The Study Of Lowered Serum Levels Of Estrogen Inducing Rat Condylar Resorption

Objective Idiopathic condylar resorption is a bone volume loss disease in the mandibular condyle inducing lower ramus height, mandibular retrusion, anterior open bite and Class Ⅱmalocclusion. ICR etiology and pathogenesis has not yet been elucidated, but it often occurs in young women, while a large number of human and animal studies have found that the temporomandibular joint presence of estrogen receptors, indicating that the temporomandibular joint is the target organ of estrogen, so the relationship of estrogen and its receptor and ICR has attracted the attention of domestic and foreign academic circle. Our previous study demonstrated that oral contraceptives and premature ovarian failure in rats can induce lowered serum levels of estrogen, and interfere with condylar cartilage into bone, leading to certain condyle degeneration. It is speculated that changes of serum estrogen may affect the expression of certain proteins in condylar chondrocytes through the ER pathway, causing chondrocytes, extracellular matrix and subchondral bone change, resulting in the loss of condylar mechanical characteristics, inducing condylar degeneration and resorption. This study was designed to observe the expression variation of ERα, ERβ, osteoprotegerin and receptor activator of nuclear factor-κB ligand in the process of rat condylar cartilage degeneration due to lowered estrogen, in order to explore the possible mechanism of ICR.Methods Thirty female 6 weeks old SD rats were randomly divided into control group, oral contraceptives group and tripterygium glycosides tablets group. The model of lowered serum estrogen level and model of premature ovarian were establishedby gastric gavage with oral contraceptives pills and tripterygium wilfordii glycosides tablets respectively. The serum levels of estradiol were detected respectively before the experiment and on the twelfth week of the experiment. After the experiment, the expression of ERα, ERβ, OPG and RANKL of condyle was detected by immunohistochemistry. SPSS16.0 software package was used for statistical data analysis.Results 1.The twelfth week of the experiment, the serum estrogen levels of oral contraceptives group and tripterygium glycosides tablets group were significantly lower than the control group, and this difference was statistically significant(P <0.05). 2. ERα and ERβ are expressed in the condylar cartilage in control group, oral contraceptives group and tripterygium glycosides tablets group, are mainly distributed in the hypertrophic chondrocytes layers. In oral contraceptives group and tripterygium glycosides tablets group rat condylar ERα and ERβ expression was decreased, and thisdifference was statistically significant(P <0.05). 3. OPG and RANKL are also expressed in the condylar cartilage in control group, oral contraceptives group and tripterygium glycosides tablets group, mainly distributed in the hypertrophic cartilage layer. In oral contraceptives group and tripterygium glycosides tablets group rat condylar OPG expression was decreased, RANKL expression was increased, and this difference was statistically significant(P <0.05).Conclusions 1.The lowered serum estrogen concentrations decreased the expression of ERα, ERβ and OPG, raised the expression of RANKL of condylar cartilage and reduced the proportion of OPG/RANKL. 2.In the lowered serum levels of estrogen state, estrogen may mediate condylar cartilage degeneration and the subchondral bone pathological reconstruction, through ER pathway by regulating the ratio of OPG/RANKL.