A revolving temporary anchorage cap connecting to an orthodontic miniscrew using in vitro experimental testing: Safety and biomechanical evaluations

Purpose: This study is to develop a plastic revolving (translation and rotation) temporary anchorage cap (TAC) as the orthodontic anchor and evaluate its biomechanical safety and clinical used feasibility. Materials and Methods: The TAC was designed to connect onto a mini-implant head with 45-degree switching unit and extended arm for tying an orthodontic elastic chain/coil spring. The removal force between the TAC and mini-implant head and torque resistance on the mini-implant/bone interface were performed to evaluate the biomechanical safety. Clinical molar uprighting and mesial drive application were performed to reveal the TAC feasibility/capacity. Results: The removal force was 43.95 N (蠑finger-pulling force 9.3 N) to prevent the TAC from detaching, and the torque resistance was 159.25 N$mm to maintain micromotion smaller than 30.4 mm between the screw and bone. The strain value in using TAC treatment was found to be about 2 times that of traditional tracing (without using TAC) in molar uprighting/mesial drive application. Conclusions: The plastic revolving TAC can provide optional use with translation/rotation features to change the angles and directions in orthodontic tractions and increase treatment efficiency under biomechanical safety considerations.