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The effect of the mode of reconstruction of the CBCT on the orthodontic diagnosis and treatment planning of impacted teeth Alebrahim, Sharifa


Introduction: Cone-beam computed tomography (CBCT) became commercially available 20 years ago and has been applied to almost every area of dental practice. This is due to its better spatial resolution, lower radiation dose, and smaller footprint than computed tomography (CT). However, the current CBCT unit still has much higher radiation dose than the standard conventional 2D dental imaging. Since there is no known safe lower radiation dose limit, radiation must be ‘as-low-as-reasonably-achievable’ (ALARA). Aims: To profile the orthodontic patient pool since the inception of the Orthodontics Graduate Program at UBC to determine the number and the reason for whom CBCTs were prescribed. To compare the orthodontic diagnostic efficiency of two different 3D reconstruction methods of the CBCT images. Methods: Ethics was approved for a retrospective review of orthodontic cases and for review by orthodontic instructors of randomized multiplanar reformatting (MPR) and curved CBCT image sets. 15 datasets of similar appearing impacted maxillary canines were reconstructed into MPR and curved screenshots. The instructors were asked to disclose their length of orthodontic service and prior experience reviewing CBCT datasets. They were asked to review the screenshots to determine factors that could affect treatment such as the position of the impacted canine, presence of root resorption and dilacerated roots. Results: The review revealed 35 prescribed CBCTs that were mostly taken to investigate impacted teeth (29 cases). Of the 15 orthodontists, although the 6 females had on average 16 years of experience to their 9 male colleagues (on average of 26 years), this was not significant (P = 0.142). Furthermore, they all have some experience at reviewing MPR reconstructions which was almost identical for either sex, around 6 years; 2 males and 2 females had considerably more experience. All appeared more comfortable with the MPR rather than the curved reconstructions. Conclusions: The number of prescribed CBCT images is low because the program policy follows the “Image Gently” guidelines and the ALARA principles. So far, orthodontists are more comfortable with the MPR rather than the more panoramic-like curved reconstruction. This simply may reflect the fact that the former is the default reconstruction for most CBCT units.

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