Influence of immediate implant loading on early bone healing processes

Objectives: The evaluation of the impact of immediate implant loading on the early phases of peri-implant bone healing. Methods: Each of 12 experimental rabbits received 5 consecutively placed titanium implants in the tibial diaphyses, which were left to heal for 3 days, 1, 2, 4 and 6 weeks respectively. Six animals received an immediate loading protocol of 2.2 N at 3 Hz for 1800 cycles/day during 5 days/week, whereas the other 6 served as unloaded controls. Histological and histomorphometrical analyses were performed and the data were statistically analysed using repeated ANOVA followed by a Tukey post-test (Ą = 0.05). Results: In the early time points, endosteal and periosteal bone formation was initiated while the original cortex showed signs of osteocytic cell death. After 2 weeks, an increasing amount of basic multicellular units was noted as well as new bone formation adjacent to the implants in the original cortex, indicating an ongoing process of bone remodelling and adaptation. Differences between the immediately loaded and unloaded implants were mainly found in the pattern of new bone formation in the later time points. Significantly larger endosteal and periosteal bone formation was observed around the immediately loaded implants after 4 and 6 weeks respectively. This endosteal and periosteal bone formation was not only more pronounced around the loaded implants but increased until a later time point compared to the unloaded controls. The bone formation in the original cortex on the other hand, was significantly higher at 6 weeks around the unloaded implants. Conclusion: The results show that the immediate loading protocol caused no significant effect on the sequential events of osseointegration in cortical bone. Immediate implant loading, however, lead to a more distinct periosteal and endosteal reaction on the one hand and less bone formation in the original cortex on the other hand.