[Effect of fluoride on the expression of MMP-20/TIMP-2 in ameloblast of rat incisor and the antagonistic effect of melatonin against fluorosis].

ABSTRACT

PURPOSE: To study the effect of concentration of fluoride on the expression of matrix metalloproteinase-20(MMP-20) and tissue inhibitors of metalloproteinase-2 (TIMP-2) in the ameloblast of rat incisor,and explore the formation mechanism of dental fluorosis. By comparing the different expression of MMP-20,TIMP-2 between fluoride group and the melatonin group,to decide whether melatonin has antagonitic effect on dental fluorosis. METHODS: Forty Wistar rats were randomly divided into 6 groups. The groups were as follows control group,low-dose group, high-dose group,normal saline group and melatonin group. The animals were sacrificed 10 weeks after treatment. HE and immunohistochemical staining were used to observe the changes of ameloblasts and the expression of MMP-20 and TIMP-2 in rat incisors. MetaMorph microscope images analysis system was used to analyze the images, and SPSS12.0 software package was used for data analysis. RESULTS: The surface of rat incisors fed with fluoride had chalky color change and cross stritations could be seen on the enamel surface.In the fluoride group,the ameloblasts were disarranged, cells arranged in multi-layer,even showing vacuolar change.The changes in the high-dose group was severer than the low-dose group. MMP-20, TIMP-2 were expressed both in the secretory ameloblasts, and in the odontoblasts.The expression of MMP-20 in rat's ameloblasts in the experimental group was significantly lower than that in the control group (P < 0.01); and no significant difference was found between the low-dose and high-dose groups(P > 0.05). The difference of expression of TIMP-2 was not significant among all the groups. The difference of expression of MMP-20 and TIMP-2 was not significant between the melatonin and the fluoride groups. CONCLUSIONS: The excessive fluoride can inhibit the secretion of MMP-20 and disturb the balance between MMP-20 and TIMP-2,which lead to the delay of amelogenin removal and enamel demineralization. Melatonin has no antagonistic effect on the dental fluorosis. Supported by National Natural Science Foundation of China (30600509) and Natural Science Foundation of Liaoning Province (20102278).