The elaboration of a novel TAD design and its comparison to an industrial design
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BACKGROUND: The temporary anchorage devices (TAD) rely on mechanical retention to achieve their function. Following dental implants, the design has not been thoroughly studied. Most of the TADs available in the market are either conical or cylindrical homogenous designs. This study aims to evaluate whether a non-homogeneous design would be able to achieve better biomechanical properties than the current mini- screw designs available on the market. MATERIAL AND METHODS: This is a preliminary study comparing two different 1.5mm TAD designs, the Spider Screw® (Ortho Technology®), and one experimental TAD, the Novel TAD Design (NTD). The two TAD designs were generally described and evaluated following the ANSI/ADA Standard No. 178, then the core diameter / TAD diameter ratio was calculated at 0, 2, 4, and 6mm using the Mitutoyo PH-3500 projection machine in combination 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. Using the same Instron machine with TADs fully inserted in the artificial bone (2 per design per angle), pull-out tests were performed at angles of 0° / 30° / 60° / 90°. The TADs were loaded up to failure. One-way ANOVA and student's t-test were used for statistical analysis. RESULTS: The Spider Screw® is a conical, self-drilling, self-tapping design with the following general dimensions (d1: 1.5mm ; d2: 0.5mm; d3: 3.4mm; k1: 1mm; k2: 2mm; L1: 9.5mm; L2: 6.5mm; L3: 6.2mm), a 0.6mm pitch, 0.3mm thread depth, asymmetrical triangular threads. NTD, it is a cylindrical-conical, self-tapping design with the following general dimensions (d1: 1.5mm; d2: 0.85mm; d3: 2.5mm; k1: 1mm; k2: 2mm; L1: 9mm; L2: 6mm; L3: 6mm), a 0.5mm pitch, double threads in the first 2mm, a variable thread depth (0-2mm: 0.2mm ; 3-5mm: 0.35mm) and symmetrical rectangular threads. The core to width ratios for the Spider Screw® and NTD were respectively 1 ; 0.64 ; 0.61; 0.54 and 0.7; 0.53; 0.56 and 0.58. Mean insertion torque, removal torque and torque ratio for the Spider Screw and the NTD were respectively (12.78 N.cm / 11.32 N.cm, 0.90 ; 12.73 N.cm / 12.65 N.cm, 0.99 ) Mean pull-out forces at 0°/30°/60° and 90° for the Spider Screw® and the NTD were respectively 124.18 N / 108.59 N / 69.67 N / 84.75 N and 137.72 N / 109.7 N / 64.96 N / 66.78 N. There were no statistically significant differences found. CONCLUSIONS: After evaluating both of the TADs, it is clear that the designs are relatively different. The NTD showed to have a higher torque ratio, and therefore it could mean that the design would be clinically more effective. The NTD showed to perform as good or even slightly better than the Spider Screw® design, but a larger variety of TAD designs is needed to be able to confirm the conclusions of this study.