Effect of the quantity and quality of cortical bone on the failure force of a miniscrew implant

This study examined the influence of the quantity and quality of cortical bone on the failure force of miniscrew implants. Twenty-six titanium alloy miniscrew implants (AbsoAnchor) 1.4mm in diameter and 5 or 7mm long were placed in cross-sectioned maxillae (n = 6) and mandibles (n = 20) of human cadavers. Computed tomography imaging was used to estimate the cortical bone thickness and bone mineral density [total bone mineral density (TBMD, values obtained from cortical bone plus trabecular bone); cortical bone mineral density (CBMD, values obtained from only cortical bone)]. Maximum force at failure was measured in a shear test. Nanoindentation tests were performed to measure the hardness and elastic modulus of cortical bone around the miniscrew implants. The mean failure force of miniscrew implants placed in mandibles was significantly greater than that for implants in maxillae, and the bone hardness of mandibles was significantly greater than that of maxillae. The length of miniscrew implants did not influence the mean failure force in monocortical placement in the mandible. Cortical bone thickness, TBMD, CBMD, and bone hardness were significantly related to the mean failure force. CBMD was related to the mechanical properties of cortical bone. In conclusion, the quantity and quality of cortical bone greatly influenced the failure force of miniscrew implants.