Rat Palatine Fissure: A Suitable Experimental Model for Evaluating Bone Regeneration

A novel animal experimental model of congenital bone defects without surgical intervention is needed to better mimic human alveolar cleft. We aimed to establish a new experimental model of human alveolar cleft using rat palatine fissures that are present in the central portion of the maxilla. The palatine fissures on the left and right sides are separated by the nasal septum. In this study, we examined potential bone repair by an autologous bone implant and beta-tricalcium phosphate (beta-TCP) using rat palatine fissure as a model. The results of the implants were evaluated by micro-computed tomography and histological analysis. All 20 rats received a palatine fissure on the left side; they were then randomly subdivided into 3 groups: group 1 received an autogenous bone graft, group 2 received beta-TCP, and group 3 received a blank defect with no implant at the implant site. Sixteen weeks postimplantation, new bone formation at the margins of the left palatine process of the maxilla was observed in all samples. To compare the effect of autologous bone grafts and beta-TCP on bone regeneration, the bone volume and bone mineral density (BMD) of newly formed hard tissues were calculated. At 16 weeks, the bone volume and BMD were significantly higher in group 1 than in group 2. Histological examination revealed abundant woven bone ingrowth in groups 1 and 2. Alkaline phosphatase (ALP) staining revealed the presence of osteoblasts along the leading edges on the surface of the newly formed bone. Tartrate-resistant acid phosphatase (TRAP) staining revealed that a few multinucleated giant cells were present on the surface of the newly formed bone. Our model demonstrated that higher bone volume and BMD were achieved with autologous bone graft than with beta-TCP. In conclusion, we have provided the first demonstration of the suitability of the rat palatine fissure as the implant site for bone graft materials to simulate the implantation of bone graft materials into human alveolar cleft. Thus, the palatine fissure can be considered as a congenital bone defect that is similar to the alveolar cleft conditions in humans. Impact Statement The rat palatine fissure is anatomically similar to human alveolar cleft. In this study, we examined potential bone repair by an autologous bone implant and beta-tricalcium phosphate (beta-TCP) using rat palatine fissure as a model. Autologous bone chips or beta-TCP granules were implanted into the rat palatine fissure. Our model demonstrated that higher bone volume and bone mineral density were achieved with autologous bone graft than with beta-TCP. We have provided the first demonstration of the suitability of the rat palatine fissure as the implant site to simulate the transplantation of bone graft materials into human alveolar cleft.