Cbct is the imaging technique of choice for comprehensive orthodontic assesment

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Cbct is the imaging technique of choice for comprehensive orthodontic assesment

  1. 1. POINT/COUNTERPOINTCone-beam computed tomography is theimaging technique of choice for comprehensiveorthodontic assessmentBrent E. LarsonMinneapolis, Minn I t is interesting to observe the adoption of new BENEFITS OF CBCT FOR ORTHODONTIC technology in dentistry and orthodontics. Of par- ASSESSMENT ticular interest is the use of cone-beam computed The benefits of CBCT for orthodontic assessment tomography (CBCT) as the imaging protocol of choice include accuracy of image geometry. Clinicians have for comprehensive orthodontic treatment. A concise learned to deal with the inherent image magnification review of the diffusion of innovation in dentistry and distortion that is part of 2-dimensional radiogra- was published by Parashos and Messer,1 who con- phy. With lateral cephalograms, structures on the left cluded that the adoption of technology is affected side are magnified less than the same structures on by factors that “include a complex interplay of per- the right because of proximity to the film. With pano- ceived benefits and advantages, and psychosocial ramic imaging, the amounts of horizontal and vertical and behavioral factors, in decision-making.” Lateral magnification vary at different rates as objects are dis- and posteroanterior cephalograms were introduced placed from the focal trough. However, CBCT offers the to orthodontics in the early 1930s by Broadbent; distinct advantage of 1:1 geometry, which allows accu- yet, adoption of this technology, which is an ac- rate measurements of objects and dimensions. The ac- cepted standard today, was still being resisted when curacy and reliability of measurements from CBCT Steiner2 wrote in 1953 about the use of cephalogram images have been demonstrated, allowing precise as- films: “It has been claimed by many that it is a tool sessment of unerupted tooth sizes, bony dimensions of the research laboratory and that the difficulties in all 3 planes of space, and even soft-tissue anthropo- and expense of its use in clinical practice are not jus- metric measurements—things that are all important in tified. Many have argued that the information gained orthodontic diagnosis and treatment planning.4-6 Ad- from cephalometric films, when used with present ditionally, to allow use of our historic growth and nor- methods of assessment, do not contribute sufficient mative data, it has been shown that landmarks can be information to change, or influence, their plans of located reliably on cephalometric images that are gen- treatment.” erated from the CBCT volumes.7 Steiner’s statement could easily be applied to the Other benefits include the localization of ectopic use of CBCT today. A recent review suggested that teeth and the assessment of root resorption. The CBCT should be used as an adjunct imaging technique accurate localization of ectopic, impacted, and super- in orthodontics.3 I propose that, although we still have numerary teeth is vital to the development of a pa- much to learn about how to best use CBCT imaging to tient-specific treatment plan with the best chance of improve the outcomes of orthodontic treatment, we success. There seems to be little debate in the literature know enough about its application to consider it the that CBCT is superior for localization compared imaging of choice for comprehensive orthodontic with conventional imaging methods.8,9 One study indi- treatment. cated that this improved localization and space estima- tion does result in changes in diagnosis and treatment recommendations.10 Another study analyzed the Associate professor and director, Division of Orthodontics, University of Minnesota, Minneapolis. “failed” treatment of 37 impacted canines, successfully Reprint requests to: Brent E. Larson, Division of Orthodontics, University delivering the canine in about 70% of these cases be- of Minnesota, 6-320 Moos Tower, 515 Delaware St SE, Minneapolis, cause of careful diagnosis and 3-dimensional imaging. MN 55455; e-mail, larso121@umn.edu. Am J Orthod Dentofacial Orthop 2012;141:402-11 Initially, failure occurred because of mistaken localiza- 0889-5406/$36.00 tion and directional traction in 40.5% of the patients. 11 Copyright Ó 2012 by the American Association of Orthodontists. There is also increasing evidence that assessment of doi:10.1016/j.ajodo.2012.02.009402
  2. 2. 404 Point root resorption, both from ectopically erupting teeth has primary biologic importance and that significant and as a side effect of orthodontic treatment, can postural adaptations to airway problems can cause un- best be done with CBCT, since much resorption occurs desirable growth changes. This is another item that was in a slanted direction that is not readily imaged without frequently noted by the radiologist in our study of inci- the use of a tomographic technique.12 dental findings in orthodontic patients. Nearly half our In orthodontics, an asymmetric malocclusion is one patient population had sinus or airway findings noted, of the most difficult problems to diagnose and treat. ranging from relatively minor sinusitis or polyps to Before CBCT, the skeletal and dental contributions to complete opacification of the maxillary sinuses. 18 the problem were assessed from clinical examinations, The need to assess the periodontal bone levels be- study models, and perhaps a posteroanterior cephalo- fore orthodontic treatment has always been important gram. Although these provided meaningful insight for and has been emphasized with the American Board of a diagnosis, the CBCT volume allows direct measure- Orthodontics’ requirement to include a formal peri- ment of the transverse dimensions and the relative po- odontal evaluation for all patients over the age of 18 sitions of the teeth within the skeletal components, and years or for those with signs of periodontal disease. has been judged to be supe- Imaging suggestions for this rior to previous methods.13 evaluation include a pano- We recently conducted a study Although we still have much to learn ramic image supplemented using CBCT to objectively as- about how to best use CBCT with bitewing and anterior sess asymmetry and found imaging to improve the outcomes of periapical radiographs, or that this method is potentially a full-mouth series of radio- orthodontic treatment, we know useful for clinicians.14 graphs including periapicals Imaging of the temporo- enough about its application to and bitewings, or images mandibular joint has not consider it the imaging of choice for taken from a CBCT volume.22 been common practice for comprehensive orthodontic The first 2 are supplemental asymptomatic orthodontic treatment. images that require additional patients. The view of the con- exposure, whereas the images dyle and the fossa on a pano- from the CBCT are recon- ramic film has been used as a screening tool with structed as needed from the acquired volume with no subsequent specific imaging ordered for the temporo- additional exposure required. Misch et al23 reported mandibular joint if bony changes are noted. The that CBCT imaging provides a significant advantage CBCT volume used for orthodontic assessment will over conventional radiographs for periodontal assess- generally include the right and left temporomandibular ment because it allows for the measurement of buccal joints, and therefore they are available for routine re- and lingual defects as well as interproximal defects. view. The orthodontist can screen for bony changes Other investigators have also found that CBCT- and get an indication of condylar position from this re- derived images offer advantages for periodontal assess- view.15-17 A recent review of nearly 200 consecutive or- ment.24,25 thodontic patients at the University of Minnesota A truly unexpected result from our study of CBCT showed that 18% had incidental temporomandibular incidental findings in orthodontic patients was the joint findings noted by a radiologist that were signifi- 10% frequency of significant endodontic findings: api- cant enough for further follow-up or referral.18 A sim- cal periodontitis, apical radiolucency, internal or exter- ilar result for incidental temporomandibular joint nal root resorption, or retained root tips.18 These are findings was reported by researchers in North Carolina important items to assess before final orthodontic in an older, nonorthodontic population.19 planning—items that could dramatically alter the treat- Traditional 2-dimensional cephalometric imaging ment plan. I was convinced that this high degree of has been limited in its ability to assess airway dimen- endodontic involvement was most likely a statistical sions, and our view of the sinuses has been limited to anomaly since it did not correspond with my clinical the tomographic slice on the panoramic image. With experience; however, Price et al19 recently reported CBCT imaging, 3-dimensional views of the airway and a similar prevalence of endodontic findings in a differ- the sinuses are clearly visible and measurable. 20,21 Al- ent population, lending additional support to the though as a specialty we still struggle to understand result. the impact of the airway on the growth and develop- Recent reports have suggested that certain regions ment of our patients, we all understand that breathing are more desirable as placement sites for temporaryApril 2012 Vol 141 Issue 4 American Journal of Orthodontics and Dentofacial Orthopedics
  3. 3. 406 Point skeletal anchorage devices.26-28 These recommen- various imaging protocols and machines should be dations are based on average cortical bone thickness done by using those guidelines and not the previous and bone depth determined from CBCT images of 1990 guidelines. skulls or patients. Although these general recommen- The question of primary importance is the radiation dations are helpful, they do not provide patient- burden of a CBCT image relative to a conventional lat- specific information. When patients have CBCT eral cephalogram, a panoramic radiograph, and any imaging as part of their initial record set, areas that supplemental films that are required. To answer this might be considered as placement sites for temporary question specifically for our facilities at the University skeletal anchorage devices can be individually assessed of Minnesota, we conducted dosimetry testing of our for bone quality without the cost or the inconvenience CBCT machine and our conventional 2-dimensional of additional imaging. digital radiography equipment. We found that the In addition to the items listed above, there are re- CBCT imaging normally used for comprehensive ortho- ports that suggest future benefits of CBCT imaging dontic patients was about 65 mSv compared with about related to risk management. The bone density mea- 26 mSv for a lateral cephalogram and a panoramic sured on CT imaging has been correlated with the image taken on our digital machine.33 Subsequent to risk of neurosensory disturbance after sagittal split our testing, a new low-dose scan protocol has been mandibular advancement.29 Although 1 limitation of added to the CBCT machine that provides the needed CBCT is that bone density in Hounsfield units is not orthodontic diagnostic information for an estimated as standardized as medical computed tomography, 35 to 40 mSv (based on our data adjusted for reduced the use of fractal dimension analysis of CBCT images milliampere-second exposure). has recently been described as a promising tool for These rapid advances in CBCT technology have re- detecting bone changes caused by bisphosphonates.30 sulted in 3-dimensional images that have about 2% Recently, the fabrication of custom lingual ortho- or less of annual background radiation, with only dontic appliances has been demonstrated by using slightly more than conventional orthodontic imaging CBCT image data with existing technology to virtually without any supplemental radiographs. 33 If full- plan a patient’s treatment and manufacture the custom mouth intraoral radiographs are taken to assess the appliances with 3-dimensional printing technology.31 periodontal status of adults, CBCT imaging typically re- Such advances appear to be rapid, and promise efficient duces the patient dose. and effective treatment that is specific for each patient. There is little published information regarding the Orametrix (Richardson, Tex) has been using CBCT tech- financial cost of CBCT technology used for orthodon- nology for the last several years to provide the data nec- tics. From my personal experience, the transition to essary for planning and executing technology-assisted CBCT imaging for orthodontic assessment did not treatment through its SureSmile system. add to the patient cost of treatment in our university clinic or our private practice. Obviously, an investment COSTS OF CBCT FOR ORTHODONTIC must be made in the equipment, and many practi- ASSESSMENT tioners have difficulty justifying the return on this in- The general argument against using CBCT as a stan- vestment, since efficiency and income are not directly dard imaging protocol for comprehensive orthodontic affected. However, in my opinion, the confidence treatment centers on the radiation burden to patients. gained in treatment decisions and the greater ability Most current recommendations are that CBCT should for patients to visualize problems dramatically im- be used as an adjunct imaging technique when con- proves my practice. ventional 2-dimensional imaging proves to be inade- quate. Comparison of effective radiation dose levels is CONCLUSIONS difficult because of the many CBCT machines now The assessment of available information, as well as available and the fact that new scanning protocols my clinical experience, has led me to believe that CBCT for the machines are constantly being implemented imaging for comprehensive orthodontic patients has based on software modifications. In addition, the Inter- substantial advantages. The ability to measure accu- national Commission on Radiological Protection re- rately, improve localization, identify and quantify leased updated guidelines in 2007 that added salivary asymmetry, visualize airway abnormalities, assess peri- glands, oral mucosa, and airway tissues to the dose odontal structures, identify endodontic problems, view equation, and this raised effective dose calculations condylar positions and temporomandibular joint bony from 32% to 422%.32 Therefore, comparisons of structures, and plan placement sites for temporaryApril 2012 Vol 141 Issue 4 American Journal of Orthodontics and Dentofacial Orthopedics
  4. 4. 408 Point skeletal anchorage devices adds to the practitioner’s 6. Lagravere MO, Carey J, Toogood RW, Major PW. Three-dimen- knowledge base at the time of orthodontic diagnosis. sional accuracy of measurements made with software on cone- beam computed tomography images. Am J Orthod Dentofacial Looking forward, CBCT might help us with risk assess- Orthop 2008;134:112-6. ment by assessing bone density, visualizing root 7. Chang ZC, Hu FC, Lai E, Yao CC, Chen MH, Chen YJ. Landmark proximity and resorption, and even providing the imag- identification errors on cone-beam computed tomography- ing data to support treatment simulation and derived cephalograms and conventional digital cephalograms. technology-aided treatment. Am J Orthod Dentofacial Orthop 2011;140:e289-97. 8. Becker A, Chaushu S, Casap-Caspi N. Cone-beam computed to- All of these advantages are currently available with mography and the orthosurgical management of impacted teeth. little increase in radiation dose relative to a modern J Am Dent Assoc 2010;141(Suppl 3):14-8S. digital panoramic and single cephalometric film. In 9. Alqerban A, Jacobs R, Fieuws S, Willems G. Comparison of two fact, compared with the standard record set I used 15 cone beam computed tomographic systems versus panoramic years ago (lateral and posteroanterior cephalograms, imaging for localization of impacted maxillary canines and de- tection of root resorption. Eur J Orthod 2011;33:93-102. panoramic film, and full-mouth set of radiographs 10. Botticelli S, Verna C, Cattaneo PM, Heidmann J, Melsen B. Two- with round collimation), the radiation burden of a sin- versus three-dimensional imaging in subjects with unerupted gle CBCT image represents more than an 80% reduc- maxillary canines. Eur J Orthod 2011;33:344-9. tion in dose—a remarkable technologic achievement! 11. Becker A, Chaushu G, Chaushu S. Analysis of failure in the treat- According to the writings of Steiner2 in 1953, he chal- ment of impacted maxillary canines. Am J Orthod Dentofacial Orthop 2010;137:743-54. lenged orthodontists with the following words: “The 12. Alqerban A, Jacobs R, Fieuws S, Nackaerts O, , SEDENTEXCT Pro- cephalometer is here to stay, and those of you who are ject Consortium, Willems G. Comparison of 6 cone-beam com- not using cephalometrics in your everyday clinical prac- puted tomography systems for image quality and detection of tices must soon bow to its importance, accept the added simulated canine impaction-induced external root resorption in burden it imposes, and master its mysteries if you are to maxillary lateral incisors. Am J Orthod Dentofacial Orthop 2011;140:e129-39. discharge your full obligation to your patients.” 13. Damstra J, Fourie Z, Ren Y. Evaluation and comparison of If you substitute CBCT for cephalometer and ceph- postero-anterior cephalograms and cone-beam computed to- alometrics in Steiner’s comment, it would summarize mography images for the detection of mandibular asymmetry. my feelings on the adoption of this technology in or- Eur J Orthod 2011 Mar 31 [Epub ahead of print]. thodontics. With the understanding that each patient 14. Sievers MM, Larson BE, Gaillard PR, Wey A. Asymmetry assess- ment using cone-beam CT A Class I and Class II patient compar- is assessed before imaging and that patient-specific im- ison. Angle Orthod 2011 Oct 6 [Epub ahead of print]. aging decisions are made, CBCT has replaced conven- 15. Alkhader M, Kuribayashi A, Ohbayashi N, Nakamura S, tional lateral cephalograms and panoramic images as Kurabayashi T. Usefulness of cone beam computed tomography the most commonly ordered imaging for comprehen- in temporomandibular joints with soft tissue pathology. 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