Effects of Relaxin on Relapse After Experimental Tooth Movement in Rats

Abstract

Long-term stability is the major goal of orthodontic treatment. However, long-term observation of treated cases after retention often reveals a disturbing degree and frequency of relapse. Relaxin is a member of the insulin/relaxin family of structurally related hormones. This hormone is produced in many mammals during pregnancy, and has been shown to promote cervical softening and elongation of interpubic ligaments in mice and cattle. Furthermore, relaxin is related to many other physiologic processes, such as collagen turnover, angiogenesis, and antifibrosis in both males and females. So far, no study concerning the effect of relaxin on orthodontic tooth movement has been done. The purposes of this study were to investigate whether local administration of relaxin in rats has an effect on relapse after orthodontic tooth movement and to explore the molecular mechanism of its role. In the present study, the upper first molars were moved mesially in 16male, 6-week-old, Wistar strain rats using a coil spring with a force of 10g. After 14days, the appliance was removed, animals in the experimental group were given attachment gingivae injections of relaxin at 20μl for 7days, and animals in the control group received phosphate-buffered saline. The results were evaluated by micro-computed tomography (μCT). At days 0, 14 and 21 after tooth movement, histopathological features were examined by immunohistochemistry based on proliferating cell nuclear antigen (PCNA). Relapse distances and percentages were significantly lower in the experimental group compared to those of the control group. Relapse in the control group was greater and faster than that in the experimental group. The ratio of PCNA-positive cells increased at day 14 after tooth movement and then decreased at day 21. Our results indicated that relaxin inhibited the relapse of experimentally moved rat molars, and this hormone might prevent relapse following orthodontic treatment.