Development of Novel Mini-Tetrapod Bone Fillers

Objectives: We fabricated new small tetrapod-shape artificial bone elements by injection molding of micro particles of alpha-tricalcium phosphate and evaluated their safety and efficacy. Materials and Methods: In vitro, surface and inside of tetrapods-shape bone fillers and OsferionŽ were observed by SEM and CT. In vivo, maxillary first molar teeth were extracted from 4 mature (5 years old) beagle dogs with preservation of the alveolar bone. Thereafter, left mesial sockets were filled with tetrapods-shape bone fillers. As a control, the right mesial sockets were filled with OsferionŽ and the left distal sockets were left unfilled. Results: Currently available granular type bone fillers are being produced by pulverizing porous calcium phosphate blocks. Because of the irregular size and shape of granules dead space is often formed and connectivity of pores is not guaranteed. In contrast, the size and shape of the tetrapod is uniform, being designed in such a way that connecting pores of the ideal size for cell and blood vessel invasion are formed when the tetrapods are assembled. Four protrusions of each tetrapod help stabilize assembled structure. The surface shape of the tetrapod bone fillers was homogeneous in SEM images and they filled space uniformly in CT image. In contrast, the surface shape of OsferionŽ was heterogeneous and they filled space nonuniformly. In animal test, the dogs were euthanized at 1, 2 months. No side effects related to the fillers were observed. CT analysis showed that the substantial osteogenesis occurred around the tetrapod bone fillers. Histological analysis revealed that substantial bone formation occurred around the tetrapod fillers with osteoclasts resorbing them. Conclusion: These data suggest that the tetrapod bone fillers were safe and effective. We plan to apply these fillers to preventing the alveolar ridge resorption after tooth extraction.