Pacific Coast Society of Orthodontists Bulletin Fall 2016 - 23

PCSO Resident Research Review increasing etch times during the resin infiltration protocol, greater amounts of the lesion surface were removed; thus, with increasing etch time, lesions became shallower. When a lesion had reduced thickness, there was a greater tendency for it to be completely filled by the resin, a finding that paralleled improved color assessments. Overall, Kaitlyn's work showed that resin infiltration had the best outcome when used to treat shallow lesions, and to achieve ideal esthetics with deeper lesions, greater surface etching was required, as additional etching reduced the overall depth of the lesion. In general, with the application of multiple etch cycles during resin infiltration procedures, the resin infiltration method served more as a hybrid approach that combined outcomes of microabrasion and resin infiltration procedures. The clinical significance of her study is that resin infiltration provides a reliable method for camouflaging shallow WSLs, whereas with well-established, deeper lesions, a loss of tooth structure will be inevitable in order to restore them if ideal esthetic outcomes are desired. Evaluating Alveolar Bone with CBCT Alex Vo completed his dental doctorate at OHSU School of Dentistry and chose to follow up on a second line of research conducted over the past few years. This research involves assessments of alveolar bone using CBCT imaging. This work began with a cadaver study by Adam Timock (Class of 2012) in which heads were scanned with an i-CAT 17-19 (Imaging Sciences International, Hatfield, PA) using the unit's default scan setting of 0.3 mm voxel size, 8.9 seconds of scan time, and 360° of rotation. The periodontium was then dissected in order to compare alveolar bone height and thickness measurements made directly from the dissection versus those detected from the scans. This project, published in the AJO DO, showed that although measurements of alveolar bone height were more reliable than those of bone thickness, CBCT bone measurements from the cadavers were relatively accurate.2 Adam's study was conducted in parallel Fall 2016  PCSO Bulletin with that of Lane Cook (Class of 2013), who obtained CBCT scans at the same time as Adam's; he studied the effects of resolution variation on the accuracy of bone height and thickness measurements. CBCT scans with acquisition settings of 0.2 mm voxel size, 26.9 seconds of scan time, and 360° of rotation were compared to those made with 0.3 mm voxel size, 4.8 seconds of scan time, and 180° of rotation. Lane's findings, published in Orthodontics and Craniofacial Research, showed that the accuracy of the measurements was reliable between the settings tested based on repeat measurements and averaging of the results.3 Less precision and lower repeatability were was found with lower resolution scans, but the mean measurements were relatively consistent among scans made using the different settings. Therefore, findings from the cadaver studies revealed that CBCT images were exceedingly accurate and that there is increased precision of alveolar bone measurements with higher resolution CBCT settings. A question that begged to be answered relative to the cadaver studies was how well the results translated to CBCT imaging of live patients. This question was addressed by the study of Vanessa Browne (Class of 2014), who compared alveolar bone height measurements made using patients scheduled for periodontal surgery, such as an osteotomy procedure or placement of dental implants. As a part of the surgical protocol, CBCT imaging was obtained utilizing the same CBCT unit and settings from Adam Timock's cadaver study. Alveolar bone height was also measured at the time of surgery, using a method that paralleled the one used in the cadaver studies. Somewhat surprisingly, results showed that CBCT underestimated bone height by an average of 2.50 ± 2.61 mm. The finding of lower accuracy in detecting thin alveolar bone in patients was attributed in part to live patients having fully hydrated, living tissues, and to the presence of micro-movement, which lead to increased "noise" during imaging. 23

Table of Contents for the Digital Edition of Pacific Coast Society of Orthodontists Bulletin Fall 2016