Biomechanische eigenschaften kieferorthopädischer minischrauben.eine in-vitro-studie

Objective: Comparing five commercially-available miniscrew types for skeletal anchorage with regard to the biomechanical properties influencing their primary stability. Material and Methods: Included in this study was a total of 196 self-tapping and self-drilling miniscrews having a diameter of 2 mm (or the largest possible diameter of the manufacturer in question), a thread shaft length of 10 mm, or the longest miniscrew supplied by the manufacturers. The screw types tested werethe FAMI 2, Orlus mini-implant, T.I.T.A.N. Pin, tomas®-pin and Vector TAS™. Insertion and loosening torque measurements, and pullout tests in axial (0°), 20° and 40° directions, as well as test series with and without pilot hole drilling were performed. Bovine femoral heads having the same bone mineral density (BMD) were used as bone-testing material. Results: Higher insertion torques were found for the cylindrical FAMI 2 screw, the conical Orlus mini-implant and the Vector TAS™ screw (with mean values of 39.2 Ncm, 32.1 Ncm and 49.5 Ncm) than for the cylindrical T.I.T.A.N. pin and tomas®-pin. Insertion without predrilling led the insertion torques of all five screws to rise significantly. We noted statistically significant differences among the five screws in the pullout tests. Those highly significant differences at axial (0°) and 20°angles were not apparent at the 40° pullout angle. Compared with the pullout forces (load) in the axial direction, the cylindrical screws' load values decreased markedly according to the angle (by up to -46.6%). The reduction in pullout force in conjunction with an increasing angle was much less pronounced in the conical screws (-0.8% to -29.0%). The tomas®-pin demonstrated the highest pullout force and stiffness values throughout the tests. A total of five tomas®-pins, two Orlus mini-implants and one FAMI 2 screw fractured during the pullout tests.Conclusions: Results from our insertion torque measurements suggest that a conical screw design will provide greater primary stability than cylindrical screw types. The cylindrical screw design's superiority was evident in the pullout tests. All the miniscrews'primary stability rose after drill-free insertion. The tomas ®-pin screws, although biomechanically superior to the other screws, were most prone to fracture.