Effects Of The Rhythm Of Estrogen During Estrous Cycle On Periodontal Tissue Remolding Induced By Orthodontic Tooth Movement

Background and Objective: Biological rhythm is a basic characteristic of all life-forms. Following the development of chronobiology, the investigation of biological rhythm attracts more attention in many fileds of biomedicine. Orthodontic treatment is a procedure that mechanical forces are applied to make teeth or bone move, which finally result in periodontal tissue remodeling.Menstrual cycle is an important physiological phenomenon of women and the concentration of estrogen in women's blood present in a fluctuation format working as the most important sex hormones to maintain menstrual cycle. Estrogen also plays an important role in keeping bone mass and architecture in the fashions of endocrine, paracrine and autocrine. The local estrogen comes from blood and precurosor transformation and will influence the bone remodeling directly. It also had been showed that mechanical environment had effects on the expression of local estrogen.Periodontal tissue is one of the target organs of estrogen. As to female patients who seeking orthodontic treatment, both the fluctuation of the estrogen during menstrual cycle and mechanical forces brought by orthodonticappliance will influence the periodontal tissue remodeling. It was established that insulin-like growth factors (IGFs) force operating on the bone remodeling not only related to the estrogen but to the mechanical stress.Therefore, it is urgent for us to know whether the physiological fluctuation of estrogen during menstrual cycle has different effects on periodontal tissue's remodeling and tooth movement. Meanwhile, from the biological rhythm point, do the orthodontic treatments would disturb the women's menstrual cycle? What is the relationship and interaction between the local estrogen and mechanical forces? Do these factors make differences in orthodontic teeth movement? In this study, we focused on the local estrogen (E2) and IGFsmRNA expression during menstrual cycle to probe into regulation mechanisms and singnaling pathways involved in periodontal tissue remoding and orthodontic treatment.Material and Methods: 200 femal 3-month-old Wistar rats, which had a stable and 5-day estrous cycle, were selected. According to the Haruyama classification, estrous cycle contains four stages, including proestrus> estrus> metestrus and diestrus . Long's methods were used to determine the estrous stage of the experimental rats. King's appliances for rat molar movement were modified and fixed and applied force on the first molar at the regular time of different estrous stages, under the group of (1) force only once (2) repeat forces four times (3) no appliance and no force (4) with appliance but no force. The control group included blank and force contraside of appliance wearing rats. The value of the forces was 50g. The distance of tooth" movement was measured. Immunehistochemistry and hybridization in situ were used to set out the estradiol, IGF-I and IGF-II mRNA expression in the periodontal tissue. The Statistic methods were One-way ANOVA and method for cosinor-rhythmometry.Results: Established a experimental model to study the effects of therhythm of estrogen during estrous cycle on periodontium remolding induced by orthodontic teeth movement.1 The tooth movement effects were different among the estrous stages. The minimum tooth movement was occurs during the proestrus and the maximum was during the estrus.2 The local expression of estradiol was consistent with the rhythum of the estradiol concentration in serum, maximum during proestrus wheres minimum during estrus. It presents a 5-day infradan rhythm accorded with cosindor rhythm.3 Mechanical force enhanced the estradiol expression in the periodontal tissue in every stage.4 The local expression of IGF-ImRNA was consistent with the rhythum of the estradiol concentration in serum. It presents a 5-day infradan rhythm accorded with cosindar rhythm.5 Mechanical force enhanced the IGF-ImRNA expression in the periodontal tissue in every stage.6 There was no difference of IGF-IImRNA expression among the different stages of estrous cycle, but Mechanical force enhanced the IGF-II expression in the periodontal tissue in every stage.Conclusion:1 The diversity of tooth movement distance due to estrous stage of rats indicated that applying forces at varied phases of menstrul cycle of women who are enduring orthodontic treatment are likely to acquire different tooth movement effects.2 Local estradiol expression had a same rhythum with estradiol in serum suggested that there was a relationship between the local and serum estradiol expression. And in the meanwhile, forces applied by orthodontics may not disturb the menstul cycle, which means the safty of orthodontic treatment to women physiological cycle.3 IGF-I, local and serum estradiol had a same rhythum clued on that there may exist some similar control mechanisms or the regulation effects on bone of estrodiol was through IGF-I. It needs further investigation.4 IGF-IImRNA was involved in the periodontal remodeling induced by mechanical force, but was not enlisted in estrogen's effect on bone.