Age changes in the articular tissue of human mandibular condyles from adolescence to old age: a semiquantitative light microscopic study.

In a previous study (Luder, Anat. Rec., 1997;248:18-28), the articular tissue of the adult mandibular condyle was characterized semiquantitatively. However, questions about age changes of mature tissue were not answered, and the time course of tissue maturation from the end of condylar growth to the attainment of the adult appearance remained unknown. These issues are addressed in the present investigation. By using a light microscope, features of the superficial, intermediate, and deep articular tissue zones as well as of the subchondral bone were assessed at nine predetermined condylar sites. The frequencies of these features were recorded as scores from 0 (absent) to 10 (continuous) and were plotted against age. Analysis of covariance served for testing the significance of age and sex effects as well as intracondylar variability. Whereas almost all age-related changes in frequencies of tissue features were similar along the whole lateromedial dimension, changes at the putatively nonload-bearing, posterior slope differed significantly from those at the putatively load-bearing, anterior slope and zenith of the condyle. Two patterns of changes were noted. Frequencies of a first group of tissue features altered mainly during the age period from 15 years to 30 years and remained more or less stable thereafter. This course was characteristic for 1) a progressive cartilaginification of the superficial zone as well as 2) the disappearance of hypertrophic growth cartilage and 3) the appearance of grid-fibrous fibrocartilage in the deep zone, which were accompanied by 4) a decline in endochondral ossification and 5) the formation of a compact, subchondral bone plate. Frequencies of a second group of tissue features disclosed changes that continued up to middle and old age. This pattern was evident regarding 1) a decrease in the prominence associated with 2) a drop in cellularity and 3) progressive fibrosis or even cartilaginification of the intermediate zone. Among the age changes of condylar articular tissue, those affecting the superficial and deep zones as well as the subchondral bone are largely complete by about 30 years of age and seem to be related primarily to a gradual transition from growth to adulthood. In contrast, a second group of alterations, which progress to old age and involve mainly the intermediate zone, appears to be associated with continued maintenance and adaptive articular remodeling as well as possibly senescence. Both maturational and later age changes seem to depend markedly on articular load bearing.