Effect of functional change on cell differentiation in the condylar cartilage.

The zygomatic process of the temporal bone forming the articulating surface of the glenoid fossa was resected in 25 young New Zealand rabbits in order to investigate the effect of function on the growth of the condylar cartilage. The reactions were studied in dry skulls, X-rays and histological sections from the temporomandibular joints. The region of the fossa had regenerated by 100 days in all the animals and was located further forward than in controls. The mandible tilted upwards immediately after resection of the zygomatic process, and an anterior cross-bite developed in four out of eight animals by 100 days. The height of the mandible was unaltered when measured from the superior surface of the condyle to the inferior border of the mandible. No differences were found in the length of the mandible as measured from the anterior edge of the condyle to the incisors, molars or mental foramen, but the anteroposterior width of the condylar process increased in the experimental animals and the articulating portion of the condylar process was less prominent. The mesenchymal cell layer was thickened 10, 15 and 20 days after the operation but the metachromasia of the intermediate cell layer decreased, as also did the thickness of the whole condylar cartilage. The metachromasia reappeared in the course of fossa regeneration. The results support the hypothesis that the growth of the condylar cartilage is regulated by its articulating function, and demonstrate that pressure reduces proliferation of the mesenchymal cells, although it is needed for the continuation of chondrogenesis in the condylar cartilage.