Bone Remodeling Following Osseointegration in a Rat Maxilla Implantation Model

Objectives: The present study aimed to examine the fate of injured bone around titanium implants after the establishment of osseointegration on an animal model using rat maxillae. In particular, it focused on the possibility of bone remodeling around the implant.

Materials and Methods: Custom-made titanium implants were inserted into prepared bone cavities of rat maxillae according to methods described by Fujii et al. (1998). Bone formation and maturation processes incident to implantation were evaluated by double-staining with alkaline phosphatase (ALP) and tartrate-resistant acid phosphatase (TRAP), immunohistochemistry for bone matrix proteins, vital staining with calcein, and elemental mapping with an electron probe microanalyzer (EPMA).

Results: The injured bone with empty osteocytic lacunae or piknotic osteocytes resulting from drilling remained between the pre-existing and newly formed woven bones after 1 mo. It gradually decreased, to disappear completely by active bone remodeling with a synchronized coordination of ALP-positive osteoblasts and TRAP-reactive osteoclasts by 3 months post-implantation. Then, the newly formed woven bone around the implant was replaced by compact bone. The immuno-intensity in bone matrix proteins appeared weaker post 3 months than at 1 month post-implantation, and showed a plateau thereafter. Dynamic labeling exhibited two clear lines in the newly formed bone around the implant throughout this experimental period. EPMA analysis demonstrated that levels of Ca and P increased chronologically in the newly formed bone, and became identical to those of the pre-existing surrounding bone at 2.5 months post-implantation.

Conclusions: These findings suggest the occurrence of bone remodeling in the newly formed and injured bones around titanium implants, even after osseointegration has been achieved. This study was supported by a Grant-in-Aid for Scientific Research from the Japan Society for Promotion of Science (JSPS, #19592232 to N.F.).