In Vitro Comparison of Orthodontic Miniscrew Implants and Design Factors Affecting Primary Stability

The purpose of this study was to evaluate how the design factors of orthodontic miniscrew (OMS) implants affect their primary stability. Two hundred thirty OMS implants were obtained from eight different manufacturers. Each manufacturer submitted from one to three different designs for inclusion in the study. The design factors evaluated were length, diameter, taper, extra-bony head height, fluting, thread pitch, and thread depth. Synthetic bone was utilized to obtain a consistent and uniform test medium for all orthodontic miniscrew implants. Tensile strength proportional limits were measured perpendicular to the angle of insertion of the orthodontic miniscrew implants. Only thread pitch was found to be significantly correlated with maximum insertion torque (p<0.05). No significant correlation was found for any of the studied design factors with the tensile proportional limit (p<0.05). No significant correlation was found between maximum insertion torque and tensile proportional limit (p<0.05). All OMS implants studied were capable of supporting clinically applied forces, and the minor differences in the design factors of the OMS implants did not affect their primary stability as assessed by tensile loading to a clinically significant extent. However, consideration should be given to the thread pitch as high insertion torques may lead to excessive bone compression surrounding OMS implants, bone loss, and subsequent OMS implant failure. Finally, using maximum insertion torque as an indication for primary stability should be avoided due to the fact that no correlation could be found between maximum insertion torque and tensile proportional limit (p<0.05).