Compare Study Between The Normal And Sclerotic Dentin On The Micro Tensile Bond Strength And Ultrastructure Change After Surface Pretreatment

In a person's life,due to chew,teeth brushing and such mechanical friction,dentine tissue can be defected,known as the wear and tear.This type of wear mainly found in the cusp and incisal edge of permanent teeth,proximal contact point and the Lip tooth neck.The tooth neck wear into a wedge,which is called a wedge-shaped defect.Neck dentin can undergo a change in defense or reactivity after chronic stimulation,with the odontoblasts denatured and swelled into the dentinal tubules,then mineral salts calm and close tubules,and the tube collagen also degenerate,which formed the cervical non-carious sclerotic dentin.Due to the high mineralization of surface layer,it is common to see filling off of resin body in clinical practice.This study aimed to compare the microtensile bond strength and the bonding surface difference between those study groups after the different surface pretreatments to the sclerotic and normal dentin.The study will provide helpful instruction to the practice of the sclerotic dentin bonding in clinical.Objective:Comparative study of the effects of different surface pretreatments on microtensile bond strength and microstructure between non-carious sclerotic dentin and normal dentin.Methods:80 extracted teeth were collected,of which 40 were premolars with typical wedge-shaped defect extracted by periodontal disease,class 3 and above were chosen according to the North Carolina dentine hardening grading,as the experimental group(S).Another 40 were normal premolars extracted by periodontal disease or orthodontic pulling as control group(N).Each group was then randomly divided into 8 groups(N1-N8,S1-S8).Pretreatments respectively were distilled water(control group),35%phosphate gel 30 s,5%NaClO solution 60 s,15%EDTA gel 60s,15%EDTA gel 60s+5%NaClO solution 60s,15%EDTA gel 60s+10%NaClO solution 60s,35%phosphate gel 30s+5%NaClO solution 60s,35%phosphate gel 30s+10%NaCIO solution 60s.Self-etching adhesive AdperTM Easy One and composite resin 3M Filtek Z250(A3)were chosen to fill and solidify.After storage for 24 hours in distilled water at 37?,the teeth were sectioned into sticks(area of 1mm2).The sticks were stressed until failure by tensile forces(1 mm/min).All the surface layer after pretreatments were examined by scanning electron.Using SPSS 17.0 software package for data analysis,multiple comparisons within normal dentin groups used the method of SNK,multiple comparisons within sclerotic dentin groups used the method of multiple independent samples rank and inspection,paired t-test used for comparison between groups,analysis of fracture model adopted diverse the rank and inspection,inspection level of ?=0.05.Results:Micro-tensile bond strength test found that:the bond strength of sclerotic dentin in the control group is lower than normal dentin in control group(P<0.05).After pretreated by 35%phosphoric acid or 5%sodium hypochlorite,the bonding strength to sclerotic dentin was still lower than normal dentin(P<0.05).15%EDTA pretreatment can improve bonding strength to sclerotic dentin(P<0.05),and had no influence on normal dentin(P>0.05).After 35%phosphoric acid+5%sodium hypochlorite or 35%phosphoric acid+10%sodium hypochlorite pretreatments,bonding strength of sclerotic dentin can be higher than normal dentin,but the difference was not significant of 35%phosphoric acid+5%sodium hypochlorite pretreatment group.The bond strength of normal dentin in 35%phosphoric acid?35%phosphoric acid+5%sodium hypochlorite?35%phosphoric acid+10%sodium hypochlorite group was improved significantly higher than control group(P<0.05),and there is no significant difference between these three groups(P>0.05).The bond strength of sclerotic dentin in 35%phosphoric acid+10%sodium hypochlorite group is significantly higher than other groups except 35%phosphoric acid+5%sodium hypochlorite group.By variety of this rank and test analysis,the fracture mode frequency of different kinds of dentin and different pretreatments has no obvious difference(P>0.05).Scanning electron microscopy observation found that:Smear layer and scattered crack could be seen on the surface of normal dentin in control group,small and lack groove can be found in natural wedge-shaped defects.Phosphoric acid pretreatment can remove smear layer,and open dentin tubules were observed more of normal dentin compared to sclerotic dentin,dentine tube week could be seen on the sclerotic dentin surface,with mineralized crystal column extruded from the dentin tubule.15%EDTA could demineralize normal and sclerotic dentin.EDTA+NaCIO increased the surface roughness of both dentin.35%phosphoric acid+5%sodium hypochlorite,35%phosphoric acid+10%sodium hypochlorite can remove the smear layer surface of normal and sclerotic dentin and open dentinal tubules significantly.The surface of the sclerotic dentin is relatively uneven.Conclusion:35%phosphate acid,35%phosphoric acid+5%sodium hypochlorite,35%phosphoric acid+10%sodium hypochlorite preprocessing all can improve the microtensile bond strength of normal dentin with self-etching adhesive.35%phosphoric acid+5%sodium hypochlorite,35%phosphoric acid+10%sodium hypochlorite preprocessing are better methods than 35%phosphoric acid and 15%EDTA in improving microtensile bond strength of sclerotic dentin.35%phosphoric acid has greater demineralisation effect on normal dentin than sclerotic dentin;15%EDTA demineralize sclerotic dentin to a certain extent.3 5%Phosphoric acid+5%sodium hypochlorite,35%phosphoric acid+10%sodium hypochlorite pretreatment have similar effect on normal dentin and sclerotic dentin in demineralization and the open of dentinal tubules.