Removal Torque Analyses of Two Self-drilling Orthodontic Temporary Anchorage Devices (TADs)

Abstract

Stability of miniscrews or Temporary Anchorage Devices (TADs) is an essential factor for successful application in orthodontics. Miniscrews removal torque can be used as an indicator of miniscrews stability. The objective of this work was to compare removal torque between self-drilling tapered mini-screws and cylindrical miniscrews. Materials and Methods: Two groups of TADs were inserted in the maxillae of orthodontic patients to provide stationary anchorage for front teeth retraction. Group 1: 20 tapered self-drilling miniscrews, Group 2: 20 cylindrical self-drilling miniscrew. Split mouth technique was used. All of the TADs were inserted parallel to the occlusal plane, between roots of the 2nd maxillary premolar and 1st maxillary molar. The TADs were immediately loaded with constant and continuous load using 8 mm long heavy short Nickel Titanium coil spring. The coil spring was stretched between the heads of the two types of TADs and crimpable hooks that fixed on arch wire just distal to the anterior six maxillary teeth. After complete retraction of the anterior maxillary teeth, TADs were removed using torque adjustable screw-removal. At the moment of movement of the TAD the torque was recorded in Newton Centimeter (Ncm). Results: Mann Whitney U Test resulted in a significant difference between the two groups, indicating that cylindrical TADs had significantly higher removal torque than tapered TADs (means were 3.20 Ncm ± 0.20 and 2.70 Ncm ± 0.10 respectively). Conclusion: Physical properties have a considerable influence on the stability of the TADs. Cylindrical TADs are showed more mechanical interlock into the bone.