihara A, Adel S, et al. Analysis of torque and force induced by rotary nickel-titanium instruments during root canal preparation: a systematic review. Appl Sci. 2021;11:3079 doi:10.3390/app11073079

24.Lopes HP, Gambarra-Soares T, Elias CN, et al. Comparison of the mechanical properties of rotary instruments made of conventional nickel-titanium wire, M-wire, or nickel-titanium alloy in R-phase. J Endod. 2013;39(4):516–20. doi:10.1016/j.joen.2012.12.006

25.Tian H, Schryvers D, Liu D, et al. Stability of Ni in nitinol oxide surfaces. Acta Biomater. 2011;7(2):892–9. doi:10.1016/j.actbio.2010.09.009 

ABOUT THE AUTHOR

Dr. Ramos received his DDS degree from the State University of Londrina in Brazil in 1987. He has a PhD in endodontics and is a former head of the endodontics department at the State University of Londrina. He has published 3 endodontic textbooks and has written more than a dozen chapters for various endodontic books. Living in the United States since 2012, Dr. Ramos lectures globally about streamlined endodontic protocols. He can be reached via email at carlos.ramos@medidenta.com.

Disclosure: Dr. Ramos is the director of clinical affairs for Medidenta.

Third Quarter of the Root Canal Game

We will use the molar No. 19 (Figures 1 to 3) as the example for these final steps.

Figure 1. Preoperative radiograph of tooth No. 19.

Figure 2. Postoperative photo following use of ProTaper Gold (Dentsply Sirona Endodontics).

Figure 3. Recall at 18 months.

Shaping: This ensures the removal of vital or necrotic pulp tissue and enables the sodium hypochlorite and, later, QMix (Dentsply Sirona Endodontics) to work in the canal and extend down to the apex. Shaping also opens the canals enough for obturation.

The best part about this RCT playbook is that you can use any orifice opener, glide path file, or set of shaping files. Just choose your desired file system. I use ProTaper Gold (Dentsply Sirona Endo-dontics) (Figure 4) and WaveOne Gold (Dentsply Sirona Endo-dontics) in my practice. I have completed thousands of cases with these file systems and have achieved excellent shaping results. 

Figure 4. ProTaper Gold.

Once you have completed the middle flare and glide path with the ProTaper Gold Shaper 1, move on to the ProTaper Gold Shaper 2 (Figure 5). Gently work this to length using 4 to 5 engagement/disengagements. At this point, it will slide and glide to working length easier than the S1, but it still may take 1 to 2 passes of 4 to 5 engagement/disengagements. The S1 is your workhorse and does a lot of what I call the “hard” shaping. Irrigate out the debris with sodium hypochlorite and recapitulate (negotiate to patency) with a #10 K-file. Always shape with bleach in the canals. Never shape dry.

Figure 5. ProTaper Gold S2.

Once the S2 reaches working length, proceed to the ProTaper Gold Finisher 1 (#20 tip) (Figure 6). This will usually fly to working length. These files shape the apical third and create a deep apical shape. If it’s a tight, twisty, curved canal, you can finish the shape with the F1, but since I am talking about “simple” root canal treatment, I usually finish with the ProTaper Gold Finisher 2 (#25 tip). In the same manner, work the F2 down to working length with 4 to 5 engagement/disengagements or slow in-and-outs. It may take one pass, or it may take 2 to 3. Take your time. Once you get to working length, gently run the F2 two to 3 times at or near working length to obtain a deep apical shape. Many dentists just “peck” the apex with their last shaping file and then wonder why the matching gutta-percha cone doesn’t fit to length or fits 2 mm short. Don’t be afraid to gently shape the apex. This will give you a deep apical shape, clean the apical foramen, and allow the cone to fit down to working length. Remove the Finisher 2 from the canal and inspect the end of the file. Are the flutes full of dental debris? If they are, then you are done shaping and do not need to upshape to the ProTaper Gold Finisher 3. 

Figure 6. ProTaper Gold F1.

Apical verification: This ensures that you have a deep apical shape and that the cone will fit to working length.

Once shaping is complete, gently verify the apical shape. If you finished with a ProTaper Gold F2 (#25 tip), select and place a #25 K hand file to working length. If it fits snugly to working length without much resistance and does not extend past working length, then apical shaping and verification are complete. If the #25 K-file stops 2 mm short of working length, you have not shaped the apical third adequately, and the soft gutta-percha cone will also stop 2 mm short of working length. Go back and reshape the apex. The easiest way to do this is to use the #25 K hand file in a reciprocating motion and gently advance it down to working length. If the #25 file won’t extend down to working length, remove it, irrigate, recapitulate with a #10 K-file, and work your way from a #15 to a #20 and finally back to a #25 K-file. You can also reshape the apical third with the ProTaper Gold F2. 

Once you feel that apical verification is complete, use the EndoActivator (sonic activation) (Dentsply Sirona Endodontics) with bleach in the canals and run it for 1 minute per canal. This enhances chemical disinfection and stirs up the bleach piranhas to eat more tissue and microbes.¹ 

Fourth Quarter of the Root Canal Game

Conefit: This ensures that the cones fit to the proper working length and are not seated short or long.

This step is often hurried through because you are now running out of treatment time, and the next patient is waiting in another treatment room. 

Still, take the appropriate time to perform a good conefit with quality cone-fit radiographs. Select the matching gutta-percha cone. In this case, select the micronized, conform fit ProTaper Gold F2 cones and place them into each canal one at a time. When they stop advancing, crimp the cone with cotton pliers at the reference point, and then remove the cone and measure to see if it advanced down to the correct working length. If a cone fits 1 mm long, then use scissors to cut 1 mm off the tip. If a cone fits approximately 1 mm short, then go back and gently shape to working length with a #25 K-file or the ProTaper Gold F2 file. 

Once you feel that the cones fit to the correct working length, place them back in the canals that are soaking with bleach and take a straight and a shift periapical radiograph. If the cone is right at the radiographic working length, then trim approximately 0.5 mm off the tip. If you are long, then cut back the appropriate length. Be as exact as possible here, and do not cut off too much of the cone. Keep at it until you have an excellent conefit (in the real world, this should just take minutes to achieve as long as you have shaped well).

Final disinfection: Now, remove the cones and suck out the bleach with a micro-vacuum or use paper points and irrigate with the final solution, QMix 2in1. QMix is a 2-in-1 irrigant that consists of EDTA and chlorhexidine² (Figure 7). This 2-in-1 solution removes the smear layer that forms circumferentially on the canal wall from shaping with the EDTA component and then provides a substantivity antibacterial effect with the chlorhexidine component.³ I have been using QMix for more than 5 years in my practice. The theory is that the EDTA removes the smear layer, and then the chlorhexidine can enter the exposed and open dentinal tubules and kill any hiding microbes. Dentinal tubules are essentially little caves that bacteria, viruses, and fungi can hang out in.³ 

Figure 7. Mix 2in1 Irrigating Solution (Dentsply Sirona Endodontics)

Place QMix with a side-vented needle and sonically agitate the QMix with the EndoActivator in each canal for 30 seconds^4,5 (Figure 8). Leave the QMix in the canals for at least one minute to remove the smear layer. Recapitulate one last time with a #10 or #15 K hand file. 

Figure 8. EndoActivator System (Dentsply Sirona Endodontics).

Paper points: This ensures the canals are dry, especially in the apical third.

Use a micro-vacuum (I prefer the EndoVac MacroCannula [Kerr Endo-dontics]) to suck out the QMix from all of the canals, and then dry with paper points. For efficiency, use the corresponding ProTaper Gold F2 paper points. You can also use any standard paper points. A good rule that I use in my practice is to use medium paper points if I finished the shape with a ProTaper Gold F1, coarse paper points if I finished with an F2, and extra coarse if I finished with an F3.

Warm Vertical Obturation: This ensures that you achieve a 3D “hermetic” seal.

Finally, it is time to fill and seal the shaped and cleaned canals. The goal of obturation is to 3-dimensionally hermetically seal the apex so microbes can’t escape or enter the root canal system. There are 4 ways to obturate a canal: (1) cold lateral, (2) warm vertical, (3) thermoplastisized gutta-percha (GuttaCore [Dentsply Sirona Endodontics] or Thermafil [Dentsply Sirona Endo-dontics]), and (4) single cone using a calcium silicate sealer like BC. In this article, we will focus on warm vertical obturation.

Pick up the “fitted and measured” gutta-percha cone with cotton pliers and butter the apical third with your preferred sealer (I use either Pulp Canal Sealer [Kerr Endodontics] or Ribbon Root Canal Sealer [Dentsply Sirona Endodontics]). Carefully place the buttered cone into the canal and gently push it down toward working length. Make sure the cone seats down to working length by checking that the crimped part of the cone is at the reference point. I then use the Gutta-Smart heat tip (Dentsply Sirona Endodontics) (Figure 9) or the EndoPro 270 (Brasseler USA) at 200℃ to “burn out” the coronal two-thirds part of the cone, leaving a 5-mm apical gutta-percha plug. To perform this technique, I prefer the black-sized tip for the Gutta-Smart heat tip or the 45/04 tip for the EndoPro 270. They are smaller and fit better into premolar and molar canals. Be gentle when using the heat tip. If it does not fit down to within 5 mm of working length, that is ok. Do not force it down the canal. Just go as far as it allows with the ideal goal of extending the heat tip to within 5 mm of working length. This allows the heat to travel down the 5-mm gutta-percha plug and to the apex. Select a small plugger (I prefer the Dovgan Pluggers with the white/green end [Prime Dental Supply]), dip the end into the sealer, and then gently tap or push on the softened, 5-mm apical plug and mold it into the irregularly shaped foramen. The goal is to obtain a nice, tight hermetic seal (in theory) and to prevent any microbial leakage.

Figure 9. Gutta-Smart (Dentsply Sirona Endodontics)

Backfill the coronal two-thirds of the canal with the Gutta-Smart Obturation Handpiece 25-ga tip (or any preferred backfill device). Place the 25-ga tip on top of the 5-mm apical gutta-percha plug, and slowly extrude the heated gutta-percha. Go slowly and allow the Gutta-Smart to push you out of the canal. I typically backfill the entire canal up to the orifice level in one shot. Select a larger plugger (Dovgan, black/blue end) and tap the gutta-percha down right at the orifice. Clean the extra sealer off the pulp chamber floor and walls with a small chloroform pellet, followed by alcohol (Pulp Canal Sealer) or just an alcohol pellet (Ribbon Root Canal Sealer).

Whew! This root canal is finally done. This is one for the books! 

CONCLUSION

Follow the root canal playbook to achieve effective, efficient, and excellent root canals (or, what I like to call E³ Endodontics). It will take practice, practice, practice, and a few missteps, but keep at it, and you will achieve endodontic success.

REFERENCES

1. Pasqualini D, Cuffini AM, Scotti N, et al. Comparative evaluation of the antimicrobial efficacy of a 5% sodium hypochlorite subsonic-activated solution. J Endod. 2010;36(8):1358-60. doi:10.1016/j.joen.2010.03.035

2. Kara Tuncer A. Effect of QMix 2in1 on sealer penetration into the dentinal tubules. J Endod. 2015;41(2):257-60. doi:10.1016/j.joen.2014.10.014

3. Azim AA, Aksel H, Zhuang T, et al. Efficacy of 4 irrigation protocols in killing bacteria colonized in dentinal tubules examined by a novel confocal laser scanning microscope analysis. J Endod. 2016;42(6):928-34. doi:10.1016/j.joen.2016.03.009 

4. Arslan D, Guneser MB, Dincer AN, et al. Comparison of smear layer removal ability of QMix with different activation techniques. J Endod. 2016;42(8):1279-85. doi:10.1016/j.joen.2016.04.022

5. Caron G, Nham K, Bronnec F, et al. Effectiveness of different final irrigant activation protocols on smear layer removal in curved canals. J Endod. 2010;36(8):1361-6. doi:10.1016/j.joen.2010.03.037

ABOUT THE AUTHOR

Dr. Pullen graduated from the University of Southern California Dental School in 1999 and completed a one-year AGD residency in Landstuhl, Germany, while in the US Army. He practiced as a general dentist for 5 years before attending the Long Beach VA Endodontic residency and graduating in 2006. Dr. Pullen started his own private practice in Brea, Calif, in 2007 and became board-certified in endodontics in 2013. He has 3 kids and enjoys surfing, reading, Brazilian jiu-jitsu, and hanging out with his wife and kids. Dr. Pullen runs both the live 2 Day Root Camp Boot Camp and rootcanalacademy.com online courses. He can be reached via email at reidpullen@rootcanalacademy.com. 

Disclosure: Dr. Pullen lectures for Dentsply Sirona.