Characteristics And Roles Of Epithelial Cell Rests Of Malassez Corrected With The Change Of Bite Force In Mice

PURPOSE::Hertwig's Epithelial Root Sheath(HERS)plays a decisive role in the tooth development,and is the important and exclusive epithelial structure which ensure a series of reciprocative signal in the epithelial-mesenchymal tissue to come true.Epithelial cell rests of Malassez(ECRM)as the residuum after HERS fragment,is the exclusive epithelial strcture in the mature periodontal ligament.In matuation,ECRM may play important role in the stabilization of the internal enviroment in the periodontal ligament and regeneration in the cementum.By the Bite force change animal model,we observed the regularity of the morphology and distribution of ECRM after the bite force change and the relationship between the Osteopontin(OPN)and the rebuilding in the periodontal ligament so as to explore its possible mechanism for remodeling of periodontal ligament.METHODS:42 adult male BALB/C mice(Research Animal Center Shandong University)were used.Bite force change animal model performed by extracting the total left side up molars.Anesthetized animals was sacrificed at the different time point by vascular perfusion through the left ventricle and into the aorta.The vasculature was pre-rinsed with 0.9%physiological saline for 30s followed by perfusion for 30min with 4% paraformaldehyde(pH 7.0).The maxillary were dissected and immersed in the same fixative solution for an additional 24h at 4℃condition.After decalcificated with complex formic acid for 2 weeks,dehydrated through graded ethanol,cleared with xylene and embedded in paraffin,and 5μm thick continuous slices were made.The sections were stained with hematoxylin and eosin(H.E.)and observed by light microscopy. Cytokeratin14(CK14)antibody was applied as a marker to trace the morphology and distribution of ECRM cells and examined the dye in different samples by light microscopy.The Morphologic change of periodontal ligament was measured using a software of micro-scale system.PV two-step immmumohistochemical method was used to detect the expression of OPN in ECRM.The number of ECRM cells at the different periods and the width of periodontal ligament were quantified using SPSS 11.0 package(P＜0.05).RESULTS:Animal model of bite force change was established successfully.The quantity of ECRM in increased bite force groups reached its peak at 7d after extraction operation, and significantly higher than that of control group,and then gradually decreased to normal level on day 28 after extraction according to CK14 labeling.Whereas,the quantity of ECRM in decreased bite force groups decreased gradually from 21d after extraction.There were not visible histological change in increased bite force groups,and the width of periodontal ligament increased obviously at 4 weeks after extraction.In decreased bite force groups,the width of periodontal ligament decreased obviously at 3weeks afer extraction.The positive expressions of OPN were observed at day 7 afer extration in increased bite force groups.CONCLUSION:There is a close relationship between bite force change and the change of the morphology and quantity of ECRM which indicate that the change.plays an important role in remodeling of periodontal tissue,maintainance of stablization of periodontal internal enviroment and width of peirodontal ligament.