LAUSR

AIM To evaluate the effects of progressive root canal enlargements on the unprepared surface area and remaining dentine thickness of three-rooted maxillary first premolars with different root configurations. METHODOLOGY Thirty three-rooted maxillary first premolars with 3 root configurations (n=10) were selected and scanned in a micro-CT device. The root canals were sequentially enlarged with rotary instruments sizes 30.02 (step 1), 30.04 (step 2), and 30.06 (step 3). After each step, a new scan was taken. Analysed parameters included morphometric measurements (length, volume and surface area), number of static voxels, and minimal dentine thickness. Statistic analyses were performed with one-way ANOVA post hoc Tukey tests and paired sample t-test at a significance level of 5%. RESULTS No statistical differences were observed among groups regarding the morphometric parameters and static voxels (p > 0.05). The minimal dentine thickness of the distobuccal root significantly changed depending on the root configuration (p < 0.05), while no differences were observed in the other roots (p > 0.05). A great variation in the position of the minimal dentine thickness was observed after preparation. Overall, mean percentage reduction of dentine thickness was higher in the buccal roots than in the palatal root (p < 0.05). In the mesiobuccal and distobuccal root, the number of slices with minimal dentine thickness lower than 0.05 mm increases 2 to 3 times and 3 to 4 times, respectively, from steps 1 to 3. CONCLUSIONS Instruments sizes 30.02 and 30.04 can be safely and effectively used to enlarge the buccal and palatal canals of three-rooted maxillary first premolars.