Evaluation of insertion torque of orthodontic miniscrew implants in relation to tooth root contact

Introduction. Miniscrew implants (MSIs) are a useful tool when absolute orthodontic anchorage is required. While helpful in many regards, problems can still arise. The purpose of this study was to quantify how insertion torque changes during insertion of a self-drilling MSI with tooth root contact. Methods. MSIs from two manufacturers (3M Unitek(TM) TAD and Dentaurum tomasRTM pin) were inserted in pig cadaver mandibles and divided into three groups: Control (miss), Glance, and Direct Hit. Cone-beam computed tomography (CBCT) was used to verify MSI location. Insertion torque was continuously recorded during MSI insertion and inspected for fracture or damage upon removal. Scatterplots of time vs insertion torque were created. Results. 3M Unitek(TM) MSIs showed higher insertion torque than TomasRTM MSIs in control groups. Self-drilling MSIs were unable to directly penetrate the roots. Self-drilling MSIs which contact teeth show a higher insertion torque than control groups with no contact. TomasRTM MSIs showed higher fracture rates at the tip, possibly due to a weaker thread-cutting design. Conclusions. Contact with a tooth root with a self-drilling MSI causes an increase in insertion torque and thus tactile feedback may help the experienced clinician determine if root contact has occurred. Additionally, thread-cutting tips appear to be more prone to breakage when a tooth root is contacted.