Preliminary Study On The Expression Of TGF-? Signaling Pathway In Epithelial Cell Rests Of Malassez And Its Functional Changes During Orthodontic Tooth Movement

Background: Modern orthodontics involves correction of the teeth,jaw and face deformity;However,tooth movement is still the main method of clinical treatment.The basis of tooth movement is the plasticity of periodontal tissue,it has shown that the orthodontic force is transferred to the alveolar bone through the periodontal ligament when applied to the tooth,and the mechanical stimulation is transformed into cellular responses,bone resorption on the pressure side while tension side bone deposition,as a result of periodontal tissue reconstruction and remodeling,and the teeth movement;so the metabolic changes of the cells in periodontal ligament are foundation of tooth movement.In the past,most studies mainly focused on the functional changes of fibroblasts,osteoclasts and osteoblasts in periodontum.Epithelial cell rests of Malassez(ERM)is the unique epithelial component in periodontal ligament,has been considered in the static state,and may become the source of jaw cyst and odontogenic tumor by inflammatory stimulation;In recent years,it has been found that ERM has the potential function in the regeneration of periodontum,formation and repair of cementum etc.;ERM may promote collagen fibers renewal and play an important role in periodontum regeneration,while the remodeling of periodontal tissue during orthodontic treatment is the basis of tooth movement,implying that ERM may play an important role during orthodontic tooth movement.Studies have found that ERM derived from Hertwig's epithelial root sheath(HERS)may directly involved in cementum formation and repair by secreting some bone/cementum related protein,on the other hand may indirectly involved in the formation and repair of cementum through undergoing epithelial mesenchymal transition.Objective: To investigate the expression of TGF-? /Smad signal pathway in ERM during orthodontic tooth movement and the functional changes of ERM.Methods: : 30 sprague?dawley adult male rats at the age of 8 weeks was selected,with the left maxillary as the experimental side and the right side as control.The nickel titanium coil springs,fixed between the first molar and incisor where thrust augmentation is conducted by 50 gram-force.The rats were sacrificed at 0,1,4,7,10 and 14 days respectively,and the expression of TGF-?,Phosphorylated Smad2 / 3 and proliferating cell nuclear antigen(PCNA)was observed by immunohistochemistry in ERM.Results: At 1,4,7,10 and 14 days,ERM was stained for TGF-?1;P-Smad2/3 at the beginning of the ERM expression from 1th day;From the 7th day after loading,the expression of proliferating cell nuclear antigen(PCNA)in ERM was detected;Staining for amelogenin was observed after 10 days.Conclusion: During orthodontic tooth movement,TFG-?/Smad signaling pathway was expressed in ERM,while ERM showed proliferation activity,indicating that ERM may regulate the process of orthodontic tooth movement through TFG-?/Smad signaling pathway;while ERM can secrete amelogenin,suggesting that it may be involved in the repair of root resorption and to maintain the homeostasis of periodontal ligament.