Comparison of primary stability of used and unused self-tapping and self-drilling orthodontic mini-implants

Background. Skeletal anchorage has been the subject of study for many years. Recently, orthodontic mini-implants (MIs) were described as effective tools for anchorage and were named temporary anchorage devices (TADs). The success of MIs depends on their primary stability, which is defined as the lack of mobility in the bone after implant insertion, and the relevant factors affecting primary stability. Objectives. This study aimed to compare the primary stability of used self-drilling (SD) and self-tapping (ST) MIs with unused ones by performing the insertion torque measurement, Periotest and pull-out test. Materials and methods. Forty-six used (23 ST, 23 SD) and 46 unused (23 ST, 23 SD) MIs (1.5 mm x 8 mm) were inserted into a synthetic bone with the use of a digital screwdriver. Maximum insertion torque (MIT) values were recorded during the placement of MIs, and then Periotest measurements were made. Following the MIT and Periotest measurements, pull-out tests were performed on all MIs. Results. The median MIT values (Ncm) of the MIs were as follows: used ST: 17.3, unused ST: 18.9, used SD: 24.1, unused SD: 25.2. The median values obtained after the Periotest were (+/-): used ST: 0, unused ST: -1, used SD: -3, unused SD: -3. Median pull-out values (N) were: used ST: 148.12, unused ST: 168.12, used SD: 173.12, unused SD: 203.20. Statistically, MIT and pull- out values of the used ST and SD implants were significantly lower compared to those of the unused ST and SD implants (p < 0.05). Conclusions. Used orthodontic MIs showed poor performance compared with unused implants when they were inserted again in the in vitro conditions.