The healing process of the injured condylar cartilage of the temporomandibular joint (TMJ) was investigated in rats to as certain the fine structural characteristics of the repaired tissue and the influence of age on healing.
Cartilage injury was prepared by cutting the condylar heads of Wistar male rats (4 weeks, 16 weeks, and 1 year old) to the subchondral bone with a # 700 dental fissure bur.
The animals were sacrificed immediately and 3 days, after the operation and 1, 2, 3, 4, 6, and 10 weeks postoperatively and were examined both histologically and ultrastructurally.
The results obtained were as follows:
1. In the young group (4 weeks old), proliferation of cartilage cells occurred in 2-3 weeks and cartilaginous repair was completed 6 weeks after operation.
2. In the young adult group (16 weeks old), the proliferation of undifferentiated mesenchymal cells from the surface proliferating cell zone to the deep layer was observed.
The above-mentioned cells differentiated to chondrocytes 4 weeks postoperatively.
The differentiation of undifferentiated mesenchymal cells in the bone marrow into chondrocytes was also suggested, and cartilaginous repair was completed by 10 weeks after operation.
3. In the old group (1 year old), the proliferation of undifferentiated mesenchymal cells was not obvious until 2-3 weeks after operation. Although the cells differentiated into chondrocytes in 4-6 weeks, collagen fibril formation was insufficient in the lower level of the repaired tissue.
4. In all of the groups, the main findings regarding healing was undifferentiated mesenchymalcells in the surface layer of TMJ condylar cartilage (initially in the proliferating cell zone).
It was shown that these cells have remarkable potential for healing in condylar cartilaginous tissue.
