Strain of bone-implant interface and insertion torque regarding different miniscrew thread designs using an artificial bone model.

OBJECTIVES To evaluate the initial stability of dual-thread miniscrews by analyzing the strain at the bone-implant interface and insertion torque during implantation in artificial bone models with different cortical bone thicknesses. MATERIALS AND METHODS Insertion torque, and strain, measured with a five-element strain gauge in 1.0, 1.5, and 2.0-mm artificial cortical bone, during insertion of single- (OAS-T1507) and dual-thread (MPlant-U3) type self-drilling miniscrews were assessed. RESULTS Both dual- and single-thread miniscrews showed greater than 7790 μstrain for all cortical bone thicknesses, and dual-thread miniscrews reached up to 19580 μstrain in 2.00 m m cortical bone. The strain of dual-thread miniscrews increased with increasing cortical bone thicknesses of 1.0-2.0mm. For single-thread miniscrews, the maximum insertion torque was relatively constant, but maximum insertion torque increased significantly in dual-thread groups with increasing cortical bone thicknesses (P < 0.0001). The maximum insertion torque with all cortical bone thicknesses was significantly lower with single- than dual-thread types (P < 0.0001). CONCLUSIONS Self-drilling dual-thread miniscrews provide better initial mechanical stability, but may cause strain over the physiological bone remodelling limit at the bone-implant interface in thick cortical bone layers.