Effect of mechanical aging and steam autoclaving on the accuracy of different mechanical torque limiting devices

Evidence is lacking regarding the accuracy of the long-term torque delivery of mechanical torque-limiting devices (MTLDs) from different manufacturers after repeated mechanical aging and sterilization.

The purpose of this in vitro study was to evaluate the accuracy of spring- and friction-style MTLDs from 6 implant manufacturers in delivering target torque values and to assess the effects of mechanical aging and steam autoclaving on their performance.

Sixty new MTLDs from 6 manufacturers (spring-style devices: Astra Tech, Nobel Biocare, Straumann, Bilimplant; and friction-style devices: Neoss and Meisinger) were included in the present study (n=10). After initial measurements (T1), all devices underwent 500 simulated clinical uses to assess the effect of mechanical aging, after which torque values were recorded again (T2). Subsequently, each device was subjected to 100 steam autoclaving cycles under standardized conditions (134 °C, 7 minutes), and final torque values were collected (T3). All torque measurements were performed using a custom-designed device. Two accuracy metrics, absolute difference (ABSDIFF) and percentage deviation (PERDEV), were used for comparison. Statistical analyses included 2-way robust ANOVA and Bonferroni-adjusted post hoc tests (α=.05).

At baseline, spring-style MTLDs demonstrated significantly lower ABSDIFF values than friction-style devices (P=.001), indicating higher initial accuracy. No significant differences were found between device types after mechanical aging (P>.05). Following sterilization, torque deviation increased in spring-style devices, particularly Astra (P<.05). All devices maintained torque delivery within the clinically acceptable ±10% threshold.

Spring-style MTLDs provided more accurate torque delivery initially, while friction-style devices demonstrated greater stability after repeated mechanical aging and sterilization. Device type and manufacturer-specific factors influence long-term accuracy.