Influence of Homogeneity of TADs Designs on Their Retention

Objectives:
Most Temporary Anchorage Devices (TADs) available have homogenous intraosseous designs unlike the bone. The aim of this study is to evaluate whether a novel TAD design prototype (NDP) with non-homogeneous intraosseous part would achieve better biomechanical properties than the current TAD designs.
Methods: NDP was compared with a commercially available same width TAD (Spider screw (SS). The core to width radio at 0, 2, 4 and 6mm was measured using the Mitutoyo PH-3500 with QM-data 200. 10 TADs from each design were inserted in a 30 PCF laminated block from SAW Bone under a 12N axial load, using the Instron 5566A to measure the insertion torques and removal torques. Torque ratios were then calculated. Pull out tests were performed at angles of 0° / 30° / 60° / 90°. Two TADs per design were loaded up to failure. Student’s t-test was used to compare the torques values of NDP and SS designs.
Results:
The core to width ratio at 0, 2, 4 and 6mm for the SS and the NDP were respectively 1, 0.64, 0.61 and 0.47 ; 0.63, 0.42, 0.38 and 0.58. The mean insertion torque, the removal torque and torque ratio for the SS and the NDP were 12.78 N.cm / 11.32 N.cm, 0.89 ; 12.73 N.cm / 12.65 N.cm, 0.99 respectively.
The mean pull-out forces at 0°/30°/60° and 90° for the SS and the NDP were respectively 124,18N/108,59N/69,67N/84,75N ; 137,72N/109,7N/64,96N/66,78N.
Conclusions:
The TAD designs are relatively different. The NDP tend to have higher torque ratio but marginally significant.
Both of the designs showed to resists to high shear forces. Non-homogeneous design showed to perform as well as the homogeneous design but with higher torque ratio. More studies are needed to be able to confirm the conclusions of this study.