Effects of mechanical load on mandibular condylar cartilage and subchondral bone of male rats.

OBJECTIVE

The mandibular condylar cartilage plays significant roles in growth and articular function. This study evaluated the influence of increased joint loading on the growth of the condylar cartilage and the morphology of the mandible.

DESIGN

Forty 7-week-old male Wistar rats were assigned to two groups: a control group and an incisal bite plane group. The condylar cartilage and subchondral bone were evaluated via histochemistry, bone histomorphometry with microcomputed tomography (micro-CT), and real-time polymerase chain reaction (PCR) at 2 and 4 weeks. The morphology of the mandible was analyzed via micro-CT.

RESULTS

The chondrocytic cell layer became thinner in the posterosuperior region after 2 and 4 weeks of wearing the bite plane. Hypertrophied chondrocytes and calcified cartilage matrix disappeared. Subchondral bone, which runs parallel to the lower border of the chondrocytic cell layer, increased. Bone volume fraction (BV/TV), trabecular thickness (Tb.Th), and trabecular number (Tb.N) increased, while the amount of endochondral bone formation decreased, in the posterosuperior region of the condyle in the bite plane group, which also had reduced mRNA levels of type II collagen, type X collagen, and tartrate-resistant acid phosphatase but increased levels of osteocalcin and alkaline phosphatase. The total mandibular length and ramus height were significantly shorter in the bite plane group, although there was no significant group difference in the length of the mandibular body.

CONCLUSIONS

The biomechanical environment regulates the cellular organization of the condylar cartilage and bone formation in its subchondral region, which may eventually change mandibular morphology.