American Journal of Orthodontics & Dentofacial Orthopedics
Volume 141, Issue 4 , Page 402, April 2012

Cone-beam computed tomography is the imaging technique of choice for comprehensive orthodontic assessment

  • Brent E. Larson

      Affiliations

    • Corresponding Author InformationReprint requests to: Brent E. Larson, Division of Orthodontics, University of Minnesota, 6-320 Moos Tower, 515 Delaware St SE, Minneapolis, MN 55455.

Associate professor and director, Division of Orthodontics, University of Minnesota, Minneapolis, Minn

Article Outline

 

It is interesting to observe the adoption of new technology in dentistry and orthodontics. Of particular interest is the use of cone-beam computed tomography (CBCT) as the imaging protocol of choice for comprehensive orthodontic treatment. A concise review of the diffusion of innovation in dentistry was published by Parashos and Messer,1 who concluded that the adoption of technology is affected by factors that “include a complex interplay of perceived benefits and advantages, and psychosocial and behavioral factors, in decision-making.” Lateral and posteroanterior cephalograms were introduced to orthodontics in the early 1930s by Broadbent; yet, adoption of this technology, which is an accepted standard today, was still being resisted when Steiner2 wrote in 1953 about the use of cephalogram films: “It has been claimed by many that it is a tool of the research laboratory and that the difficulties and expense of its use in clinical practice are not justified. Many have argued that the information gained from cephalometric films, when used with present methods of assessment, do not contribute sufficient information to change, or influence, their plans of treatment.”

Steiner’s statement could easily be applied to the use of CBCT today. A recent review suggested that CBCT should be used as an adjunct imaging technique in orthodontics.3 I propose that, although we still have much to learn about how to best use CBCT imaging to improve the outcomes of orthodontic treatment, we know enough about its application to consider it the imaging of choice for comprehensive orthodontic treatment.

Back to Article Outline

Benefits of CBCT for orthodontic assessment 

The benefits of CBCT for orthodontic assessment include accuracy of image geometry. Clinicians have learned to deal with the inherent image magnification and distortion that is part of 2-dimensional radiography. With lateral cephalograms, structures on the left side are magnified less than the same structures on the right because of proximity to the film. With panoramic imaging, the amounts of horizontal and vertical magnification vary at different rates as objects are displaced from the focal trough. However, CBCT offers the distinct advantage of 1:1 geometry, which allows accurate measurements of objects and dimensions. The accuracy and reliability of measurements from CBCT images have been demonstrated, allowing precise assessment of unerupted tooth sizes, bony dimensions in all 3 planes of space, and even soft-tissue anthropometric measurements—things that are all important in orthodontic diagnosis and treatment planning.4, 5, 6 Additionally, to allow use of our historic growth and normative data, it has been shown that landmarks can be located reliably on cephalometric images that are generated from the CBCT volumes.7

Other benefits include the localization of ectopic teeth and the assessment of root resorption. The accurate localization of ectopic, impacted, and supernumerary teeth is vital to the development of a patient-specific treatment plan with the best chance of success. There seems to be little debate in the literature that CBCT is superior for localization compared with conventional imaging methods.8, 9 One study indicated that this improved localization and space estimation does result in changes in diagnosis and treatment recommendations.10 Another study analyzed the “failed” treatment of 37 impacted canines, successfully delivering the canine in about 70% of these cases because of careful diagnosis and 3-dimensional imaging. Initially, failure occurred because of mistaken localization and directional traction in 40.5% of the patients.11 There is also increasing evidence that assessment of root resorption, both from ectopically erupting teeth and as a side effect of orthodontic treatment, can best be done with CBCT, since much resorption occurs in a slanted direction that is not readily imaged without the use of a tomographic technique.12

Although we still have much to learn about how to best use CBCT imaging to improve the outcomes of orthodontic treatment, we know enough about its application to consider it the imaging of choice for comprehensive orthodontic treatment.

In orthodontics, an asymmetric malocclusion is one of the most difficult problems to diagnose and treat. Before CBCT, the skeletal and dental contributions to the problem were assessed from clinical examinations, study models, and perhaps a posteroanterior cephalogram. Although these provided meaningful insight for a diagnosis, the CBCT volume allows direct measurement of the transverse dimensions and the relative positions of the teeth within the skeletal components, and has been judged to be superior to previous methods.13 We recently conducted a study using CBCT to objectively assess asymmetry and found that this method is potentially useful for clinicians.14

Imaging of the temporomandibular joint has not been common practice for asymptomatic orthodontic patients. The view of the condyle and the fossa on a panoramic film has been used as a screening tool with subsequent specific imaging ordered for the temporomandibular joint if bony changes are noted. The CBCT volume used for orthodontic assessment will generally include the right and left temporomandibular joints, and therefore they are available for routine review. The orthodontist can screen for bony changes and get an indication of condylar position from this review.15, 16, 17 A recent review of nearly 200 consecutive orthodontic patients at the University of Minnesota showed that 18% had incidental temporomandibular joint findings noted by a radiologist that were significant enough for further follow-up or referral.18 A similar result for incidental temporomandibular joint findings was reported by researchers in North Carolina in an older, nonorthodontic population.19

Traditional 2-dimensional cephalometric imaging has been limited in its ability to assess airway dimensions, and our view of the sinuses has been limited to the tomographic slice on the panoramic image. With CBCT imaging, 3-dimensional views of the airway and the sinuses are clearly visible and measurable.20, 21 Although as a specialty we still struggle to understand the impact of the airway on the growth and development of our patients, we all understand that breathing has primary biologic importance and that significant postural adaptations to airway problems can cause undesirable growth changes. This is another item that was frequently noted by the radiologist in our study of incidental findings in orthodontic patients. Nearly half our patient population had sinus or airway findings noted, ranging from relatively minor sinusitis or polyps to complete opacification of the maxillary sinuses.18

The need to assess the periodontal bone levels before orthodontic treatment has always been important and has been emphasized with the American Board of Orthodontics’ requirement to include a formal periodontal evaluation for all patients over the age of 18 years or for those with signs of periodontal disease. Imaging suggestions for this evaluation include a panoramic image supplemented with bitewing and anterior periapical radiographs, or a full-mouth series of radiographs including periapicals and bitewings, or images taken from a CBCT volume.22 The first 2 are supplemental images that require additional exposure, whereas the images from the CBCT are reconstructed as needed from the acquired volume with no additional exposure required. Misch et al23 reported that CBCT imaging provides a significant advantage over conventional radiographs for periodontal assessment because it allows for the measurement of buccal and lingual defects as well as interproximal defects. Other investigators have also found that CBCT-derived images offer advantages for periodontal assessment.24, 25

A truly unexpected result from our study of CBCT incidental findings in orthodontic patients was the 10% frequency of significant endodontic findings: apical periodontitis, apical radiolucency, internal or external root resorption, or retained root tips.18 These are important items to assess before final orthodontic planning—items that could dramatically alter the treatment plan. I was convinced that this high degree of endodontic involvement was most likely a statistical anomaly since it did not correspond with my clinical experience; however, Price et al19 recently reported a similar prevalence of endodontic findings in a different population, lending additional support to the result.

Recent reports have suggested that certain regions are more desirable as placement sites for temporary skeletal anchorage devices.26, 27, 28 These recommen-dations are based on average cortical bone thickness and bone depth determined from CBCT images of skulls or patients. Although these general recommen-dations are helpful, they do not provide patient-specific information. When patients have CBCT imaging as part of their initial record set, areas that might be considered as placement sites for temporary skeletal anchorage devices can be individually assessed for bone quality without the cost or the inconvenience of additional imaging.

In addition to the items listed above, there are reports that suggest future benefits of CBCT imaging related to risk management. The bone density measured on CT imaging has been correlated with the risk of neurosensory disturbance after sagittal split mandibular advancement.29 Although 1 limitation of CBCT is that bone density in Hounsfield units is not as standardized as medical computed tomography, the use of fractal dimension analysis of CBCT images has recently been described as a promising tool for detecting bone changes caused by bisphosphonates.30

Recently, the fabrication of custom lingual orthodontic appliances has been demonstrated by using CBCT image data with existing technology to virtually plan a patient’s treatment and manufacture the custom appliances with 3-dimensional printing technology.31 Such advances appear to be rapid, and promise efficient and effective treatment that is specific for each patient. Orametrix (Richardson, Tex) has been using CBCT technology for the last several years to provide the data necessary for planning and executing technology-assisted treatment through its SureSmile system.

Back to Article Outline

Costs of CBCT for orthodontic assessment 

The general argument against using CBCT as a standard imaging protocol for comprehensive orthodontic treatment centers on the radiation burden to patients. Most current recommendations are that CBCT should be used as an adjunct imaging technique when conventional 2-dimensional imaging proves to be inadequate. Comparison of effective radiation dose levels is difficult because of the many CBCT machines now available and the fact that new scanning protocols for the machines are constantly being implemented based on software modifications. In addition, the International Commission on Radiological Protection released updated guidelines in 2007 that added salivary glands, oral mucosa, and airway tissues to the dose equation, and this raised effective dose calculations from 32% to 422%.32 Therefore, comparisons of various imaging protocols and machines should be done by using those guidelines and not the previous 1990 guidelines.

The question of primary importance is the radiation burden of a CBCT image relative to a conventional lateral cephalogram, a panoramic radiograph, and any supplemental films that are required. To answer this question specifically for our facilities at the University of Minnesota, we conducted dosimetry testing of our CBCT machine and our conventional 2-dimensional digital radiography equipment. We found that the CBCT imaging normally used for comprehensive orthodontic patients was about 65 μSv compared with about 26 μSv for a lateral cephalogram and a panoramic image taken on our digital machine.33 Subsequent to our testing, a new low-dose scan protocol has been added to the CBCT machine that provides the needed orthodontic diagnostic information for an estimated 35 to 40 μSv (based on our data adjusted for reduced milliampere-second exposure).

These rapid advances in CBCT technology have resulted in 3-dimensional images that have about 2% or less of annual background radiation, with only slightly more than conventional orthodontic imaging without any supplemental radiographs.33 If full-mouth intraoral radiographs are taken to assess the periodontal status of adults, CBCT imaging typically reduces the patient dose.

There is little published information regarding the financial cost of CBCT technology used for orthodontics. From my personal experience, the transition to CBCT imaging for orthodontic assessment did not add to the patient cost of treatment in our university clinic or our private practice. Obviously, an investment must be made in the equipment, and many practitioners have difficulty justifying the return on this investment, since efficiency and income are not directly affected. However, in my opinion, the confidence gained in treatment decisions and the greater ability for patients to visualize problems dramatically improves my practice.

Back to Article Outline

Conclusions 

The assessment of available information, as well as my clinical experience, has led me to believe that CBCT imaging for comprehensive orthodontic patients has substantial advantages. The ability to measure accurately, improve localization, identify and quantify asymmetry, visualize airway abnormalities, assess periodontal structures, identify endodontic problems, view condylar positions and temporomandibular joint bony structures, and plan placement sites for temporary skeletal anchorage devices adds to the practitioner’s knowledge base at the time of orthodontic diagnosis. Looking forward, CBCT might help us with risk assessment by assessing bone density, visualizing root proximity and resorption, and even providing the imaging data to support treatment simulation and technology-aided treatment.

All of these advantages are currently available with little increase in radiation dose relative to a modern digital panoramic and single cephalometric film. In fact, compared with the standard record set I used 15 years ago (lateral and posteroanterior cephalograms, panoramic film, and full-mouth set of radiographs with round collimation), the radiation burden of a single CBCT image represents more than an 80% reduction in dose—a remarkable technologic achievement!

According to the writings of Steiner2 in 1953, he challenged orthodontists with the following words: “The cephalometer is here to stay, and those of you who are not using cephalometrics in your everyday clinical practices must soon bow to its importance, accept the added burden it imposes, and master its mysteries if you are to discharge your full obligation to your patients.”

If you substitute CBCT for cephalometer and cephalometrics in Steiner’s comment, it would summarize my feelings on the adoption of this technology in orthodontics. With the understanding that each patient is assessed before imaging and that patient-specific imaging decisions are made, CBCT has replaced conventional lateral cephalograms and panoramic images as the most commonly ordered imaging for comprehensive orthodontic patients, in both our university clinic and my private practice. Although better scientific evidence of improved outcomes is desired, I truly believe its use results in better patient care.

Back to Article Outline

References 

  1. Parashos P, Messer HH. The diffusion of innovation in dentistry: a review using rotary nickel-titanium technology as an example. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2006;101:395–401
  2. Steiner C. Cephalometrics for you and me. Am J Orthod. 1953;39:729–755
  3. Kapila S, Conley RS, Harrell WE. The current status of cone beam computed tomography imaging in orthodontics. Dentomaxillofac Radiol. 2011;40:24–34
  4. Berco M, Rigali PH, Miner RM, DeLuca S, Anderson NK, Will LA. Accuracy and reliability of linear cephalometric measurements from cone-beam computed tomography scans of a dry human skull. Am J Orthod Dentofacial Orthop. 2009;136:17.e1–17.e9discussion, 17-8
  5. Fourie Z, Damstra J, Gerrits PO, Ren Y. Accuracy and repeatability of anthropometric facial measurements using cone beam computed tomography. Cleft Palate Craniofac J. 2011;48:623–630
  6. Lagravere MO, Carey J, Toogood RW, Major PW. Three-dimensional accuracy of measurements made with software on cone-beam computed tomography images. Am J Orthod Dentofacial Orthop. 2008;134:112–116
  7. Chang ZC, Hu FC, Lai E, Yao CC, Chen MH, Chen YJ. Landmark identification errors on cone-beam computed tomography-derived cephalograms and conventional digital cephalograms. Am J Orthod Dentofacial Orthop. 2011;140:e289–e297
  8. Becker A, Chaushu S, Casap-Caspi N. Cone-beam computed tomography and the orthosurgical management of impacted teeth. J Am Dent Assoc. 2010;141(Suppl 3):14-8S
  9. Alqerban A, Jacobs R, Fieuws S, Willems G. Comparison of two cone beam computed tomographic systems versus panoramic imaging for localization of impacted maxillary canines and detection of root resorption. Eur J Orthod. 2011;33:93–102
  10. Botticelli S, Verna C, Cattaneo PM, Heidmann J, Melsen B. Two- versus three-dimensional imaging in subjects with unerupted maxillary canines. Eur J Orthod. 2011;33:344–349
  11. Becker A, Chaushu G, Chaushu S. Analysis of failure in the treatment of impacted maxillary canines. Am J Orthod Dentofacial Orthop. 2010;137:743–754
  12. Alqerban A, Jacobs R, Fieuws S, Nackaerts O SEDENTEXCT Project Consortium, Willems G. Comparison of 6 cone-beam computed tomography systems for image quality and detection of simulated canine impaction-induced external root resorption in maxillary lateral incisors. Am J Orthod Dentofacial Orthop. 2011;140:e129–e139
  13. Damstra J, Fourie Z, Ren Y. Evaluation and comparison of postero-anterior cephalograms and cone-beam computed tomography images for the detection of mandibular asymmetry. Eur J Orthod. 2011 Mar 31;[Epub ahead of print]
  14. Sievers MM, Larson BE, Gaillard PR, Wey A. Asymmetry assessment using cone-beam CT A Class I and Class II patient comparison. Angle Orthod. 2011 Oct 6;[Epub ahead of print]
  15. Alkhader M, Kuribayashi A, Ohbayashi N, Nakamura S, Kurabayashi T. Usefulness of cone beam computed tomography in temporomandibular joints with soft tissue pathology. Dentomaxillofac Radiol. 2010;39:343–348
  16. Cevidanes LH, Hajati AK, Paniagua B, Lim PF, Walker DG, Palconet G, et al. Quantification of condylar resorption in temporomandibular joint osteoarthritis. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2010;110:110–117
  17. Chandrasekhara D, Tahir F, Kaliaperumal G, Balasubramanian S. A protocol for evaluating condylar position in symptomatic TMD patients. J Clin Orthod. 2011;45:560–565
  18. Pliska B, DeRocher M, Larson BE. Incidence of significant findings on CBCT scans of an orthodontic patient population. Northwest Dent. 2011;90:12–16
  19. Price JB, Thaw KL, Tyndall DA, Ludlow JB, Padilla RJ. Incidental findings from cone beam computed tomography of the maxillofacial region: a descriptive retrospective study. Clin Oral Implants Res. 2011 Sep 30;[Epub ahead of print]
  20. Ritter L, Lutz J, Neugebauer J, Scheer M, Dreiseidler T, Zinser MJ, et al. Prevalence of pathologic findings in the maxillary sinus in cone-beam computerized tomography. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2011;111:634–640
  21. Pazera P, Bornstein MM, Pazera A, Sendi P, Katsaros C. Incidental maxillary sinus findings in orthodontic patients: a radiographic analysis using cone-beam computed tomography (CBCT). Orthod Craniofac Res. 2011;14:17–24
  22. Case preparation. American Board of Orthodontics. Available at: http://www.americanboardortho.com/professionals/clinicalexam/casereportpresentation/preparation/radiographs.aspx. Accessed on December 26, 2011.
  23. Misch KA, Yi ES, Sarment DP. Accuracy of cone beam computed tomography for periodontal defect measurements. J Periodontol. 2006;77:1261–1266
  24. Mol A, Balasundaram A. In vitro cone beam computed tomography imaging of periodontal bone. Dentomaxillofac Radiol. 2008;37:319–324
  25. Vandenberghe B, Jacobs R, Yang J. Detection of periodontal bone loss using digital intraoral and cone beam computed tomography images: an in vitro assessment of bony and/or infrabony defects. Dentomaxillofac Radiol. 2008;37:252–260
  26. Baumgaertel S. Cortical bone thickness and bone depth of the posterior palatal alveolar process for mini-implant insertion in adults. Am J Orthod Dentofacial Orthop. 2011;140:806–811
  27. Ludwig B, Glasl B, Bowman SJ, Wilmes B, Kinzinger GS, Lisson JA. Anatomical guidelines for miniscrew insertion: palatal sites. J Clin Orthod. 2011;45:433–441
  28. Ludwig B, Glasl B, Kinzinger GS, Lietz T, Lisson JA. Anatomical guidelines for miniscrew insertion: vestibular interradicular sites. J Clin Orthod. 2011;45:165–173
  29. Yoshioka I, Tanaka T, Khanal A, Habu M, Kito S, Kodama M, et al. Correlation of mandibular bone quality with neurosensory disturbance after sagittal split ramus osteotomy. Br J Oral Maxillofac Surg. 2011;49:552–556
  30. Torres S, Chen C, Leroux B, Lee P, Hollender L, Schubert M. Fractal dimension evaluation of cone beam computed tomography in patients with bisphosphonate-associated osteonecrosis. Dentomaxillofac Radiol. 2011;40:501–505
  31. Ye N, Li J, Zhang K, Yang Y, Lai W. Computer-aided design of a lingual orthodontic appliance using cone-beam computed tomography. J Clin Orthod. 2011;45:553–559
  32. Ludlow JB, Davies-Ludlow LE, White SC. Patient risk related to common dental radiographic examinations: the impact of 2007 International Commission on Radiological Protection recommendations regarding dose calculation. J Am Dent Assoc. 2008;139:1237–1243
  33. Grünheid T, Kolbeck Schieck JR, Pliska BT, Ahmad M, Larson BE. Dosimetry of a cone-beam computed tomography machine compared with a digital x-ray machine in orthodontic imaging. Am J Orthod Dentofacial Orthop. 2012;141:436–443

PII: S0889-5406(12)00143-6

doi:10.1016/j.ajodo.2012.02.009

American Journal of Orthodontics & Dentofacial Orthopedics
Volume 141, Issue 4 , Page 402, April 2012
Access this article on ScienceDirect

Article Tools