Variability of Mechanical Torque-Limiting Devices in Clinical Service at a US Dental School

Purpose: The purpose of this study was to measure the variability of torque produced by a population of mechanical torque‐limiting devices in clinical service in a US dental school. The torque‐limiting devices were divided into two categories according to their mode of action: toggle‐type and beam wrenches. Proper action of these devices is essential for calibrated delivery of preload to implant prosthetic screws. Materials and Methods: Seventeen torque‐limiting devices (35 Ncm) were obtained from graduate prosthodontic, predoctoral, and faculty practice clinics. Nine of these were toggle‐type devices, and eight were beam‐type wrenches. Torque from each wrench was measured using an MGT electronic torque meter. Wrenches were tested in two modes, slow (over 4 seconds) and fast (over 1 second). Results: Toggle‐type torque wrenches produced a mean (± SD) torque of 38.1 ± 16.0 Ncm; beam‐type wrenches produced 32.8 ± 1.1 Ncm. These results were not significantly different. When tested in fast mode (1 second), toggle‐type wrenches produced 28.0 ± 9.6 Ncm; in the slow mode (4 seconds) they produced significantly more force, 36.6 ± 14.0 Ncm (p < 0.001). Beam‐type wrenches produced 33.2 ± 1.1 Ncm and 32.8 ± 1.1 Ncm in fast and slow modes, respectively. Conclusions: Both types of wrenches tested were capable of producing accurate torque values; however, variability was higher in the toggle‐type group. Some toggle‐type torque wrenches in clinical service delivered unacceptably high torque values. It is recommended that clinicians calibrate toggle‐type wrenches frequently. Torque wrenches should be activated slowly, over 4 seconds, when using a correctly calibrated toggle‐type wrench.