COMPARATIVE EVALUATION OF METALLURGY, MECHANICAL PERFORMANCE, AND FRACTURE RESISTANCE IN HEAT-TREATED NITI ENDODONTIC INSTRUMENTS

Abstract

Background: Nickel–titanium (NiTi) endodontic instruments have undergone significant metallurgical advancements through proprietary heat-treatment protocols aimed at improving mechanical performance and clinical safety. However, variations in phase transformation behavior and mechanical properties among different heat-treated NiTi systems remain incompletely understood.

Aim:  This study aimed to comparatively evaluate the metallurgical characteristics and mechanical performance of four heat-treated NiTi endodontic instrument systems— Martenistic (M)-Wire, Controlled Memory (CM) Wire, Blue, and Gold—with respect to austenite finish (Af) temperature, cyclic fatigue resistance, flexibility, torsional resistance, and angular deflection before fracture.

Materials and Methods:  Sixty NiTi instruments (n = 15 per group) were evaluated. Af temperature was assessed using differential scanning calorimetry. Mechanical tests included cyclic fatigue resistance (number of cycles to failure), flexibility (force required for 45° deflection), maximum torsional resistance, and angular deflection before fracture, performed under standardized laboratory conditions. Data were analyzed using one-way Analysis of Variance (ANOVA) followed by Tukey post hoc testing (p < 0.05).

Results:
Statistically significant differences were observed among all groups for Af temperature, cyclic fatigue resistance, flexibility, torsional resistance, and angular deflection before fracture (p < 0.05). CM Wire instruments exhibited the highest Af temperature, greatest cyclic fatigue resistance, highest flexibility, and maximum angular deflection before fracture. Blue instruments demonstrated the highest torsional resistance. M-Wire instruments consistently showed inferior performance across most parameters.

Conclusion:
Heat-treatment protocols significantly influence the metallurgical and mechanical behavior of NiTi endodontic instruments. CM Wire instruments demonstrated superior flexibility, fatigue resistance, and deformation capacity, suggesting enhanced clinical safety, particularly in curved canals.