Reconstruction of rabbit mandibular bone defects using carbonate apatite honeycomb blocks with an interconnected porous structure.

Carbonate apatite (CO 3 Ap) granules are useful as a bone substitute because they can be remodeled to new natural bone in a manner that conforms to the bone remodeling process. However, reconstructing large bone defects using CO 3 Ap granules is difficult because of their granular shape. Therefore, we fabricated CO 3 Ap honeycomb blocks (HCBs) with continuous unidirectional pores. We aimed to elucidate the tissue response and availability of CO 3 Ap HCBs in the reconstruction of rabbit mandibular bone defects after marginal mandibulectomy. The percentages of the remaining CO 3 Ap area and calcified bone area (newly formed bone) were estimated from the histological images. CO 3 Ap area was 49.1 ± 4.9%, 30.3 ± 3.5%, and 25.5 ± 8.8%, whereas newly formed bone area was 3.0 ± 0.6%, 24.3 ± 3.3%, and 34.7 ± 4.8% at 4, 8, and 12 weeks, respectively, after implantation. Thus, CO 3 Ap HCBs were gradually resorbed and replaced by new bone. The newly formed bone penetrated most of the pores in the CO 3 Ap HCBs at 12 weeks after implantation. By contrast, the granulation tissue scarcely invaded the CO 3 Ap HCBs. Some osteoclasts invaded the wall of CO 3 Ap HCBs, making resorption pits. Furthermore, many osteoblasts were found on the newly formed bone, indicating ongoing bone remodeling. Blood vessels were also formed inside most of the pores in the CO 3 Ap HCBs. These findings suggest that CO 3 Ap HCBs have good osteoconductivity and can be used for the reconstruction of large mandibular bone defects. The CO 3 Ap HCB were gradually resorbed and replaced by newly formed bone.