OBJECTIVEThe aim of this investigation was to study the expression of collagen type II in the cartilage of mandibular condyle following asymmetric inter-maxillary traction.

METHODSTwo hundred and twenty SD rats were used in this study (one hundred and four rats loading 0.39 N elastic force, another one hundred and four rats loading 1.18 N elastic force, while twelve rats for control). The extra-joint device was fixed on the right side by surgery. Half of the experimental group was killed at 3, 7, 14, 28 days. The devices were removed at the 28th day in the rest rats, and the rats were sacrificed at 3, 7, 14, 28 days after removing the device. The type II collagen expression levels of all the joints were measured using immunohistochemical techniques.

RESULTSThe positive expression of the type II collagen was mainly observed in the cytoplasm of chondrocyte, especially in maturative and hypertrophic layer. The expression intensity was different in different stages and different sides. Both of the two experimental groups showed the same tendency, while the changes in the light force group were more obviously than the heavy force group. In the right side (force-loading side), the type II collagen expression decreased at the early force-loading period. After the device was removed, the expressions increased immediately but then reach the lowest level. The expression almost recovered to normal level at the end of experiment. In the left side (none force-loading side), the expression remained increasing after force-loading and reached the peak at the 14th day.

CONCLUSIONThese results suggest that even in the adult individuals, the chondrocyte showed reaction to the mechanical force by altering type II collagen expression patterns and it may be the cause of the cartilage remolding after asymmetric inter-maxillary traction. A forward elastic force showed a depressant effect in matrix synthesis, and heavy force had stronger effect. But the rotation of condyle accelerated the matrix synthesis.