[Involvement in morphological changes of the articular cartilage of rat temporomandibular joint induced by experimental malocclusion].

The effect of malocclusion induced by increase in unilateral occlusal vertical dimension on the articular cartilage of rat mandibular condyle was histologically and immunohistologically examined. WKA rats (8 weeks) were divided into three group A: untreated (control) rats, group B: rats forced to mouth open just for 20 min, and group C: rats given malocclusion by putting the 1 mm diameter wire on the right upper molar continuously. After treatment, each rat was sacrificed periodically up to 9 weeks, and the morphological changes of condylar cartilage (articular, embryonic and transitional zones of cartilage layer) were histologically investigated. The thickness of articular cartilage in all groups was decreased in a time-dependent manner (up to 9 weeks after treatment). In group C rats, whose articular cartilage was thinnest in three groups, the reduced thickness of cartilage in the non-treated side (the left side) was same as that in the treated side which was presented with excessive molar contact. But, its occurrence in the treated side was seen 2 weeks earlier than that in the non-treated side. Even in group B rats which were only forced to open the mouth for 20 min without setting of permanent malocclusion, the thickness of condylar cartilage was decreased more than that of group A rats. When the condylar cartilages of all three groups were immunohistologically examined with anti-interleukin-1 (IL-1) antibody in order to investigate the pathophysiological involvement of IL-1, which is well-known catabolic factor to cartilage, some chondrocytes in articular cartilage were positively stained. The ratio of IL-1 positive cells increased time-dependently. IL-1-producing cells in group B and the non-treated side of group C reached to the maximal ratio at the same time when the condylar cartilage markedly decreased in thickness. However, the ratio of IL-1-positive chondrocytes in the treated side of group C was maximal four weeks after the decrease of cartilage thickness. In respect with the size of cells in cartilage, the occurrence of decreased thickness in condylar cartilage corresponded to that of the reduction of cellular size, especially in the embryonic zone of group C. These results described above suggest that malocclusion, unilateral immature occlusion, can induce the thinning of condylar cartilage which may result from the reducing size of articular chondrocytes (differentiated chondrocytes) and the accompanying decreased cartilage matrix. This change of cartilage may be caused by IL -1 that articular chondrocyte seemed to produce.(ABSTRACT TRUNCATED AT 400 WORDS)