Manufacturing Order Matters? Exploring the Impact of Heat Treatment and Machining Sequences on the NiTi Instruments Properties.

This study assessed how manufacturing sequence affects the metallurgical and mechanical properties of two nickel-titanium instruments: Procodile Q (heat-treated before machining) and Procodile +HT (heat-treated after machining). Both instruments (n = 74 each, size 25/0.06) were analysed for design, NiTi composition, phase transformation temperatures and mechanical performance (cyclic fatigue at 20°C and 35°C, torsional fatigue, bending load, buckling strength, cutting ability, microhardness and roughness). The Student's t-test and Mann-Whitney test were used for statistical analysis (α = 5%). Results showed that both instruments had similar design and composition. Procodile Q had a slightly higher austenitic start temperature and superior cyclic fatigue resistance at 20°C and 35°C (p < 0.001), along with higher surface roughness (p = 0.041). Other mechanical properties showed no significant differences (p > 0.05). These findings suggest that the order of machining and heat treatment of Procodile instruments had minimal impact on overall performance, primarily affecting cyclic fatigue resistance and surface roughness.