Cone-beam computed tomography is theimaging technique of choice for comprehensiveorthodontic assessment

Brent E. LarsonMinneapolis, Minn

It is interesting to observe the adoption of newtechnology in dentistry and orthodontics. Of par-ticular interest is the use of cone-beam computed

tomography (CBCT) as the imaging protocol of choicefor comprehensive orthodontic treatment. A concisereview of the diffusion of innovation in dentistrywas published by Parashos and Messer,1 who con-cluded that the adoption of technology is affectedby factors that “include a complex interplay of per-ceived benefits and advantages, and psychosocialand behavioral factors, in decision-making.” Lateraland posteroanterior cephalograms were introducedto orthodontics in the early 1930s by Broadbent;yet, adoption of this technology, which is an ac-cepted standard today, was still being resisted whenSteiner2 wrote in 1953 about the use of cephalogramfilms: “It has been claimed by many that it is a toolof the research laboratory and that the difficultiesand expense of its use in clinical practice are not jus-tified. Many have argued that the information gainedfrom cephalometric films, when used with presentmethods of assessment, do not contribute sufficientinformation to change, or influence, their plans oftreatment.”

Steiner’s statement could easily be applied to theuse of CBCT today. A recent review suggested thatCBCT should be used as an adjunct imaging techniquein orthodontics.3 I propose that, although we still havemuch to learn about how to best use CBCT imaging toimprove the outcomes of orthodontic treatment, weknow enough about its application to consider it theimaging of choice for comprehensive orthodontictreatment.

BENEFITS OF CBCT FOR ORTHODONTICASSESSMENT

The benefits of CBCT for orthodontic assessmentinclude accuracy of image geometry. Clinicians havelearned to deal with the inherent image magnificationand distortion that is part of 2-dimensional radiogra-phy. With lateral cephalograms, structures on the leftside are magnified less than the same structures onthe right because of proximity to the film. With pano-ramic imaging, the amounts of horizontal and verticalmagnification vary at different rates as objects are dis-placed from the focal trough. However, CBCT offers thedistinct advantage of 1:1 geometry, which allows accu-rate measurements of objects and dimensions. The ac-curacy and reliability of measurements from CBCTimages have been demonstrated, allowing precise as-sessment of unerupted tooth sizes, bony dimensionsin all 3 planes of space, and even soft-tissue anthropo-metric measurements—things that are all important inorthodontic diagnosis and treatment planning.4-6 Ad-ditionally, to allow use of our historic growth and nor-mative data, it has been shown that landmarks can belocated reliably on cephalometric images that are gen-erated from the CBCT volumes.7

Other benefits include the localization of ectopicteeth and the assessment of root resorption. Theaccurate localization of ectopic, impacted, and super-numerary teeth is vital to the development of a pa-tient-specific treatment plan with the best chance ofsuccess. There seems to be little debate in the literaturethat CBCT is superior for localization comparedwith conventional imaging methods.8,9 One study indi-cated that this improved localization and space estima-tion does result in changes in diagnosis and treatmentrecommendations.10 Another study analyzed the“failed” treatment of 37 impacted canines, successfullydelivering the canine in about 70% of these cases be-cause of careful diagnosis and 3-dimensional imaging.Initially, failure occurred because of mistaken localiza-tion and directional traction in 40.5% of the patients.11

There is also increasing evidence that assessment of

Associate professor and director, Division of Orthodontics, University ofMinnesota, Minneapolis.Reprint requests to: Brent E. Larson, Division of Orthodontics, Universityof Minnesota, 6-320 Moos Tower, 515 Delaware St SE, Minneapolis,MN 55455; e-mail, larso121@umn.edu.Am J Orthod Dentofacial Orthop 2012;141:402-110889-5406/$36.00Copyright Ó 2012 by the American Association of Orthodontists.doi:10.1016/j.ajodo.2012.02.009

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root resorption, both from ectopically erupting teethand as a side effect of orthodontic treatment, canbest be done with CBCT, since much resorption occursin a slanted direction that is not readily imaged withoutthe use of a tomographic technique.12

In orthodontics, an asymmetric malocclusion is oneof the most difficult problems to diagnose and treat.Before CBCT, the skeletal and dental contributions tothe problem were assessed from clinical examinations,study models, and perhaps a posteroanterior cephalo-gram. Although these provided meaningful insight fora diagnosis, the CBCT volume allows direct measure-ment of the transverse dimensions and the relative po-sitions of the teeth within the skeletal components, andhas been judged to be supe-rior to previous methods.13

We recently conducted a studyusing CBCT to objectively as-sess asymmetry and foundthat this method is potentiallyuseful for clinicians.14

Imaging of the temporo-mandibular joint has notbeen common practice forasymptomatic orthodonticpatients. The view of the con-dyle and the fossa on a pano-ramic film has been used as a screening tool withsubsequent specific imaging ordered for the temporo-mandibular joint if bony changes are noted. TheCBCT volume used for orthodontic assessment willgenerally include the right and left temporomandibularjoints, and therefore they are available for routine re-view. The orthodontist can screen for bony changesand get an indication of condylar position from this re-view.15-17 A recent review of nearly 200 consecutive or-thodontic patients at the University of Minnesotashowed that 18% had incidental temporomandibularjoint findings noted by a radiologist that were signifi-cant enough for further follow-up or referral.18 A sim-ilar result for incidental temporomandibular jointfindings was reported by researchers in North Carolinain an older, nonorthodontic population.19

Traditional 2-dimensional cephalometric imaginghas been limited in its ability to assess airway dimen-sions, and our view of the sinuses has been limited tothe tomographic slice on the panoramic image. WithCBCT imaging, 3-dimensional views of the airway andthe sinuses are clearly visible and measurable.20,21 Al-though as a specialty we still struggle to understandthe impact of the airway on the growth and develop-ment of our patients, we all understand that breathing

has primary biologic importance and that significantpostural adaptations to airway problems can cause un-desirable growth changes. This is another item that wasfrequently noted by the radiologist in our study of inci-dental findings in orthodontic patients. Nearly half ourpatient population had sinus or airway findings noted,ranging from relatively minor sinusitis or polyps tocomplete opacification of the maxillary sinuses.18

The need to assess the periodontal bone levels be-fore orthodontic treatment has always been importantand has been emphasized with the American Board ofOrthodontics’ requirement to include a formal peri-odontal evaluation for all patients over the age of 18years or for those with signs of periodontal disease.

Imaging suggestions for thisevaluation include a pano-ramic image supplementedwith bitewing and anteriorperiapical radiographs, ora full-mouth series of radio-graphs including periapicalsand bitewings, or imagestaken from a CBCT volume.22

The first 2 are supplementalimages that require additionalexposure, whereas the imagesfrom the CBCT are recon-

structed as needed from the acquired volume with noadditional exposure required. Misch et al23 reportedthat CBCT imaging provides a significant advantageover conventional radiographs for periodontal assess-ment because it allows for the measurement of buccaland lingual defects as well as interproximal defects.Other investigators have also found that CBCT-derived images offer advantages for periodontal assess-ment.24,25

A truly unexpected result from our study of CBCTincidental findings in orthodontic patients was the10% frequency of significant endodontic findings: api-cal periodontitis, apical radiolucency, internal or exter-nal root resorption, or retained root tips.18 These areimportant items to assess before final orthodonticplanning—items that could dramatically alter the treat-ment plan. I was convinced that this high degree ofendodontic involvement was most likely a statisticalanomaly since it did not correspond with my clinicalexperience; however, Price et al19 recently reporteda similar prevalence of endodontic findings in a differ-ent population, lending additional support to theresult.

Recent reports have suggested that certain regionsare more desirable as placement sites for temporary

Althoughwe still havemuch to learnabout how to best use CBCT

imaging to improve the outcomes oforthodontic treatment, we knowenough about its application to

consider it the imaging of choice forcomprehensive orthodontic

treatment.

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skeletal anchorage devices.26-28 These recommen-dations are based on average cortical bone thicknessand bone depth determined from CBCT images ofskulls or patients. Although these general recommen-dations are helpful, they do not provide patient-specific information. When patients have CBCTimaging as part of their initial record set, areas thatmight be considered as placement sites for temporaryskeletal anchorage devices can be individually assessedfor bone quality without the cost or the inconvenienceof additional imaging.

In addition to the items listed above, there are re-ports that suggest future benefits of CBCT imagingrelated to risk management. The bone density mea-sured on CT imaging has been correlated with therisk of neurosensory disturbance after sagittal splitmandibular advancement.29 Although 1 limitation ofCBCT is that bone density in Hounsfield units is notas standardized as medical computed tomography,the use of fractal dimension analysis of CBCT imageshas recently been described as a promising tool fordetecting bone changes caused by bisphosphonates.30

Recently, the fabrication of custom lingual ortho-dontic appliances has been demonstrated by usingCBCT image data with existing technology to virtuallyplan a patient’s treatment andmanufacture the customappliances with 3-dimensional printing technology.31

Such advances appear to be rapid, and promise efficientand effective treatment that is specific for each patient.Orametrix (Richardson, Tex) has been using CBCT tech-nology for the last several years to provide the data nec-essary for planning and executing technology-assistedtreatment through its SureSmile system.

COSTS OF CBCT FOR ORTHODONTICASSESSMENT

The general argument against using CBCT as a stan-dard imaging protocol for comprehensive orthodontictreatment centers on the radiation burden to patients.Most current recommendations are that CBCT shouldbe used as an adjunct imaging technique when con-ventional 2-dimensional imaging proves to be inade-quate. Comparison of effective radiation dose levels isdifficult because of the many CBCT machines nowavailable and the fact that new scanning protocolsfor the machines are constantly being implementedbased on software modifications. In addition, the Inter-national Commission on Radiological Protection re-leased updated guidelines in 2007 that added salivaryglands, oral mucosa, and airway tissues to the doseequation, and this raised effective dose calculationsfrom 32% to 422%.32 Therefore, comparisons of

various imaging protocols and machines should bedone by using those guidelines and not the previous1990 guidelines.

The question of primary importance is the radiationburden of a CBCT image relative to a conventional lat-eral cephalogram, a panoramic radiograph, and anysupplemental films that are required. To answer thisquestion specifically for our facilities at the Universityof Minnesota, we conducted dosimetry testing of ourCBCT machine and our conventional 2-dimensionaldigital radiography equipment. We found that theCBCT imaging normally used for comprehensive ortho-dontic patients was about 65 mSv compared with about26 mSv for a lateral cephalogram and a panoramicimage taken on our digital machine.33 Subsequent toour testing, a new low-dose scan protocol has beenadded to the CBCT machine that provides the neededorthodontic diagnostic information for an estimated35 to 40 mSv (based on our data adjusted for reducedmilliampere-second exposure).

These rapid advances in CBCT technology have re-sulted in 3-dimensional images that have about 2%or less of annual background radiation, with onlyslightly more than conventional orthodontic imagingwithout any supplemental radiographs.33 If full-mouth intraoral radiographs are taken to assess theperiodontal status of adults, CBCT imaging typically re-duces the patient dose.

There is little published information regarding thefinancial cost of CBCT technology used for orthodon-tics. From my personal experience, the transition toCBCT imaging for orthodontic assessment did notadd to the patient cost of treatment in our universityclinic or our private practice. Obviously, an investmentmust be made in the equipment, and many practi-tioners have difficulty justifying the return on this in-vestment, since efficiency and income are not directlyaffected. However, in my opinion, the confidencegained in treatment decisions and the greater abilityfor patients to visualize problems dramatically im-proves my practice.

CONCLUSIONS

The assessment of available information, as well asmy clinical experience, has led me to believe that CBCTimaging for comprehensive orthodontic patients hassubstantial advantages. The ability to measure accu-rately, improve localization, identify and quantifyasymmetry, visualize airway abnormalities, assess peri-odontal structures, identify endodontic problems, viewcondylar positions and temporomandibular joint bonystructures, and plan placement sites for temporary

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skeletal anchorage devices adds to the practitioner’sknowledge base at the time of orthodontic diagnosis.Looking forward, CBCT might help us with risk assess-ment by assessing bone density, visualizing rootproximity and resorption, and even providing the imag-ing data to support treatment simulation andtechnology-aided treatment.

All of these advantages are currently available withlittle increase in radiation dose relative to a moderndigital panoramic and single cephalometric film. Infact, compared with the standard record set I used 15years ago (lateral and posteroanterior cephalograms,panoramic film, and full-mouth set of radiographswith round collimation), the radiation burden of a sin-gle CBCT image represents more than an 80% reduc-tion in dose—a remarkable technologic achievement!

According to the writings of Steiner2 in 1953, he chal-lenged orthodontists with the following words: “Thecephalometer is here to stay, and those of you who arenot using cephalometrics in your everyday clinical prac-tices must soon bow to its importance, accept the addedburden it imposes, and master its mysteries if you are todischarge your full obligation to your patients.”

If you substitute CBCT for cephalometer and ceph-alometrics in Steiner’s comment, it would summarizemy feelings on the adoption of this technology in or-thodontics. With the understanding that each patientis assessed before imaging and that patient-specific im-aging decisions are made, CBCT has replaced conven-tional lateral cephalograms and panoramic images asthe most commonly ordered imaging for comprehen-sive orthodontic patients, in both our university clinicand my private practice. Although better scientific evi-dence of improved outcomes is desired, I truly believeits use results in better patient care.

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