Interfacial Shear Strength of Endosseous Implants

Purpose: Surface roughness is known to affect the load-bearing strength of implants. However, the underlying mechanisms are not completely understood. This study sought to investigate the potential effects of bone-to-implant contact (BIC) and mechanical interlocking on the stability of titanium implants using a newly established assessment system that combines nondestructive microcomputed tomography (µCT) and the biomechanical push-in test. Materials and Methods: Cylindric implants with a machined or a dual acid-etched (DAE) surface were placed into the distal femurs of Sprague-Dawley rats. At weeks 2 and 4, the femur-implant specimens were harvested and scanned in a desktop µCT device, and the BIC was calculated. The implants were then loaded axially using a universal mechanical testing machine and the breakage force was recorded as a push-in value. Machined and DAE implants were also embedded in histology-quality resin to serve as a nonbiologic reference. Two-way analysis of variance and the Mann-Whitney U test were used for statistical analysis. Results: BIC showed no surface- or time-dependent differences. The mean push-in value of DAE implants was four times greater at week 2 and three times greater at week 4 than that of machined implants. The shear strength at the interface (push-in value/BIC) was greater for DAE surfaces than for machined surfaces in a proportionate manner. When the implants were embedded in the resin with virtually 100% implant-resin contact, DAE implants showed 30% greater push-in values and shear strength than machined implants (P .05). Conclusions: These findings suggest that the percentage of BIC and mechanical interlocking cannot fully explain the surface roughness-related increase in osseointegration, as opposed to the common understanding of osseointegration. Further studies must include more details to discover the precise understanding of the physiology of osseointegration and the potential biologic mechanisms involved. Keywords: dental implants, microcomputed tomography, osseointegration, shear strength