Influence of Periosteum on the Healing Process for Porous Hydroxyapatite Block Implants of Mandibular Bone Defect in Domestic Rabbits

In the oral and maxillofacial area, we often encounter cases in which the periosteum involved in bone defects cannot be preserved. Therefore, porous hydroxyapatite (HAP) blocks are inserted into the bone defect in such cases. The purpose of this experiment was to investigate the influence of the periosteum on the porous HAP block implants. Bone defects measuring 5×5mm were made at the region of the inferior border of the mandible in 15 mature domestic rabbits, and a porous HAP block (pore size 200μm ; porosity rate 70±3% ; firing temperature 1200℃) was inserted. In one group, the periosteum was preserved, and in other groups, the periosteum had been removed before the HAP block was inserted. These specimens were examined histopathologically at 3, 5, 7, 14, 21, 30, 60 and 90 days after operation. Histomorphometrical analysis of bone formation within the HAP pores was performed at 14, 21, 30, 60 and 90 days after operation. The following results were obtained : 1. On histopathological examination, the whole healing process and new bone formation within the HAP pores were more rapid in the periosteum-preserved group than that in the groups without periosteum. 2. On histomorphometrical analysis, the average of bone formation within HAP pores did not vary much during the short term, however it was larger in the periosteum-preserved group than that in the groups without periosteum during the long term. 3. In the periosteum-preserved group, new bone extending from the bone stump covered almost all of the HAP surface and the bone surface developed smoothly. However, new bone was not well formed in some regions of the HAP surface and the bone surface was rough in the groups without periosteum. 4. In this experiment, wound healing around HAP implantation was better in the periosteum-preserved group than that in the groups without periosteum. However, bone formation average tended to increase gradually even in the groups without periosteum. It is suggested that the bone conductivity of HAP provides a good influence on the healing of bone defect whether the periosteum exists.