Effect of Implant Thread Geometry on Secondary Stability, Bone Density, and Bone-to-Implant Contact

PURPOSE: This study evaluated the effect of 2 different thread designs on secondary stability (micromotion) and osseointegration rate in dense and cancellous bones. MATERIALS AND METHODS: Forty large threaded and 40 small threaded implants (Cortex) were placed in low- (iliac crest) and high-density (mandible) bone of sheep. Two months later, micromobility tests and histological analysis were performed to measure secondary stability, osseointegration (bone-to-implant contact percentage [%BIC]), and bone density (bone volume percentage [%BV]). The value of actual micromotion of implant is introduced as a new parameter to evaluate secondary stability. RESULTS: Large threaded implants showed significantly higher %BIC and %BV than small threaded implants in low-density bone and statistically higher secondary stability in cancellous and cortical bones. CONCLUSIONS: Implants in dense bone reach higher secondary stability than those in cancellous bone, despite the lower %BIC. Implant geometry and bone density play a key role in secondary stability. Large thread design improves bone anchorage mechanically and histologically as compared with small threaded implants.