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. GRAPHICAL ABSTRACT: [Figure: see text]