Manufacturing Order Matters? Exploring the Impact of Heat Treatment and Machining Sequences on the <scp>NiTi</scp> 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.