It is an inconvenient truth: the foundation of most dental procedures is diagnostic, radiologic guesswork derived in large part from the use of two-dimensional (2D) film and digital-based imagery. While the guesswork is a distillation and integration of accumulated data synergized by years of education, experience and deductive reasoning, it is guesswork nonetheless.
Cone Beam Computed Tomography (CBCT) 3D systems, such as the KODAK 9000 3D Extraoral Imaging System (Fig. 1), provide the capability to visualize three orthogonal planes without overlying anatomic obstruction or anatomic “noise” such as the zygoma, the sinus or the incisive foramen. Advanced computational software removes the constraints of 2D images and empowers the clinician to achieve detailed and accurate diagnoses. The result provides an elevated standard of patient care and enhances treatment understanding and acceptance with an unprecedented level of integrated efficiency. Image-guided treatment strategies are the present mandate of dentistry, not its future objective.
The global dental industry is rapidly transitioning to newer generations of volumetric imaging. The cross sectional imaging derived from these 3D systems is an invaluable adjunct to intraoral and panoramic radiographs, enhancing diagnostic accuracy with very minimal risk. In Canada today, only Ontario dentists (with some exceptions) are forced to send their patients to a dental radiologist for craniofacial 3D scans. In addition to inconveniencing the patient and risking a lack of follow-up on treatment, these scans are more suited to full-mouth reconstruction cases than diagnostic perplexities in quadrants or localized areas. There are other negative results as well: the patient receives a greater radiation dose over a larger area of the craniofacial anatomy than is necessary, treatment is delayed, and treatment acceptance is often comprised because of higher costs.
The focused field of view found in the latest CBCT systems have been approved for “in office” use in the majority of the United States and Canada. These systems are ideal for single-tooth or quadrant dentistry. Since these units are programmed to capture only the images necessary, radiation exposure is further reduced in contrast to traditional medical CT imaging source detection. Multiple modalities, such as panoramic and cephalometric features, further enhance the value of these systems and their contribution to diagnosis and treatment planning. Perhaps the single greatest advantage to cone beam derived volumetric images is the ability to first perform complex surgical tasks in three dimensions on a computer model so that unexpected anatomic reality can be anticipated in advance.
Previously, dentists and dental specialists had to spend several hundreds of thousands of dollars to implement large-size, large-field 3D systems. Today’s CBCT systems are more affordable than ever. More importantly, the scales of economy for rendering an optimal diagnostic standard of care on an as-needed basis, at the time of examination, are highly favorable. Given today’s realities, we are left to question why the bulk of dentists in Ontario are forced to advocate outside imaging examinations rather than inside imaging examinations to our patients. By preventing the majority of dentists in Ontario from in-office access and usage, no one’s interests are being served.
WHAT IS CBCT?
The CBCT scanner, which made its commercial debut in the United States in 2001, uses a cone shaped x-ray beam rather than a conventional linear fan beam to provide images of the bony structures of the skull. The X-ray tube and a 2D image detector (either image intensifier with CCD or flat panel detector) are mounted opposite each other and perform one rotation (180 or 360) around the region of interest (ROI), similar to panoramic radiography. The resulting primary data (461 basis projections in the KODAK 9000 3D System) are converted into slice data using the filtered back projection. The reconstructed slice data can then be viewed in user-defined planes according to the requirements of the clinician.
This cone beam geometry provides the image with high contrast, faster scanning and reconstruction time at a lower dose and with higher noise than conventional medical CT scanners. Medical CT scanners use a single row or a series (4, 8, 12, 32 and now 64) of solid state detectors paired with a fan shaped beam to capture the attenuated x-ray. 2 CBCT differs from conventional computed tomography imaging in that the whole volume of data is acquired in the course of a single sweep of the scanner.
Conventional intraoral and panoramic radiography offer a 2D view of the ROI in a buccal-lingual perspective. Because of superimposition, both techniques are of limited value for detecting subtle anatomical and pathological structures. For a long time, dentists have expressed the need for a 3D radiological view of the teeth, jaws and surrounding structures for improved diagnosis and treatment planning.
Since the introduction of computed tomography (CT), digital 3D imaging has become increasingly prominent in dental radiology. However, until 1997 dentists lacked the ability to capture and view 3D anatomy of teeth and jaws in a simple, affordable manner with minimal dosage. The answer came in the form of CBCT technology, designed for high-resolution imaging of hard tissues. One of the most important innovations in dental diagnostics, CBCT has proven effective for applications in all fields of dentistry.
Three dimensional (3D) volumes, or images, are measured in voxels (VOLume piXEL), just as 2D images are measured in pixels. CBCT voxels are isotropic, or equally measurable from all sides in a perfect cube, leading to accurate measurements without algorithms to interpret the data set. In contrast, the axial height of a medical CT voxel is determined by the slice thickness, resulting in an anisotropic voxel (not a perfect cube), making measurements made in multiple planes inaccurate. Simulated bone defects in acrylic blocks and the human mandible prove that CBCT is an accurate way to measure osseous lesion size and volume. The KODAK 9000 3D System, for example, features an edge size (or minimum slice thickness) of 0.076mm — providing 3D images that are the highest resolution in the industry.
The dose of radiation to which patients are exposed with CBCT technology is significantly reduced compared with conventional medical CT scanners, which limits the health risk associated with radiation exposure. And CBCT exposures are only slightly higher than standard panoramic imaging. For example, the dose of the KODAK 9000 3D System is the level of 1.8 times that of standard panoramic images. Conversely, at a radiology center, a full 3D craniofacial scan is 30-1,000 times that of a standard panoramic image. 2
THE LEVEL OF CARE IS A STANDARD, NOT AN OPTION
Everything we do as dentists is “transitional,” with the exception of extractions. No result is everlasting, none is permanent; thus our treatment plans must reflect this reality. Artifice versus a natural state is not a panacea for successful treatment outcomes. The area where this has been tragically reversed is the endodontic / implant algorithm; the computational solution for determining the viability of retaining a compromised tooth, or removing it and providing an orthobiologic replacement. As endodontics is based on radiologic diagnostic determination, it is fair to say that 3D imaging should create more positive outcomes through its ability to visualize previously undetectable anatomic variability and pathology.
Endodontics includes the diagnosis of periapical pathosis due to pulpal inflammation, visualization of the complexity of the root canal system, elucidation of internal and external resorption, and detection of root fractures. The classic study by Seltzer and Bender3,4 demonstrated the limitations of intra-oral radiography for the detection of periapical lesions. For radiographic ch
anges to occur, the cortical bone must be involved. The problem of conspicuity, essentially the quality or state of being, remains the limiting factor of 2D imaging, digital or otherwise.
The Toronto Treatment Outcome studies 5-7 have demonstrated categorically that the success rate of teeth with existing apical lesions is less than those without. Lofthag-Hansen et. al. 8 demonstrated that CBCT enabled the detection of 38% more periapical lesions than conventional radiographs in posterior maxillary and mandibular teeth. This was most apparent in the maxillary and mandibular second molar regions. Similar findings have been reported by Low et. al. 9 This is paramount in determining the thickness of the cortical plate, the cancellous bone pattern, fenestrations as well as root inclination prior to root end surgery.
The increased sensitivity and specificity of CBCT is indeed the “gold standard” for detection of periapical pathosis and by extension, the diagnosis of poorly localized odontogenic pain. The Patel study10 found CBCT to have 100% sensitivity in the detection of artificially created periapical lesions in dry human mandibles. Whether it be in regard to raising the level of diagnosis and management of dento-alveolar trauma, assessment of teeth with unusual anatomy, numbers of roots, dens in dente or dilacerations, the corner has been turned.
Since the service mix in endodontics has grown to include implant replacement of hopelessly compromised teeth, CBCT has become the cornerstone of enhanced treatment outcomes. Real guided implant surgery relates to a new generation of surgical template and offers a precise transfer of the planned implant position into the surgical field. Therefore, pre-operative planning and production of surgical templates are either model based (for single-tooth and small partial cases) or computer generated (long-span partial and edentulous cases). Guided implant surgery is the current level in quality assurance as the surgeon is able to select the optimal locations for implant placement, taking into account specific anatomic characteristics of the patient and using the optimal bone densities. 11-13
CONCLUSION
Cone beam computed tomography is an expansive new paradigm in dental diagnosis and treatment planning. From the diagnosis of anatomic structural perplexities to pre-surgical planning, treatment is enhanced as the maxillo-facial complex is rendered in three dimensions and in real time. Including the patient immediately in the case analysis and treatment planning is an extension of the new generation of online health where the focus is on the integration of more technology into traditional healthcare settings. It is an ideal supplement to conventional two-dimensional radiographic techniques for diagnostic determination, and with software enhancement, it will supersede their value over time. The downside risks of dose level have already diminished with new technologies and advances.
It is time for the Ontario Government to evaluate the enhanced level of care that could be delivered by allowing den- tists in this province to offer in-house CBCT imaging to their patients.
OH
Dr. David Gane is a graduate of the University of Western Ontario with an honors degree in physiology and pharmacology and a doctorate degree in dental surgery. Dr. Gane has authored many publications and technique videos on digital radiography and has lectured internationally on digital imaging topics. Dr. Gane currently serves as Vice President of Dental Imaging for PracticeWorks Inc., the exclusive maker of Kodak Dental Systems and is founder of Orbit Imaging Inc. a company that owns and operates Craniofacial imaging centers in Canada and the United States.
Dr. Ken Serota is the founder of ROOTS — an online educational forum for dentists from around the world who wish to learn cutting edge endodontic therapy. He recently launched IMPLANTS ( www.rximplants.com)and www.tdsonline.orgin order to provide a clear understanding of the endodontic/implant algorithm in foundational dentistry. As well, he lectures on the empowerment digital technologies provide to the sophistication of the dental team and the propagation of comprehensive care.
Frederick Barnett is Chairman and Program Director, The I. B. Bender Division of Postdoctoral Endodontics, Albert Einstein Medical Center; associate editor, Journal of Endodontics and maintains a private practice limited to endodontics
Oral Health welcomes this original article.
REFERENCES
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2. Ludlow JB, Davies-Ludlow LE, Brooks SL. Dentomaxillofacial Radiology. 2003; 32;229-234.
3. Bender B, Seltzer S. Roentgenographic and direct observation of experimental lesions in bone I. J Am Dent Assoc 1961;62:152-60.
4. Bender B, Seltzer S. Roentgenographic and direct observation of experimental lesions in bone II. J Am Dent Assoc 1961;62:708-16.
5. de Chevigny C, Dao TT, Basrani BR, Marquis V, Farzaneh M, Abitbol S, Friedman S. Treatment outcome in endodontics: the Toronto study — phase 4: initial treatment. J Endod. 2008 Mar;34(3): 258-63.
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8. Lofthag-Hansen S, Huumonen S, Gndahl K, Grndahl HG. Limited cone-beam CT and intraoral radiography for the diagnosis of periapical pathology. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2007 Jan;103(1):114-9.
9. Low KM, Dula K, Brgin W, von Arx T. and Estrela et al. Comparison of periapical radiography and limited cone-beam tomography in posterior maxillary teeth referred for apical surgery J Endod. 2008 May;34(5):557-62.
10. Patel S, Dawood A, Mannocci F, Wilson R, Pitt Ford T. Detection of periapical bone defects in human jaws using cone beam computed tomography and intraoral radiography. Int Endod J. 2009 Feb 28.
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13. Balshi SF, Wolfinger GJ, Balshi TJ. Surgical planning and prosthesis construction using computer technology and medical imaging for immediate loading of implants in the pterygomaxillary region . Int J Periodontics Restorative Dent. 2006 Jun;26(3):239-47.
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CBCT has great potential to become a valuable tool in the modern endodontic practice
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CBCT showed 34% more lesions than PA radiography
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Artifice versus a natural state is not a panacea for successful treatment outcomes
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Diagnostic information directly influences clinical decisions. Accurate data lead to better treatment planning decisions and potentially more predictable outcomes
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We treat 3D patients with 3D patholgy. We apply 3D forces and provide 3D restorations and prostheses. Why shoudln’t we use 3D technolgy for diagnosis and treatment planning?
