Bone Remodeling And Stability Of Mini-implants After Delayed Orthodontic Force Loading

Objective: The aim of this study was to assess the bone remodeling and stability of mini-implants after delayed orthodontic force loading by resonance frequency analysis and histologic observation.Methods: Fouty-eight mini-implants(Abso Anchor, Dentos, Korea) were inserted into the tibias of twelve male New Zealand white rabbits, with two implants for each side of tibia. Nickel-titanium springs were set between the two mini-implants bilaterally on day 28 after insertion. A 180 g orthodontic force was applied on the right side, while the left side remained unloaded. The rabbits were sacrificed on day 31, 35, 42 and 56 after insertion(n=3). At the time of insertion, loading and animal sacrification, resonance frequency analysis(RFA) was performed for all implants and implant stability quotient values(ISQ) were recorded. Paired t-test was used to compare the differences of ISQ values between loaded and unloaded groups. All the specimens were assigned to histologic observation after decalcification and paraffin section.Results: On the unloaded side, woven bone was formed on the implant–bone interface 31 days after insertion, and mature dense lamellar bone was observed 56 days after insertion. No difference of bone remodeling was observed after force loading compared to the unloading sides on each time point. Resonance frequency analysis showed that ISQ values gradually increased after insertion. The ISQ values of loaded and unloaded groups were 20.40±2.87 and 20.98±3.17 on the day of insertion, followed by a significant increase to 39.50±2.05 and 36.33±2.30 on day 56 respectively. There was no significant difference between the loaded groups and the unloaded groups at all time points(P> 0.05).Conclusion: Orthodontic loading of 180 g force 28 days after insertion has no effect on bone remodeling and the stability of mini-implants.