Microvascular Changes During Osseous Healing of Mandibular Segmental Defects in Rabbits after Placement of HAP Granules and Blocks

Abstract

I examined osseous healing after placement of HAP granules (APACE-RAM G^®) and HAP blocks (APACERAM B^®) in mandibular segmental defects of 8×4×3mm in rabbits. An ultrasonic scalpel was used to preserve the preexisting vessels from the inferior alveolar artery. Sequential changes in the histological structures and microvasculature were investigated on microvascular corrosion castings under light and scanning electron microscopy.
     One week after the operation new bone formation, which was similar for both the granules and blocks, was seen on the bone marrow side of the defect. In the HAP granule group, the granules were surrounded by new sinusoidal capillaries which developed to form a new capillary network at two weeks. Newly-formed bone spread between the new capillary network and impacted the granules at four weeks. Spaces of less than 50μm were observed between the granules, new bone formation was delayed, and fibrous tissue remained. In the HAP block group, new capillary networks and new bone formation were observed in the larger pores (greater than 200μm) at two weeks. At three weeks, one new capillary was observed entering a l00-200μm pore where new bone formation had been delayed.
     These results suggest that new capillary and bone formation occur when the spaces between the HAP granules is greater than 50μm and when the pores in the HAP blocks are greater than 50μm.