ウサギ下顎骨仮骨延長中に発現した軟骨組織の骨化様式に関する研究

Abstract

The use of distraction techniques to correct the craniofacial skeleton has expanded treatment options for patients with maxillofacial abnormalities and defects.During distraction osteogenesis of tubular bones, newly deposited bone is formed by both in tramembranous and endochondral ossification. The mandible differs from tubular bones in its origin, structure, and function. It is well known that bone formation generally involves intramembranous ossification in the mandible. However, several reports suggest that cartilage is observed not only in tubular bone lengthening but also in mandibular distraction models. It is unclear, however, whether cartilage in the distraction gap is transformed into new bone. This experimental work investigated the morphological features of cartilage during distraction osteogenesis in a rabbit model.Corticotomy was performed just anterior to first premolar, and custom-made devices were applied. The devices were lengthened 0.25mm immediately after surgery, and then repeatedly every 12 hours for 10 days. Four rabbits were sacrificed immediately after lengthening, and 4 more were sacrificed 5 and 10 days after the completion of lengthening. Histological staining, immunohistochemistry, and terminal deoxynucleotidyltransferase dUTP-biotin nick end labeling (TUNEL) were performed.Immediately after lengthening, a substantial amount of cartilage had developed from the central fibrous tissue. The cartilage decreased gradually between 5 and 10 days. Five days after distraction was completed, chondrocytes appeared to be hypertrophic and showed a TUNEL-positive reaction indicating apoptosis. Blood capillaries developed around the cartilage with hypertrophic chondrocytes and increased gradually. Immunoreactivity for type II collagen was not noted around hypertrophic chondrocytes near new bone trabeculae, but type I collagen protein was observed in these cells. Ten days after distraction was completed, TRAP-positive cells were observed around hypertrophic chondrocytes.Five days after distraction was completed, chondroid bone, a tissue intermediate between bone and cartilage, was formed directly by chondrocyte-like cells between the cartilage and new bone trabeculae. These cells showed positive staining for type I collagen. Furthermore, there was no TUNEL expression in chondroid bone.These results indicate that cartilage in the distraction gap was transformed into new bone. Transition of cartilage into bone was classified into two types: endochondral ossification and trans-chondroid bone formation.