| Objective: In this experiment,EDTA,EDC,EDTA and EDC were used to pretreat the dentin surface before bonding and the hot and cold cycle was used to simulate aging environment in oral cavity.In order to study the effect of pretreatment of EDTA and EDC and combined application of EDTA and EDC on the bonding strength and bonding durability as well as the influence of the bonding interface of two-step self-etching adhesive,the dentin shear strength was determined by the universal mechanical testing machine,failure mode and the fracture surface morphology was analysed by stered microscope,and the longitudinal profile morphology was observed by scanning electron microscopy.These can provide a theoretical basis for improving the durability of dentin adhesion.Methods: 56 third molars which were fresh,cary-free and completely extracted were collected.The surface calculus and periodontal tissues were scraped and stored in 0.5% chloramine-t solution,and stored in 4 ℃ for 2 months.In the first part of the experiment,40 third molars were selected and divided into 8 groups randomly(A,B,C,D,A1,B1,C1,D1,n=5).The middle dentin was exposed to low speed cutting machine and then 240,320,400,600,800,1000 mesh silicon carbide sandpaper were used to polish the dentin surface under the flowing water for 30 s to form the standard stain layer,which was placed in the ultrasonic cleaning machine and cleaned for 5 min.Different dentin surface treatments were performed on dentin according to experimental groups: group A and A1: Clearfil SE Bond;group B and B1:17% EDTA+Clearfil SE Bond;group C and C1:0.3 M EDC+Clearfil SE Bond;group D and D1:17% EDTA+ 0.3 M EDC+Clearfil SE Bond.After surface treatment,the mold with a radius of 1.5mm and a height of 4 mm was used to accumulate resin blocks on the dentin bonding surface by layered curing.Specimens of A,B,C and D were stored in normal saline in 37 ℃ for 24 h and then the immediate shear strength was measured on a universal mechanical testing machine.Specimens of A1,B1,C1 and D1 were conducted 5000 times aging test after stored in normal saline at 37 ℃ for 24 h and then measured shear strength.The fracture patterns of each specimen were observed under stereoscopic microscope and the fracture surface morphology was observed under scanning electron microscope.In the second part of the experiment,16 third molars were selected and randomly divided into 8 groups(n=2),numbered a,b,c,d,a1,b1,c1 and d1.After exposing the middle dentin of maxillofacial,polishing by silicon carbide sand paper and cleaning for 5 min in the ultrasonic cleaning machine,the surface of dentin was pretreated in A,B,C,D,A1,B1,C1 and D1 groups respectively.After the surface treatment was completed,resin blocks were deposited on the surface of dentin with a mold with a radius of 2 mm and a height of 4 mm.After all the specimens were placed in normal saline at 37 ℃ for 24 h,the specimens of a1,b1,c1 and d1 were conducted 5000 times aging test.All specimens were prepared into 1mm thin slices perpendicular on the bonding interface,and each specimen was cut to form 3 thin slices.The mixing layer of bonding interface and the resin tag were observed under scanning electron microscope.Results: 1.The results of the first part of the experiment showed that: in the immediate experiment,compared with the shear strength of group A,the shear strength of group B,C and D was improved,and the immediate shear strength of group D was the highest.The difference between group A and B,group A and C was no statistically significant(P>0.05),and the difference between group A and D was statistically significant(P<0.05)After the aging test,the shear strength of each group decreased,with statistically significant differences between group A and group A1,group B and group B1(P<0.05).The difference between group C and C1,group D and D1 was no statistically significant(P>0.05),indicated the adhesive durability.The results of stereoscopic microscopy showed that the fracture modes in each group were mainly mixed fracture,followed by adhesive fracture,and cohesive fracture was the least common.The distribution of fracture modes in each group was not statistically significant.2.The results of the second part of the experiment showed that the number and length of resin tags of the four groups of specimens(b,d,b1 and d1)pretreatment with EDTA increased compared with those of four groups(a,c,a1 and c1)pretreatment without EDTA.The hybrid layer of the immediate experimental groups was completed and continuous.The groups of a1 and b1 without EDC pretreatment was damaged,and cracks appeared after aging test.After pretreating with EDC,the hybrid layer of c1 and d1 groups was completed,and no obvious cracks were observed.Conclusion: 1.Pretreatment with 17% EDTA gel has no significant effect on the bonding strength of two-step self-acid etching adhesive Clearfil SE Bond either immediately or after aging.2.Pretreatment with 0.3 M EDC do not improve the immediate bonding strength of Clearfil SE Bond,but significantly improves the post-aging bonding strength.3.Using 17% EDTA gel and 0.3 M EDC can significantly improve the immediate adhesion strength of dentin and the adhesion durability.4.The improvement of dentin bonding durability by 0.3 M EDC may be related to the stable hybrid layer. |
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