Influence of Aging on the Torque Accuracy of Two Different Spring-Style Implant Torque Wrenches: An in vitro Study

Accurate torque delivery is critical for achieving proper implant preload and preventing screw loosening, yet torque wrenches may lose precision with repeated clinical use. This study aimed to assess how aging influences the torque accuracy of spring-type dental torque wrenches.

Five new spring-type dental torque wrenches from Neodent^® and Intra-Lock^® were tested at their lower and upper torque limits. Torque was measured using a calibrated digital torque meter; each wrench was activated 10 times per setting, and the mean of three consistent readings was recorded. Mechanical aging was simulated through 1000 continuous tightening-loosening cycles at each wrench's maximum torque. Torque measurements were repeated after 500 and 1000 cycles following the same protocol. Data were analyzed using one-way ANOVA (α = 0.05).

Both torque wrench brands showed a significant reduction in torque accuracy at the upper limit after 500 and 1000 mechanical aging cycles (p < 0.001). At 1000 cycles, upper-limit torque decreased by 0.67 N·cm (2.2%) for Intra-Lock and 0.55 N·cm (1.7%) for Neodent compared with baseline values. At the lower limit, a significant change was observed for Intra-Lock (p = 0.014), whereas no significant change was observed for Neodent (p = 0.132). Across all measurement stages, Neodent delivered significantly higher upper-limit torque than Intra-Lock (p = 0.020), whereas no significant difference was observed at the lower limit (p = 0.132).

Within the limitations of this in vitro study, repeated mechanical aging significantly reduced torque accuracy at the upper torque limit, although the observed reductions were small in absolute terms and remained within commonly used clinical tolerance thresholds. These findings support routine monitoring and calibration of spring-type torque wrenches to maintain reliable torque delivery and implant stability.