実験的下がく骨骨折離断が成長期の下がく頭に及ぼす影響に関する病理組織学的研究

Abstract

The purpose of the present study was to elucidate the effect of mandibular fracture, one of causes of retardation of the postnatal mandibular development, on the growing condyle. Three groups (Groups A, B and C) of young rats, five weeks old, were used. In Group A, the mandible received no treatment. In Group B, the right mandible was sectioned with a dental fi ssure bur, and then the wound was merely closed. In Group C, the right mandible was also sectioned, but an aluminium foil was placed between the two fragments. The animals of the above three groups were killed 1, 2, 4, 6, and 8 weeks after treatment, and the mandibular condyles were examined radiographically and histopathologically.1. Radiographic observations(1) The mandibular condyles in Groups B and C were similar in size to those in Group A at 1 and 2 weeks. However, the mandibular condyles in both groups were smaller than those in Group A at 4, 6, and 8 weeks.(2) In Group B, a clear radiolucent line was observed in the fracture site at 1 week. However, the line became indistinct with weeks. The fracture line was not clearly identified at 8 weeks. In Group C, the fracture line was clearly distinguished throughout the entire experimental period.2. Histopathological observations(1) In Group B, all zones (the zones of articulation, proliferation, differentiation, and hypertrophy) in the mandibular condyle were similar in structure to those in Group A at 1 week. However, the zones of proliferation, differentiation, and hypertrophy in the condyle were less cellular and thinner than in Group A at 2, 4, and 6 weeks. The above three zones in the condyle became similar in structure to those in Group A at 8 weeks.(2) In Group C, all zones in the mandibular condyle were similar in structure to those in Group A at 1 week. However, the zones of proliferation, differentiation, and hypertrophy in the condyle were less cellular and thinner than those in Group A at 2, 4, 6, and 8 weeks.(3) In Group B, the two fragments in the fracture site were connected with each other by fibrous and cartilagenous tissues throughout the entire experimental period. The connection of these fragments became tighter with weeeks.(4) In Group C, because of insertion of an aluminium foil, the two fragments in the fracture site were not connected with each other throughout the entire experimental period.