Objective: The purpose of this study was to evaluate the cortical and trabecular bone activity by means of tetracycline bone labeling of a surface-modified (IBAD) versus a non-surface-modified titanium alloy implant in a canine model. Methods: Implants were surgically placed in the dogs tibiae and the model provided specimens that remained 2 and 4 weeks in vivo. Prior to euthanization, 10mg/Kg oxytetracycline was administered for bone labeling. The limbs were retrieved by sharp dissection, and non-decalcified thin sections containing the implant in their centers were prepared for microscopy evaluation under UV light. Bone activity determination (amount of tetracycline labels) was evaluated dividing the specimens in regions of interest along the length and away from the implant surface (to 2 mm) by quantitative microscopy techniques. Physiologic activity was obtained by tetracycline labeling acessment away (> 3 mm) from the implant surface and comprised the normalizing data. Results: Results showed that the 4-week surface-modified implant had significantly higher (P = 0.05) amount of tetracycline labeling than other groups and demonstrated that there is significantly more labeling in regions of trabecular bone than in regions of cortical bone. Quantification of the amount labeled for the different regions of interest at different distances from the implant surface (to 2 mm) revealed that the only region that had significantly higher activity than physiologic levels was the region adjacent from the implant surface (to 0.5 mm) and the amount of labeling was significantly higher for the 4-week surface-modified group. Determination of bone activity gradients from the implant surface was performed by linear regression and presented negative slopes from the implant surface. Conclusions: These results indicated that there is a time-dependent increased osteoconductivity for the surface-treated implants and that increased bone activity after implantation is restricted to the first 0.5 mm region adjacent from the implant surface.

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