Cone-Beam Computed Tomography in Orthodontics

Dear Editor,

The article by Parveen et al. was read with interest and curiosity. ¹ The authors have mentioned in the “Principle of Justice” section of the article that exposing a patient to posttreatment cone-beam computed tomography (CBCT) for acceptance of paper in journals is not justified. It is not clear in the article on how the authors deduced that certain authors are exposing patients to posttreatment CBCT just for publication? Do the authors have any citation for this claim? In the “Research Ethics” section, the authors have mentioned that it is unethical to prescribe CBCT for prospective research to produce data for future research projects. It would be helpful to readers if the authors mention on how this unethical act can be curbed? The authors should mention why strict regulation should be made for accumulating routine CBCT imaging and later storing it as a retrospective database. Storing the data as retrospective database does not increase the collective effective dose for patients but instead eliminates the need for taking fresh CBCT scans (when it is indicated) for doing prospective research, and hence, unnecessary exposure to the patients for research purpose will greatly be minimized. The authors mention that CBCT studies should not be repeated. But it is not clear in the article on what regulations can be enacted to prevent this repetition.

In the “Principles of Autonomy” section, the authors have mentioned about stochastic effects of radiation associated with CBCT. Stochastic effects such as cancer can occur with even low exposures and with no evidence of a threshold dose. ² This implies that the risks associated with stochastic effects are not limited only to CBCT, but even can occur with radiation associated with intraoral periapical radiograph, cephalometric radiograph, or panoramic radiograph.

CBCT is particularly useful in cases of craniofacial syndromes, cleft palate, assessment of multiple impacted teeth and supernumerary teeth and for planning orthodontic surgery. ³ It is to be agreed that CBCT should not be recommended routinely by orthodontists in lieu of conventional radiographs, and utmost precaution should be exercised while prescribing it for children. The radiation dose of CBCT is approximately 3–6 times a panoramic radiograph and 15–26 times a conventional lateral depending upon the scan mode. ⁴ When compared with conventional dental radiography, the effective dose of CBCT is several to hundreds of times higher. ⁵ If conventional imaging techniques like panoramic or lateral cephalogram provide sufficient information for diagnosis and treatment planning, CBCT should not be prescribed by orthodontist. Whenever possible, the dentist should use low-dose CBCT machine. ² While performing the CBCT scan, patients should be adequately protected from radiation by using thyroid collars, lead aprons, and leaded glasses, provided they do not obstruct the area of interest or reduce the image quality and diagnostic information obtained. Using leaded glass can reduce the radiation dose to eye lens by 60% without having any adverse effect on the quality of the obtained image. ⁵ Prins et al. in their study observed 67% reduction in the radiation dose to the lens of the eye due to deployment of leaded glasses and recommended their use in both adult and pediatric patients during CBCT scans. Also in the study, leaded glasses did not appear to have deleterious effects on the image quality in the area of clinical significance for dental imaging. ⁶ Using one thyroid collar tightly on the front of the neck or two thyroid collars tightly on the front and back of the neck can significantly reduce the effective organ dose to the thyroid tissues. ⁵ Thyroid collars should particularly be used for children, whenever possible. Hidalgo et al. in their study concluded that thyroid shielding reduces effective dose to the thyroid gland in pediatric phantom model especially when large field of views (FOVs) are used and should be recommended in all child patients undergoing large FOV CBCT scans. The study also observed that the thyroid shield of 0.25 mm lead equivalent thickness that wraps around the neck offers best thyroid protection. ⁷ Also, according to principle of as-low-as-reasonably-achievable, the clinician should employ lowest FOV required to image the area of interest and use the lowest combination of tube output and scan time (in milliamperes) required to produce an adequate diagnostic image. ⁸ A study by Goren et al. concluded that leaded glasses, thyroid collars, and collimation minimize the CBCT radiation dose to organs outside the FOV. ⁹ It should be mentioned that CBCT should only be prescribed by a dentist who is well trained in CBCT imaging and has knowledge of the significance of CBCT selection and image findings. ⁸ The ethical committee of University/Institution should particularly not approve research associated with CBCT, where none of the researchers associated with the study have training/expertise in CBCT imaging and interpretation.