A comparison of the released forces from three different types of nickel-titanium wires at three different deflection positions: an in-vitro study

NiTi archwires are distinguished by their ability to deliver gentle, continuous forces over a wide activation range, over time, their crystalline structure has evolved: beginning with conventional NiTi, progressing to super-elastic variants, and then advancing to heat-activated. In this study, we examined three 0.016″ × 0.022″ NiTi rectangular wires: (1) super-elastic NT3 SE®, (2) heat-activated Thermal Ti-D® (active at ~ 25 °C), and (3) heat-activated Thermal Ti-Lite® (~ 35 °C)—by measuring their force release at molar, premolar, and incisor positions to determine whether unloading forces differ by location. A randomized, in-vitro trial was conducted at Aleppo University. Each group included six 30 mm wire sections for each wire type and position (total n = 18 per position). A three-point bending test at 37 °C (Deflection: 3.1 mm at 1 mm/min over a 10 mm span) measured unloading forces at 0.5, 1-, 2-, and 3-mm. Plateau length (3 to 0.5 mm), average force, and slope were recorded. Data were analyzed using one-way ANOVA with post-hoc Sidak’s test; reliability was confirmed via Pearson correlation (r = 0.877). NT3 SE® and Thermal Ti-D® wires showed similar unloading forces across positions (molar: 2.65 ± 0.11, 1.60 ± 0.18, 1.40 ± 0.18, 1.09 ± 0.19 N; incisor: 2.55 ± 0.12, 1.50 ± 0.18, 1.30 ± 0.18, 1.00 ± 0.15 N at 3, 2, 1, and 0.5 mm, respectively), with molar values approximately 10% higher than incisor values; differences were not statistically significant (p > 0.05), and 95% confidence intervals overlapped. Thermal Ti Lite® wires exhibited significantly lower forces overall and clear site-dependent differences (molar: 2.28 ± 0.21, 1.76 ± 0.10, 0.52 ± 0.09, 0.56 ± 0.14 N; premolar: 1.92 ± 0.12, 0.56 ± 0.10, 0.32 ± 0.09, 0.31 ± 0.09 N; incisor: 1.57 ± 0.20, 0.36 ± 0.10, 0.12 ± 0.09, 0.12 ± 0.09 N at 3, 2, 1, and 0.5 mm, respectively), with molar forces on average 50% higher than premolar and 70% higher than incisor values (p < 0.05); average and slope also varied significantly by position, though plateau lengths were consistent—only Ti Lite® showed positional force variability. Thermal Ti-Lite® archwires, with higher austenite-finish temperature (~ 34 °C), demonstrated significant positional force differences, suggesting their potential for site-specific biomechanical control. In contrast, NT3-SE® and Thermal Ti-D® provided uniform force profiles across arch positions. Considering crystalline transformation temperatures and anatomical variation may improve clinical force application during alignment.