Histodynamics of bone tissue formation around immediately loaded cylindrical implants in the rabbit

Objectives: The local mechanical environment influences early peri-implant tissue formation. It is still unclear whether immediate loading limits or promotes peri-implant osteogenesis and which mechanical parameters are important herein. The present study evaluated the influence of well-controlled mechanical stimuli on the tissue response around immediately loaded cylindrical turned titanium implants at two different observation periods. Material and methods: A repeated sampling bone chamber, consisting of dual-structure perforated hollow cylinders with a cylindrical implant, was installed in the tibia of 14 rabbits and used to conduct three displacement-controlled immediate loading experiments: (i) 30 μm – 400 cycles/day – 1 Hz frequency – 2 ×/week – 6 weeks; (ii) 30 μm – 400 cycles/day – 1 Hz – 2 ×/week – 6 weeks, followed by another 6 weeks with a 50 μm – 800 cycles/day – 1 Hz – 2 ×/week loading protocol; and (iii) 0 μm implant displacement for 12 weeks. A linear mixed model and logistic mixed model with α=5% were conducted on the data set. Results: The tissue area fraction was significantly the highest after 12 weeks of loading. The bone area fraction was significantly different between all three loading conditions, with the highest values for the 12-week loading experiment. Twelve-week stimulation resulted in a significantly higher mineralized bone fraction than 6 weeks. Loading did have a significantly positive effect on the mineralized bone fraction. The incidence of osteoid-to-implant and bone-to-implant contact increased significantly when loading the implant for 12 weeks. Conclusion: Immediate loading had a positive effect on the tissue differentiation and bone formation around cylindrical turned titanium implants. Controlled implant micro-motion up to 50 μm had a positive effect on the bone formation at its interface.