Influence of initial implant mobility on the integration of titanium implants. An experimental study in rabbits

In the present study, the influence of initial instability on the healing of titanium implants was studied in 9 lop-eared rabbits. Titanium implants (Brånemark System) were inserted in the tibiae, a location with cortical bone only, in such a way that they were either stable (control), rotation-mobile, or totally mobile. Implants were also inserted in the distal femoral condyles, representing an implantation bed with mainly cancellous bone, so they either showed no initial mobility (control) or were rotation-mobile. After 12 weeks of healing, the implants were retrieved, together with surrounding bone, fixed, dehydrated, and embedded in plastic resin. About 10 micron thick ground sections were prepared for light microscopic morphometry. The mineralized bone to titanium contact, and the amount of bone occupying the threads, were calculated, whereafter the outcome of the different locations were compared. All retrieved implants were clinically stable at the of the experiment. For the tibia sites, a statistically significant less bone to titanium contact, and a less amount of bone in the threads, were found for the totally mobile implants, as compared to the corresponding initially stable controls. Moreover, a statistically significant higher amount of bone was found in the threads of the rotation-mobile implants inserted in the femoral condyle as compared to their initially stable controls. The study indicated that initial rotation-mobility, independent if it occurs in cortical or trabecular bone, does not necessarily lead to an inferior integration of unloaded implants. However, initial total implant mobility within the cortical layer results in a statistically significant less amount of bone around the implants, as compared to stable controls.