In many cases, orthopaedic and dental implants can restore function to diseased or damaged joints and edentulous jaws. However, in several challenging clinical situations, it is difficult to achieve adequate fixation (osseointegration) between the implant and bone. Since osseointegration is necessary for clinical success, implant failure rates in these cases are unacceptably high. Understanding the factors that allow bone-interfacing implants to osseointegrate rapidly and reliably should lead to improvements in their use and design.

With this being our goal, we investigated the influence of implant surface geometry and local tissue strains on peri-implant tissue formation. Using a rabbit model, we evaluated the histological and mechanical characteristics of the early healing tissues around nonfunctional implants with Ti6A14V sintered porous surfaces and Ti plasma-sprayed surfaces. We found that the early healing tissues integrated with the three-dimensional interconnected structure of the sintered porous surface and mineralized more rapidly than the tissues around the irregular geometry of the plasma-sprayed surface. Consequently, the stiffness and strength of attachment was greater for the porous-surfaced implants. These results demonstrate that implant surface geometry influences early peri-implant tissue formation and, as a result, the early mechanical stability of implants.

To investigate the relationship between implant surface geometry, the local mechanical environment, and peri-implant tissue formation, we developed a computational micromechanical model based on homogenization methods to describe the effective and local properties of the porous-surfaced and plasma-sprayed peri-implant regions. In validation tests, we showed that the model provided reasonably accurate initial predictions of the properties of the peri-implant regions. Using the computational model, we compared the local mechanical environments around porous-surfaced and plasma-sprayed implants. In cases with minimal implant loading, the model predicted local tissue strains that permitted localized and appositional bone formation around porous-surfaced implants, but only appositional bone formation for plasma-sprayed implants. Based on the model predictions and experimental data from earlier studies, we proposed a quantitative model for the mechanical regulation of peri-implant tissue formation. The mechanoregulatory model is consistent with observations of tissue formation around poroussurfaced and plasma-sprayed implants, and provides initial criteria to evaluate the osseointegration potential of bone-interfacing implants.