Let’s face it. Most of us have had some exposure to the TMJ in dental school, but it was just too complicated or too abstract that we just didn’t pay attention. How can this joint so far away from the teeth affect our dental work? We focused on the details and the techniques of cavity and crown prep, did the lab work necessary for our prosthodontics courses, and paid lip service to the diagnostic sciences. But where did this TMJ thing fit in? If a TMD condition arises, we were taught to fabricate splints and send the patient off to an oral surgeon or orofacial pain specialist, and, for the majority of us, that was about it. 

Imagine this scenario, which is an amalgamation (no pun intended) of multiple true stories. You have spent the past 9 to 18 months perfecting your full-mouth reconstruction/orthodontic plus or minus orthognathic surgery/All-on-4/implant-supported prosthesis for your patient. Your patient is particularly difficult to deal with, and, after multiple adjustments and many months and dollars later, you have what you think is the perfect outcome, and the patient walks out of your clinic happy until a few months or years later, when he or she comes back complaining that his or her front teeth don’t touch anymore. You look in the mouth, and, lo and behold, there is a gap between the upper and lower anterior teeth, and you can find nothing in the mouth that could possibly have caused it. You could have sworn you had even contacts all around when you finished your work. Now, a few teeth are conspicuously bare of articulating paper markings, and the patient is complaining that his or her bite does not feel right or that his or her teeth don’t look good. This is a frustrating position for dentists to find themselves in, especially after extensive and tedious dental work and/or surgery, but it is a situation that can occur if the TMJ condition and orthopedic stability of the TMJ and occlusion are not assessed prior to treatment planning and execution. 

While it is impossible to comprehensively review every single type of bite change and every TMJ condition leading to this kind of change in this article, the basic understanding of this process is the knowledge that the TMJ condyle is connected to the mandible…which houses the mandibular teeth…which articulate with the maxillary teeth…which are housed in the maxilla…which is connected to the palatine bone…which is connected to the sphenoid bone…which is connected to the temporal bone…which contacts the other half of the TMJ, the glenoid fossa. This aforementioned relationship sounds like a variation of the popular children’s song “Dem Bones.” Still, the connectedness of the human body in this fashion is really something that slips under the radar in many dental school programs. In summary, your upper jaw and lower jaw articulate in 2 places (if one was to consider the entire cranium an extension of the upper jaw)—the TMJs and the teeth—and structural and positional changes in one of these articulations can affect the other. 

DISCUSSION

The orthopedic stability of a joint means that it is in a centered and reproducible position in which it functions optimally. The head of the humerus or the femur needs to be in an orthopedically stable situation to function to the best of its ability and range of motion without ligament or muscle strain. In the TMJ, the situation is a little different because we have 2 points of articulation between the cranium and the mandible: the 2 TMJs and the upper and lower dentitions. The orthopedically stable condition is when the teeth are in maximum intercuspation (what some circles call “centric occlusion [CO]”), and the condyles are seated in the fossa (what the same circles call “centric relation [CR]”). If the teeth are together and the condyles are not seated, then this is an orthopedically unstable occlusion (what those same circles call “CR-CO shift or discrepancy”). The terminology and the concepts are ever-evolving, but the principle is the same: If you want your final dental or prosthetic occlusion to be stable, you need to diagnose and respect the TMJ condition and position and understand the role of that joint and its dysfunction in the emergence of bite changes. 

One orthopedically unstable occlusion is called “dual bite formation,” which is technically a CR-CO discrepancy, as it has been called in the past. It can form as a result of an acquired anterior position of the mandible. This anterior position can be due to auto-advancement or iatrogenic factors, which draw the condyles down and forward (Figure 1). Patients can auto-advance and hold their mandibles forward for various reasons, such as vanity because of a recessive and unattractive mandible, bringing a Class II mandible into function, or an attempt to increase airway dimensions by drawing the tongue and floor of the mouth forward through the attachment of these muscles to the mandible. Some dental treatments, such as orthodontic appliances and sleep appliances, can also advance the mandible. If the occlusion is altered in this forward position, or if the teeth super-erupt and come into occlusion in this forward mandibular position, the condyles will remain down and forward despite the teeth occluding fully. With time and relaxation of the muscles of mastication, the condyles will seek orthopedic stability (ie, they will seat gradually into the fossa), and as the condyle creeps back into the fossa, the mandible rotates back around a second molar tooth fulcrum and opens up the bite anteriorly (Figure 2). There are many patients who present to us as clinicians with teeth that seem to fit well but, in reality, have a condylar position that is not orthopedically stable, and it is our job to diagnose these prior to altering the occlusion or restoring it extensively because if the TMJ foundation is not stable, the dental house that we are building will not be stable. 

Figure 1. When teeth are in maximum intercuspation (MIP), the condyles should be seated in the fossae. These images show condyles in 2 separate patients that are (a) inferiorly and forward and (b and c) inferiorly positioned in the fossae with teeth in MIP; thus, the suspicion of orthopedic instability arises and should be confirmed clinically.

Figure 2. (a to d) The anterior open bite seen here is due to a dual bite relapse. The condyles are normal in height and morphology (d) with the posterior height of contour being lower than the anterior height of contours (compare to red arrows on Figure 6a). This morphology differentiates a dual bite relapse open bite from one caused by bilateral condylar height loss, where the height of contours can be at the same level (see Figures 4c, 5c and 6b).

Another orthopedically unstable situation occurs with structural and volumetric changes to the condyles, such as in the case of degenerative joint disease (osteoarthritis). Anything that reduces the height of the condyles will generate a space between the condyle and the fossa, and this extra space constitutes an orthopedically unstable situation. The condyles will gradually seat into the fossa and create that same phenotype of posterior rotation of the mandible and opening of the bite anteriorly. Patients can present to us with teeth that seem to fit well but may have degenerated condyles that are not completely seated in the fossae (Figure 3). The condylar height loss may have occurred before your treatment and the unseated condyles may not have been diagnosed prior to commencing work, or the degeneration may have occurred after your treatment. When we understand that degenerative joint disease is a biomechanical breakdown of the hard tissues that is preceded by the biomechanical breakdown of the soft tissues (internal derangement and disc displacement), it becomes clear that it is important to diagnose potentially vulnerable joints with disc displacements prior to starting treatment to inform the patient of the presence of this pre-existing condition that may compromise the stability of the treatment outcomes. In a few words, a clicking and popping joint is not normal. It is a biomechanically compromised joint that needs to be approached with care and diagnosed properly prior to starting dental treatment because a disc displacement is part of a continuum of articular tissue breakdown that may lead to jaw position changes and subsequent bite changes.   

Figure 3. This patient’s condyles are undergoing active degeneration, resulting in loss in condylar height and increased joint space, creating an orthopedically unstable situation. Although the teeth are together now, this is an open bite waiting to happen.

Figure 4. (a) Bilateral end-stage degenerative joint disease with condylar height reduction and seating in the fossae has resulted in (b) the posterior rotation of the mandible and (b and c) the anterior open bite.

Anterior open bites are just one of the bite changes that can occur as a result of orthopedic instability of the condyles. When the TMJ condition and position change and consequent seating of the condyles occur bilaterally and synchronously, we can expect an even posterior rotation of the mandible and opening of the bite anteriorly (Figure 4). But there are variations of this orthopedic instability that can create different presentations of the open bite. If the culprit TMJ condition is unilateral, one can expect a subsequent rotation of the mandible in the coronal plane to seat the smaller condyle. This leads to the opening of the posterior bite on the contralateral side. If left unattended, the predicted teeth supereruption will occur, resulting in an occlusal cant with the affected side being more elevated (Figure 5). These conditions can also be asynchronous, where one TMJ undergoes these changes, resulting in the aforementioned outcomes, and then the other TMJ undergoes similar changes, resulting in the posterior rotation of the mandible and opening of the bite anteriorly. Thus, it is important to identify potentially vulnerable TMJs prior to commencing dental treatment to avoid adjusting or redoing the work and causing frustration for the dentist and the patient.

Figure 5. Unilateral condylar height loss due to end-stage degenerative joint disease has resulted in (a) seating of the condyle and (b to d) subsequent changes in mandibular symmetry and (c and d) occlusal canting (b), with the right side (affected side) being more elevated.

Figure 6. (a) A normal condyle morphology has a posterior height of contour that is lower than the anterior height of con- tour and a gradual forward bend of the condyle. (b) A condyle that has undergone degeneration and remodeling is smaller, has a flattened articular surface, and has a height of contour that can be at the same level as each other.

The assessment of orthopedic stability is mainly a clinical one, with multiple philosophies teaching different ways of diagnosing and treating it. As a radiologist, when examining a patient’s CBCT scan with teeth in maximum intercuspation (which is what I recommended), if his or her condyles are normal in morphology but their position is down and forward, then I suspect orthopedic instability typical of dual bite formation (Figure 1). If the condylar morphology is altered and they are not seated, then I suspect orthopedic instability as a result of condylar height loss (Figure 3). The key is the examination of the heights of contour of the condyles (Figure 6). In a normal condyle, the posterior height of contour should be lower than the anterior height of contour with a gradual forward bending of the condyle (Figure 6a). The end-stage remodeling result of degenerative changes is an alteration of the morphology of the condyle, with flattening of the articular surface and the heights of contours ending up nearly at the same level (Figure 6b). If there is an anterior open bite on the scan, I quickly look at the condyles to see if the condylar morphology is normal or degenerated to give the etiology of the bite change. I also note if there is still more potential for occlusal changes (ie, still more space potential for the condyles to seat further), which need to be verified clinically. 

CONCLUSION

Of course, there are multiple other etiologies for bite changes that are more clinical diagnoses (such as digit sucking or tongue thrusting) or more complex diagnostic processes than I have space to describe here. The bottom line is this: If you do not diagnose your patients’ craniofacial conditions fully, you do not treat them fully and may run into issues with the stability of your treatments in the future. When you bring an oral and maxillofacial radiologist onto your dental team to help you diagnose your patient’s condition using his or her CBCT scans, we (the radiologists) will do what we can to help you (the clinicians) get to the bottom of the mystery of the changing bite.

ABOUT THE AUTHOR

Dr. Tamimi is the author of Specialty Imaging: Temporomandibular Joint and Sleep-Disordered Breathing and is a world-renowned speaker on the subject of oral and maxillofacial radiology. She runs her private practice in Orlando. She can be reached via her website at inspire-imaging.com or via email at info@inspire-imaging.com.

Disclosure: Dr. Tamimi reports no disclosures. 

There is no doubt that one of the greatest additions to the dentist’s diagnostic and treatment planning toolbox in recent years has been CBCT imaging. This is a radiographic imaging modality that has opened up a whole new field of view (no pun intended) when it comes to visualizing dental patients’ anatomy and pathology. It has almost eliminated the guesswork in trying to determine the morphology and position of structures, such as the relationship of impacted teeth to their surrounding structures, as well as the determination of the presence, etiology, and behavior of infections and other jaw pathologies. This is most evident when examining a tooth for infection that lies in planes that are not easily examined in 2D imaging, such as the buccal, lingual, and furcation aspects of the teeth, enabling an accurate diagnosis for a patient with occult dental infection. This ability to correctly diagnose the patient’s condition enables the dentist to treat him or her appropriately. 

But with this incredible improvement in diagnostic capability comes great responsibility to our patients, which is to become proficient in the examination and interpretation of CBCT scans. The interpretation of radiographic imaging is considered a dental procedure, and just like all dental procedures, an immense amount of learning needs to occur to make the examiner effective and efficient in this procedure. The time and commitment to reach this proficiency may vary from one practitioner to the next, but the fact remains that unless you have been formally trained in the review of CBCT, it is not a skill that comes intuitively. Building the vocabulary and methodology can be overwhelming if no formal training in this field has been undertaken. Radiographic diagnosis is an important link in the diagnostic chain.

As an oral and maxillofacial radiologist, I have witnessed an amazing change in our ability to observe and diagnose our patients’ conditions. These changes are a paradigm shift from how most of us were taught radiology in dental school. The interest in using this modality has multiplied tremendously. Still, not every dentist who uses CBCT in his or her office has the proper training to review the scans as many dental schools have still not incorporated 3D CBCT in their dental education curricula. One of my professional goals is to fill this educational gap and help dentists learn how to diagnose their patients’ conditions on CBCT scans. Throughout the years, I’ve compiled some fundamental pointers that can help shift your thinking and start you on the path of 3D analysis.

1. Lose the tunnel vision. This is probably the most important trait that you have to learn. All human beings have biases and preferences. When it comes to dentists, we like to look at the things we are comfortable with and tend to have a fine-tuned aesthetic eye. When it comes to radiographic imaging evaluation, our eyes tend to drift to the area of interest we are treating, and teeth always grab our attention. The problem with doing that is that it satisfies our curiosity, and we are not driven to look further, thus increasing the likelihood of “missing something” (Figure 1). The advice that I give dentists I am training is to consciously and purposefully avoid looking at the area of interest, namely, the teeth, and follow a systematic review process of the images that are repeatable and replicable on every single patient scan. Once you are done with all other structures, then analyze teeth systematically. 

Figure 1. A dentist acquired and analyzed this scan for implant placement. The dentist missed the lesion in the nose. Establishing an evaluation method that eliminates tunnel vision is imperative to avoid missing non-dentoalveolar pathology.

2. Reorient the scan. This step is crucial as it aligns the complex structures of the head with the anatomical planes and allows for a more symmetric analysis. This is important as the multitude of anatomic structures and conditions that occur in the head and neck can be confusing and difficult to visualize if the right and left sides of the head are not at the same level. Most scans will be acquired with the patient’s head off-center, depending on how they were seated in the CBCT unit. This reorientation corrects for these tilts and allows for a more systematic and symmetrical analysis (Figure 2).

Figure 2. (a) Unoriented CBCT scan. (b) Scan reoriented to the external auditory canals to allow for a more symmetric evaluation.

3. Recognize that CBCT interpretation requires “2 brains.” While not quite anatomically accurate, the reality is that, because of the complexity of the task at hand, it is best to approach it in 2 steps: (1) thinking like a radiologist and (2) thinking like a dentist. The radiologist’s part of the brain starts the process by analyzing the structures of the craniofacial complex for abnormalities. This requires an intimate knowledge of head and neck anatomy as well as disease processes in the craniofacial complex. The process is facilitated by the reorientation of the scan (see above) and the adaptation of a systematic method of review. When the review of all the head and neck structures on this scan is complete, the dentist part of the brain can kick in, looking at the teeth systematically as we count from the upper right quadrant and then across and around to the lower right quadrant. Once the search for dental abnormality is complete, we can move on to the primary indication of the scan (implant analysis, dental impaction, boundary conditions in orthodontics, TMJ, airway, etc). 

4. Develop a systematic method and stick to it. The method you learn will depend on your teacher. Due to the complexity of the task, it is best to learn from an oral and maxillofacial radiologist. These professionals have dedicated their lives to understanding this anatomy and the conditions that may arise in this area of the human body. They are also familiar with the dental procedures you are performing and can guide you on how best to optimize the visualization of the anatomy to fit your procedure. In general, when visualizing the anatomy, it helps to look at one structure at a time, compare both sides, and do that systematically from the top of the scan to the bottom. Needless to say, knowledge of anatomy is key to accurate and successful analysis. 

5. Learn your anatomy. This is half of the game. If you know the lay of the land, you will easily pick up a variation in that landscape. This is a daunting task, especially if your last encounter with anatomy was in dental school, but this task should be taken in small bites over time. Some resources that have helped me tremendously are cadaver courses, Netter’s Head and Neck Anatomy for Dentistry, and investing time learning radiographic anatomy from books and online resources. 

6. Know how to use your CBCT reading software. The CBCT volume has a great deal of information on it. This information may not be readily displayed on the scan as it presents. Understanding the bells and whistles that come with your software enables you to extract this information by creating the views, cross sections, and reformations necessary to cinch the diagnosis (Figures 3 to 6).

Figure 3. Diagnostic CBCT reformations that can be used to evaluate the patient’s overall jaw condition and skeletal morphology. (a) A panoramic reformation can be used to assess the overall dentoalveolar condition and jaw anatomy. Three-dimensional reforma- tions in the (b) frontal and (c) lateral views are static representations of a movable 3D model of the skull that can be evaluated in any plane.

Figure 4. TMJ cross sections in the corrected sagittal, coronal, and axial planes can be used to demonstrate the TMJ condition and the spatial relationships of the TMJ osseous components.

Figure 5. A 3D volumetric reformation of the oropharyngeal airway can be created from CBCT data.

Figure 6. Custom cross sections can be used to assess teeth and other structures in any plane for the presence of abnormality.

CONCLUSION

Of course, there is much more to learn. These points are meant to at least start you on the path of thinking required for the CBCT evaluation and interpretation procedure. It is a magnificent new world of diagnosis for you and your patients, and I hope you will enjoy your learning journey!

ABOUT THE AUTHOR

Dr. Tamimi runs her home-based oral radiology private practice in Orlando. She has authored multiple textbooks and book chapters and offers multiple courses and private instruction on how to read CBCT and MRI scans. She lectures worldwide on these topics. Her online courses can be found on beamreaders.com/courses. She can be reached at info@inspire-imaging.com.

Disclosure: Dr. Tamimi reports no disclosures. 

The introduction of cone-beam computed tomography (CBCT) scanners for the oral and maxillofacial region in the late 1990s has revolutionized dentistry. CBCT technology provides a 3D view of anatomical structures in the head and neck area, making it the preferred modality for diagnosis and treatment planning in many dental tasks. Its clinical applications range from dental implants, endodontics, airway  and TMJ analysis, to the diagnosis of jaw lesions and advanced surgical procedures. The clinician’s professional judgment in selecting the imaging modality types, including intraoral, panoramic, CBCT, or a combination of them, could play an essential role in timely diagnosis and management of pathological conditions of the jaws.¹

While the CBCT scan provides valuable information about the task at hand, it may also reveal incidental findings. These findings range from benign soft-tissue calcifications and idiopathic sclerosis of the jaw bones to more significant abnormalities, such as cystic or neoplastic (tumoral) lesions, inflammatory and fibro-osseous conditions, and radiographic bone changes related to systemic diseases. This information may not be the primary intent of the CBCT exam. Still, it should not be overlooked since it may provide valuable information with high clinical significance regarding a patient’s oral and overall health.

In dental imaging, a practitioner could be prone to focusing on his or her area of interest, which is the specific area that is being further evaluated in 3D, and he or she is also likely to detect well-demarcated jaw lesions at a higher rate. On the other hand, poorly demarcated lesions with blending or diffuse borders may present a diagnostic challenge. This is especially important since multiple pathologies, such as fibro-osseous lesions, osteomyelitis, medically related osteonecrosis of the jaws, or malignant neoplastic processes, share some overlapping radiographic presentations. Thus, evaluating CBCT scans requires a methodical and systematic assessment of the entire scan in axial, sagittal, and coronal planes. Each of the lesion’s radiographic characteristics needs to be carefully noted and given value in providing information about the abnormality’s nature. In the following radiographs, we will review some of the information that could be gathered based on a lesion’s radiographic presentation. 

The location of the lesion(s) and their relation to the mandibular canal, above (Figure 1), within (Figure 2),²  or below (Figure 3), could suggest that the pathology could be more likely odontogenic, of neural or vascular origin, or non-odontogenic, respectively.

Figure 1. Well-demarcated, corticated radiolucency above the right mandibular canal associated with the crown of impacted No. 32 was suggestive of an odontogenic process. Histologic diagnosis was of a dentigerous cyst.

Figure 2. Well-demarcated radiolucency within the boundaries of the right mandibular canal was suggestive of a lesion with neural or vascular origin. The confirmed diagnosis was neurofibroma.

Figure 3. Well-demarcated, corticated radiolucency inferior to the right mandibular canal was consistent with the non-odontogenic entity Stafne bone defect.

The number of lesions: Most jaw lesions present as a single entity. Yet, in cases where 2 or more lesions are present, clinical correlation with the patient’s health history could be beneficial in ruling in or out the possibility of the patient having other inclusion criteria for a specific syndrome. One example is in individuals who present with multiple odontogenic keratocysts (OKCs) in their jaws (Figure 4). Clinical signs, such as hypertelorism, deep plantar pits, intracranial ectopic calcifications, and facial dysmorphism, can also be evident. These findings of multiple OKCs and cutaneous, skeletal, ocular, and neurologic abnormalities are usually associated with nevoid basal cell carcinoma syndrome, also known as Gorlin syndrome, a hereditary condition characterized by a wide range of developmental abnormalities and a predisposition to neoplasms, specifically basal cell carcinoma of the skin.³

Figure 4. Multiple well-demarcated, corticated radiolucent lesions in the right maxilla, right mandible, and crossing the midline were noted. Histologic diagnosis was multiple odontogenic keratocysts.

Periphery of the lesion: Boundaries (well-demarcated, ill-demarcated, or blending borders); cortication or lack thereof; internal density (radiolucent, radiolucent or mixed density); expansion (cystic vs tumoral); and the lesion’s effects on surrounding structures (resorption of bone, PDL, and teeth), tooth displacement, and periosteal reactions need careful evaluation as well. The following 2 cases highlight how the above-mentioned radiographic features are utilized in generating a differential diagnosis and the tremendous value of a multidisciplinary approach to care when identifying jaw abnormalities.

After assessing the above parameters, a “diagnostic impression” about the lesion’s possible nature (benign, malignant, developmental, or self-limiting) and origin (odontogenic/non-odontogenic) is formed. This impression serves as the basis for generating a differential diagnosis that directs the next steps. The suggested following actions could range from watchful waiting and radiographic re-evaluation of the area to immediate treatment; referral to a specific dental specialty; biopsy; or referral for further imaging, such as an MRI or a medical CT.

CASE REPORTS

Case 1 

A 42-year-old female with a history of bisphosphonate use for a duration of 8 years was referred to WesternU Patient Care Center for evaluation of a white soft-tissue lesion on the lateral border of her tongue. Panoramic imaging was acquired as part of the new-patient assessment.

Radiographic Findings 

At the initial evaluation stage, panoramic and periapical radiographs were acquired. Radiographic findings (Figures 5 and 6) of irregular interdental and periapical radiolucency and periodontal ligament (PDL) space widening associated with teeth Nos. 26, 27, and 28 were noted. Since the radiographic appearance of irregular PDL widening did not resemble a lesion with odontogenic (endodontic) etiology (which is usually centered at and around the tooth’s apical exit), a decision was made to take a CBCT scan and evaluate the lesion’s effect and extension within the mandible.¹

Figures 5 and 6. Panoramic and periapical radiographs showed the loss of bone support and irregular widening of the PDL associated with Nos. 26, 27, and 28—mott-eaten bone appearance.

CBCT findings (Figures 7 to 9) included multiple areas with permeative changes (small 1- to 3-mm radiolucencies) and interruption of buccal and lingual plates in the mandible with no sign of cortical expansion.

Figures 7 and 8. Axial and cross section views of the CBCT showed multiple areas of interrup- tion of buccal and lingual plates of the mandible with no sign of expansion.

Figure 9. A 3D volume rendering from CBCT volume of the anterior mandible.

Irregular PDL widening, loss of lamina dura, and interruption of the cortices without expansion could be found in association with generalized malignancies such as leukemia, multiple myeloma, and non-Hodgkin’s lymphoma infiltrates. Also, metastatic disease, where malignant cells travel through the bloodstream, can randomly infiltrate the bone in a generalized manner. Those infiltrates can be transported to different parts of the PDL space and cause irregular PDL widening, resorption of lamina dura, and bone loss. Considering the radiographic and clinical findings mentioned above, a decision for a biopsy referral was made (completed by Dr. Jeffery Elo, oral surgeon, WesternU Dental Center). The final diagnosis based on the histopathological findings (Figure 10) was metastatic breast carcinoma invading the mandible.  

Figure 10. Histologic findings of cords and islands of metastatic breast carcinoma.

Case 2

A 25-year-old female with no contributing medical history presented to WesternU Patient Care Center for teeth cleaning in January 2019. Clinical examination of teeth Nos. 26 to 29 tested vital and positive to percussion and intermittent pain in the area.

Radiographic Findings

In the recent periapical radiograph in 2019 (Figure 11, right), areas of loss of lamina dura and irregular PDL space widening at the distal aspect of No. 27 and mesial and distal apical aspects of No. 26 were noted. The border of the lesion appeared irregular with no notable cortication. A wide region of intermediate density called the “transition zone” (the area between the totally radiolucent region of the lesion and the normal-appearing bone) is present. No tooth resorption was noted. A comparison of periapical radiographs from June 2018 and January 2019 suggested a rather significant amount of bone destruction in this period (Figures 11 and 12).

Figures 11 and 12. (Figure 11, left) No radiographic sign of a resorptive lesion in No. 26 or 27 was noted. (Figure 11, right, and Figure 12 [coronal CBCT]) Areas of loss of lamina dura and irregular PDL space widening at the distal aspect of No. 27 and mesial and distal apical aspects of No. 26 were noted. A wide transition zone was present.

Figure 13. A 3D volume rendering from CBCT volume.

Figure 14. Axial view CBCT showed localized interruption of buccal cortical plate in the area of Nos. 26 and 27; no expansion was noted.

In the 3D volume rendering of the CBCT (Figure 13) residual floating spicules of trabecular bone and irregular borders of the lesion were present. The lesion appeared to have larger dimensions compared to what was visualized in the PA radiograph. The axial view of the CBCT (Figure 14) demonstrated a localized area of interruption of buccal cortical plate at the region of No. 27. In cross-sectional presentation of the CBCT (Figure 15), significant destruction of the buccal cortical plate was noted in the area of Nos. 26 and 27 with no sign of bone expansion or periosteal reaction. 

Figure 15. Cross section CBCT showed an interruption of the buccal cortical plate with no expansion.

Considering the radiographic and clinical findings mentioned above, a decision for biopsy referral was made (completed by Dr. Elo). The final diagnosis based on the histopathological findings was diffuse large ß-cell lymphoma.⁴ The specimen was evaluated by Dr. Mark Mintline, director of the Oral Pathology Lab, WesternU College of Dental Medicine.

CONCLUSION

CBCT technology can be a valuable tool in the diagnostic process for identifying jaw abnormalities. However, dentists who use CBCT technology must have appropriate training in evaluating normal maxillofacial structures in 3D and be competent in identifying potential pathologic findings in CBCT scans. The topic of practitioners’ responsibility in diagnosing and reporting on any abnormality present within the acquired CBCT scan area, even if that finding is beyond his or her scope of knowledge or radiology training, is  related to a generalized health condition manifested in the jaws, or is unrelated to the initial intent of the scan, has been discussed extensively and published. In the executive opinion statement published in 2008 on performing and interpreting diagnostic CBCT by the American Academy of Oral and Maxillofacial Radiology,⁵ the standard under “Practitioners’ responsibility” states that “The responsibility of interpreting the findings of the CBCT images lies with the practitioner who obtains them, and an imaging report should accompany the scan, similar to how a biopsy requires a report.” The standard also mentions that it is essential to note that dentists who use CBCT technology should meet the same standards as board-certified oral and maxillofacial radiologists (OMFRs).  

It is essential to recognize that CBCT scans are just one piece of the diagnostic puzzle mostly related to evaluating hard-tissue structures (teeth and bone) with minimal soft-tissue contrast resolution. For this reason, there must be an effective collaboration between multiple diagnostic specialties to accurately assess the hard- and soft-tissue abnormalities and their possible overlap, including oral radiology, oral pathology, oral surgery, and oral medicine.

To streamline the oral diagnosis process, more work must be done to create HIPAA-compliant communication infrastructures that could facilitate a harmonious workflow between diagnostic specialties. By working together and ensuring that dentists who utilize CBCT imaging have the appropriate training and competency in interpreting the CBCT scans as well as having access to expert consultation from qualified oral and maxillofacial radiologists in the form of radiology reports, we can improve the accuracy and efficiency of the diagnostic process and ultimately provide better care for our patients.

 REFERENCES

1. Lavasani S. Oral and maxillofacial radiology diagnosis: the role of image modality selection, interpretation skills and use of cone beam computed tomography technology. CDA Journal. 2022.

2. Mortazavi H, Baharvand M, Safi Y, et al. Common conditions associated with mandibular canal widening. A literature review. Imaging Sci Dent. 2019. Jun;49(2):87-95. doi:10.5624/isd.2019.49.2.87 

3. Lo Muzio, L. Nevoid basal cell carcinoma syndrome (Gorlin syndrome). Orphanet J Rare Dis 3, 32 (2008). https://doi.org/10.1186/1750-1172-3-32

4. Mintline M, Elo JA, Lavasani S, et al. The synergistic role of 2D and 3D imaging in evaluating tumors of the jaws: a case report of diffuse large B-cell lymphoma of the mandible. J Calif Dent Assoc. 2022;50(9):519–25. doi:10.1080/19424396.2022.12224337

5. Carter L, Farman AG, Geist J, et al. American Academy of Oral and Maxillofacial Radiology. American Academy of Oral and Maxillofacial Radiology executive opinion statement on performing and interpreting diagnostic cone beam computed tomography. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2008;106(4):561–2. doi:10.1016/j.tripleo.2008.07.007 

ABOUT THE AUTHOR

Dr. Lavasani is a board-certified oral and maxillofacial radiologist and an associate professor and the director of oral radiology and advanced imaging at Western University of Health Sciences, College of Dental Medicine in Pomona, Calif. She is a Diplomate of the American Board of Oral and Maxillofacial Radiology and maintains an active dental imaging practice at Western University Patient Care Center’s 3D CBCT Imaging Lab and Interpretation Center. She serves as the national oral radiology advisor on the board of General Dentistry, the peer-reviewed journal of the AGD. With numerous lectures, hands-on courses, and book chapters published, she is an internationally recognized voice in the field of 3D radiographic diagnosis, applications of CBCT in dentistry, and topics related to radiation dose and biological effects of ionizing radiation on tissues. Dr. Lavasani is the founder of the California Academy of Oral Radiology where she provides on-demand and customized educational activities, seminars, and hands-on CBCT courses for dentists and DSOs. Dr. Lavasani serves as a member of the board of directors at the Tri-county Dental Society (TCDS) and is a voting delegate representing the TCDS at the California Dental Association House of Delegates. She can be reached at slavasani@westernu.edu or via the Instagram handle @slavasanidds.

Disclosure: Dr. Lavasani reports no disclosures.  

RADIATION EXPOSURE

All of us are exposed to different types of radiation on an ongoing basis. We have little control over this exposure. However, what we as dentists do have control over is the radiation we dispense.
To obtain images of the oral cavity one must at all times be aware of our basic rule: ALARA. This means we are taking images using As-Low-As-Reasonably-Achievable doses. Modern radiographic techniques and digital sensors, as well as new film products, ensure that this is possible. It is in the best interest of our patients that we strive to reduce the dental radiation that they accumulate over their lifetimes.
In today’s dental practice, one should only use a well-designed x-ray machine where the time exposure controls are electronic and thus accurately deliver the proper exposure to patients. In most states, these are the only types of controls that pass inspection. If you are not using a machine that uses electronic controls, then replace it as soon as possible.

X-RAY GEOMETRY

Figure 1. The paralleling concept.	Figure 2. The sensor holder assembly.

Along with accuracy of exposure, there are 5 basic rules of the “geometry” of dental intraoral x-rays that the operator should fully understand and follow at all times (Figure 1):

• The source of radiation should come from a point source. This is not controllable by the operator, but rather by the x-ray machine manufacturer, and again gets back to the point that one should only use modern equipment.
• The source-to-object distance should be as long as is practical (the object being the tooth; in this case long cone versus short cone).
• The object-to-film distance, or object-to-digital sensor distance, should be as short as is practical.
• The object (tooth or teeth) and the film or the digital sensor should be parallel.
• The central beam should be 90° to the object as well as the film or the face of the digital sensor.

By taking radiographs following the above 5 rules, we can be sure that the image shown on the film or on the computer screen will be accurate in its shape and size.
There are many devices to help the operator achieve the proper “geometry.” Utilizing XCP or paralleling devices first developed by the RINN Corporation (now DENTSPLY RINN) have stood the test of time in usefulness. Most digital x-ray systems have wisely styled their own holders after the RINN products, allowing the operator to transition quickly from film to digital (Figure 2).

FILM AND SENSORS

Film Selection

The next important factor of imaging is the use of the proper film speed. Several film speeds are available to dentists, the most recent of which are extremely fast. These high-speed films can render good image quality and require minimal exposure.

Digital Sensors

Digital sensors can be much more sensitive to radiation and, therefore, compared to D and E speed film can require much less radiation to yield good image quality. The actual percent of lowered radiation would depend on the age and overall total use of your existing x-ray machines and what type of film you currently use.

Positioning

The operator can use the very best in technology and use great care in the selection of radiation dosage, but the image can still be poor if the patient and the film or sensor are not properly placed.

Patient Positioning

The patient should be seated upright with his or her head in a straight position.
The arch in which you plan to take your image should be parallel to the floor. This means that the operator must take the time and care to reposition the patient’s head when moving from the mandible to the maxilla.

Intraoral Positioning

Figure 3. Anterior film.	Figure 4. Anterior film.
Figure 5. Mandibular bicuspid exposure.	Figure 6. Maxillary molar esposure.
Figure 7. Bicuspid bite-wing film.	Figure 8. Molar bite-wing film.

In the case of a full-mouth series, there should be no less than 4 exposures to cover the teeth in each quadrant. Some practices routinely use a higher number of exposures in the anterior region. This is based on the prescribing dentist’s needs. This means that if presented with a patient who has longer than average arch length, or one with overlapping teeth, the operator should take the proper number of exposures that yield sufficient diagnostic information, even if it is more than the traditional number.
Please note that the film or sensor is not adjacent to the tooth or teeth to ensure parallelism. Using the long cone technique provides us the luxury of aligning the film or sensor at a greater distance from the object (the teeth) while still obtaining an accurate image. Placing the film or sensor in this way, in the deeper areas of the mouth, also happens to coincide with patient comfort.
It is advisable that the operator start with the anterior exposures first since this area is the least sensitive part of the oral cavity. Capture these exposures:

• Central-lateral exposure (Figure 3).
• Canine exposure (open the embrasure between the lateral and canine; Figure 4).
• Bicuspid or premolar exposure (ensure that the distal of the canine is imaged; Figure 5).
• Molar exposure (should include all 3 molars or at least all 3 molar areas; Figure 6).
• Bicuspid or premolar bite-wing exposure (should include the distal of both canines; Figure 7).
• Molar bite-wing exposure (Figure 8).

“TROUBLE” SPOTS

In my years of teaching radiographic techniques, the most requests from my students are for guidance on the exposure of canines and molars. It’s true that these are the 2 most difficult areas to image in the whole oral cavity.

Canine Exposure

Figure 9. Cuspid positioning.

To gain the most useful image of a canine tooth, the operator must ensure that the mesial of the canine is separated from the lateral incisor, or that the central beam goes through the embrasure between the canine and lateral (Figure 9).

Molar Exposure

Figure 10. Distal molar positioning.

Molar x-rays should include all 3 molars, or at least all 3 molar areas. On the distal molar exposure, the central beam should come from a distal position to ensure the inclusion of the distally hidden anatomical landmarks (Figure 10).

Bending Film

There are many times when one cannot achieve complete parallel placement, and the operator may be tempted to bend the film. This is an unacceptable step, as it will distort the final image. This is not even an option when using digital sensors since they don’t bend. In addition, although it is widely used by many clinicians, the bisection of angle technique can also produce an undesirable image as it distorts the crown-root ratio.

RESPONSIBILITY

As dentists, we have a great responsibility to patients. We also have a responsibility to our team members to help them acquire the knowledge to be the best in their fields. Making the commitment to learning, understanding, and practicing good intraoral radiographic technique helps us meet our goals toward responsible dentistry.

Dr. Schiff has served as professor and chair of Oral and Maxillofacial Radiology and Emergency Services, as well as the director of clinical research, at the University of the Pacific School of Dentistry in San Francisco. During his tenure, he became the first-named endowed professor. Dr. Schiff has been recognized worldwide for his contributions to dentistry and radiology, and has received many honors and awards for his outstanding work in both of these fields. He is a fellow of the American College of Dentists, the International College of Dentists, the International Association of Dental Maxillofacial Radiology, and the Pierre Fauchard Academy. He is also a diplomate of the American Academy of Oral Medicine. He can be reached at (415) 789-0060 or thomasschiff@comcast.net.

VARIABLES FOR FILM RADIOGRAPHS

Film radiographs have a large number of variables to manage. If not executed properly, any one of these variables can affect the x-ray images and thus lead to negative consequences for the treatment process and, in some cases, for the quality of patient care. Several of the variables are controllable by the implant dentist; however, a few of them are beyond our control. An understanding of these variables and of the procedures needed to maintain image consistency and quality will help to improve the ability to provide uniformly high-quality care.
Among the variables that are nominally under the control of the dentist using film radiographs are those associated with the film-processing equipment, including things such as temperature and chemical concentration. Image distortion creating difficulty in using manual overlays is another variable that is nominally under the dentists control.
The ideal way to maintain the quality of film processor chemicals is to monitor the number of films that have been developed using a given batch rather than the amount of time chemicals have been in the developer. In cases where only a few films have been processed during the course of a day, it is unnecessary to change developer. However, automatic developers are programmed to replenish chemicals at time-based and not usage-based intervals. This means that on days where many films are processed, developer quality will deteriorate due to usage. By the end of a busy day, x-ray quality may be significantly affected. In addition, exposure to air causes chemical deterioration, regardless of usage. The result is that even though this variable is managed automatically and is technically under the dentists control, actually keeping it within certain limits can be difficult. In cases where deterioration of image quality is noticed during the workday, an interruption in the normal flow of film processing must occur to replenish chemicals, which contributes to increasing overhead costs.
Temperature is another such variable. Of course, processing equipment is equipped with thermostatically controlled temperature maintenance. Water temperature is automatically maintained at the desired temperature for proper processing. However, while these units are equipped with heating elements, it may be the case that, under certain circumstances, the water temperature may rise above the desired temperature. In this case, the processor is not equipped to lower the temperature.
The orientation of the radiographic image and the associated development of an implant design overlay also contribute to the variables that must be managed when film-based x-rays are used. Even when head position is ideal at the time a panoramic x-ray is taken, image distortion can be significant, often approaching 20%.1 And when slight variations in head positioning are taken into account, the distortion factor can be even greater.2 This can mean that the creation of a manual design overlay is based on an approximation of the patients jaw and tooth structure, rather than on an image that is highly representative.
Other variables associated with film radiography are not so directly under the dentist’s control; or when they are, they result in additional expense to implement. These include water quality, shelf life of chemicals, shipping and storage conditions for chemicals, storage of unexposed film, and deterioration over time of x-ray images.
Water quality varies by region of the country, location within a region, municipal water management, and delivery systems within the office or office building. The chemicals added to a water supply to ensure drinking quality vary widely among municipalities, as do the amount of minerals naturally occurring in the source water as well as substances, such as fluorides, which are added to some water. Within a building, the age and composition of water pipes can also contribute to contaminant levels. Water filtering systems are often necessary to ensure consistent water quality, but even these need regular routine maintenance. When they are not properly maintained, the result can be water that compromises the quality of film processing.
Chemical packaging always shows an expiration date, but how many dentists pay strict attention to this variable? In order to get price breaks, many dentists order fairly large quantities of chemicals and sometimes keep them beyond recommended expiration dates. In addition, the quality of chemicals depends on such variables as the conditions under which they were shipped and stored. Exposure to wide temperature variations, including extremes of heat and cold, certainly go beyond the recommended storage conditions for most chemicals and can compromise quality and freshness.
Storage conditions for unexposed film in warehouses also represent a variable that can affect outcomes. Do the (often) tens of thousands of packages of film many distributors keep on hand remain refrigerated, or at least in conditions of optimal temperature control? Again, the answer to this question is unknown, although variations in film storage conditions can significantly impact image quality. In addition, potential accidental light contamination of a batch of stored film is also a variable that needs to be considered, although its effect won’t be known until it is time for the film to be used.
Finally, the image quality of the exposed x-ray film itself can deteriorate fairly rapidly under typical storage conditions, eg, in filing cabinets. When a comparison is needed between x-rays taken at different points over a long time period, the problem often becomes compounded because an older (and thus possibly compromised) image is being compared with a newer one.

THE ADVANTAGES OF DIGITAL RADIOGRAPHY

Figure 4. Computer-generated radiograph with implant overlays visible and called out.

Digital radiography systems provide the most effective way to manage x-ray variables in the dental office. Obviously, since film is not involved in the digital radiography process, variables associated with water quality, temperature, film storage and exposure, chemicals, and processing equipment no longer need to be considered. But these aren’t the only variables to be considered. Digital radiography also positively impacts variables associated with image distortion, the creation of overlays, and image quality deterioration associated with the storage of x-rays.
Digital radiography is of particular interest to dentists specializing in implants. Several dental implant procedures exist for which eliminating variables provides important benefits. These procedures include the ability to monitor the maturity of hard-tissue regeneration from the preoperative state, monitoring tissue production, often over a period of months, and assessing the success of the implant itself. These procedures also include obtaining consistent image orientation and a reduction through the use of digital rather than manual overlays in the margin of error previously tolerated in creating an overlay. The need to have consistent image quality over time for comparison purposes is another area in which digital radiography offers important advances compared to film.
Film-based x-rays taken to monitor radiopacity indicating calcium uptake that represents new hard-tissue growth are frequently unreliable because of the impact of variables affecting their consistency (Figures 1 and 2).
A digital radiograph, on the other hand, because it eliminates the variables associated with film, provides a radiograph whose quality is constant over time.
Where eliminating distortion associated with panoramic x-rays used in implant dentistry is concerned, one manufacturer, DEXIS, has introduced an auto-callibration feature to correct for image distortion. In the DEXimplant module of its digital radiography software, DEXIS provides for the use of 5-mm ball bearings as references when the radiograph is taken. The DEXimplant process begins with a panoramic digital x-ray, and these radiographic ball bearings are used for reference as the image is captured. As the image is manipulated and enhanced during the design process, the ball bearings provide reference points, and the computer software uses them to automatically correct for the distortion that is problematic in manual implant design (Figures 3a and 3b).
DEXimplant also contains an extensive library of images of all popular dental implants categorized by manufacturer and size. Once the panoramic x-ray has been captured and displayed, these implant images can be placed on the panoramic image. DEXimplant then automatically adjusts the implant overlay in 2 dimensions to compensate for distortion. The software enables the dentist to gain a more accurate picture of the proposed treatment than otherwise would be possible (Figure 4).
DEXimplant software works with images captured from any panoramic x-ray system, and includes a second module, DEXbone, that enables dentists to monitor the success of the implant. These 2 modules are also important tools for communicating the design and progress of dental implants to patients.
Finally, digital radiography completely eliminates variables associated with the conditions under which images are stored. The implant dentist has images for comparison that have been stored under exactly the same conditions and represent exactly the image captured at the time it was taken. There are no storage variables to be considered with digital radiography.

CONCLUSION

The implications of virtually eliminating the variables associated with film x-rays in implant dentistry are profound. Where distorted and compromised images are the basis of designing treatment, there is an associated increase in risk for the patient as well as for the dentist. Thus, risk management becomes an important component of using the best available technology in the diagnosis, design, and installation of implants. Where small mistakes can result in serious health consequences, it is important to take every measure to ensure that the patients well-being is not compromised by the use of technology that is subject to variables that no longer need to be part of the process.

References

1. Scarfe WC, Eraso FE, Farman AG. Characteristics of the Orthopantomo-graph OP 100. Dentomaxillofac Radiol. 1998;27:51-57.

2. McKee IW, Glover KE, Williamson PC, et al. The effect of vertical and horizontal head positioning in panoramic radiography on mesiodistal tooth angulations. Angle Orthod. 2001;71:442-451.

Dr. Callan is a periodontist in Little Rock, Ark. His focus is on dental implants and hard- and soft-tissue regeneration for conventional and implant dentistry. He has written numerous articles on these subjects and provides over-the-shoulder, live surgical training to clinicians. He can be reached at (501) 224-1122,  dcallan@doncallan.com, or by visiting doncallan.com.

Most dentists infer that using digital sensors will cut costs and improve workflow by automating the process of taking x-rays with film. However, digital radiology improves the ease of taking multiple x-rays through an entirely new process that saves you time. Any dentist knows that more time means more money. Unfortunately, dentists are missing the point.

The fact that practically every dental office needs effective digital x-ray imaging is a testament to the need for digital radiography. Despite the potential benefits of digital radiography, many dentists still assume that it is too expensive and problematic. Why is there such aversion to digital radiology, when it has been created as a tool to improve workflow?

Dental professionals have long had a love-hate relationship with digital radiography. One explanation is that when digital systems were first introduced in the late 1980s, available computer systems lacked the processing power and practice management software to maximize this new technology. Furthermore, digital systems were expensive, and the sensors that accompanied digital systems were bulky and uncomfortable compared to x-ray film. Thus, from the beginning dentists have viewed digital radiology with a cautious eye.

With time, integrated software and faster computers made digital radiology more affordable and accessible. Yet dentists continued to expect digital radiography tools to simply automate what they were doing by hand. As this is not the case, they were disappointed by the results. A perfect example of the perpetuation of this idea can be seen in the way that digital sensor companies market to dentists. They try to lure dentists by highlighting how much money will be saved by going digital. They calculate how many x-rays we take each day, film and chemical costs, and processor maintenance and costs. They speak to dentists in their current language and lead them to believe that digital sensors will perform their usual x-ray processes for less money.

However, the time saved by digital radiography is far more valuable than any money you’ll save on film and chemicals. With digital sensors, the time it takes to capture and see an image is cut probably by 85%. Emergency visits are faster, and you can fit more procedures, such as endodontic treatment, into your schedule. Digital sensors involve less radiation, and the resulting images are impressive. Further-more, you can catch and correct angle and exposure mistakes instantly, not after the patient has already left.

CLINICAL EXAMPLE

Figure 1. Using digital radiography to take these 6 images saved significant time compared to conventional film radiographs.

The following example illustrates how digital radiography can save you time. Porcelain broke off of a retrievable implant crown I had delivered a few years ago, so I removed the crown and sent it to the lab for rebaking. I had the patient keep his old implant models. The crown came back with the new porcelain, but would not seat according to the radiograph. Cautiously, I removed a little porcelain from the contacts and reseated the crown, each time taking a new radiograph (Figure 1). Had I used film, processing time would have been 6 images at 5 minutes each, or 30 minutes. Instead, I had instant, accurate results.

Dentists need to realize that digital radiography will increase the efficiency of taking x-rays when evaluating the return on investment of digital sensors. Imagine the effect on your schedule and other patients of running 30 minutes late while waiting for the film to be processed. What is that value?

FEAR OF THE LEARNING CURVE

In addition to receiving mixed messages about the benefits of digital sensors, dentists fear that their assistants won’t be able to use them. This is easily overcome through practice management, training, and using the correct sensor holders. Certainly, it is not a reason to avoid technology. There is a learning curve for taking and reading digital radiographs. The artifacts are different than those of film, but those are quickly learned. Dentists need to embrace, not avoid, new digital processes and reap the benefits for both practice and patient.

I have often heard that dentists don’t want digital sensors because they cannot take vertical bite-wings. However, digital sensors capture quality images of the proximal bone between the teeth, thus eliminating the need for vertical bite-wings. This is a perfect example of the misconstrued idea that digital sensors will automate current x-ray processes.

Dentists are also concerned with the pain and discomfort sensors cause. However, technique and the design of the sensor holder are critical. Most of our digital sensor holders are simply film holders redesigned to hold the sensors. Some holders are so confusing that the staff and doctor get frustrated and revert to film when in a hurry. Some sensor holders don’t permit the use of rings, and many are costly. So, with the great strides previously made in the digital radiography field, the basic problem of patient comfort persists. As I mentioned, the original shift from standard x-rays to digital radiography was done utilizing adaptations of prior x-ray holding systems to the new digital systems. With the familiarity of using these existing holders it was hoped that the transition to digital sensors would go smoothly. Unfortunately, the coupling of rigid holders to flexible x-ray film did not translate well when coupling rigid sensors with rigid holders. They tend to hurt, so using a flexible holder with a rigid sensor helps to ameliorate that discomfort problem. In addition to this fact, the prior systems were designed for multiple film use in a complete radiographic series. Putting aside x-ray films to use with certain holders was an easy thing to do. With digital radiography, most offices had few sensors, and the majority had only one to use with a holding system that required assembly and many parts. The adaptation of existing holder systems to transition to digital radiography was a stop-gap solution at best.

Only recently, and long overdue, have we seen some sensor holders finally designed from the ground up. I tried one of the first, the ClikRay from ClikTech  (877) 251-0594 or clikray.com), and it reduced the time to take a full set of digital radiographs in half. And only one holder is used for the entire mouth. (It can also be used with film and phosphor plates for those offices with “dual” technologies; Figures 2a and 2b).

The design allows the operator to use parallel cone and/or bisecting angle techniques to obtain the required views. The combination of a flexible holder with a rigid sensor has helped us reduce patient discomfort to virtually a non-issue. What is really amazing to me is that this sensor holder was not designed by a holder company, but by a local dentist in my community! Credit to Dr. Harold Schmulenson of Glenview, Ill.

CONCLUSION

Patient comfort, staff (and doctor) acceptance, speed, and ease of use are the keys to achieving acceptance of digital radiography in the dental office. In particular, the time saved compared to conventional film-based radiography makes digital radiography an excellent investment.

Dr. Freydberg, a full-time practitioner, is a 1968 graduate of the University of Illinois College of Dentistry, receiving its “Most Distinguished Alumni Award” in 2004. He is a fellow of the AGD, the International College of Dentists, the American College of Dentists, and the International Academy for Dental-Facial Esthetics. He has lectured and published on the subject of computerization of the clinical and management aspects of the dental practice. He is also a consultant to the ADA Council on Dental Practice. Dr. Freydberg, an active member of the Chicago Dental Society, can be reached at barry@hitech2thdoc.com, or by visiting hitech2thdoc.com.

When taking a periapical radiograph, the size of the object and the image should ideally be the same. On a correctly taken panoramic radiograph with the patient correctly positioned, and with all the images of the anterior region clearly outlined, there is always a magnification of 15% to 20% in the vertical dimension. Thus, when determining the height of the alveolar bone above the mandibular canal in the body of the mandible during the planning of implant surgery, this magnification must be included in the calculations. This also applies to measuring the amount of alveolar tooth support. If requested, several panoramic machine companies will supply a ruler that takes this magnification into consideration. However, in the horizontal plane, particularly in the anterior region of the mouth, there can be magnification or demagnification, depending on the horizontal positioning of the patient.

For older machines the correct patient position in the horizontal plane is such that the whole of the tragus (the prominence anterior to the external opening of the ear) must be able to be felt immediately behind the head support. If the whole of the tragus cannot be felt, the patient is seated too far forward. If the skin anterior to the tragus can also be felt, the patient is seated too far back.

Several panoramic radiographs shown have been cropped so that the technical errors can be visualized more clearly.

NARROW, “FUZZY,” ANTERIOR TEETH (FIGURES 1, 2, 3, AND 6)

When exposing a panoramic radiograph, the patient must be positioned with the incisor teeth in the middle of the focal trough. Fuzzy images of the incisor teeth will appear when the patient is seated too far forward in the focal trough. It is important to stress that a positioning error of only 3 to 4 mm in the horizontal plane can make a dramatic difference to the width of the images. In these cases, interproximal caries may not appear or may appear much smaller. The appearance of periapical pathology may be similarly affected.

To avoid this problem with older units, one should check that the correct amount of tragus is felt bilaterally; on newer machines the correct patient position is assured by the vertical indication beams positioned on anterior teeth. Missing teeth in this region may make it difficult to correctly position the patient (Figure 2).

BROAD ANTERIOR TEETH (FIGURE 2)

If the patient is positioned too far back (posteriorly), the skin anterior to the tragus can be felt immediately posterior to the head support. The further back the patient is positioned in the focal trough, the progressively wider the images of the anterior teeth will become until they are so wide that the outlines of the crowns of the teeth cannot be discerned.

To correct the problem when using older machines, the patient must be positioned further forward so the operator does not feel the skin anterior to the tragus. In the newer machines this problem occurs because the vertical beam of light is positioned on a tooth anterior to the position recommended by the manufacturer. It is important to check on both sides that the position of the beam is on the same teeth. Again, missing teeth in this region can create a positioning error. Because of this distortion periapical pathology may not be visible.             

ELONGATED MAXILLARY ANTERIOR TEETH AND FORESHORTENED MANDIBULAR ANTERIOR TEETH (FIGURE 1)

For lack of a better descriptive term, “smile line” is accepted when describing the correct horizontal appearance of the images of the occlusal plane of all the teeth on the panoramic radiograph. If the head/chin is positioned too low, the images of the maxillary anterior teeth will appear elongated and the mandibular anterior teeth will appear foreshortened. Also, the anatomy of the mandibular midline area will appear blurred. This is also because, when the chin is dropped, it goes down but also backward, and out of the focal trough. The lower the position of the head, the higher the images of the hyoid bone will appear. This may superimpose on the mandible or the apices of the mandibular premolar or first molar teeth. Because dropping the head increases the vertical height of the image of the face, the TMJ may not be visualized. To avoid this problem the operator must check that the ala of the nose is positioned only slightly inferior to the height of the tragus (Figure 3).

BROAD, HORIZONTAL OPACITY OVER THE MAXILLARY ANTERIOR TEETH (FIGURES 3 AND 4)

If the head/chin position is too high (a lack of negative vertical angulation), the images of the hard palate and the ghost image of the contralateral hard palate superimpose creating a broad, horizontal opaque line. This opacity usually lies mainly over the apices of the maxillary anterior and premolar teeth, thus preventing visualization of variations from the norm in this region. On the radiograph, the images of the occlusal plane of the teeth will then appear horizontal or, with a positive occlusal plane, as a “frown line.” The higher the chin is raised, the broader the opacity and more likely the opacity will superimpose on the apices of the anterior and premolar teeth. Also, the more the chin is elevated, the lower the opacity will appear and will obstruct more of the apical area of the anterior teeth. In addition, the higher or lower the position of the head away from the ideal vertical angulation, the more the images of the premolar teeth will appear to overlap. The problem here is the ala of the nose was positioned higher than the tragus. To avoid this problem the operator must check that the ala of the nose is positioned only slightly inferior to the height of the tragus (Figure 4).

HORIZONTAL LUCENCY OVER THE MAXILLARY ANTERIOR TEETH (FIGURES 4, 5, AND 7)

The pharyngeal air space creates a horizontal lucency over the images of the apices of the maxillary anterior teeth from the second premolar area on one side to the second premolar on the opposite side, thus preventing the visualization of the apices of these teeth and obscuring pathology. In Figure 4, the lucency extends from the second molar on one side to the second molar on the opposite side.

Ideally, no lucency created by the pharyngeal air space should appear over the images of the apices of the maxillary anterior teeth. To avoid the image of the pharyngeal air space, the tongue must be placed against the hard palate in the swallowing position and it must be maintained in that position during the entire exposure. If the technician does not instruct the patient “in the swallowing position,” patients often will double the tongue backward creating an even larger pharyngeal air space and a larger lucency on the resultant radiograph. To avoid the problem, instruct the patient to maintain/elevate the tongue against the hard palate, in the swallowing position, for the duration of the exposure (Figure 5).

MIDLINE VERTICAL OPACITIES (FIGURES 2, 4, 5, AND 6)

In the midline area of the mandible, the images of the teeth should not be obscured by opacities. There are two main causes of vertical triangular midline opacities. The completely opaque artifact is because of the lead apron being placed too high at the back of the neck.

The less opaque vertical opacity is because of the slumped spine/vertebra (Figures 2, 4, and 6) when the patient is not positioned with the neck straight. It is important that the patient is seated/standing with the neck completely upright when making the exposure. A patient will often straighten their neck only when they are requested to push forward or to push out their chest.

If the neck is bent only slightly, the midline opacity will not be marked and the images of the mandibular anterior teeth in this region will still be seen. The more the spine is slumped, the more opaque this will appear.

To avoid this problem, check that the neck is straight at all times. With older patients who are unable to straighten the neck, an occlusal projection of the mandibular region may be needed for a greater diagnostic yield.

IMAGES OF TEETHAPPEARING WIDER ON ONE SIDE THAN THE OTHER (FIGURE 2)

If the patient is not positioned symmetrically, the images in the cuspid/premolar region on one side will appear wider than the other side. One can avoid this problem by checking that the amount of tragus felt immediately posteriorly to the head support bilaterally is the same. In the newer machines this can be avoided by checking that the vertical beam is pointing to the same position on the same teeth bilaterally. Where a patient is missing a lateral incisor or a cuspid tooth, this can present a problem with the newer machines. To further assist in positioning the patient, some machines also have a vertical light that should correspond to the mid-sagittal plane of the patient’s face.

The head of the condyle may also then appear larger on one side of the radiograph than the other. If the teeth bilaterally are the same size but the head of the condyle on one side is much larger, further investigation is warranted. To avoid the problem, check that the patient is positioned symmetrically.

By applying this principle to an image of an impacted tooth that appears broader mesio-distally than the contralateral tooth or the adjacent teeth, it can be concluded that this tooth is positioned lingually/palatally to the adjacent teeth in the arch (Figures 6 and 7).

IMAGES OF REMOVABLE OBJECTS AND APPLIANCES (FIGURES 2, 6, AND 7)

All patients must be requested to remove metal objects and appliances in the area about the oral cavity, and in the oral cavity, prior to the exposure of the panoramic radiograph. The technician must observe whether the patient is wearing eyeglasses, earrings, nose rings, or hair clips at the back of the head and request the patient to remove them. There is no need to remove hair clips on top of the head, as they are not in the path of the primary beam.

Figure 1. The head has been dropped too much as evidenced by the excessive smile line, elongated maxillary anterior teeth, and foreshortened mandibular anterior teeth. There is overlapping of the maxillary premolar teeth. The images of the anterior teeth are also narrow and fuzzy.

Figure 2. The images of the maxillary central incisor teeth in particular (also the mandibular central incisor teeth) appear very broad because the patient is positioned too far back. The lateral incisor and cuspid on the patient’s right side are broader than on the left side because the patient is not positioned symmetrically. Apical to the maxillary right posterior teeth are two elongated, horizontal opacities, double images of an earring on the patient’s left side. Apical to the left mandibular lateral incisor is a small triangular opacity caused by the lead apron positioned at the back of the neck. A slumped vertebra created the poorly demarcated vertical opacity superimposed over the mandibular incisor teeth.

Figure 3. There is a broad, horizontal opacity over the images of the apices of the maxillary incisor and premolar teeth caused by the pharyngeal air space. The smile line has been lost and there is a broad horizontal opacity apical to the maxillary teeth because the chin was raised too much. The anterior teeth are fuzzy because the patient is seated too far forward.

Figure 4. The lucency of the pharyngeal air space is preventing visualization of the images of the apices of the maxillary teeth. The lucency over the ascending ramus of the mandible should not be mistaken for a fracture. The anterior teeth are slightly fuzzy. The midline vertical opacity of the vertebra is observed and the opacity of the lead apron is seen to the left of the midline at the bottom of the radiograph.

Figure 5. The lead apron at the back of the patient is obliterating the mandibular anterior teeth. A vague pharyngeal space is visible.

Figure 6. Patient denied having any removable appliances, which can clearly be seen in the maxilla. Midline opacity of the spine is evident, partially obliterating the images of the mandibular anterior teeth. The anterior teeth are fuzzy. On the left side of the radiograph, the hyoid bone is superimposed on the posterior region of the mandible

Figure 7. The part of the necklace that is at the back of the neck can be seen superimposed over the apices of the mandibular anterior teeth. A mandibular removable chromium cobalt denture is visible. The dorsum of the tongue, inferior to the pharyngeal space, is prominent.

Sometimes a patient is embarrassed to inform the technician that they are wearing removable bridges, and these images will then appear on the radiograph (Figures 6 and 7). Also, patients sometimes are reluctant or are unable to remove tongue rings, nose rings or earrings. Removal of all such jewelry is desirable, as metallic objects will often throw a large ghost image on the opposite side of the face (Figure 2), or prevent visualization of the images of teeth. Double images are always larger, more poorly demarcated, and positioned in a more superior location on the opposite side of the radiograph.

Where patients are wearing complete dentures with no metal clasps or bars, it is advisable to leave the dentures in the mouth as the patient can then be better positioned in the focal trough, resulting in clearer images. When the teeth are acrylic nothing will be seen on the radiograph; where the denture has porcelain teeth, these images will appear between the alveolar ridges but will not interfere with viewing relevant anatomy or pathology.

VIEWING THE TMJ

When purchasing a panoramic machine it is preferable to buy one that utilizes a film size that has a 6-inch width rather than a 5-inch width. With the smaller film width, the TMJ more often does not appear on the radiograph (Figures 1, 4, and 6); this can be seen particularly for patients with a large face. Also, the more the face/chin is dropped, the greater the vertical distance of the face and the less likely the TMJ will be imaged on a radiograph that is 5 inches wide. In the radiograph in Figure 1, the film is 5 inches wide and the outline of the superior head of the head of the condyles is not completely observed. These structures would be seen with a 6-inch film. Also, if the patient is seated too far back in the focal trough, the TMJ area will move posteriorly and the images will not appear on the radiograph. Images of carotid calcifications or calcified lymph glands (which may be present in tuberculosis) are also more likely to be seen on a 6-inch wide film

CONCLUSION

Some of the more common technical errors seen in panoramic radiographs have been discussed and illustrated, and approaches to correction and avoidance have been reviewed.

Awareness and avoidance of the errors discussed will improve the quality of panoramic radiographs in clinical practice, thus providing a higher diagnostic yield.

Dr. Serman is professor of oral radiology, Division of Oral and Maxillofacial Surgery, at the School of Dental and Oral Surgery, Columbia University in New York, NY. Dr. Serman is also the American director on the board of directors of the International Association of Dento Maxillo Facial Radiology. At the Scientific Congress of the International Association of Dento Maxillo Facial Radiology (IADMFR), held in Glasgow, Scotland, in 2001, Dr. Serman was elected as a fellow of the IADMFR, the tenth time in the history of the association that this award has been made.

Dr. Horrell is an assistant professor of oral radiology, Division of Oral and Maxillofacial Surgery, at the School of Dental and Oral Surgery, Columbia University in New York, NY.

Dr. Singer is an associate professor in the Division of Oral and Maxillofacial Radiology, University of Medicine and Dentistry of New Jersey, in Newark, NJ.

A major reason that many panoramic (or other) radiographs are not of interpretive quality is a lack of density. There must be sufficient density to enable the investigator to identify the outlines of structures on the radiograph. In the majority of cases a lack of density is because of a lack of a quality assurance program in processing radiographs, but that is not the purpose of this article. Here it is assumed that a correct screen/film combination has been used. Other major problems arise from the preparation and positioning of the patient at the time of the exposure.

Figure 1. The type of high-quality radiograph that should be consistently obtained in private practice.

Figure 2. An average shape of a focal trough of a panoramic x-ray machine.

PANORAMIC CONCEPTS: FOCAL TROUGH
Panoramic radiography is a form of tomography. In tomography, slices are created by blurring images in front and back of the area of interest through controlled simultaneous movement of the source of radiation and the image receptor. In panoramic radiology the image layer is called the focal trough. The focal trough is a specific, curved volume within which images of structures of the maxillofacial region can be clearly seen on the panoramic radiograph. The basic shape of the focal trough is indicated in Figure 2.

The focal trough for different panoramic machines varies slightly, but the basic shape remains the same. The vertical height of the volume of tissue is limited to the width of the film, and a 6-inch wide film is preferable to a 5-inch film. With the narrower width film, the images of the TMJ area often are not captured. This choice of film size can only be made at the time of the purchase of the machine. The focal trough in the anterior part of the maxillofacial region is much narrower than in the posterior region and thus, it is more critical that the patient is positioned correctly in this area. From Figure 2 it can be seen that the anterior teeth should be positioned in the middle of the focal trough (position 2). If the teeth are placed in position 1, the teeth have been positioned too far forward and in position 3 the teeth are positioned too far back in the focal trough.

The clearest images of the region of interest will appear with the teeth positioned in the middle of the focal trough. As structures progressively are situated more toward the periphery of the focal area they become more and more blurred until they reach a point where the images are not seen at all because of motion blurring. The term fuzzy is often used to describe the poor outline of these images. Thus, the patient must be positioned with the neck straight and symmetrical so that the anterior maxillofacial structures will fall within the optimal region of the focal trough. The focal trough is much wider posteriorly, and thus it is easy to obtain clear images of the posterior teeth and anatomy in this area. The focal trough in the posterior region of the jaws is large and varies between 1 and 1.5 cm. Therefore, the images of posterior teeth are usually clearly seen. From position 4 in Figure 2, it can be seen that posterior teeth can be moved markedly forward or backward, laterally or mesially, and still be well within the focal trough. Thus, when inspecting the diagnostic quality of a panoramic radiograph, the images of the anterior teeth are the areas that must be inspected more critically to determine the technical quality of the radiograph.

Thus, with the incisor teeth placed in position 1 (Figure 2), the outlines of the images of the crowns and the roots, as well as the trabecular bone pattern surrounding these teeth, will be seen most sharply. If the teeth are placed in position 2, the outlines of the images of the crowns of the teeth become narrow and fuzzy. In this position, the teeth are considered as being positioned too far forward in the focal trough and the further forward the narrower and fuzzier the images of the incisor teeth will appear. If the teeth are placed in position 3, they are considered as positioned too far back in the focal trough and the wider the images of the crowns of the teeth will appear. Again, the further back in the trough, the wider they will become.

In some panoramic machines the size of the focal trough can be made smaller or larger to fit the size of the patient. Changing the size of the focal trough to fit the size of the patient is known as creating the profile index for that patient. Newer machines with LED displays will indicate a number that can be recorded for taking future panoramic projections to assure that same position of the patient for future exposures. Alternatively, if the patient is not positioned correctly when the exposure is made, this number can be utilized to assist in positioning the patient in better postero-anterior alignment should another panoramic radiograph be required in the future.

When taking a periapical radiograph, the sizes of the object and the image should be the same. With a well-taken panoramic radiograph, with all the images of the anterior region clearly outlined, there is always a magnification of 15% to 20% in the vertical dimension. When determining the height of the alveolar bone above the mandibular canal in the body of the mandible when planning implant surgery, this magnification must be included in the calculations.

IDENTIFYING THE CAUSES OF THE ERRORS AND MAKING THE CORRECTIONS

When determining the quality of a panoramic radiograph, check whether there are any errors in the vertical or horizontal positioning of the head; whether the patient is positioned symmetrically; and whether there are errors in patient instruction such as not moving during the exposure, not elevating the tongue, or having removed metal objects about the face. The first step is to check whether the smile line is correct.

Horizontal Positioning Errors

When exposing the panoramic radiograph, the patient must be positioned with the incisor teeth in the middle of the focal trough. For dentate patients, a notched bitestick is generally used to position the incisor teeth of both jaws. As mentioned above, positioning the patient only a few millimeters too far forward or backward will greatly affect the position of the incisor teeth in the focal trough and will markedly alter the width of the images of these teeth. It is important to stress that a positioning error of merely 3 to 4 mm can make a dramatic difference to the appearance of the images.

If the patient is positioned too far backward, (Figure 2, position 3) the skin anterior to the tragus can be felt immediately posterior to the head support. The further the patient is positioned backward in the focal trough, the wider the images of the anterior teeth will become until they are so wide that the outlines of the crowns of the teeth can hardly be discerned. In the older machines this is because the patient is positioned so that the skin anterior to the tragus can be seen or felt. In the newer machines it is because the vertical beam of light is positioned on a tooth anterior to the position recommended by the manufacturer. It is important to check bilaterally that the position of the beam is on the same teeth. Again missing teeth in this region can create a positioning error.

Vertical Positioning Errors

For lack of a better descriptive term, “smile line” is accepted when describing the correct appearance of the images of the occlusal plane of the teeth on the panoramic radiograph. To determine if the smile line is correct, one can draw an imaginary line on the radiograph from the mesial incisal tip of the first maxillary molar tooth on one side to the same point on the contralateral tooth (or on the second molar tooth if the first one is missing). The incisal surface of the maxillary central incisor teeth should appear 0.5 to 0.75 cm inferior to this line. This positioning will prevent the opaque image of the hard palate from being superimposed over the apices of the maxillary anterior and premolar teeth. The more the head is elevated the broader and more opaque the image of the hard palate appears.

If the head/chin position is too high (a lack of negative vertical angulation), the images of the hard palate and the ghost image of the contralateral hard palate superimpose creating a broad horizontal opaque line. This opacity usually lies mainly over the apices of the premolar and anterior teeth preventing visualization of variations from the normal in this region. The smile line will also then not be seen. On the radiograph, the occlusal plane of the teeth will then appear horizontal or, with a positive occlusal plane, as a “frown line.”

If the head/chin position is too low the images of maxillary anterior teeth will appear elongated and the mandibular anterior teeth will appear foreshortened. Also the anatomy of the mandibular midline area will appear blurred. The lower the position of the head, the higher the image of the hyoid bone will appear. This image will superimpose on the mandible.

Because dropping the head increases the vertical height of the image of the face, the TMJs will more likely not be visualized.

In addition, the higher or lower the position of the head away from the ideal vertical angulation, the more the images of the premolar teeth will appear to overlap.

There is one advantage to placing the atient in this position. The maxillary and frontal sinuses can be viewed clearly with the head dropped a little too much. The higher or lower the position of the head in relationship to the smile line, the more the images of the premolar teeth will appear to overlap each other.

Pharyngeal Air Space

The pharyngeal air space can create a horizontal lucency over the images of the maxillary anterior teeth from the second premolar area on one side to the second premolar on the opposite side, thus preventing the visualization of the apices of these teeth. Ideally, no lucency created by the pharyngeal air space should appear over the images of the apices of these teeth.

To avoid the image of the pharyngeal air space, the tongue must be placed against the hard palate “in the swallowing position,” and it must be maintained in that position during the entire exposure. If the technician does not instruct the patient in the swallowing position,patients often double their tongues backward creating an even larger pharyngeal air space and a larger lucency on the resultant radiograph. It is often an advantage initially to ask the patient to feel where the position of the tongue is when swallowing naturally. Many patients only elevate the tongue after having been instructed to do so.

If one looks at the panoramic radiograph (Figure 1) in this area, it can be seen that the tongue was elevated when the right side of the face was exposed; but the tongue was slowly dropped when the left side was exposed, showing the dorsum of the tongue and vague pharyngeal lucency.

Eliminating the Midline Vertical Opacities

In the midline area of the mandible, the images of the teeth should not be obscured by opacities. There are two main causes of vertical triangular midline opacities. The completely opaque artifact is because of the lead apron being placed too high at the back of the neck. When taking a panoramic radiograph, the x-ray tube movement begins on the side of the patient and moves around the back of the patient to the opposite side. Thus, the lead apron is placed on the front of the patient primarily for their emotional comfort. In addition, the beam is very limited in diameter and is directed in an upward direction. Thus, the front of the body of the patient does not require lead shielding.

The less opaque vertical opacity is because of the slumped spine/vertebra when the patient is not positioned with the neck straight. The more the spine is slumped the more opaque this opacity will appear. It is important that the patient is seated/standing completely upright when making the exposure. A patient will often straighten their neck when they are requested to push out their chest.

Some older patients are not able to straighten the cervical spine. If one suspects problems in the midline area of the face in such a patient, it would be preferable to take an occlusal radiograph of this region.

Images of Teeth Appearing Wider on One Side Than the Other

If the patient is not positioned symmetrically, the images in the cuspid/premolar region on one side will appear wider than the other side. One can avoid this problem by assuring that the amount of tragus felt immediately posteriorly to the head support bilaterally is the same. In the newer machines this can be avoided by ensuring that the vertical beam is pointing to the same position on the same teeth bilaterally. Where a patient is missing a lateral incisor or a cuspid tooth, this can present a problem. To further assist in positioning the patient, some machines also have a vertical light that should correspond to the mid-sagittal line of the face of the patient.

The head of the condyle will also then appear larger on the one side of the radiograph than the other. Where the images of the premolar teeth bilaterally appear symmetrical in width on the radiograph, the one head of the condyle may actually be larger than the other side and may require further investigation.

Images of Removable Appliances

The patient must be requested to remove removable metal appliances in the oral cavity prior to the exposure of the panoramic radiograph. The technician also must observe whether the patient is wearing eyeglasses, earrings, nose rings, or hair clips at the back of the head and request the patient remove these too. There is no need to remove hair clips on top of the head as they are not in the path of the primary beam. Sometimes a patient is embarrassed to inform the technician that they are wearing removable bridges, and these images will appear on the radiograph. Also, patients sometimes are reluctant or unable to remove tongue rings or earrings. Removal of all such appliances is highly desirable as metallic objects will often result in a large double image on the opposite side of the face or vice versa. Double images are always larger, more poorly demarcated, and positioned in a more superior location on the opposite side of the radiograph.

When patients are wearing complete dentures with no metal clasps or bars, it is advisable to leave the dentures in the mouth as the patient can be positioned better in the focal trough and as the outlines of anatomy and pathology are more clear. Where the teeth are acrylic, nothing will be seen on the radiograph; where the denture has porcelain teeth, these images will be seen between the alveolar ridges but will not interfere with viewing relevant anatomy or pathology.

Viewing the TMJ

When purchasing a panoramic machine it is preferable to buy one that utilizes a film size that has a 6-inch rather than a 5-inch width. With the smaller width, the TMJ more often does not appear on the radiograph. This is particularly true in patients with large faces. Also, the more the face/chin is dropped the greater the vertical distance of the face and the less likely the TMJ will be imaged on a radiograph that is 5 inches wide. In the radiograph in Figure 1, the film is 5 inches wide and the outline of the superior head of the head of the condyles is not seen as completely as one would with a 6-inch wide film.

Also, if the patient is seated too far back in the focal trough, the TMJ area will also move posteriorly and may be out of the focal trough; thus the images will not appear on the radiograph.

CONCLUSION

The more common technical errors for panoramic radiographs and explanations for these errors have been reviewed. Awareness and avoidance of the errors discussed above will improve the quality of panoramic radiographs in clinical practice. In a follow-up article, examples of panoramic radiographs with the errors described here will be shown, and explanations will be given for correcting the problems.

Dr. Serman is professor of oral radiology, Division of Oral and Maxillofacial Surgery, at the School of Dental and Oral Surgery, Columbia University in New York, NY. Dr. Serman is also the American director on the board of directors of the International Association of Dento Maxillo Facial Radiology. At the Scientific Congress of the International Association of Dento Maxillo Facial Radiology (IADMFR), held in Glasgow, Scotland, in 2001. Dr. Serman was elected as a fellow of the IADMFR, the tenth time in the history of the association that this award has been made.

Dr. Horrell is an assistant professor of oral radiology, Division of Oral and Maxillofacial Surgery, at the School of Dental and Oral Surgery, Columbia University in New York, NY.

Dr. Singer is an associate professor in the Division of Oral and Maxillofacial Radiology, University of Medicine and Dentistry of New Jersey, in Newark, NJ.

Digital imaging offers several advantages. Information obtained in digital form can be processed, stored, and transmitted from one place to another using communication networks. The lower dose of radiation and time saved in acquisition and viewing of an image is an improvement over conventional radiography. Images produced by digital systems can also be manipulated using computer software applications to increase diagnostic utility and electronically transmitted for referrals. In addition, digital imaging does not require chemical processing. Other advantages include image analysis and image reconstruction. There is also evidence that utilization of digital radiography is not only more economical to establish than a conventional radiographic system, but also less expensive to maintain.2

The purpose of this article is to review technologies basic to digital imaging that enable acquisition and viewing of an image, and to recognize limitations of the technology. 

ELEMENTS OF DIGITAL IMAGING CYCLE

There are five basic elements of an imaging cycle: acquisition of a digital image; processing the acquired image using image analysis, and image manipulations using software applications; storage for easy access and retrieval; communication  or image transmission between peers; and presentation or viewing of the image using monitors or workstations.  This article examines each  these elements and also identifies concerns that are essential to the clinical practice of dentistry.

Figure 1. Elements of imaging.

Figure 2a. CCD image sensors.	Figure 2b. PSP image plates.

Figure 3a. Gendex image scanner.	Figure 3b. Digora image scanner.

The steps involved in a digital imaging cycle are illustrated in Figure 1. There are three basic components of a digital imaging system: computers (desktops, viewing stations), detectors (image acquisition devices) (Figures 2a and 2b), and scanners (Figures 3a and 3b). The computer controls acquisition, storage, processing, retrieval, and display of a digital image. Detectors are primarily used to capture or acquire images from the source and store them until they are processed. A detector converts the x-ray beam into an electronic signal. Scanners are used to process the image acquired by the detectors and convert them into digital form to be displayed on a computer screen. The electronic signal from the detector is converted from an analog form to a digital form.

Computers allow for the input and output of data. They also provide the storage functions required for easy access and retrieval of image data, and they perform these functions with great speed. Input devices are used to collect external information. These may be a keyboard or an electronic detector system. Memory is required to store both instructions to perform functions and data for processing. A central processing unit is required for processing instructions. Internal storage of data may be on hard disks, and external storage can be on CDs or zip drives. Output devices are printers and video monitors that are used to present the information in the form that can be interpreted by the user. The computer “bus” allows for the communication between all these components and makes the device functional.

DIGITAL RADIOGRAPHIC ACQUISITION

Several methods are available to acquire a digital image. A conventional radiograph can be digitized using a flatbed scanner and transparency adapter. Conventional radiographs can also be digitized using a charge couple device (CCD) video camera. There are two common types of detector or sensor systems currently available: direct digital systems and semidirect digital systems. The CCD, complementary-metal-oxide-semiconductor (CMOS), and the bulk charge modulated device are classified as direct digital systems. Direct digital systems use an electronic device consisting of a light sensitive element, and output from these devices is transferred to a computer as an electric signal and then digitized. With this system the image is displayed on the computer monitor almost immediately. Semidirect digital imaging systems use photo stimulable phosphor plates (PSP) to acquire a digital image. PSP holds a latent x-ray image that is the result of excitation of electrons in the phosphor crystals by the x-ray photons. A laser beam is used to scan the plate and a photo-multiplier device captures the resultant image. The output from the photo-multiplier is converted to pixels and displayed on a computer screen.

Image Sensors

The most common type of sensor is the CCD (Figure 2a). In CCD systems a wire connects the sensor and the computer, and the image is displayed almost immediately. The first intraoral radiography system utilized a CCD sensor and processing unit with the digital radiographic image being displayed on a computer monitor.3,4 A radiation-sensitive device inside the sensor determines the amount of voltage received from the x-ray beam. The voltage is then converted to a numerical value that is assigned to gray level displayed on the screen. The CMOS sensor is also finding acceptance in dental practice. These sensors have the same makeup as the CCD sensors except they use active pixel technology. The major advantages of the CMOS sensors are the integration of control circuits directly into the sensor, low power utilization, and low cost. Schick Technologies is a digital imaging system vendor that uses active pixel sensors with CMOS technology.

The second type of image sensor is the PSP. This type of sensor has properties similar to intensifying screen phosphors. The PSP sensor consists of an imaging plate (Figure 2b). This imaging plate consists of phosphor particles embedded in a polymer binder and coated onto a plastic base.5 In a PSP system a plate is exposed to radiation and a latent image is created and stored on the plate to be scanned and transferred to a computer for viewing. As the phosphor layer of the plate is irradiated, the electrons become trapped in the detector. During processing of the plate the electrons are released and emit a blue light proportional to the intensity of the x-rays attenuated in the phosphor layer. The light is then converted to a digital form, and data is displayed on the screen. The information contained in the plate is released by exposure to a laser scanner. The storage phosphor plate is approximately the same size and body as conventional film, and there are no connecting wires. Sordex and Gendex are two vendors that use PSP technology for digital imaging.

DIGITAL IMAGE PROCESSING

Digital image enhancement in its simplest form results in a new image that is visually more appealing. Another form of image enhancement is aimed at correcting the image for known deficiences, for example to remove blur or to compensate for defective pixels in the image receptor. The most common image enhancement operations used in dentistry are contrast enhancement, filtering, digital subtraction, and color. A user can enhance the digital contrast by changing the distribution of gray values in the image without changing the image itself. Some studies have shown increased diagnostic utility of contrast enhancement in digital radiographs.6 Filtering is another method used to improve the image quality by removing features such as high-frequency noise (speckling) or low-frequency noise (intensity changes). Filters for image enhancement have been applied to dental digital radiographs to increase sharpness or reduce various types of noise.7 Digital subtraction radiography (DSR) has been developed to detect mineral changes that have occurred over time. DSR allows for more meaningful comparison of serial radiographs over time. Numerous studies have shown the high diagnostic utility of DSR.8

Image analysis operations offer meaningful functionality compared with conventional radiography. These operations are designed to extract information from the image that is diagnostically relevant. This type of information can range from a simple measurement to a fully automated classification procedure. Digital radiography allows detailed measurements; however it does not imply that these measurements are valid and that the measurements are consistent. The literature contains numerous reports on studies assessing the utility of digital measurements with applications in endodontics, orthodontics, periodontics, implantology, and other areas of dentistry. Most of these reports pertain to digital equivalents of existing methods, such as measuring length, distance, and angles. Digital length measurements using PSP plates in endodontics have been shown to be as accurate as conventional methods.9 The use of digital measurements in orthodontics has enhanced cephalometric analysis especially when combined with automated landmark identification.10 Measurement of alveolar bone height changes adjacent to teeth and implants has many applications.11 In addition, digital images have made it possible to determine bone density change within an area. Change in bone density has been used to evaluate the healing of periapical lesions after endodontic treatment.12 The overall goal of image analysis is to improve the diagnostic utility of images. The most important question remains as to whether the image is a valid and accurate representation of the patient’s status. The value of digital image processing as a part of digital imaging depends on aspects of image acquisition, as well as on aspects of vision and cognition. When used properly, image processing can improve diagnostic outcomes.

DIGITAL RADIOGRAPHIC IMAGE STORAGE

Once a radiograph is made available in digital form, it is archived in a computer. Image compression as a part of image analysis has been used to reduce the size of digital images for storage or transmission. Managing large files of images is a challenge even with the current generation of storage media and high-speed fiber-optic networks. Compression algorithms have been developed to achieve high levels of compression while retaining image quality. The compressed images are stored in standard formats in common storage systems such as hard disks, magnetic tapes, and optical devices such as DVDs or CDs. Selection of storage technology is based on storage capacity, required access speed, and cost. The fundamental question is whether a compressed image will retain its diagnostic value. Studies have explored the effects of image compression on the diagnosis of caries,13 and for determining the endodontic file length.14 These reports established that compressed images were diagnostically equivalent to uncompressed images.

DIGITAL IMAGE COMMUNICATION

Images are stored in computers in various image formats for easy communication, access, and retrieval. The challenge is to use a format that can accommodate all diagnostic imaging data, be scalable, and be shared between systems. Most dental digital systems that are being marketed today are stand-alone systems and do not necessarily interface or exchange information with each other. This means that an image obtained with a Digora scanner (Figure 2b) cannot be viewed or displayed on a Gendex user interface or viewer. This will make exchange of images between disparate systems difficult. An alliance of the American College of Cardiology,  American College of Radiology (ACR), and companies that manufacture medical equipment  (National Electrical Manufacturer’s Association or NEMA) developed the ACR-NEMA standard. This standard evolved into the digital image communication in medicine standard (DICOM). This standard defines a set of communication protocols allowing the interchange of information and images from different digital radiographic systems. The DICOM standard has long been used by the medical establishment and specifies file formats to allow images to be viewed across different platforms. Once manufacturers of dental equipment become compliant with the DICOM standard, dentists will be able to easily exchange images.

DIGITAL PRESENTATION AND DISPLAY

The digital image can be displayed for viewing on a desktop computer monitor screen or a laptop liquid crystal display. Studies have reported that laptop displays are diagnostically comparable with desktop monitors and conventional film for accuracy of caries detection.15 Images displayed on a computer screen need to possess fidelity, diagnostic clarity, and also be appealing to the human eye. Fidelity can be expressed in terms of spatial resolution, gray scale resolution, gray scale linearity, signal-to-noise ratio, and absence of distortion. Image clarity can be expressed in terms of diagnostic accuracy. Image appeal concerns the perceived aesthetics of the displayed image.16

CONSIDERATIONS

The selection of a digital imaging system should consider the following questions.

(1) How will the digital image be captured or acquired? Digital images may be obtained either by using a direct image system such as a CCD device or an indirect system such as PSP, or by exposing film and then capturing the film image with a computer scanner or frame grabber. For offices that want to change from film to digital, both methods can be used. The direct system could be used for all new images, and the film-to-digital system could be used to convert existing film images to digital images.

(2) How much storage is required for digital images? This will be based on volume of radiographic images taken on a routine basis. Digital images occupy a large amount of data storage. Based on the projected radiographic image requirements for another 5 years, large capacity hard disks or optical disks will be needed to satisfy storage requirements. Additionally, image compression and decompression algorithms should also be considered to reduce the disk space needed for storage.

(3) How will the images be visualized? Computer monitors are inexpensive compared with flat screen LCD panels. When choosing a monitor, size should be considered in relation to its planned location in the office. Images can also be visualized by printing them using laser printers. Table 1 will assist in decision-making before selecting a system. A user must also have an idea of the range of specifications of components that comprise a digital dental imaging system (Table 2).

CONSTRAINTS OF DIGITAL IMAGING

There are some constraints to the use of a digital system or when changing from a conventional system to a digital system. The initial cost of introducing a digital system can be high. The cost of digital imaging equipment including computer hardware can range from $20,000 to $30,000 per unit. There are significant costs associated with network installation and training. There is also a learning curve for system users. Competency takes time to acquire. There is also concern regarding infection control and care of the sensors. As with other clinical procedures, infection control is essential. Plastic bags have been used to protect the plate or sensor and also to prevent cross-contamination. It is important to remember that sensors are not disposable and if damaged can be expensive to replace. Damage can result in production of artifacts that will interfere with the diagnostic utility of the image. The cost of replacing a PSP plate is approximately $50, and a CCD detector can cost more than $6,000 per unit.

CONCLUSION

Digital imaging technology offers some distinct advantages. Computers aid in the rapid and convenient storage, retrieval, transmission, and display of radiographic images. The information can be used prospectively and/or retrospectively to develop a treatment plan or assess treatment over a period of time. In the future, the use of digital radiography will expand. There will be more practitioners using PSP and CCD technology, and advances in scanner and viewing technology will increase the amount of information obtained from digital radiography.

Acknowledgment

The authors would like to thank Dr. Ira B. Lamster, Dean of Columbia University School of Dental and Oral Surgery, for his valuable advice and help in the preparation of this manuscript.

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15. Lim KF, Loh E E-M, Hong YH. Intra-oral computed radiography: an in vitro evaluation. J Dent. 1996;24:359-364.

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Dr. Pai is an assistant professor of clinical dentistry and director of clinical information systems at the Columbia University School of Dental and Oral Surgery in New York City.

Dr. Zimmerman is an associate professor of clinical dentistry and assistant dean for information resources at the Columbia University School of Dental and Oral Surgery in New York City.

Radiographically there are four signs that can help the clinician when examining radiographs of patients suspected of having fractures. They are: (a) a linear lucent line; (b) a step in the cortex of the bone; (c) a change in morphology; and (d) an increase in opacity.

However, most linear lucent lines, steps, or apparent changes in morphology do not indicate fractures but sutures, margins of overlapping bones, or nutrient canals. An increased opacity may be seen when the sides of the fractured bone are superimposed. There are many anatomic structures that may mimic fractures and may be mistaken for a fracture in those cases where one is already suspected. Thus, it is essential that radiographic anatomy be known in detail. At the same time, it is essential never to attempt to make a diagnosis solely from radiographs. A basic requirement of radiographic interpretation of fractures is the need to have at least two projections taken at 90° to each other.

The aim of this article is to indicate some radiographic anatomy that may simulate the appearance of a fracture in the maxillofacial region.

MANDIBLE

Pharyngeal Air Space Versus Suspected Fracture of the Ramus of the Mandible

Figure 1. Linear lucency (opposing arrows) seen on a panoramic radiograph and suggestive of fracture of ascending ramus of mandible.	Figure 2. a. The right coronoid process (two adjacent parallel arrows) has a linear, horizontal lucency suggesting the outline of a fracture. Immediately inferior to this line is the outline of the zygomatic process overlapping coronoid process. b. Panoramic radiograph showing an almost horizontal opacity of the hyoid bone in the middle of the right body of the mandible and indicated by the large arrow. c. The linear lucency (three adjacent arrows) inferior to the inferior concha and superior to the opacity of the hard palate simulating a fracture in the maxillary sinus. d. Two vertical linear lucencies (opposing arrows) in the left body of the mandible created by nutrient canals.
Figure 3. Linear lucent lines seen in the mandibular anterior periapical radiograph mimicking the appearance of a fracture. Some nutrient canals can be seen ending in nutrient foramina.	Figure 4. Inferior border of C1 giving the appearance of an alveolar fracture inferior to the mandibular incisor teeth. The superior border of C2 is also visible.
Figure 5. a. Sutures in zygomatic arch bilaterally (single arrows). The lucency, the step, and the apparent change in morphology can be seen. b. Opposing arrows indicating linear lucency in maxillary sinus suggestive of a fracture. c. Adjacent arrows indicating overlapping of hyoid bone over body of mandible. d. Horizontal arrows indicating the outline of the head support over the ascending ramus of the mandible.	Figure 6. a. A midline linear lucency (opposing arrows) seen in panoramic projection appearing between and above the apices of the central incisors. b. Double image of inferior border of contralateral mandible (adjacent arrows).
Figure 6c. Image of midline vertical lucency in maxilla as seen on a panoramic radiograph, appearing to extend to the floor of the nose.	Figure 7. Periapical radiograph of mandibular anterior region showing the mental ridge and the outline of the lower lip.
Figure 8. Periapical radiograph of maxillary posterior region showing a linear lucency (white arrows) in the maxillary sinus.	Figure 9. Panoramic radiograph of an older, edentulous patient showing the images of the nasolabial fold.
	Figure 10. A periapical radiograph of the maxillary anterior region showing a horizontal lucency of the upper lip over the roots of both central incisors giving the impression of dental fractures. The midline, linear vertical lucency is visible as well between the central incisors.

When taking a panoramic radiograph, it is essential to instruct the patient to place the tongue against the hard palate in the swallowing position and to maintain that position throughout the exposure. If this is not done, patients often double the tongue backwards creating an even larger pharyngeal air space. It is equally important to instruct the patient to maintain the elevated position of the tongue throughout the exposure time as patients often initially elevate the tongue but do not keep it elevated throughout the exposure (Figure 1).

The pharyngeal lucency may appear over the apices of the maxillary teeth obstructing the view of the apices of these teeth and may hide periapical pathology. The lucency may also continue or may only appear over the ascending ramus of the mandible giving the appearance of a fracture in that area. A fracture will end at the cortical plates of the bone whereas the pharyngeal lucency usually continues anteriorly and/or posteriorly to the ramus. Where a fracture of the mandible is suspected, a postero-anterior projection should be requested.

Lateral Pterygoid Plate Versus Suspected Fracture of the Coronoid Process of the Mandible

The lateral pterygoid plate is a very thin bone that often does not attenuate the beam on its own and therefore is often not often seen on the panoramic radiograph. However, when the lateral pterygoid plate overlaps the coronoid process of the mandible, the beam is often sufficiently attenuated by the coronoid process for the edges of the pterygoid plate to be partly or totally visualized on the panoramic radiograph (Figure 2a). The outline of the plate often appears as a sharp, linear but irregular lucency overlying the coronoid process, giving the impression of a coronoid fracture. The coronoid process is protected by a muscular cushion, the temporal muscle and also by the zygomatic arch. Thus, fractures of the coronoid process constitute a very small percentage of fractures of the mandible. In most cases of fractures of the coronoid process, there is also a fracture of the zygomatic arch. Should a fracture of the coronoid process be suspected, in addition to the panoramic radiograph, a postero-anterior projection with the mouth wide open will clearly show the coronoid process.

Occasionally the lateral pterygoid plate overlaps with the zygomatic arch resulting in a similar appearance.

Nutrient Canals in the Mandible Versus a Suspected Fracture of the Mandible

Nutrient canals are not an uncommon finding in images of the mandible. They may be seen anywhere in tooth-bearing area but are more common in the anterior part of the mandible. They are seen on the radiograph as vertical, linear lucencies ending at the top of the alveolar ridge in the mandible and at the bottom of the ridge in the maxilla. The mandibular nerve divides into the mental and incisive nerves. Accompanying the nerves are blood vessels. The incisive nerve (and blood vessels) run forward in the bone giving off nutrient canals (vessels) and, in the area of the midline, anastamose with the incisive vessels from the contralateral side and then run upward close to the midline as nutrient canals.1 These lucencies are often so evident that they simulate fractures (Figures 2d and 3).

Cervical Vertebra Versus Suspected Mandibular Alveolar Fracture

If the patient is seated with the head/chin tilted too far down in the focal trough when a panoramic radiograph is being taken, the outlines of the cervical spines are sometimes seen very clearly. The inferior border of C1 or the superior border of C2, superimposed on the mandibular midline region, often gives the appearance of a horizontal, linear lucency indicative of a mandibular midline alveolar fracture. The lucency of the intervertebral disc space can be seen between the two opacities. If the patient is seated with the head too far forward in the focal trough, these outlines are often seen even more clearly (Figure 4).

Hyoid Bone Versus Suspected Fracture of the Body of the Mandible

The appearance of the image of the hyoid bone on a panoramic radiograph is very variable depending on the seating of the patient and the tilting of the neck. If the patient is correctly seated, the hyoid will be seen bilaterally, ending mesially inferior to the body of the mandible and approximately inferior to the first mandibular molar teeth. As the patient is seated further forward in the focal trough, the hyoid bone also moves further into the focal trough and becomes elongated. The further forward the patient is seated, the longer the appearance of the image of the hyoid bone, and this structure may appear to extend completely across the body of the mandible from one side continuously to the opposite side. The more the patient drops the chin, the higher the appearance of the hyoid bone. The elongated outline of the hyoid bone superimposed over the body of the mandible may give the appearance of a fracture of the body of the mandible with an increased opacity of the sides of the fracture. The increased opacity can be seen extending distally and inferior to the mandible, and this is the diagnostic clue (Figures 5c and 2b).

Panoramic Head Support Versus Vertical Fracture of Ascending Ramus of the Mandible

Many panoramic machines have a head support on either side of the face to assist in centering the patent during the exposure. The outline of the head support is seen on most of the images but sometimes appears so definite and with such a sharp outline as to be suggestive of a vertical fracture. Some clues in assisting the diagnostician are: the fact that an image of a fracture is never seen as a completely straight line; the appearance is often seen bilaterally; and the appearance extends inferior to the body of the mandible (Figure 5d).

Contralateral Double Image of the Mandible Versus Horizontal Fracture of the Body of the Mandible

When the patient is positioned in the panoramic machine with the chin raised or dropped only very slightly, the double image of the inferior border of the body of the contralateral mandible often appears and may give the appearance of an increased opacity simulating the sides of a fracture that are superimposed. This image is usually not seen if the patient is seated correctly or if the chin is raised or lowered excessively. The increased opacity is always situated superiorly to the line, and the line can be seen extending distally to the posterior border of the ascending ramus of the mandible (Figure 6b).

Mental Ridge Versus Suspected Fracture of the Anterior Mandible

Opposing sides of a fracture appear radiographically as areas of increased opacity. When a periapical radiograph of the mandibular anterior region appears foreshortened, the mental ridge is seen more clearly. The greater the foreshortening the better the image of the mental ridge, which may simulate the overlapping sides of a fracture. Immediately inferior to the opacity, in the midline area, along the inferior border of the mandible, the genial tubercles give the appearance that there may also be a step (Figure 7).

MAXILLA Zygomatic Process Versus Suspected Zygomatic Fracture

The zygomatic process is often seen on a panoramic radiograph. The zygomatic process consists of the temporal process of the zygomatic bone and the zygomatic process of the temporal bone, which together form the zygomatic arch.2 The suture between these processes has three of the four radiographic signs of a fracture. A linear lucency can be seen running from the superior border of the zygomatic process, distally and inferiorly. Particularly in younger people, the lucency may be quite wide and almost horizontal. Along the inferior border of the zygomatic process, immediately mesial to the suture of the two bones, there often appears to be a step, again often pronounced in younger people. Also, the two processes do not appear to lie in a continuous line, giving the appearance of a change in morphology  (Figure 5a). Where the clinical and radiographic findings suggest a fracture, a submentovertix projection should be requested to confirm the presumptive diagnosis.

Nutrient Canals in Maxillary Sinus Versus Suspected Fracture of the Maxilla

A thin, almost horizontal radiolucent line is often seen in posterior periapical radiographs in the region of the maxillary sinus and it may mimic a fracture. This image is a groove on the lateral wall of the maxillary sinus and consists of a neurovascular canal3 in which the posterior superior nerves to the teeth also lie (Figure 8). A recent fracture of the maxillary sinus is usually accompanied by bleeding into the sinus, and the bleeding will be seen as cloudiness in the sinus. This cloudiness often helps to distinguish the groove from pathology. When pathology of the maxillary sinus is suspected a Waters or occipitomental (OM) projection should be requested.

Intermaxillary Suture Versus Suspected Midline Maxillary Fracture

Between the maxillary incisor teeth is the intermaxillary suture, which appears on radiographs as a vertical, midline linear lucency that must not be mistaken for a fracture or a nutrient canal (Figures 6a, 6c, and 10). It is seen more clearly on the periapical, intraoral projection of the maxillary anterior teeth but sometimes is seen very clearly on the panoramic radiograph as well. In older people the lucency appears to end immediately superiorly to the central incisor (Figures 6a and 10). In younger people however, the lucency often appears to extend superiorly to or into the osseous floor of the nasal cavity (Figure 6c).

Inferior Concha Versus Suspected Fracture of the Maxilla

The images of the inferior concha often appear to be superimposed on the maxillary sinuses on panoramic radiographs. Often the superior or inferior (often both) borders appear as linear lucencies that may be mistaken for fractures in the sinus. The linear lucency is often seen inferior to the inferior concha and superior to the linear opacity of the hard palate, which appears to exaggerate the linear lucency (Figures 5b and 2c).

Should one suspect pathology of the maxillary sinus, a Waters or OM projection is the view of choice.

Nasolabial Fold Versus Suspected Maxillary Alveolar Fracture

The image(s) of the nasolabial fold are seen more clearly on older patients and in edentulous patients. They are seen running from the lateral borders of the alae of the nose in a disto-inferior direction and may mimic a maxillary alveolar fracture. This appearance may be seen in periapical as well as panoramic projections of this area. The clue for the diagnostician here is that the line continues inferior to the maxilla. The lines are usually visible bilaterally and symmetrically on a panoramic radiograph, and that is another clue to distinguish the anatomic structure from a fracture (Figure 9).

TEETH

Alveolar Bone Height Versus Suspected Dental Fracture

In the majority of cases the images of the alveolar bone height lying buccally and palatally/lingually to the teeth are not seen. Occasionally however, the outline of alveolar bone height lying palatally/lingually to the teeth is seen so clearly that it simulates a fracture of a tooth or teeth. The appearance of the line is more likely to be seen in images of  teeth that have been foreshortened. Depending on the type of bone loss, the appearance may be horizontal or oblique. Here clinical and radiographic findings must be considered together, as the linear lines appear to be limited to the tooth structure. However, usually there is more than one tooth with this appearance and the height of the alveolar bone adjacent to the line is the clue (Figure 10).

Lip Line Versus Suspected Fracture of the Anterior Teeth

The outline of the lip superimposed on the incisor teeth may give the appearance of fractures of anterior teeth in either jaw. When lowering the kVp, the outline of the image of the lips sometimes appears to be very sharp. The clue here is the fact that the line is continuous over several teeth and is at about the same height throughout (Figure 7). Also, the height of the line is over the crowns of the teeth which permits clinical inspection.

Conclusion

Some radiographic findings that may appear to mimic fractures were discussed. This knowledge is important for anyone wishing to interpret radiographs. Never attempt to diagnose fractures solely from radiographs. Where fractures are suspected, a clinical examination is essential as are radiographs taken 90° to the initial view.

References

1. Wang PD, Serman NJ, Kaufman E. Continuous radiographic visualization of the mandibular nutrient canals. Dentomaxillofacial Rad. 2001;30:131-132.

2. Grant JCB. A Method of Anatomy: Descriptive and Deductive. Philadelphia, Pa: Williams and Wilkins Co;1958:693-694.

3. White SC, Pharoah MJ. Oral Radiology: Principles and Interpretation. 4th ed. St Louis, Mo: Mosby; 2000:182.

Dr. Serman is professor and head of the Division of Oral Radiology at the School of Dental and Oral Surgery at Columbia University, NY. He is also the American director on the board of directors of the International Association of Dento-Maxillo-Radiology, which named him a fellow in August 2001. He can be reached at njs2@columbia.edu.

Dr. Horrell is assistant professor in the Division of Oral Radiology at the School of Dental and Oral Surgery at Columbia University, NY.