THE GROWTH CHANGES OF RAT MANDIBLE FOLLOWING POSTURAL HYPERPROPULSION OF MANDIBLE

백서 하악골의 기능적 전방위가 하악골 성장에 미치는 영향

The purpose of this study was to investigate the growth changes of the mandible and associated structure in response to postural hyperpropulsion and changes after removal of postural hyperpropulsor. The experimental animals were four-week-old Sprague-Dawley males rats. The animals were worn the postural hyperpropulsor diurnally for 10 hours per day. The animals were sacrified after 1-week, 2-week, 4-week postural hyperpropulsion and 4-week postural hyperpropulsion 4-week removal period. The growth changes of rat mandible and associated structures following postural hyperpropulsion on the growing rat mandible were observed biometrically, radiographically and histologically. The finding were as follows. 1. The angle between the chief axis of the bone trabeculae in the condyle and the mandibular plane of rats observed for 4 weeks after worn the hyperpropulsor for 4 weeks was directed posteriorly as compared with that of control rats. 2. The ratio of mandibular length to maxillary length of experimental rats was higher than that of control rats. 3. The tooth axis of mandibular first molar of rats worn the postural hyperpropulsor for 4 weeks was mesially inclined as compared with control rats. 4. Histologically, the cartilage layer at the superior region of the condyle of rats worn the postural hyperpropulsor for 2 weeks appeared thicker than that of same aged normal rats, and generalized increase of the cartilage layer was shown on the condyle of rats worn the postural hyperpropulsor for 4 weeks. 5. There was no significant histologic difference between rats observed for 4 weeks after worn the postural hyperpropulsor for 4 weeks (8 week experimental rats) and same aged normal rats. 6. The newly formed bone at anterior region of articular fossa of rats worn the postural hyperpropulsor for 2 weeks and 4 weeks was thicker than that of same aged normal rats.