Effects Of Light Curing Modes And Ethanol-wet Bonding On Dentin Bonding Properties

Object:In this study different light curing modes and ethanol-wet bonding technology are used to total-etch adhesive systems.By the universal testing machine measuring microtensile strength and the scanning electron microscopy observing mixed layer morphology,we explored the effects of different light curing modes and ethanol-wet bonding on dentin bonding strength and durability to provide theoretical guidance for clinical application.Methods:A total of 54 thirdmolars without caries were cut crown occlusal surface enamel to expose shallow dentin.After that,stereomicroscope observed the interface that was no enamel remained.In order to simulate the clinical dentin smear layer interface,the surface of dentin were polished 60 s each using 600-grit SiC paper with the running water.All samples were randomly divided into the following three groups:Single Bond 2,Gluma Comfort Bond and N-Bond.According to the three different light-curing modes and whether through ethanol pretreatment,the samples were assigned to the following Six subgroups:High-light mode,Ethanol Pretreatment +High-light mode,Soft-start mode,Ethanol Pretreatment + Soft-start mode,Standard mode,Ethanol Pretreatment + Standard mode.The dentin surface was etched for 15s by 37%phosphoric acid gel and rinsed for 30s by distilled water,and the excess water was sucked with a dry cotton ball.Then,the right amount of adhesive was gently smeared on the moist dentin surface for 10s using a small brush and was lightly dry for 5s.Afterwards the adhesive surface was irradiated under different light curing modes according to experimental groups.For the ethanol pretreatment groups,the etched dentin surface was inserted into 100%ethanol for 2min,and the excess ethanol was sucked with a dry cotton ball.After the curing of adhesives,Z350 resin was stacked.After 24 hours and 6 months water storage the universal testing machine measured microtensile strength.The stereo microscope observed fracture types of microtensile specimen and the scanning electron microscopy observed mixed layer morphology.For data analysis,SPSS 17.0 was used.Multi-way ANOVA and multiple comparisons with Tukey’s test(5%)were used to analyze microtensile results.Result:The 24-hour and 6-month microtensile strengths of the ethanol pretreatment groups are significantly(P<0.05)higher than the non-ethanol pretreatment groups at the same light modes;whether through ethanol pretreatment,the microtensile strengths of the high-light modes are significantly(P<0.05)lower than those of the soft-start modes and the standard modes and the soft-start modes are lower than the standard modes,but the results are no statistical difference(P>0.05).The microtensile strengths of 6-month water storage compared with 24h strengths decrease significantly(P<0.05).In the same experimental conditions,the strengths of SB groups are higher than GB groups and NB groups at 24-hour and 6-month water storage,but the difference is not significant(P>0.05).The decline of the ethanol pretreatment groups is obviously less than non-ethanol pretreatment groups,and the decline of the soft start modes and the standard modes groups is far less than high-light modes groups.The fracture type of all groups is mainly interfacial fracture.The soft-start groups and the standard groups formed longer and more uniform resin tags and relatively more continuous and uniform mixed layers than the high-light mode groups;ethanol pretreatment groups formed much longer and more uniform resin tags and more compact and uniform mixed layers than those without ethanol pretreatment.Conclusion:1.Dentin bonding performance is closely related to the quality of the mixed layers,the more dense and homogeneous mixing layer and the more and longer resin tags can get better bond strength and durability.2.Ethanol pretreatment can significantly improve the performance of total-etch dentin bonding systems and the quality of the mixed layer.3.Soft start mode and standard mode can get better dentin bonding properties and the quality of the mixed layer.4.The three total-etch adhesives have no significant difference on microtensile results and the quality of the mixed layers.