Abstract: Objective: To investigate the effect of different loading time on the osseointegration between mini-implant and bone under large loading force. Methods: Twenty-four mini-implants were implanted into the mandibles of six beagle dogs. 350g force was loaded onto the corresponding mini-implants immediately (0 w group), 2 weeks (2w group), 4 weeks (4w group), and 8 weeks (8w group) after implantation. Maximum removal torque (MRT) was tested and histology of the interface of implant-bone tissue was observed using HE staining after 4 weeks of loading. Results: Two of the mini-implants in 2w group were lost and 1 in 0w group was unstable. Other mini-implants were stable. The MRT of the 8w group was higher than that of 4w group (P=0.03). The interface of mini-implant-bone tissue in 8w group was composed of mature bone tissue, while it was composed of newly formed bone in 4w group. The lowest MRT was detected from the 0w group and 2w group, and no significant difference was found between these two groups (P=0.78). Furthermore, more obvious fibrous tissue was observed in the 2w group in contrast to 0w group. Conclusion: Some risks may occur if loaded immediately or 2 weeks after implantation. It is suggested to load 4 weeks later after implantation.

Key words: Large loading force, Loading time, Mini-implant, Osseointegration