In an attempt to investigate whatever changes might occur to mandibular head, mandibular fossa, superior and inferior articular cavity and articular disc under normal mandibular movement without intermaxillary fixation, conformational changes such as mutilation and shortening of the mandibular process were experimentally prepared in rats and histological observations were made employing the H-E staining method until the postoperative 3rd month. The results are as follows:
1) The mandibular fossa and articular disc showed the most marked changes. The superior articular cavity and mandibular head showed less marked changes. The inferior articular cavity showed the least change.
2) Generally, proliferative changes such as tylosis of the fibrous layer of the mandibular fossa, proliferation of the connective tissue of the articular cavity, tylosis of both the articular disc and the fibrous layer of the articular cartilage of the mandibular head were the major findings.
3) In the mandibular fossa, tylosis of the fibrous layer, morphological assymetrization and emergence of cells in the fibrous layer were the major changes noted. The shape itself tended to recover its regularity with the passage of time.
4) In the superior articular cavity, proliferation of fibrous connective tissue as well as granules cohering within the connective tissue structure were observed. The fibrous connective tissue diminished with the passage of time. Over the same time, the shape of the cohering granules first became irregular, then took on a tonguelike shape.
5) The major change observed in the articular disc was tylosis. In the initial stage, blood vessels emerged, so the outer layer of the disc appeared heterogeneous. However with the passage of time the emergence of vessels ceased and the outer layer became homogeneous.
6) In the inferior articular cavity, shrinking of the cavity was observed, and a few cohering granules were seen. In the initial stage this site showed the least change.
7) In the mandibular head, tylosis of the fibrous perichondral layer was observed throughout the observation period.
8) In general all of the locations tended to return to their normal shape with the passage of time, with some actually regaining close to normal shape by the postoperative 3rd month.
9) No specific changes were observed in the joint of the unaffected side.
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