Abstract: Objective To evaluate the stability and histological manifestation at implant-bone interface of the microscrew implants under various loadings and to provide the theoretical basis for the clinical treatment. Methods Microscrew implants(length 7 mm,diameter 1.4 mm) were implanted in the tibae of the rabbits,120 in total,and they were divided into 4 groups,30 in each group.After implantation the implants were loaded immediately with 0,150,300 and 450 g by NiTi coil.The loading period was 20 weeks.After the experiment the rabbits were sacrificed and the displacement of the implants were measured and peri-implant tissues were analyzed histologically.Results The average displacements of the implants in 0 g group,150 g group and 300 g group  were  very small,they were 0.09,0.20, and 0.16 mm; the difference had no significant difference(P>0.05). The average displacement of the implants in 450 g group was decreased (0.60 mm),and the difference of displacement before and after loading was significant(P<0.05).The implant-bone interface in 0 g group  and 150 g group were similar,mainly in the cortical bone.The implant-bone interface in 300 g group was much wider.And the interface in 450 g group  almost contained  all the implants.Conclusion The implants are stable with no displacement under certain amount of loading.Although microscrew is stable,it will have some displacement in some conditions.The implant-bone interface becomes longer with the increasing of loading.

Key words: implant, anchorage, animal experiment, orthodontics