Figure 1. The MixStar-eMotion (DMG America).

Figure 2. The rigid Honigum Putty (DMG America) keeps implant transfers firmly in place to ensure accuracy for the work to be done by our dental laboratory team.

Figure 3. Metal nonflexing impression trays are the first step to success.

Figure 4. Patient practices biting into maximum habitual intercuspation (centric occlusion).

Figure 5. Bite registration paste (O-Bite [DMG America]) is placed on the contralateral opposing arch (nonprep side) to create a lock bite that will ensure that an accurate restorative bite is taken (see Figure 6).

Figure 6. Capturing the centric occlusion lock bite.

Figure 7. Occlusal lock-bite registration left in place to act as bite jig.

Figures 8a and 8b. Practicing accurate placement of the tray.

INTRODUCTION
Today’s dentists are exposed to a multitude of dental materials, with each manufacturer claiming the benefits and superiorities of its respective products. Sometimes, I feel that the “prehistoric” techniques that we learned in dental school years ago display more benefits than what is in vogue today. This is especially true for crown and bridge impression materials and techniques. One has to only look back and visualize copper band impressions taken with dental compound, and picture the definition, accuracy, margin detail, and meticulous dies that these impressions provided. Even now, we are still seeing the results of the “copper band masters” decades after the restoratons were placed. I sometimes wonder if the restorations fabricated from today’s materials are as accurate, or will last as long?
     We all know that a meticulous impression is paramount for a precision fit of the permanent indirect restoration. Unfortunately, for many clinicians, taking a crown and bridge impression is one of the most stressful procedures in restorative dentistry. The good news is that taking great impressions can be simple if a dentist chooses the correct impression tray, achieves adequate retraction with controlled bleeding, and uses a rigid impression material with a light body wash to clearly capture every detail of the preparation.
     The purpose of this article is to share material choice rationale and technique protocols that we use in our office for taking consistently accurate impressions.

IMPRESSION MATERIALS
Throughout the last 2 centuries, different types of impression materials have been developed for use in dentistry. The nonelastic materials include: plaster, dental compound, and zinc oxide eugenol pastes. The elastic materials include: alginate (irreversible hydrocolloid), agar (reversible hydrocolloid), polysulfide, condensation silicone, addition silicone (polyvinyl siloxane [PVS]), and polyether.¹
      When evaluating an impression material, dentists tend to focus mainly on 3 factors:hydrophilicity, setting time, and cost. However, there are physical and mechanical characteristics which are far more critical to consider such as: detail reproduction, dimensional stability, ease of removal, gypsum (die and model stone) compatibility, elastic recovery/strain in compression, tear resistance, viscosity, complete conversion to an elastic solid, acceptable odor and taste, shelf life, and having the capability to be poured multiple times while still maintaining accuracy.² Dental marketing seems to be focused on the concepts of hydrophilicity as if it were the only standard on which to judge the product.
     It is also paramount for the dentist to understand that not all impression materials and impression situations are the same. As a result, one should choose an impression material accordingly. The dentist must evaluate what type of impression is being taken (whole arch, sectional, multiple, or single tooth) and chose an appropriate impression tray, method of tissue retraction, and impression material.
     In my opinion, when taking sectional-arch impressions, or when picking up implant impression transfers; a thick consistency putty-like material is preferable, since its rigidity offers greater support. The putty material is a kneadable material that is used as a base material. After a low viscosity material is injected around the tooth, the impression tray filled with putty is then placed over the teeth, displacing the light body (low viscosity), into the crevices surrounding the preparation. After setting, the impression tray is removed, yielding an extremely accurate reproduction.
     The choice of impression materials, coupled with the appropriate impression-taking techniques, is critical to success. In my opinion, it seems that we have traded accuracy for convenience. Most dentists are using disposable plastic trays, as opposed to metal (rigid) ones. Then, the flexible plastic trays are filled with impression materials that flow, rather than with a stiff material that would provide less chance for distortion. This is, in part, due to the manufacturers’ need to have a flowable impression material with a viscosity that works with automix delivery systems (where the base and catalyst are combined and mixed in a small mixing tip). These flowable impression materials lack the rigidity of the previous generation of putty systems that had to be hand mixed.
      Despite the introduction of dynamic mixing devices (cartridges or automated), many dentists still value the consistency of the previous generation of putties and continue to mix their materials manually. Manual mixing putty systems such as Silagum (DMG America), Aquasil Putty (DENTSPLY Caulk), Express Penta Putty (3M ESPE), Flextime and Provil (Heraeus Kulzer), Panasil Putty (Kettenbach LP), and President and Affinis Putty (Coltène/Whaledent) have continued to be manufactured.
      Until recently, I have not experienced an automix impression system displaying the benefits of the copper band technique or the putty systems where the dentist would mix 2 balls of catalyst and base together. (This stiff material, when placed in an impression tray, would displace a light body wash material injected into the sulcus surounding the preparation, resulting in an impression with sharp definable margins.) For clinicians like me, who value a thick consistency, an innovative putty (Honigum-MixStar Putty [DMG America]) has been recently introduced in an automix cartridge that is mixed in an automix machine (MixStar-eMotion [DMG America]) (Figure 1).
     Since I have been using this material in my own practice, I feel that the definition and sharpness of my margins have improved. I do not need to retake impressions as frequently since the stiff putty displaces the light body material easily into the preparation sulcus. As a result, I have now been able to return to my “old school” roots with the benefit of modern convenience. Furthermore, I also find that this putty material, which has neither an unpleasant smell nor taste for the patient, is easier to remove from the mouth than regular heavy body materials. We have found that it maintains excellent dimensional stability and does not distort over time, making it unnecessary for it to be poured immediately. In addition, since dental implants have become a major part of our restorative practice, accurate impressions are vital to the success of these procedures. A firm putty impression system captures the implant transfer postion very accurately. In the dental laboratory, the rigidity provided by the putty allows the transfers to be precisely poured into an analog model (Figure 2).

IMPRESSION TRAYS
When a dentist places an impression material in the patient’s mouth, using many of the commercially available plastic impression trays, any flexing of the plastic tray causes the impression to be distorted.³ It is the lack of tray rigidity that leads to flexure, resulting in incaccurate dies in the buccal-lingual and occlusal dimension. Although the impression may look perfect, even the most minute bending of the tray on placement will create inaccuracies in the final restoration, causing adjustment to be necessary when placed in the patient’s mouth.
      Dentists often receive cases back from their dental laboratory team that appear to be perfect. The occlusion looks accurate, the marginal ridges line up, and the contacts are tight. However, when tried in the patient’s mouth, the case has to be adjusted significantly. Sometimes a new impression must be taken and the case totally remade. There are many possible reasons for these inaccuracies. Perhaps the stone used to create the model was not poured according to the manufacturer’s instructions and specified proportions, causing too much expansion, yielding a totally inacurate model. Perhaps the stone dies were not properly prepared, preventing the restorations to fully seat in the mouth. There are many factors that can affect the fit of our restorations, so we must eliminate inaccuracies and distortions right from the beginning of the process. Using rigid impression trays is the first step to accuracy in your impressions (Figure 3).⁴

Figure 9a. The doctor injects the light-bodied (Honigum [DMG America]) impression material. Figure 9b. Simultaneuosly, while the doctor injects the light-bodied impression material, the assistant is dispensing the putty (Honigum Putty [DMG America]) from the MixStar-eMotion. Figures 10a and 10b. Closing into the putty using the bite jig, which serves to guide the teeth into the proper predetermined bite relationship. Figure 11. Precise details, using the impression technique protocol as outlined, were easily attained. Figure 12. Gingival retraction paste (Expasyl [Kerr]) was used in this case for tissue and fluid control, instead of packing retraction cord. Figure 13. A beautiful and accurate impression was achieved on a multiple unit full-arch impression using the putty-wash technique protocol and materials as described in this article.

Full-Arch Impression Trays
Full-arch metal impression trays are the “gold standard.” When accurate full-arch impressions are taken of the opposing arches and poured and prepared in a consistent and precise manner, many sources of inaccuracy are eliminated resulting in restorations that should require minimal adjustment intraorally.
     Rigid protocols are essential for reliability and consistency in dental procedures. All full-arch impressions in our practice (PVS, alginate) are taken with Rim-Lock Impression Trays (DENTSPLY Caulk). When I place and remove these trays from the patient’s mouth, I am confident that these trays are not flexing, thus eliminating the first source of error from the impression-taking process. It is then up to the dental laboratory team to follow the remainder of the protocol and to produce consistent restorations requiring minimal adjustment.

Dual-Arch Impression Trays
Dual-arch impressions continue to be very popular and, if done properly, will produce single-unit restorations requiring minimal or no adjustment.^5,6 Dual-arch trays have several advantages: only one tray is needed for the impression of both of the opposing arches; the bite is registered simultaneously in the impression; it provides improved patient comfort versus full-arch trays; less impression material is used, resulting in lower cost; and, because 3 procedures (2 impressions, bite registration) are performed simultaeously, it takes less time, further reducing the costs associated with impression taking.
     However, one must keep in mind that the dual-arch impression procedure is very technique sensitive and should only be used when the following criteria are met:

• It should be used with an intact dentition (Braley Class I) and the single prepared unit should have intact teeth adjacent to it.
• The occlusal surfaces opposing the prepared teeth should be ideal.
• The patient should be able to close down into maxiumum intercuspation without interference.

     In my opinion, plastic impression trays should never be used because they flex, creating inaccuracies. Instead, a metal dual-arch impression tray should be chosen. It should fit passively and the operator must ensure that it does not rub against any tooth/anatomic structures to avoid any potential interferences when the patient bites together. If passive fit of the tray cannot be achieved, then conventional full-arch impressions should be taken. In our practice, we use the Quad Tray Plus (CLINICIAN’S CHOICE). It is designed in its shape and dimensions to accommodate most patients’ dental arches. Its rigidity creates extremely accurate impressions when used with compatible rigid impression materials.

DUAL-ARCH IMPRESSION TECHNIQUE
After selecting the appropriate dual-arch impression tray, the dentist should practice inserting the tray into position in the patient’s mouth. Also, the patient should practice biting into maximum intercuspation (Figure 4). After several practice runs of placing the tray and having the patient bite down, place some O-Bite (DMG America) bite registration material on the opposing arch (Figure 5) on the contralateral arch (the nonprepped side of the patient’s mouth). Then, have the patient bite together to capture this contraleteral bite; this bite will serve as a “lock” to ensure that the patient is biting consistently into maximum intercuspation (Figure 6). Leaving this bite registration in place (Figure 7), the clinician once again practices accurate placement of the dual-arch impression tray (Figures 8a and 8b). Next, light body Honigum (DMG America) is injected into the sulcus of the preparation by the doctor (Figure 9a), while the dental assistant simultaneously dispenses the Honigum Putty from the MixStar-eMotion (Figure 9b). The dual-arch tray loaded with putty is placed in the manner that was previously practiced. The bite registration will serve as a guide to ensure that the patient is in complete habitual centric occlusion closure (Figures 10a and 10b). Using this impression technique protocol will allow the dentist to easily achieve consistently accurate impressions with precise detail (Figure 11).

RETRACTION TECHNIQUE
In order to take consistently accurate impressions, we must be able to visualize the margins of our preparations clearly. If our margins are placed supragingivally, capturing them is relatively simple. However, much of the time, the margins are placed subgingivally beyond the presence of existing large restorations, or for aesthetic reasons. Dentists sometimes proceed to take subgingival impressions without being 100% able to visualize the prepared margins, “hoping” that the impression will succeed. If they miss the first impression, they often take it again, while still not being able to totally visualize their margins. They are basically again “hoping for a miracle.” They blame the lack of hydrophilicity of the material (or some other reason?) for their own fundamental errors.
      Hydrophilicity is not an issue if there is no bleeding and the dentist can totally visualize the margin of the preparation. Dentists are obsessed with hydrophilicity. However, there is really no such thing as a hydrophilic PVS impression material.⁷ A clear field, free of blood and other oral fluids/contamination, is the most important factor in capturing a good impression. All PVS materials have the same weakness: they are unable to consistently make an impression in the presence of blood/fluids. Since 2 materials cannot occupy the same space at the same time, sulcular bleeding must be controlled prior to taking the impression. Adequate retraction must be accomplished in all subgingival areas to guarantee that the impression material will flow under the margin. Several different methods of retraction are in vogue today, the most popular of which are: retraction cords, laser or electrosurgery techniques, and paste systems (such as Expasyl [Kerr]) (Figure 12).

CONCLUSION
Capturing an accurate dental impression (Figure 13) is one of the most stressful and challenging steps in restorative dentistry! And, although digital impression and CAD/CAM technologies are being touted as a new alternative for accurate impressions and definitive restorations to the dental profession, it will likely take quite some time for these technologies to be implemented into the majority of private practices. In the meantime, with the majority of dentists still involved with taking physical (nondigital) impressions, many different protocols, techniques, and materials are being used. By understanding fundamental dental principles, following a technique protocol; carefully choosing materials, impression trays, method of retraction, and appropriate impression materials; dentists everywhere can easily achieve stress-free and consistently accurate impressions.

References

1. Terry DA, Leinfelder KF, Geller W. Aesthetic & Restorative Dentistry: Material Selection & Technique. Everestpublishingmedia.net and quintpub.com.
2. Electric handpiece systems. ADA Professional Product Review. 2007;2:6.
3. Cho GC, Chee WW. Distortion of disposable plastic stock trays when used with putty vinyl polysiloxane impression materials. J Prosthet Dent. 2004;92:354-358.
4. Samet N, Shohat M, Livny A, Weiss EI. A clinical evaluation of fixed partial denture impressions. J Prosthet Dent. 2005;94:112-117.
5. Cox JR, Brandt RL, Hughes HJ. A clinical pilot study of the dimensional accuracy of double-arch and complete-arch impressions. J Prosthet Dent. 2002;87:510-515.
6. Kaplowitz GJ. Trouble-Shooting Dual Arch Impressions. J Am Dent Assoc. 1997;128:548, 550.
7. Wayne J. Flavin. Beyond Hydrophilicity. CERP course. February 2004.

Dr. Mechanic received his bachelor of science (1975) and doctor of dental surgery (1979) degrees from McGill University. He practices aesthetic dentistry in Montreal, Canada, and he is the aesthetic editor of Canada’s Oral Health dental journal and is on the editorial board of Dentistry Today. He also is the co-founder of the Canadian Academy for Esthetic Dentistry, program coordinator of the University of Toronto Advanced Restorative Continuum, and is recognized as a leader in continuing dental education. He can be reached at info@drmechanic.com.

Disclosure: Dr. Mechanic reports no disclosures.

Figure 1. Initial radiograph showing a short root on the second premolar root and a molar with a vertical fracture. Figure 2. Occlusal view after the bridge was removed, showing the abscess from the fractured root. Figure 3. UniAbutments (Astra Tech Implants) in place on the implants. Figure 4. Impression posts were placed for the open-tray technique. Figure 5. The tray was filled and inserted over the impression posts.

Consistent, predictable, and reproducible procedures in restorative dentistry are expected from our impression materials and techniques. When taking an impression, clinicians must consider the true costs of retakes. Their true cost is calculated not only in the materials used, but also in the extra time involved. Retakes due to inadequate impressions are not simply inconveniences; they are also drains on the practice, requiring both materials and time, and affecting the patient’s perception of the dentist and his/her practice. Clearly, instead of being forced to adjust one’s schedule and make time for retakes, getting an impression right the first time is worth using quality materials and paying close attention to the techniques employed. In my experience, choosing an appropriate technique, along with a material that has the right qualities for the case, help to ensure clinical success in one take.

IMPRESSION MATERIALS AND TOOLS FOR SUCCESS WITH IMPLANT PROSTHETICS
When I completed my specialty program in periodontal prostheses in the early 1980s, we were instructed to take single-tooth to full-arch impressions with rubber base using custom trays. One advantage of using rubber base was the time factor—the material allowed ample time for taking an impression of the entire arch. In addition, it was also accurate, if poured-up only once.
      After working with rubber base for many years, a drawback became apparent. When I began restoring implants in my practice, I soon found out that rubber base impressions were not accurate for the procedure, due to the greater rigidity of implants versus a natural tooth. When taking an impression on implants, the biggest test of a material is when the implants are connected restoratively as a multiple unit. It is critical to obtain a passive fit with the framework, so that undesirable forces are not transferred onto the implant. Rubber base did not provide enough accuracy for the reproduction of the implant position, so the search for a new, more stable and rigid material began.
      I utilized polyvinylsiloxane materials for several years in putty form, as well as all types of viscosities in the syringeable material. I found that in using these materials, I had inconsistent results; sometimes the fit of the prosthetic framework was excellent, but other times the framework had to be sectioned and soldered. With the increase in the number of dental implant cases in my office, I began utilizing a polyether impression material (Impregum [3M ESPE]). I immediately recognized that it proved to be an accurate impression material in my hands; therefore, it has become my material of choice for any procedure requiring dental laboratory work. Having performed my own laboratory work for several years, I am able to evaluate the fit of restorations from both a laboratory and clinical point of view. In my experience, I have found polyether to be extremely reliable for both the dentist and the dental laboratory technician.

THE IMPORTANCE OF CONSISTENT MIXES
Prior to the introduction of impression materials that could be dispensed from a gun or cartridge system, all impression materials were mixed with a spatula. While generally effective, in some instances, this method can produce inconsistent mixes and results. Once I found the dependability and consistency of polyether and its mixing characteristics, it became essential to have an automatic dispensing and mixing unit (Pentamix Automatic Mixing Unit [3M ESPE]). I acquired a mixing unit for each operatory, because I wanted to be productive and use each treatment room to its full capacity. Automatic mixing units offer several advantages that make them particularly helpful: they ensure a completely consistent and homogeneous mix, allowing for void-free impressions; they help save material by dispensing only the required amount.
      There are a number of advantages to using a polyether impression material that I have found to be particularly relevant. Primarily, its excellent dimensional stability and tear strength make it an excellent choice for traditional crown and bridge but especially useful for implant cases. Compared to vinyl polysiloxane, the polyether material provides superior detail reproduction in the presence of moisture.¹ It is also the most precise with the direct impression technique.² Polyether can be poured up several times with the fit of a framework remaining the same on the first and subsequent model(s). Finally, there is no need to make a custom tray using the material since plastic stock trays work extremely well.
      A critical and essential aspect of taking an impression with a polyether is its consistent rigidity, which is a significant benefit for its stability. Because of the rigidity, undercuts are always blocked with laboratory rope wax, thus facilitating the removal of the impression from the mouth without distortion. The material performs accurately and consistently, giving the lab technician the best possible reproduction of the teeth or implant position in the mouth.

Figure 6. A full-arch impression (Impregum Penta Soft [3M ESPE]) helps the dental technician team create an accurate restoration that may reduce/eliminate the chance for occlusal adjustments. Figure 7. Occlusal view of stone model with soft-tissue reproduction. Figure 8. Occlusal view of metal try-in procedure with only one screw on the middle implant to verify passive fit. (Notice that the metal has not been sectioned or soldered.) Figure 9. Buccal view of final prosthesis. (Laboratory work by Fujiki Toshi, RDT.) Figure 10. Radiograph showing excellent fit of the final prosthesis on 3 Astra Tech Implants. (Implants placed by Dr. Jeffrey Bressman.)

ADDITIONAL TOOLS: ELECTRIC HANDPIECE AND MAGNIFiCATION
In my experience, the use of an electric handpiece and visual magnification are also especially helpful in performing highly accurate direct and indirect procedures in dentistry. The use of an air-turbine handpiece has been the treatment norm for several decades, but the introduction of the electric handpiece represents a great leap forward in preparing teeth quickly, accurately and easily. I have used one (NSK Brasseler Electric Handpiece) for a little more than 8 years and have found it to be extremely reliable, durable, and precise. The advantages of an electric handpiece include: high torque, which easily cuts off old restorations and crowns (especially nonprecious alloys and zirconia restorations); the ability to accurately quantify the torque via a control box; and most importantly, the ability to finish margins at a high definition, leaving a smooth and polished surface.
Additionally, the use of visual magnification, either with loupes or with the use of a microscope, is a must if excellence is to be achieved. We clearly cannot treat what we do not see! I have used telescopic loupes (Designs for Vision) for more than 20 years and could not practice precise high-level dentistry without them. One major advantage of these particular loupes is that they are completely customized to the individual, not only from a health perspective of one’s individual eye needs, but also from a working distance standpoint.
      By maximizing the magnification that one desires to work with, the customized settings of the loupes allow work to be accomplished with the best possible posture and reduces/ eliminates back problems. Protecting our eyes with lenses, while enabling us to see with higher magnification at the correct position the work to be performed in the mouth, is not an option today…from my perspective, it is a must!
      As outlined above, research and technological advances have helped make modern implant dentistry routine in treatment planning and clinical practice. The following case demonstrates the use of these tools in the restoration of implants with a fixed bridge.

CASE REPORT
Diagnosis and Treatment Planning
A 57-year-old female presented to the office with a 3-unit fixed bridge on her maxillary left quadrant. Both abutment teeth, Nos. 13 and 15, had been endodontically treated. The patient’s anterior abutment (premolar) had a short root and the posterior abutment (molar) had a vertical fracture, rendering a hopeless prognosis for the molar and very poor long-term prognosis for the premolar (Figures 1 and 2). The patient’s wish was to replace the missing teeth and prosthesis via a treatment that would provide the most stable long-term result.
     It was determined that implants would provide the most stable treatment in this case, as opposed to placing a new, longer-span bridge. A new bridge would have required cutting down healthy adjacent teeth, and the patient understood that if anything happened to one abutment (eg, caries), the entire bridge would be compromised.
An interdisciplinary approach is essential to correct patients’ existing problem(s) and to provide patients with the expected result. Therefore, from the diagnosis phase to the start of treatment, close communication with everyone involved on the treatment team is a must. In this case, several meetings took place among the oral surgeon, the dental laboratory technician, and me (the restorative dentist). There is very little leeway for laboratory technicians once the case is on their bench. If the dental technician is involved from the onset, extremely valuable recommendations can be incorporated in the treatment planning (such as the design of the prosthesis: cemented versus screw retained, use of stock versus customized components, straight or angled abutments, titanium versus gold or zirconium oxide).

Treatment Protocol
Teeth Nos. 13 and 15 were extracted, and the area was allowed to heal for 3 months. Then, Astra Tech Implants were placed. These implants were selected due to their ability to consistently preserve bone and their excellent soft-tissue response, as well as their record of no clinically detectable micromovement between the implant and the abutments.
      Following an additional 3-month healing phase, the patient returned to the office for impression-taking and evaluation of the implants. While the implants were properly integrated, it was determined to connect them for a bridge rather than restore the implants individually due to softer supporting bone around the implants. Different techniques are available to measure level of osseointegration of the implants, such as the use of a Periotest (Siemens) or the Osstell ISQ instrument, which provides a resonance frequency analysis to determine the clinical status of a dental implant. One of the major advantages of the Osstell ISQ Instrument is that the measuring results are not clinician-dependent, which could, as with other systems, provide diverse results.
UniAbutments (Astra Tech Implants) were placed on the implants prior to taking the impression to eliminate the need to transfer abutments from the model to the mouth. This also eliminated any future need to disrupt the prosthetic connection at the implant level while helping preserve optimum soft tissue health (Figures 3 and 4). In cases like this, when the impression is taken on multiple implants, I use the open-tray technique for higher accuracy since there is no need to transfer the impression copings into the impression. To capture the impression, an automatic mixing unit (Pentamix 3 Automatic Mixing Unit) was used to mix the material. A medium body polyether impression material (Impregum Penta Soft [3M ESPE]) was syringed around the abutments and the tray was filled and inserted (Figure 5). The rigidity of the material makes it excellent for use in the tray, while its flowability also makes it good for use around the implant impression post. The tray was held in place for 8 minutes and then removed. To prevent distortion, the impression tray was removed by first loosening it on the opposite side from the implants (moved slowly with an up-and-down and side-to-side motion), with the area to be restored being removed last (Figure 6).
      The dental laboratory team fabricated a metal framework for the try-in step (Figures 7 and 8). After verifying a passive fit during the try-in, the laboratory work proceeded with the creation of a fixed screw-retained bridge. The completed bridge was seated a month later, and the final result was a well-fitting and aesthetic restoration (Figures 9 and 10).

DISCUSSION AND CLOSING COMMENTS
A patient seeking treatment to replace a failing bridge expects long-term, stable results. Proper diagnosis and treatment planning as well as meticulous treatment and attention to detail enable us to provide patients with the expected results. While accuracy is important for any restoration, it is especially critical for implant procedures. It is also more difficult, given the osseointegration process. An accurate impression is vital in this procedure in order to ensure that the dental laboratory team has an accurate working model, thus enabling them to create a high quality final restoration or prosthesis and eliminating the possibility of a remake.
      Many impression materials tout a fast set, but in implant cases this is not necessarily a virtue. Depending on the number of implant impression posts that must be captured, a faster setting material may not allow enough time to syringe material before the tray material begins to set. One technique that I have found useful to increase the working time for an impression is refrigerating (cooling) the impression material for a few minutes before taking the impression. This is effective at increasing the working time, but does not change the catalyst to base ratio of the material and does not compromise its accuracy.
      The polyether impression material used in this case was stable and accurate enough to allow the dental technician to pour the model multiple times, enabling an accurate fit for restorative work; either for natural teeth, or for an implant-supported crown or prosthesis. This can significantly reduce adjustments at the delivery stage, saving time and ensuring a more satisfactory experience for the patient.

References

1. Walker MP, Petrie CS, Haj-Ali R, et al. Moisture effect on polyether and polyvinylsiloxane dimensional accuracy and detail reproduction. J Prosthodont. 2005;14:158-163.
2. Bambini F, Ginetti L, Memè L, et al: Comparative analysis of direct and indirect impression techniques. An in vitro study. Minerva Stomatol. 2005;54:395-402.

Dr. Rubinstein is a founder and partner at the Oral Rehabilitation Center in Skokie, Ill. He received his dental degree in 1980 from the Universidad Tecnológica de Mexico. From 1980 to 1982, he completed his specialty training in periodontal prosthesis at the University of Illinois at Chicago, where he was an assistant professor until 1992. He is past president of the Chicago Academy of Dental Research and the inventor of a custom abutment to prosthetically correct misaligned implants. He is a consultant to several companies regarding adhesive dentistry and implant prosthodontics and has lectured internationally, giving hands-on courses in adhesive dentistry. He has also published several articles in Adhesive Dentistry and Implant-Prosthodontics. He is a lecturer at DentalXP and is the author of 2 book chapters in Implant Prosthodontics and Treatment Planning. He can be reached via e-mail at the address oralrehab1@gmail.com.

Disclosure: Dr. Rubinstein is a speaker for Astra Tech Implants and has not received an honorarium for writing this article.