Bone Regeneration with Self-Setting Alpha-TCP Cement at Implant Placement Sites

Objectives: To histologically evaluate the regenerated bone after application of a self-setting alpha-tricalcium phosphate (a-TCP) bone substitute concomitantly to dental implant placement. Methods: Four weeks-old male Wistar rats had their maxillary molars extracted and, 4 weeks later, dental implants were inserted at the edentulous space. Standardized bone defects neighboring the implants were filled with a-TCP cement. Histochemical examinations, bone mineral density (BMD) assessment and element mapping were conducted, the bone regenerate being evaluated at 1, 2, 4, and 8 weeks post-operatively in two areas: 1) the a-TCP surface corresponding to the previous alveolar ridge (alveolar ridge area), and 2) the cement/implant interface (interface area). Results: In the alveolar ridge area, many tartrate-resistant acid phosphatase-reactive osteoclasts accumulated on the a-TCP surface, migrating from the preexisting bone towards the implant. Alkaline phosphatase-positive osteoblasts followed the osteoclasts and deposited new bone matrices, demonstrating the phenomenon of cellular coupling between osteoclasts and osteoblasts. Up to the 8th week, the alveolar ridge area of a-TCP was gradually being covered with thick lamellar/compact bone. In the interface area, again, initial presence of osteoclasts between implants and the a-TCP was followed by osteoblastic migration. Osteoblasts secreted new bone on the a-TCP which was once resorbed by osteoclasts, and at the 8th week most of the regenerated bone had directly attached the implant surface. In both areas, the new bone featured the traits of compact rather than those of woven bone, as evidenced by the histological findings, the high BMD values, and the Ca, P, and Mg concentrations, which were shown to be similar to those of the preexisting cortical bone. Conclusion: Application of a-TCP cement concomitantly with dental implant placement appears to induce a physiological-like cellular coupling between osteoclasts and osteoblasts, resulting in a regenerated bone with good “bone quality”, the desired final outcome in implant dentistry.