• The korean journal of orthodontics
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• v.21 no.3
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• pp.521-541
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• 1991

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.

• The korean journal of orthodontics
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• v.24 no.4 s.47
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• pp.917-932
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• 1994

This study was conducted to examine the changes in the shape of the Sprague-Dawley rats' articular disk following postural hyperpropulsion by observing their articular specimens through light and electronic microscopes after following 2-week and 4-week postural hyperpropulsion from their four weeks of age. The findings of this study are summarized as follows. It was shown that as compared with the control group, the experimental group indicated a significant increase in thickness of the 2-week groups' anterior and postreior portion of the articular disc. The experimental group showed statistically more significant increase in thickness of the 4-week groups' anterior portion of the articular disc than the control group. Light micrograph showed that the experimental group had more fibroblast in the anterior portion of the 2-week and 4-week groups than the comparing group. The 2-week groups showed in the findings through the electronic microscope that there were found the well developed and dilated RER which seems to actively synthesize the extracellular matrix including collagen, the cells with the well developed RER without distention which seems to actively synthesize the intracellular microfilaments due to the well developed free ribosome, and the typical chondroid cells. In addition, there was more fibroblast cell with the distended and well developed RER in the anterior area of the experimental group than that of the control group. The 4 week experimental group's anterior area of the disk had more cells than that of the control group while fibroblast with the well developed RER and free ribosome was quite abundat. Based on the above result of this study, it was shown that the functional hyperpropulsion of the mandible causes the changes in the nature of the mechanical load to the certain portion of the articular disk. As a result, it seems that there may be occurred some changes in morphology of the disc by adaptation or confrontation with these changes at the cellular level.