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Cbct is not the imaging technique of choice for comprehensive orthodontic assesment


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  • 1. POINT/COUNTERPOINT 403Cone-beam computed tomographyis not the imaging technique of choicefor comprehensive orthodontic assessmentDemetrios J. HalazonetisKifissia, Greece I t was a pleasure to see that Dr Larson did not take A similar conclusion was adopted by the Ameri- the extreme view of proposing cone-beam com- can Association of Orthodontists in 2010: “the puted tomography (CBCT) as a routine diagnostic AAO recognizes that while there may be clinical sit- modality—ie, for every patient, irrespective of maloc- uations where a cone-beam computed tomography clusion or other patient-specific factors—as some or- (CBCT) radiograph may be of value, the use of thodontic postgraduate programs in the United States such technology is not routinely required for ortho- seem to do.1 Even so, he does recommend CBCT as dontic radiography.”4 the standard procedure, stating in his conclusions If guidelines already exist, what is the purpose of that “CBCT has replaced conventional lateral cephalo- this debate? First, it is an opportunity to make these grams and panoramic images as the most commonly guidelines well known to the orthodontic community ordered imaging for comprehensive orthodontic pa- at a time when CBCT use is increasing. The SEDEN- tients.” In my Counterpoint, I will try to present argu- TEXCT guidelines are based on a systematic review of ments against CBCT as the imaging technique of choice the literature, thus representing current evidence- for comprehensive orthodontic assessment. based knowledge at a confidence level much higher Assuming that use for every patient is not advo- than this debate can achieve.2 Most importantly, how- cated, what are the patient selection criteria? The an- ever, is that these guidelines are not compulsory. The swer should stem from a comprehensive assessment use of ionizing radiation is governed by law in most of the benefits and burdens to each patient. This as- countries, but all the law requires is clinical justifica- sessment cannot be completely objective, but our deci- tion. The guidelines are designed to assist the clinician sion making should be based on current evidence, in the justification process.3 I hope that this debate will which could also serve as the basis to develop general convince clinicians to follow the guidelines’ recom- guidelines. Such guidelines already exist. The SEDEN- mendations. TEXCT project of the European Union had as its pri- mary goal “to acquire key information necessary for RADIATION BURDEN sound and scientifically based clinical use of CBCT” and “to use this information to develop evidence- The effects of ionizing radiation are considered sto- based guidelines dealing with justification, optimiza- chastic events. This signifies that the risk, not the sever- tion and referral criteria for users of dental CBCT.”2 ity, of the condition (eg, cancer) depends on the dose. The guidelines section dealing with orthodontic diag- Using a low-dosage vs a high-dosage CBCT machine nosis concludes that “large volume CBCT should not will not result in cancers that are easier to treat, only be used routinely for orthodontic diagnosis.” fewer of them. The probability of an important sto- The British Orthodontic Society guidelines give chastic effect (cancer and severe hereditary effect) is a similar recommendation: “routine use of CBCT even 7.3 3 10À2 Sv.5 For patients aged 10 to 20 years, for most cases of impaction of teeth . . . cannot yet this doubles to approximately 0.15 Sv. Since a large be recommended.”3 field-of-view CBCT will provide a dose of 68 to 368 mSv6 compared with approximately 30 mSv for the cephalometric and panoramic combination, this trans- Associate professor, School of Dentistry, University of Athens, Athens, Greece. Reprint requests to: Demetrios J. Halazonetis, 6 Menandrou St, Kifissia GR-145 lates to a risk of about 1 in 170,000 to 1 in 20,000 61, Greece; e-mail, above the current customary procedure.5 In the United Am J Orthod Dentofacial Orthop 2012;141:402-11 States, more than 1.6 million orthodontic patients start 0889-5406/$36.00 Copyright Ó 2012 by the American Association of Orthodontists. treatment every year.7 If each patient had 1 CBCT im- doi:10.1016/j.ajodo.2012.02.010 age, this would result in 10 to 80 additional cancerAmerican Journal of Orthodontics and Dentofacial Orthopedics April 2012 Vol 141 Issue 4
  • 2. Counterpoint 405 cases per year. Is this a risk worth taking? This is not anmeasurements. Due to the relatively large voxel size, easy question and depends mainly on the benefit to the thin structures are difficult to detect, and alveolar patient.8 What significant improvements in patient bone covering the incisors might be underestimated, outcomes does CBCT offer? To answer, we should although the results are conflicting.14,15 Errors in mea- not confuse the benefits to the patient with the techni- suring bone thickness can exceed 1.4 mm for a 0.4-mm cal capabilities of CBCT technology. The fact that CBCT voxel size.15 Fenestrations and dehiscences are overes- images are 3-dimensional is not directly relevant. Jus- timated to a large degree.15,16 tification for CBCT images can only be considered At present, there are no diagnostic accuracy studies when the treatment outcome will not only be better be- regarding the localization of impacted canines, and cause of them, but also significantly better to outweigh none are expected because this question is not seriously the above risks. debated.2,17 Regarding resorption of adjacent teeth, CBCT images show improved sensitivity and specificity over panoramic radiography.18 CBCT has been shown EFFICACY to have increased diagnostic accuracy over posteroante- The following terms are used to evaluate the effi- rior cephalograms in patients with skeletal asymmetry.19 9 cacy of diagnostic imaging procedures : technical effi- Concerning periodontal assessment, although it has cacy, diagnostic accuracy efficacy, diagnostic thinking a definite 3-dimensional advantage, CBCT comple- efficacy, therapeutic efficacy, ments but cannot replace in- patient outcome efficacy, and societal efficacy. These Assuming that use for every patient traoral radiography, resolu- because of reduced mainly efficacies constitute a hierar- is not advocated, what are the pa- tion.20 Studies on skull mate- chy of levels of increasing im- tient selection criteria? The answer rial have shown that CBCT portance. The top 2 levels should stem from a comprehensive images provide better diag- evaluate whether the imaging nostic information,21 but method produces a net bene- assessment of the benefits and there is no consensus regard- fit to the patient and society burdens to each patient. ing the accuracy of these in general, and should dictate measurements.20,22 The SED- our imaging policy. Regarding CBCT and its use in or- ENTEXCT guidelines conclude that “CBCT is not indi- thodontics, no such studies have been conducted. We cated as a routine method of imaging periodontal will consider the relevant evidence for each of the lower bone support,” although it might be indicated in se- 4 levels, focusing on large field-of-view protocols, lected patients, but preferably not with a large field of since only these can provide reconstructed lateral ceph- view.2 The American Board of Orthodontics includes alometric and panoramic views, similar to conventional CBCT images as an option to document periodontal sta- radiographs. tus but does not consider radiographic images, in gen- Technical efficacy is related to the quality of the im- eral, as compulsory data and gives priority to clinical age. The dimensional accuracy of CBCT images has been examination and conventional radiography.23 10 well established. Voxel size is typically 0.3 to 0.4 mm, Diagnostic thinking efficacy evaluates whether the corresponding to a lower resolution than that of conven- imaging method changes the diagnosis from the pre- tional intraoral radiographic imaging. Artefacts and noise test situation. Therapeutic efficacy assesses whether are higher than those observed in multi-slice computed the test produces changes to the treatment plan. These tomography, making it difficult, if not impossible, to efficacies have been evaluated for impacted third obtain consistent density values and resulting in low molars24 and impacted canines.25-27 CBCT images 10-12 contrast and poor depiction of soft tissues. Segmen- are perceived to be more useful than traditional radio- tation is problematic, and even high-contrast objects, graphs for such cases26 and might change the such as teeth, are measured with errors that can exceed recommended treatment plan in approximately 1 mm, limiting clinical usefulness.13 30% of them.25,27 However, no patient outcome effi- Diagnostic accuracy efficacy measures the accuracy cacy studies have been conducted, and CBCT is recom- of diagnosis by using CBCT in comparison with a refer- mended only when “the information cannot be ence standard—in our case, a cephalogram or pano- obtained adequately by lower dose conventional (tradi- ramic radiograph. Alveolar bone thickness and height, tional) radiography.”2 Dr Larson referred to the study of and the presence of fenestrations and dehiscences, Becker et al28 of 28 failed cases of impacted canines, have been compared between CBCT images and direct but the main reason for failure was inadequateAmerican Journal of Orthodontics and Dentofacial Orthopedics April 2012 Vol 141 Issue 4
  • 3. Counterpoint 407 anchorage rather than improper localization. The au- serves as an adjunctive tool and has been shown to thors acknowledged that the initial clinical and radio- be superfluous in some circumstances, affecting graphic signs were sometimes sufficient to diagnose treatment-planning decisions in some patients and to properly but were misinterpreted by the clinician. There a limited degree.34,35 are numerous cases when an impacted maxillary canine can be clearly localized based on conventional radio- INCIDENTAL FINDINGS graphs and clinical examination (eg, palpation, posi- tion, and inclination of adjacent teeth), and no Incidental findings are no justification for radio- further imaging is justified.3 graphic exposure. The European guidelines on radia- Regarding resorption of adjacent teeth, diagnostic tion protection state that “‘Routine’ radiography is thinking efficacy and therapeutic efficacy studies unacceptable practice” and define a ‘routine’ or showed that resorption defects can be identified better ‘screening’ examination as “one in which a radiograph with CBCT images, but these studies mostly used a me- is taken regardless of the presence or absence of clinical dium or small field of view.25,26,29 signs and symptoms.”5 If we put this recommendation Dr Larson also referred to the temporomandibular to the side for a moment, CBCT undoubtedly provides joint, but asymptomatic patients surely do not need many findings, although incidence varies.36,37 Price temporomandibular joint imaging. Condylar position et al37 reported that 90% of all CBCT images examined in the fossa can certainly be seen on CBCT images, had at least 1 finding, and 16.1% of the findings re- but this information should not affect our diagnosis quired further investigation. In contrast, incidental and treatment plan.30 The value of temporomandibular findings from conventional orthodontic radiographs joint imaging even for patients with temporomandibu- seem much lower, although no direct comparison has lar disorders is a debatable subject, and there is no ev- been made.38 By far, the most common pathologic idence to show that CBCT images will provide better findings seen in CBCT images that could require inter- treatment.31 vention were carotid artery calcification and periapical It seems, therefore, that CBCT might benefit some osteitis.37 These are not outside the detection capabil- patients with the conditions mentioned above, but no ities of the panoramic radiograph.39 Therefore, one evidence exists for the remaining majority of our should consider that a significant number of incidental patients. The application of 3-dimensional cephalo- findings in CBCT images (1) represent normal anatomic metrics, or increased measurement accuracy, could be variants or are benign and do not require further inter- an indication. However, currently, there are no estab- vention, (2) might already be known to the patient, (3) lished 3-dimensional cephalometric analyses and no can be detected on traditional radiographic images, or 3-dimensional normative data. CBCT images are (4) might be false-positive findings. In the absence of used to simulate old technology—ie, reconstruct any signs or symptoms, the taking of CBCT images 2-dimensional lateral cephalometric views. In this tran- just in case an occult pathologic finding appears is sitory, backward step, we should not carry with us the not justified. misconceptions of the early cephalometric era: strict adherence to cephalometric standards and blind faith COMPREHENSIVE EVALUATION in numbers. Dr Larson seems to base his recommendations on Cephalometric analyses have significant, well- the premise that a comprehensive imaging modality recognized deficiencies, and increased accuracy of will prove useful on any occasion, so, why not take measurements does not address them.32 There is, as it from the start? After all, a CBCT image includes yet, no evidence that increased accuracy from CBCT a cephalogram and a panoramic image for orthodon- contributes to a change of treatment plan or better tic assessment, and additional images for any poten- treatment. Even though such a notion might seem tial periodontal evaluation, temporomandibular joint self-evident, one should consider that our treatment evaluation, temporary anchorage device placement, modalities are not so fine tuned to specific craniofacial and airway analysis, plus the benefit of any incidental patterns that a conventional cephalometric radiograph findings. More extensive diagnostic knowledge is as- is inadequate to serve. Furthermore, identifying land- sumed to lead to better treatment. This proposition marks on CBCT images introduces significant errors is alluring but precarious and biased for several rea- that might mitigate the advantage of increased accu- sons. First, most of our patients are known not to racy.33 Lastly, most of our diagnostic information is have any of the problems listed, so extra radiation is gained from clinical evaluations. The cephalogram used just to rule out additional incidental findings,American Journal of Orthodontics and Dentofacial Orthopedics April 2012 Vol 141 Issue 4
  • 4. Counterpoint 409 over those that would be found with a cephalogram 2. SEDENTEXCT project. Radiation protection: cone beam CT for den- and a panoramic radiograph. Second, if more diag- tal and maxillofacial radiology. Evidence based guidelines 2011. Available at: nostic information is the goal, why stop at a CBCT? Accessed on January 20, 2012. Why, to take it to the extreme, not perform a full- 3. Isaacson K, Thom A, Horner K, Whaites E. Guidelines for the use body computed tomography scan instead? Have we of radiographs in clinical orthodontics. London, United King- determined that a CBCT is the optimum choice in dom: British Orthodontic Society; 2008. the risk-benefit balance? Third, in our quest for 4. American Association of Orthodontists. Statement on the role of CBCT in orthodontics (26-10 H). eBulletin; May 7, 2010. Avail- more information, why not perform other diagnostic able at: tests that might be more relevant and do not incur 05-06-10.cfm. Accessed on January 20, 2012. a radiation burden? Such tests could include evalua- 5. European Commission. Radiation Protection 136. European tion of thyroid and growth hormone levels, magnetic guidelines on radiation protection in dental radiology. Luxem- resonance imaging examination of the head (to assess bourg: Office for Official Publications of the European Commu- nities; 2004:Available at: temporomandibular joint disc position, measure the radioprotection/publication/doc/136_en.pdf:Accessed on Janu- sizes of the muscles of mastication, examine the pitu- ary 20, 2012. itary gland for adenomas, and evaluate the airway), 6. Pauwels R, Beinsberger J, Collaert B, Theodorakou C, Rogers J, nasal endoscopy or rhinomanometry, and bite-force Walker A, et al., The SEDENTEXCT Project Consortium. Effective measurement. Have we specifically selected large dose range for dental cone beam computed tomography scan- ners. Eur J Radiol 2012;81:267-71. field-of-view CBCT based on evidence that it will re- 7. American Association of Orthodontists. 2010 AAO member and sult in better patient outcome than these other tests, patient census study. Final report; June 23, 2011. or are we just using it because it is convenient? 8. Kokich VG. Cone-beam computed tomography: have we identi- Fourth, with each diagnostic test comes more knowl- fied the orthodontic benefits? Am J Orthod Dentofacial Orthop edge but also more false-positive findings that can 2010;137(4 Suppl):S16. 9. Fryback DG, Thornbury JR. The efficacy of diagnostic imaging. lead to increased patient anxiety, unnecessary Med Decis Making 1991;11:88-94. follow-ups, and further tests. Diagnostic evaluations 10. Ballrick JW, Palomo JM, Ruch E, Amberman BD, Hans MG. Image should be focused and designed to answer specific distortion and spatial resolution of a commercially available questions, not be a fishing expedition. cone-beam computed tomography machine. Am J Orthod Den- tofacial Orthop 2008;134:573-82. 11. Nackaerts O, Maes F, Yan H, Couto Souza P, Pauwels R, Jacobs R. CONCLUSIONS Analysis of intensity variability in multislice and cone beam com- As more research is conducted, and with continual puted tomography. Clin Oral Implants Res 2011;22:873-9. improvements in technology, CBCT might prove valu- 12. Schulze R, Heil U, Gross D, Bruellmann DD, Dranischnikow E, Schwanecke U, et al. Artefacts in CBCT: a review. Dentomaxillo- able for all of our patients in the future. However, at fac Radiol 2011;40:265-73. the present time, evidence for the efficacy of CBCT im- 13. Nguyen E, Boychuk D, Orellana M. Accuracy of cone-beam com- aging is lacking. Except for certain patients, replacing puted tomography in predicting the diameter of unerupted teeth. the conventional cephalometric and panoramic radio- Am J Orthod Dentofacial Orthop 2011;140:e59-66. graphs with a large field-of-view CBCT is simply over- 14. Timock A, Cook V, McDonald T, Leo MC, Crowe J, Benninger B, et al. Accuracy and reliability of buccal bone kill, potentially leading to a public health problem.40 It height and thickness measurements from cone-beam computed is the responsibility of the clinician to carefully select tomography imaging. Am J Orthod Dentofacial Orthop 2011; patients when CBCT imaging will provide a tangible 140:734-44. benefit and resist the lure of technology for technol- 15. Patcas R, M₠ ller L, Ullrich L, Peltom₠ki T. Accuracy of cone-beam u a ogy’s sake. computed tomography at different resolutions assessed on the bony covering of the mandibular anterior teeth. 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