TYPE-II COLLAGEN EXPRESSION IN THE MANDIBULAR CONDYLE DURING GROWTH ADAPTATION - AN EXPERIMENTAL-STUDY IN THE RABBIT

An experiment was designed to mimic orthopedic functional appliances i n order to investigate the spatial and temporal characteristics of typ e II collagen secretion as a marker of cartilage maturation in the man dibular condyle of young rabbits. The position of the glenoid fossa in relation to the condyle was altered so that articulation now took pla ce more posteriorly. Histological sections of the condyles of 15-, 20- and 30-day-old experimental and control animals were stained with tol uidine blue and with an anti-type II collagen antibody. A widened prog enitor cell layer was found posteriorly in the experimental condyles a nd a narrow layer was found anteriorly to the articulating region. The chondroblast layer was also widened posteriorly, whereas the hypertro phic cell zone was narrower; the opposite was seen anteriorly. The eff ect was marked in 15- and 20-day-old animals and weak in 30-day-old an imals. Type II collagen stain and strong toluidine blue metachromasia were not observed in the progenitor cell zone until the chondroblasts had acquired a flattened, slightly hypertrophic morphology, which was found deeper in the experimental condyles than in the controls. This i s interpreted as a slowing down of the differentiation of chondroblast s as a result of the force applied. The effect of masticatory function may also be explained in terms of delayed differentiation of chondrob lasts and increased growth.