Effect of radiotherapy on the biomechanical preparation of different instrumentation kinematics

To evaluate the effect of biomechanical preparation on irradiated root dentin after the use of different endodontic instrumentation techniques. Sixty mandibular canines were randomly assigned to two groups: non-irradiated (30 canines) and irradiated (30 canines subjected to 30 cycles of 2 Gy, totaling 60 Gy). After radiotherapy, the samples were scanned using micro-CT to assess the 3D morphology of the root canal and to calculate the length, thickness, volume, surface area and transport of the canal. The groups were redistributed into 3 subgroups (n = 10) according to the instrumentation protocol: GI-manual M-easy Ni-Ti file up to #50.05; GII-rotary instrument ProTaper Next up to #50/.06; GIII-reciprocating instrument Reciproc #R50. After instrumentation, the specimens were scanned again in micro-CT following the same parameters as the initial acquisition. Statistical analysis was performed using two-factor analysis of variance (ANOVA) test with Tukey's post-test considering the variables "instrumentation protocol" and "radiotherapy". The three-factor ANOVA test with Tukey's post-test was carried out to compare the influence of radiotherapy, instrumentation and root thirds (cervical, middle and apical) on root canal transportation data. Irradiated teeth showed a greater increase in surface area and percentage of walls touched, while for root canal transport and volume, differences were observed only in relation to the type of preparation, in ascending order for the manual, rotary and reciprocating systems. Descriptive analysis showed that altered thickness in the middle-apical thirds occurred mainly in teeth irradiated with rotary and reciprocating instrumentation protocols. Irradiation of teeth can affect biomechanical preparation parameters of different instrument kinematics used to prepare canine root canals.