OBJECTIVEThis study aimed to evaluate the influence of loading in different healing periods on implant stability and to establish an animal model of anchorage implant screws.

METHODSAnchorage implant screws were implanted in sheep alveolar bone to establish the implant screw animal model. The animals were randomly divided into four groups: group A, sheep without loading; group B, sheep loaded immediately after implant; group C, sheep loaded after two weeks; and group D, sheep loaded after four weeks. The maxillary and mandibular tissue specimens with implants were dissected. The maxillary tissue specimens were used to make undecalcified bone grinding slices, and the healing mode of the implant-bone interface was observed by light microscope. The maximum shear strength of loose mandibular specimens was measured by a material testing machine. The differences in group data were statistically analyzed. RESULTS 1) A general difference in shear strength exists among the four groups. The shear strengths in groups A and B were lower than those in groups C and D. 2) No significant difference in healing mode was found between the pressure side and the tension side of the longitudinal-grinded bone slices with implants. Both fiber combination and osseointegration of transverse-grinded slices could be found in the interface in all four groups. The major integration mode of the implant-bone interface of groups A and D was osseointegration, whereas that of the implant-bone interface of groups B and C was fibrous tissue transformation. The surrounding bone tissue regenerated toward the implants of group C.

CONCLUSIONResults show that loading time influences the stability of implant anchorage.