Detection of alkaline and acid phosphatases around titanium implants: a light microscopical and histochemical study in rabbits

Alkaline phosphatase (ALP) may play a very important role in the mineralization process of bone, while acid phosphatase (ACP) is implicated in bone resorption. The aim of the present study was a histochemical characterization of ALP and ACP at the bone-implant interface after the insertion of smooth screw-shaped threaded titanium implants in rabbit tibia. In the first 3 weeks it was possible to observe a very strong positivity in the cytoplasm of osteoblasts near the implant surface. These osteoblasts surrounded islands of soft tissue or trabeculated woven bone. In the first 4 weeks a large quantity of newly formed bone originating from the periosteal and endosteal surfaces was observed; a remodelling of the cortical bone was also present. A sharp decrease of the ALP activity was observed from the third week onwards, and at 2 months it was possible to observe that the ALP and ACP activities were similar, possibly in relation to the remodelling of bone. From 2 to 6 months there were no morphological differences in the microscopical appearance of the bone around the implants. The bone was mature, compact and the new bone had staining features similar to pre-existing bone.