| Objective:To compare the effects of two antioxidants(sodium ascorbate,SA and proanthocyanidins,PA)on the immediate bond strength of bleached dentin,aiming to provide a theoretical basis for the bonding of bleached dentin.Methods:Thirty intact mandibular third molars(complete,free of caries,cracks,non-fluorosis and tetracycline teeth,etc.)extracted within the one month were collected.Using a hard tissue slicer under water spray,the buccal enamel of the third molars was removed.The remaining dentin was then prepared into specimens with a size of 5mm × 5mm × 3mm(confirmation of complete removal of buccal enamel was done using a stereoscopic microscope).The buccal dentin surfaces were ground flat using three different grit sizes of silicon carbide waterproof sandpaper(400,600,800grit)under water spray,followed by ultrasonic cleaning for 5 minutes and drying with oil-free air.The experiment was divided into two control groups(unbleached-bonded group,bleached-bonded group);two experimental groups(bleached-treated with 10%SA solution-bonded group,bleached-treated with 5% PA solution-bonded group),which were further divided into four subgroups according to the antioxidant treatment time(15,30,45,60 minutes).There are a total of ten groups.The dentin specimens in each group were acid-etched,adhesive applied,and light-cured resin filled to complete dentin-resin bonding.The specimens were then placed in a 37°C incubator for 24 h.Subsequently,micro-tensile specimens with the size of 1mm×1mm×10mm were prepared using a hard tissue slicer under water spray.The micro-tensile bond strength(μTBS)of the micro-tensile specimens was tested using a micro-tensile testing machine.The bonging interface fracture types were observed using a stereomicroscope,and the longitudinal section of the bonding interface were observed using a scanning electron microscope(SEM).Statistical analysis of the micro-tensile bond strength data was performed using SPSS 26.0.Results:1.Two-way analysis of variance(ANOVA)of the micro-tensile strength values showed no interaction between antioxidant treatment and antioxidant treatment time on the micro-tensile strength(P=0.968,P>0.05).Antioxidant treatment had a significant effect on the micro-tensile strength(P<0.05),and different antioxidant treatment times had a significant effect on the micro-tensile strength(P<0.05);2.LSD test for pairwise comparisons revealed that the micro-tensile strength of the unbleached group was significantly higher than the bleached group(P=0.000,P<0.05).The micro-tensile strength of the 10% SA treatment group and the 5% PA treatment group both showed statistical significance compared to the bleached group(P<0.05).Additionally,the micro-tensile strength of the 10% SA treatment group and the 5% PA treatment group both showed statistical significance compared to the unbleached group(P<0.05);3.There was no significant difference in micro-tensile strength between the 10%SA treatment group and the 5% PA treatment group with the same treatment time(P>0.05).However,the micro-tensile strength between the 10% SA and 5% PA treatment groups at 15,30,and 45 minutes showed statistical significance(P<0.05),while there was no significant difference in micro-tensile strength between the 45 and60 minutes treatment groups(P>0.05);4.The mainly failure mode in all groups was adhesive interface failure,with fewer cohesive and mixed failures.Statistical analysis using chi-square test for failure modes showed no significant difference among the groups(P=0.851,P>0.05).Conclusion:1.Tooth bleaching significantly reduces the immediate bond strength of dentin;2.The application of 10% sodium ascorbate and 5% proanthocyanidins can improve the immediate bond strength of blesched dentin,and their effects are similar at the same treatment time;3.Within the 45-minute antioxidant treatment period,the immediate bond strength of bleached dentin increases with longer antioxidant treatment time. |
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