The Chronobiologic Study Of The Orthodontic Tooth Movement During Estrous Cycle In Female Rats

Biological rhythm and chronotherapy are the soul of traditional medicine. In life sciences, further studies should be performed to explore the relationship between the Biologic Clock and the interfering time of therapy. In orthodontic clinics, there are more female patients than male patients. Furthermore, there are an increasing numbers of adult female patients seeking orthodontic treatment worldwide. Menstrual cycle is an important physiological phenomena of adult female patients. Therefore, it is necessary to study whether the orthodontic force applied during different phase of menstrual cycle would affect the penodontal tissue's remodeling and tooth movement, and whether the orthodontic treatment would cause the change of biologic rhythm (menstrual cycle).It has been demonstrated the normal menstrual rhythms could not be maintained without the normal feedback of hypothalamic -pituitary -gonadal axis. Sex hormones secreted by ovary exerts their physiological effects by binding to their receptors.Recent studies showed sex hormones' receptors also exist in penodontal tissues. The penodontal bone remodeling and the periodontal fiber synthesizing and degrading are affected by sex hormones.Therefore, it is important to investigate whether circatrigintan rhythm's changes according with sex organ's also existed in penodontal sex hormone receptor. If it does,was the effect of tooth movement different when the force was applied during different time ? Didthe orthodontic treatment affect menstrual rhythms and the level of corresponding sex hormones?These questions still remained unknown.This study focuses on the interaction between the circatrigintan (or circannual ) rhythm changes of the periodontal sex hormones and their receptors and the periodontal tissue's remodeling,which is the final effect of orthodontic tooth movement. The aim of this study is to explore the relationship between the biologic clock and the orthodontic treatment's interventing time so as to provide a deep insight into the mechanism and the perfect effects of female orthodontic treatments.200 female 3-month-old Wistar rats ,which had a stable and five-day estrous cycle, were used.They were assigned to control group,sham-treated group and loading force group.The tooth movement appliances were weared and forces were loaded during specific phase of estrous cycle. Serum estradiol was measured by radioimmunoassay (RIA). The changes of estrous cycle and the amount of tooth movement were investigated. Immunohistochemistry and in situ hybridzation stains were conducted to reveal the expression and distribution of periodontal estrogen receptor at protein and mRNA levels.The data were analyzed by one-way ANOVA and S-N-K test.Depending on vaginal smear to determine the phase of estrous cycle and appling force during specific phase of estrous cycle,the animal models of orthodontic tooth movement during estrous cycle were stable and successful.It was found that the physiological fluctuation of serum E2 and expression of ER protein and mRNA were related to the phase of estrous cycle in rats. Whether wearing appliance or loading force,the trend of their fluctuation during one estrous cycle had not been changed. Regardless of the estrous phase appling force,the serum E2 level was elevated and the expression of ER protein and mRNA expression declined in all loading-force groups. The greatest amount of tooth movement wereobtained in groups receiving force during estrus and the lest amount were obtained in groups receiving force during proestrus. So it was concluded that when the orthodontic tooth movement were performed during estrus, the level of E2, estrous cycle, expression of ER protein and mRNA could be affected as slightly as possible, and the perfect tooth movement could be obtained.This study gives a indication to clinical treatment: As far as the effect of estrogen on tooth movement is concerned, it is better to choose the period of time between the ovulatory phase to the next menses to apply force,and it should be avoided to apply force during one to two days just before the ovulatory phase .