Experimental analysis of the influence of cortical bone layers and bone quantity on implant primary stability

The systematic analysis of parameters impacting implant primary stability is difficult to achieve with human cadavers or animal models, particularly for complex trans-sinus procedures to determine the effects of cortical layers and bone engagement on implant stability before and after a simulated load in vitro. Solid rigid polyurethane blocks, partially intersected by an 8-mm-thick space, were created to imitate tri-cortical situations, the presence of the sinus cavity, and the posterior maxilla with different degrees of bone atrophy. Implants were inserted through the cavity at an angle of 30˚ (scenarios 1 and 2) to imitate the clinical protocol. Controls simulating uni-cortical anchorage and no sinus cavity were also included (controls 1 and 2). Four parameters were measured: peak insertion torque, insertion work, resistance to lateral bending loads and extraction torque. Scenarios 1 and 2 displayed similar peak insertion torque to control 2, where all three groups anchored equal amounts of bone surrogate. The distribution of surrogate bone in contact with trans-cavity implants influenced both extraction torque and the degree of lateral bending. Sufficient peak insertion torque can be attained with a trans-sinus tricortical implant anchorage providing sufficient apical and coronal bone is engaged.