Post-Instrumentation Morphology Analysis in Simulated Root Canals Using Nickel–Titanium Instruments

Modifications in instrument design and manufacturing processes include mechanical and thermal treatments of the nickel–titanium alloy surface to improve fracture resistance, flexibility, and performance in cleaning and shaping curved canals, resulting in reduced distortion of the original anatomy. Objective: To compare the thickness of resin removed and the post-instrumentation morphology in simulated root canals in acrylic resin blocks using endodontic instruments manufactured from different nickel–titanium alloys. Materials and Methods: Thirty blocks (EndoTrainingBlocks® Dentsply/Sirona) with controlled length, diameter, taper, curvature angle, and radius were selected. Specimens were randomly assigned to six groups: Group 1: conventional NiTi alloy. Group 2: M-Wire NiTi alloy. Group 3: thermally treated Gold NiTi alloy. Group 4: thermally treated Blue NiTi alloy. Group 5: controlled-memory (CM) NiTi alloy. Group 6: Max-wire NiTi alloy. Each group was instrumented according to the manufacturer’s instructions, and the images were subsequently digitally processed to compare the changes produced in each specimen with those in a non-instrumented block. Using a calibrated digital millimetre template, six measurement sections were determined along the length of the root canal. Data were statistically analyzed (p < 0.05) using two-factor repeated-measures analysis of variance (ANOVA), Bonferroni test, and Scheffé post-hoc test. Results: Intergroup comparisons revealed statistically significant differences (p = 7.4E-08), although some similarities were observed between certain alloy groups. Differences between sections were highly statistically significant (p = 1.3E-25) in all cases. Conclusions: The NiTi alloys analysed exhibited distinct wear patterns. Similar post-instrumentation effects were observed between the MaxWire and HyFlex CM alloys, characterised by a more conservative dentine removal pattern. The Gold alloy demonstrated the greatest amount of resin removal along the entire canal length, with a marked modification in post-instrumentation morphology.