Comparative evaluation of apical crack formation and propagation in root dentin following retreatment using hand files and four rotary retreatment file systems: An in vitro study

Background: Nonsurgical endodontic retreatment remains the treatment of choice for teeth with persistent apical periodontitis. Although rotary nickel–titanium (NiTi) retreatment systems facilitate efficient removal of root filling materials, the stresses generated during instrumentation may induce dentinal defects that predispose teeth to vertical root fracture. Limited evidence is available comparing the incidence of apical crack formation among contemporary rotary retreatment systems. Aim: The aim of the study was to compare the incidence of apical crack formation and crack propagation in apical root dentin following retreatment using hand files and four rotary retreatment file systems: ProTaper Universal Retreatment (PTR), ProTaper Next (PTN), R-Endo, and D-RaCe. Materials and Methods: Ninety extracted human mandibular premolars with single straight canals were standardized to a root length of 14 mm. Following chemo-mechanical preparation and thermoplasticized obturation, specimens were randomly allocated into six groups ( n = 15): untreated control, hand files, PTR, PTN, R-Endo, and D-RaCe. Baseline stereomicroscopic images were obtained before instrumentation and after obturation. Retreatment procedures were performed according to manufacturers’ recommendations, followed by standardized apical enlargement. Specimens were examined under a stereomicroscope (×20 magnification) for apical crack formation. Data were analyzed using the Chi-square test with statistical significance set at P < 0.05. Results: No dentinal defects were observed in the control specimens. Rotary retreatment systems demonstrated a higher incidence of apical crack formation than hand instrumentation. PTR exhibited the highest incidence of cracks, followed by PTN, R-Endo, and D-RaCe. Pairwise comparison revealed significantly greater crack formation in rotary groups than in the hand file group ( P < 0.05), whereas differences among the four rotary systems were not statistically significant. Conclusion: All retreatment techniques induced apical dentinal defects; however, rotary NiTi retreatment systems produced significantly more cracks than hand instrumentation. Among the rotary systems evaluated, R-Endo and D-RaCe demonstrated comparatively lower crack incidence than PTR and PTN, suggesting that instrument design and taper influence dentinal stress during retreatment.