This study aimed to evaluate the histological characteristics of the new bone formed at dental implant placement sites concomitantly grafted with a self-setting tricalcium phosphate cement (BIOPEX-R?). Standardized defects were created adjacent to the implants in maxillae of 4-week-old male Wistar rats, and were concomitantly filled with BIOPEX-R?. Osteogenesis was examined in two sites of extreme clinical relevance: (1) the BIOPEX-R?-grafted surface corresponding to the previous alveolar ridge (alveolar ridge area), and (2) the interface between the grafting material and implants (interface area). At the alveolar ridge area, many tartrate-resistant acid phosphatase (TRAPase)-reactive osteoclasts had accumulated on the BIOPEX-R? surface and were shown to migrate toward the implant. After that, alkaline phosphatase (ALPase)-positive osteoblasts deposited new bone matrix, demonstrating their coupling with osteoclasts. On the other hand, the interface area showed several osteoclasts initially invading the narrow gap between the implant and graft material. Again, ALPase-positive osteoblasts were shown to couple with osteoclasts, having deposited new bone matrix after bone resorption. Transmission electron microscopic observations revealed direct contact between the implant and the new bone at the interface area, although few thin cells could still be identified. At both the alveolar ridge and the interface areas, newly formed bone resembled compact bone histologically. Also, concentrations of Ca, P, and Mg were much alike with those of the preexistent cortical bone. In summary, when dental implant placement and grafting with BIOPEX-R? are done concomitantly, the result is a new bone that resembles compact bone, an ideal achievement in reconstructive procedures for dental implantology. ? 2007 Wiley-Liss, Inc.