| Lateral functional shift of the mandible was one of the most frequent diseases in stomatology, usually being associated with a unilateral posterior crossbite. Changes of the mode of exercise between the left and right condyle have substantial effects the environmental function and the load on local area of condyle which could induce remodeling in local area of cartilage. The chondrocytes of condyle have the ability of growth remodeling, which secret many kinds of cytokines and growth factors to regulate the chondrocytes proliferation and differentiation,extracelluar matrix, which maintains the environments of chondrocytes. The balance between anabolic metabolism and atabolism of condylar cartilarge may be broken after the changes of functional load induced by lateral functional shift of the mandible. We have found that the mandibular lateral functional shift may lead to the remodeling activities of condylar cartilage and mandibe asymmetry. The present study, based on the experiments of adolescent rats, established a model of lateral functional shift of the mandible. The expression of PCNA,VEGF of condylar cartilage in process of inducing and removing lateral functional shift of the mandible were observed by immunohistochemical stain. The effect of the mandibular lateral functional shift and its removing on proliferative activity and enchondral bone formation of condylar cartilage was measured in order to investigated its growth remodeling activities.Eighty four-week-old male Sprague-Dawley(SD) rats were divided randomly into three groups: shift group(n=40), recovery group (n=20), and control group(n=20). Each animal in the shift and recovery groups received an appliance designed to produce a 2 mm lateral functional shift of the mandible to the left side. For the recovery group, the appliance was removed after 14 days to allow for TMJ recovery. The animals in the control group received no appliances. All rats were raised in the same environment with farina food till the end of the experiment. Ten and Five animals in the shift and control groups were sacrificed at four time points (7, 14, 21, and 28 days). All animals in the recovery group had the appliances removed after 14 days, and ten animals were sacrificed at each point 7 days and 14 days after appliance removal. Sagital and frontal sections were cut from left and right condyles, immunohistochemistry for PCNA and VEGF were applied. The left mandibular condyle the shift group and recovery group were designated the ipsilateral side, and the right side was designated the contralateral side. Results:(1) In the condylar cartilage, PCNA was predominantly localized in proliferative zone and upper hypertrophic zone. In chondrocytes, PCNA was located in nucleus. Its expression decreased gradually from the proliferative zone to the superficial hypertrophic zone. In the shift group, PCNA expression in the central and posterior region of the right side were significantly increased at 7,14,21and 28 days(P<0.05)compared with the control group and left side; while the lateral and posterior region on the left side were significantly decreased at 7,14,21 and 28 days(P<0.05)compared with the control group and right side. In the recovery group, it showed no significant difference from the control group of each region at 28 days.(2) In the condylar cartilage, VEGF was predominantly localized in proliferative zone and upper hypertrophic zone. The upper hypertrophic zone is the most predominantly localized zone in condylar cartilage. In chondrocytes, VEGF was located in plasma membrane and cytoplasm. In the shift group, VEGF expression in the posterior region of the right side were significantly increased at 7,14,21,28days(P<0.05)compared with the left side;while it was significantly increased at 14,21,28days(P<0.05)compared with the control group. The central region of the right side were significantly increased at 14,21and 28 days(P<0.05), compared with the control group and left side. The expression in lateral and posterior region of the left side of the shift group were significantly decreased at 14,21and 28 days(P<0.05),compared with the control group and right side. In the recovery group, it showed no significant difference from the control group of each region at 28 days.Conclusions:(1) The lateral functional shift of the mandible in adolescent rat may promote the enhancement of the ability of proliferating of condylar cartilage cell in the central and posterior region of the contralateral side. However, the proliferating ability of condylar cartilage cell declined in the lateral and posterior region of the ipsilateral side.(2) The lateral functional shift of the mandible in adolescent rat can promote the expression of VEGF in the central and posterior region of the contralateral side, which promotes the growth of vessel and transformation of cartilage to bone. While it decreased in the lateral and posterior region of the ipsilateral side may hinder the transformation of cartilage to bone.(3) Early treatment can promote the recovery of the ability of chondrocyte proliferation and the transformation of cartilage to bone. The result emphasize the importance of early treatment to normalize occlusion and create appropriate conditions for normal occlusal development.
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