Age-dependent physiological changes in the histoarchitecture of the articular cartilage of the rabbit mandibular condyle: a morphological and morphometric study.

Mandibular condyle articular cartilage participates in condylar postnatal growth and is responsible for adaptations to anatomical and/or biomechanical alterations throughout life. In a preliminary study in rabbits, differences were observed in the thickness of the layers of articular cartilage in control animals at 5 and 6 months (generally considered adults for this purpose). This study aimed to describe sagittally sectioned condylar cartilages stained with Picrosirius-hematoxylin in rabbits at 40 days and 5, 6, 8, 13, and 18 months to determine when histological maturity is reached. At 40 days, 5 layers were seen: fibrous, proliferative, transition, maturation, and hypertrophic. Older animals (5-18 months) lacked the transition layer. Fibrous, proliferative, and hypertrophic regions were considered for morphometric analysis. The thickness of the fibrous region did not change during the analyzed period (p = 0.1899). When proliferative and hypertrophic regions and the total thickness of the cartilage were compared, a difference was detected (p < 0.001). The thickness of the proliferative region was greatest at 40 days and decreased at 5 months; however, it increased at 6 months, when it was significantly thicker than at 5, 8, 13, and 18 months. Both the hypertrophic region and the total thickness were thickest at 40 days, intermediate at 5, 6, and 8 months, and thinnest at 13 and 18 months. In summary, our data suggest a physiological period of increased cartilage growth at 6 months. Additionally, rabbits at this age should be avoided in experiments involving condylar cartilage. Finally, 13-month-old rabbits have reached histological maturity of the condylar cartilage.