| Objective:By exploring the effect of procyanidins(PA)pretreatment on the bonding strength and microleakage of the fiber post at the neck,middle and tip of the root,this experiment provides theoretical basis for improving the bonding durability of fiber post.Methods: At the 2 mm above the enamel cementum boundary,each crown of 36 teeth was cut perpendicular to the long axis of teeth by low speed cutting machine.After the root canal preparation,AH plus paste was used to fill and press the root canal vertically with thermoplasticized gutta-percha,and canalorifice was temporarily sealed with 2 mm of glass ionomer.The samples were stored in water bath which kept 37 ? constant temperature for one week.And then,the samples were taken out and glass ionomer was removed.Each prepared root canal was drilled with RTD fiber post set.4 mm long root filling of root tip remained.Each root canal was etched by 35% phosphoric acid for 15 s,washed by steam for 30 s,and excess moisture was absorbed by the tip of the moisture absorption paper.Fiber post was selected to match the prepared post space.The samples were randomly divided into 4 groups(n = 9),A: 6.5% PA + not aging,B: 6.5% PA + aging,C: 95% ethanol + not aging,D: 95% ethanol + aging.The procedure was as follows: in group A and B,6.5% PA was applied to coat post space for 1 min;in group C and D,ethanol was applied to coat post space for 1 min.Then,excess moisture of each sample was absorbed by the tip of the moisture absorption paper.Each sample was coated with adhesive and accepted 10 s light curing,and then,accepted light curing 40 s after placing fiber post.All samples were placed in normal saline for 24 hours after bonding.Group A and C were used for the test of immediate adhesive strength,and group B and D were put into the cold and hot circulator for aging experiment.5 ? and 55 ? were retained for 30 s respectively,with 10 s interval,and the distilled water was circulated for 10000 times.7 samples were randomly selected from each group.1 mm slices of the root neck,the root middle and the root tip of the fiber post were cut in the flowing water with a low speed cutting machine.Universal testing machine was used to carry out slice micropush experiment.The adhesive strength was calculated by the formula P = F / S,in which P(MPa)was the adhesive strength,F(N)was the corresponding maximum loading force when the fiber post was pushed,and S was the adhesive area.S=p(R+r)[1+(R-r)2]1/2(where R represented the square radius of fiber post crown and represented the square radius of fiber post root).SPSS software(IBM SPSS 21.0;IBM,Armonk,NY)was used.Adhesive strength was analyzed via variance of three factors,and the test standard was bilateral P < 0.05,with statistical difference.The statistics of fracture modes of pushed slices after magnified by 20 times via stereomicroscope was gathered.Chi square test and Fisher exact probability method were used to compare the differences of fracture modes from each group.The test standard was bilateral P < 0.05,with statistical difference.Scanning electron microscope(SEM)was used to observe the fracture interface.The remaining two samples in each group were dyed with Indian ink.The nail polish was applied evenly on the surface of the tooth,which covers area higher than 2 mm from the root tip for 2 times.Samples were dried by air.After,let them soak in 37 ? Indian ink and dye for 7 days,then took out.The nail polish of samples was scraped and cleaned thoroughly under flowing water.After drying,samples were soaked in 5% nitric acid solution and protected from light.When the fine needle could penetrate the samples smoothly,the samples were taken out and fully washed with distilled water.Then,after ethanol gradient dehydration,the samples were soaked in methyl salicylate before they became totally transparent.And last,the samples were taken out and store it in glycerin.Corresponding observation of microleakage will be conducted via stereomicroscope in 20 times magnification.Results: 1.Micropush experiment: concerning adhesive strength of different parts of root canal(The difference was statistically significant(P < 0.05)),the highest adhesive strength was found in the neck and the lowest in the tip;the adhesive strength of PA pretreated group was higher than that of ethanol group(The difference was statistically significant(P < 0.05));the adhesive strength decreased after aging(The difference was statistically significant(P < 0.05));There was no statistical significance(P>0.05)of the effect on the adhesive strength from the interaction between different parts of root canal and PA pretreatment;There was statistical significance(P<0.05)of the effect on the adhesive strength from the interaction between different parts of root canal and aging;There was statistical significance(P<0.05)of the effect on the adhesive strength from the interaction between PA pretreatment and aging;There was no statistical significance(P>0.05)of the effect on the adhesive strength from the interaction among different parts of root canal,PA pretreatment and aging.Fracture mode statistics and SEM representative images: mixed failure is the main fracture mode of the root neck,middle,and tip.Dentin cohesive destruction did not appear.There were not statistically significant differences among these groups.2.Microleakage results: by observing the dyeing results of samples via stereomicroscope,in group A,there was a little dyeing of the root tips,and in group B,there was a small amount dyeing of root tips.In group C,a small amount of dyeing can be seen at the root of fiber post,and in Group D,dyeing can be seen both at the lateral side and root side of fiber post.Conclusion: When PA is used as the pretreatment agent to treat the dentin bonding surface,the adhesive strength of the root neck,middle and tip of the fiber post can be improved immediately and after aging.PA pretreatment of root canal dentin can reduce the occurrence of microleakage of fiber post before and after aging treatment. |
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