Accuracy of torque-limiting devices used for mini-implant placement—an in vitro study

Abstract

Mini-implants are used when enhanced orthodontic anchorage is needed. Documented risks include damage inflicted to tooth structures and implant loosening, but also fracture. An important factor in minimizing adverse side effects is to control the insertion torque. The goal of the present study was to investigate the accuracy of various torque-limiting devices available for this purpose. Eight torque-limiting devices were analyzed, including a group of manually-operated drivers (n=3), a group of battery-operated drivers (n=4), and a surgical unit (n=1). The accuracy of these devices was tested over the entire range of applicable torque levels, using an experimental design simulating the insertion of mini-implants. No significant differences were noted between the group of manually-operated and the group of battery-operated devices within the clinically relevant range of 10-25 Ncm. Comparing the individual devices revealed several significant differences. Some devices yielded both effective torque levels very close to the set levels and small standard deviations. Mini-implants can be put in place in a controlled fashion regardless of whether the torque-limiting device used for this purpose is a manual- or battery-operated driver or a surgical unit. However, we observed that the accuracy of torque limitation differed greatly between individual devices across these groups. Our results can therefore help clinicians select an appropriate insertion device for mini-implants.