Effect of controlled early implant loading on bone healing and bone mass in guinea pigs, as assessed by micro-CT and histology.

Without controlled loading, the failure of early loaded oral implants is higher than in delayed loading, unless loading regimens can be identified that stimulate bone formation. The purpose of this study was to investigate whether controlled early loading optimizes osseointegration. Six series of guinea pigs received percutaneous implants in both tibiae. One implant was stimulated, the contra-lateral served as the control. The strain rate amplitude varied from 1,620 to 12,000 microstrain s(-1). In vivo microfocus computed tomography (micro-CT) was used to study the peri-implant bone at three time points: 1 wk after implantation, but before starting stimulation (V1); 2 wk after stimulation (V2); and 4 wk after stimulation, after the guinea pigs were killed (PM). Bone implant contact and bone mass [BM (%) bone occupied area fraction] were analyzed. The implant failure was 5.9% (six control/one test). Although bone implant contact did not significantly differ, bone mass in the distal half peri-implant marrow cavity was significantly higher around test implants. Strain rate amplitude and the difference in bone mass between test and control implants were inversely correlated. A strain rate amplitude of 1,620 microstrain s(-1) in the cortical bone at a distance of 1.3 mm from the implant showed the highest effect. Based on these results, early loading did not negatively affect the implant outcome. On the contrary, an improved bone reaction in the marrow cavity around early loaded implants was achieved.