Scanning Electron Microscopic Analysis of Surface Alterations in Third-Generation NiTi Rotary Instruments Following Clinical Simulation
DOI:
https://doi.org/10.64149/J.Carcinog.24.3s.838-849Keywords:
Nickel-titanium endodontic files; Root canal preparation; Scanning electron microscopy; Instrument failure; Controlled memory.Abstract
Introduction: Third-generation nickel–titanium (NiTi) rotary files undergo proprietary thermomechanical processing intended to enhance flexibility and fatigue resistance.
Objectives: This study evaluated the qualitative and quantitative wear and fatigue behavior of four third-generation NiTi rotary systems following repeated use in extracted posterior human teeth using a simulated clinical model.
Materials and Methods: One hundred files (n=25 per group across four brands: ProFile Vortex™, Vortex Blue™, ProTaper Gold™, and Coltene HyFlex® CM™) were examined using Scanning Electron Microscopy (SEM) at 200x magnification at the same four positions along their length. Files were used to prepare root canals in extracted human posterior teeth (premolars and molars) in a simulated clinical model for up to three uses. Two blinded evaluators analyzed the SEM micrographs to score wear and deformation, categorizing files as usable, microscopically unacceptable, or visually unacceptable.
Results: Twelve files (12.0%) exhibited visual failure, most commonly during the first use. Canal curvature distribution differed significantly among brands; ProTaper Gold™ files were exposed to fewer severely curved canals, introducing confounding when interpreting comparative failure rates. Third-generation instruments predominantly failed by plastic deformation rather than separation. Regression analysis revealed no significant differences in wear between brands. Although microscopic wear increased significantly after initial use, it did not progress significantly with subsequent uses. Baseline manufacturing defects, present in 8% of files, did not significantly predict catastrophic failure.
Conclusions: Third-generation controlled-memory NiTi instruments tend to deform plastically rather than undergo abrupt separation, which may provide a visual warning of impending failure. While microscopic manufacturing defects were relatively common, they did not reliably predict fracture; however, absence of visible defects does not preclude internal fatigue accumulation.
