A Study On The Cellular Response Of The Cementum During Orthodontic Tooth Movement

Objectives:The aims of this study were to evaluate the cementocytes by morphologic,structural,molecular and spatial analysis,to discuss the effects of different ex vivo forces on the cementocytes and related cementum resorption,to establish an in vivo model of orthodontic tooth movement,and to discuss the response and role of the cementocytes to orthodontic force by in vivo assays.Materials and Methods:1.HE staining and SEM scanning were used on the C57BL/6J wide type mice to compare the cellular cementum and the alveolar bone.2.Culture and differentiation of the IDG-CM6 and IDG-SW3 cell line were conducted to compare the difference between the cementocytes and the osteocytes by fluorescence,ALP staining,RT-qPCR techniques.3.The ex vivo 3D hydrogel based cell differentiation model was established and tested.The continuous compression force were applied on 3D cell model.The different cell response were evaluated by LIVE/DEAD cell viability test,RTqPCR,HE staining and immunochemistry staining.4.The in vivo rat model of molar intrusion was established.Rats were randomly selected by light force,heavy force and control group.Micro-CT,TRAP staining,RT-qPCR and immunofluorescence staining were used to evaluate the tissue remodeling and cell response of the cementocytes.Results 1.The cementocytes of the mice shared similarities and differences with theosteocytes.IDG-CM6 expressed GMP1-GFP,Opg,Rankl and Sost under differentiation.The ALP activity reached peak value on Day 14.The expression of Sost mRNA was featured by biphasic tendency.The expression of Opg and Rankl on Day 21 were significantly lower than IDG-SW3.2.The cell viability of IDG-CM6 subjected to 0.2g/cm2 was not changed over time,while 2g/cm2 for 6 hours significantly decreased the cell viability.When the force was increased,the viability dropped down.When 0.2g/cm2 force was applied,Rankl/Opg ratio was significantly decreased and OPG was increased.Under 2g/cm2 force,Rankl/Opg and Sost expression was significantly increased as well as sclerostin and RANKL.3.Under low forces,osteoclasts distributed more on the bone side than root side.Under high forces,both sides suffered osteoclasts infiltration.In the low force group,the cementocytes downregulated Sost,Opg mRNA and lower Rankl/Opg ratio over time and expressed less compared to the osteocytes on each time points.In high force group,both cementocytes and osteocytes upregulated Sost and Rankl/Opg ratio on day 7 and 14,and the cementocytes expressed more than the osteocytes.Conclusions1.The cementocytes are sensitive to mechanical loading.Direct loading induced the cementocytes to change the expression profile of osteogenesis and osteoclastogenesis related genes.2.Orthodontic intrusion forces induce the regulatory role of cementocytes in osteogenic and osteoclastogenic promotion,which may contribute to the homeostasis of the cementum during orthodontic tooth movement.This role is regulated by the force type,magnitude and duration time.