Accuracy of the implant torque wrench following time in clinical service.

Thirty-five implant torque wrenches were tested for torque delivery accuracy. Seven of these drivers had a 10-Ncm value, 12 had a 20-Ncm value, 10 had a 30-Ncm value, and six had a 35-Ncm value. All of the wrenches had been in clinical service for a minimum of 1 month or a maximum of 3 years and were assumed by the clinicians to be fully effective in delivering the required torque values. Torque delivery accuracy was determined using a Tohnichi torque wrench calibrated to +/- 1% of the scale value. All torque wrenches had been subjected to steam sterilization following clinical use. Data collected on all wrenches included (1) age since purchase, (2) number of sterilization cycles to which each wrench had been subjected during the use period, and (3) 10 sequential torque readings using the Tohnichi wrench as the torque reading device. The results of this study showed that there was no significant correlation of delivered torque with (1) age or (2) number of sterilization cycles. Furthermore, in each torque category there were torques both above and below the control values. For the 10-Ncm torque wrenches, the largest value was 455.0% greater than the control, the largest values were 41.6% greater for 20-Ncm wrenches, 17.0% greater for the 30-Ncm torque wrenches, and 58.6% greater for the 35-Ncm wrenches. Corrosion of the spring in the handle of the torque wrench was found to be the reason for the 455.0% value.