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Written by Jack S. Roth, DDS Monday, 07 March 2011 16:42
The entire spectrum of 3-dimensional (3-D) imaging has advanced dramatically in the past decade. More importantly, cone beam computed tomography (CBCT) technology has become instrumental throughout dentistry and is now entering the primary care arena. This new ability to image in the third dimension has created a paradigm shift for clinicians all around the world. CB imaging is slowly becoming the gold standard in an evidence-based approach to diagnosis, treatment planning, and in delivering optimal care to our patients.
CBCT IS HERE TO STAY
CBCT is probably the newest and best technology advancement in dentistry in the past 50 years. However, as with any technology coming to market, it may take years before there is a saturation level into enough clinical settings. CB imaging has only been exposed to dental practice for less than one decade.1 Once this technology and its enhanced benefits become more clearly understood by all dental professionals, CB imaging will transform how dental decisions are made and it will become the standard for achieving accurate diagnoses (when indicated) in the dental practice.
Most clinicians are aware of 3-D imaging in relation to implant dentistry. Its utilization in that arena has been well documented.2-6 CBCT has the ability to help determine the quality and quantity of bone around any abutment or extraction site. In addition it is able to accurately correlate specific anatomical landmarks such as the mandibular nerve and sinus membrane. However, it is the author's strongest contention that the greatest benefit of 3-D imaging will take place in the primary care setting where most diagnostic and treatment planning decisions are made.
COMPARING 2-D DENTAL RADIOGRAPHY TO CBCT
Besides a thorough clinical exam, the dental radiograph has been one of our best diagnostic aides for more than a century. However, when critically analyzing its benefits, there are some glaring shortfalls. Many dentists believe that a radiograph is completely evidence-based. Unfortunately, a radiograph is a 2-dimensional (2-D) image not dissimilar to a photograph. In a 2-D analysis, all images are open to interpretation and are subjective in nature. One can also question the accuracy and quality of the information that is being seen. More importantly, an image such as a dental radiograph may have incomplete information since it lacks the third dimension.
The limitations of dental radiography can also relate to operator error. If any aspect of the imaging process from poor angulation to poor geometric configuration of the tooth onto the sensor will lead to substantial errors in interpretation. These "poorly-taken" radiographs can lead to artifact and missed diagnosis.7 Various investigators, including Goldman, et al8 have confirmed a poor correlation (47%) amongst examiners in the healing of periapical pathology utilizing dental radiography.
Effectively a 2-D image is not reality. It is a valuable but limited technology resource. With that said, for most routine dental procedures (ie, diagnosing dental caries) the resolution and quality of a standard radiograph is more than sufficient. However, CBCT technology has created a forum with limitless boundaries.
With 3-D imaging there is not a single image. A CBCT scan captures a volume of information, creating hundreds of images in all 3 dimensions. The fluid nature of the technology creates these images in all 3 planes with limitless visibility. A mathematical algorithm is then able to seamlessly transform these images onto a 2-dimensional screen for analysis. 3-D imaging is not limited by operator error. As long as the field of view (FOV) captures the oral cavity location contained in the volumetric scan, it can be reconstructed without distortion. I like to call this self-correcting technology.
The main advantage of CBCT relates to the quality of information attainable. CBCT imaging creates a wealth of information not available by any other source. Our usual expectations, as advancements are made in dental care, are in efficiency, delivery, and/or product improvement. CBCT offers all dentists information no other modality can. This ability to see in the third dimension standardizes care and turns anecdotal information into an evidence-based approach to dental delivery.
In part 1 of this article, we began laying a framework analyzing cone beam technology from a dental perspective. CBCT is not a variation of a medical CT scan, which takes thousands of slices with a concomitant need for significantly more radiation to the patient. The newest generation of CBCT machines creates a cone-shaped volume of information. Effectively this reduces unnecessary radiation. A CBCT scan can be made incorporating a FOV to include both arches and temporomandibular joint or as small as 5 x 5 cm to analyze an individual tooth. These newer CBCT machines (Vatech, Planmeca, KODAK, and others) can isolate an individual tooth from 360° with an extremely high resolution. The smaller the FOV, the greater the resolution; resolution at this 5 x 5 cm FOV can be in the 0.08 voxel range.
In addition, there appears to be some misinformation from various sources about the amount of radiation in a CBCT scan. A medical CT subjects a patient to approximately 1,200 to 3,000 µs of radiation. A CBCT scan in my office, where we use a Picasso Duo [Vatech]) at 5 x 5 FOV, exposes a patient to approximately 25 µs with a resolution of 0.08 voxels. In comparison, a full-mouth set of dental radiographs exposes the patient to approximately 150 µs. It is apparent that a high-resolution CB scan, utilized in a diagnosis mode to evaluate an individual abutment, is analogous to taking just 3 periapical radiographs. It's hard to imagine radiation exposure being an overriding issue when CBCT technology is applied in a prudent manner to obtain information that is simply not available using other methods.9,10
THREE-DIMENSIONAL IMAGING INVOKES A PARADIGM SHIFT
As CB imaging expands its presence in dental settings, several factors should become crystal clear; 3-D imaging will:
1. Become a case specific resource of quality information not available by any other modality
2. Standardize decision making by verifying an evidence-based diagnostic protocol
3. Help eliminate operator subjectively and restore balance and objectivity to dental care delivery
4. Bridge the gap in deciding between endodontics and implantology
5. Recreate an interdisciplinary dialogue amongst all dental professionals.
As with all anecdotal information, the longer and more often it is repeated, the more firmly we hold onto it as fact. As an example, during the past 2 decades there has been a concerted effort to "lump" all teeth with "fracture" lines together as teeth with a guarded prognosis. It is my contention that the role of dentistry is to save teeth whenever possible. Tangentially, this has led to decision making that was suspect, at best. Abutment teeth that might have needed full-coverage restorations or endodontic intervention may have been extracted in favor of a dental implant. All endodontists know that there is a significant difference between cracked teeth and teeth with craze lines. Inadvertently defining them synonymously has mistakenly led to improper diagnosis and misinformation for our patients. True crack lines have a width of at least 0.1 mm. With present day CBCT imaging, cracks of clinical significance can be visualized, and then through an interdisciplinary dialogue, a patient can be presented all appropriate treatment options including a dental implant.
It is my contention that CBCT will have a profound effect on all dental decision making over the next decade. In a case specific manner when 2-D radiography and clinical examination cannot offer verifiable and complete information, it must be the prudent choice to take a 3-D scan.
Only 3-D analysis offers the technology to help differentiate a tentative diagnosis into a verified evidence-based diagnosis and treatment plan. In effect, as CBCT slowly becomes the standard of care, when indicated, a final treatment plan will have to incorporate the information in a 3-D scan prior to implementing therapy.
There are several other areas that CBCT is able to offer invaluable information. Three-dimensional imaging can help in:
• Differentiating odontogenic from nonodontogenic pathology
• Determining accurate dental anatomy, verifying number of roots or anomalies
• Differentiating resorptive defects and locating them anatomically to determine a prognosis
• Visualizing iatrogenic defects
• Diagnosing periapical pathology encased in cancellous bone that 2-D radiography cannot see.
The following cases represent clear examples of information that can only be available by using 3-D CBCT imaging.
In Case No. 1, a patient presented with an acute abscess associated with tooth No. 14. Endodontic therapy was performed and symptoms abated, but not completely (Figures 1a to 1g). The patient returned 7 years later with periapical pathology. An apicoectomy was performed utilizing a surgical microscope and an MTA Retrofill. All clinical and radiographic pathology seemed to disappear, but the patient continued to have sporadic symptoms. A dental radiograph appeared to show healing, but a CBCT scan revealed clear evidence of new pathology in this refractory case.
|Figure 1a. No. 14 root canal therapy (RCT) completion 11/2000.||Figure 1b. Periapical pathology now evident.|
|Figure 1c. Apicoectomy No. 14 MTA Retrofill.||Figure 1d. Recall radiograph.|
|Figure 1e. Follow-up radiograph continuing to show evidence of healing.||Figure 1f. Clear evidence of pathology not visible on 2-dimensional radiograph.|
|Figure 1g. Another view of 3-dimensional (3-D) scan to visualize extent of pathology.|
In case No. 2, a patient presented with several multilocular swellings along the lingual aspect of tooth No. 19. This tooth was nonresponsive to all vitality tests and root canal therapy (RCT) was indicated (Figures 2a to 2f). The patient was cautioned that these swellings might be unrelated. Endodontic therapy was completed; however, the swellings persisted. A CBCT scan was taken and it revealed a "tunneling" infection through the lingual cortical plate consistent with an infected lingual tori.
|Figure 2a. Pre-op radiograph.||Figure 2b. Intraoral view of several multilocular swellings.|
|Figure 2c. Completion of endodontic treatment.||Figure 2d. Patient returned with persistent swelling.|
|Figure 2e. The 3-D scan shows tunneling infection of lingual cortical plate.||Figure 2f. Enhanced view of extent of cortical bone destruction.|
Case No. 3 represents iatrogenic pathology (Figures 3a to 3d). This patient had recent RCT on tooth No. 9 with post/core and crown but then continued to have midroot tenderness. Multiple dental radiographs appear to show misalignment of post but no perforation. A CB scan demonstrated midroot perforation of post with slight cement extrusion.
|Figure 3a. Postendodontic treatment radiograph.||Figure 3b. Postendodontic treatment |
radiographs, second view.
|Figure 3c. The 3-D scan verifies post perforation.||Figure 3d. The 3-D scan demonstrates cement extrusion through buccal.|
In case No. 4, a patient presented in 2004 with cracked tooth syndrome and irreversible pulpitis on tooth No. 18 (Figures 4a to 4e). RCT was performed and a full crown was placed. The patient was asymptomatic until 2010, when she presented with some intermittent chewing discomfort. A dental radiograph showed no periapical pathology, and clinical exam revealed minimal probing. A CBCT scan was taken demonstrating a J-shaped lesion with tremendous bone loss apically and around the buccal aspect of the tooth.
|Figure 4a. Pre-op cracked tooth syndrome, 2004.||Figure 4b. Endodontics completed in 2004.|
|Figure 4c. Intermittent chewing pain—dental radiograph not conclusive.||Figure 4d. The 3-D scan shows extensive bone loss.|
|Figure 4e. Enlarged view demonstrating J-shaped lesion apically and extending through cancellous bone on buccal.|
In Case No. 5, a patient presented for consultation to consider a retreat and to determine the long-term prognosis of No. 18 (Figures 5a to 5c). This tooth had a history of RCT followed by the placement of a post/core and a full crown. There was significant furca and apical pathology. A CBCT scan was taken to help complete the diagnosis. The scan revealed an oblique fracture/resorption as the cause of the pathology. The patient was told to extract this tooth and place a dental implant. This patient was confident in knowing the diagnosis was finally clear.
Figure 5a. Dental radiograph, history of RCT post/core and crown, demonstrating apical and furca pathology.
|Figure 5b. The 3-D scan shows extent of furca bone loss.|
|Figure 5c. A 360º view of this tooth revealed a fracture and resorption as |
cause of pathology.
There is a saying that knowledge is power. Without realizing it, 2-D imaging has created a large information gap due to its limitations as a technology resource. As dental professionals, we have relied on this technology while rarely questioning its validity or the quality of information it provided to us. With the advent of 3-D imaging, that information gap has been narrowed. CBCT imaging has stretched our boundaries, allowing for complete and accurate information in all 3 dimensions. This new knowledge is a most powerful force in dentistry that will dynamically change our ideas, diagnoses, and treatment options. It is the author's belief that the implementation of this technology will lead to new innovations and better care in all specialties of dentistry.
- Scarfe WC, Levin MD, Gane D, et al. Use of cone beam computed tomography in endodontics. Int J Dent. 2009;2009:634567.
- Kobayashi K, Shimoda S, Nakagawa Y, et al. Accuracy in measurement of distance using limited cone-beam computerized tomography. Int J Oral Maxillofac Implants. 2004;19:228-231.
- Lascala CA, Panella J, Marques MM. Analysis of the accuracy of linear measurements obtained by cone beam computed tomography (CBCT-NewTom). Dentomaxillofac Radiol. 2004;33:291-294.
- Marmulla R, Wörtche R, Mühling J, et al. Geometric accuracy of the NewTom 9000 Cone Beam CT. Dentomaxillofac Radiol. 2005;34:28-31.
- Ludlow JB, Laster WS, See M, et al. Accuracy of measurements of mandibular anatomy in cone beam computed tomography images. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2007;103:534-542.
- Loubele M, Van Assche N, Carpentier K, et al. Comparative localized linear accuracy of small-field cone-beam CT and multislice CT for alveolar bone measurements. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2008;105:512-518.
- Gröndahl H-G, Huumonen S. Radiographic manifestations of periapical inflammatory lesions. How new radiological techniques may improve endodontic diagnosis and treatment planning. Endodontic Topics. 2004;8:55-67.
- Goldman M, Pearson AH, Darzenta N. Endodontic success—who's reading the radiograph? Oral Surg Oral Med Oral Pathol. 1972;33:432-437.
- Nesari R, Rossman LE, Kratchman SI. Cone-beam computed tomography in endodontics: are we there yet? Compend Contin Educ Dent. 2009;30:312-318.
- The SEDENTEXCT Project. Radiation protection: cone beam CT for dental and maxillofacial radiology. Provisional guidelines, v1.1, May 2009. www.sedentexct.eu/system/files/sedentexct_project_provisional_guidelines.pdf. Accessed January 3, 2011.
Disclosure: Dr. Roth reports no disclosures.
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