Objectives: To evaluate the micro-shear bond strength to enamel and dentin, pH and hardness of two self-etching adhesives over a period of 60 weeks storage at different temperatures.
Materials and methods: Two self-etching systems, an all-in-one adhesive, Clearfil Tri-S Bond (TS) and a two-step adhesive, Clearfil SE Bond (SE) were used in this study (both by Kuraray Medical, Osaka, Japan). Their micro-shear bond strengths to enamel and dentin were measured. The materials were then stored at 4, 23 or 37 degrees C. Their bond strengths were measured again after 1, 4, 16 and 60 weeks and compared to the base line. The nano-indentation hardness of the polymerized bonding, pH of SE primer and TS were also measured at the baseline and after 60 weeks of storage at three different temperatures. Bond-strength and hardness data were analyzed using ANOVA and post hoc tests at the significance level of 0.05.
Results: Two-way ANOVA analysis showed that both storage conditions and material type had significant effects on bond strength to enamel or dentin but the interactions of these factors were not significant for any of the substrates. One-way ANOVA post hoc tests revealed that the bond strength of adhesives stored at 37 degrees C significantly decreased during the storage period; with the earliest significant decreases observed at 4 weeks for TS and at 16 weeks for SE. After 60 weeks of storage, the hardness obtained for SE bonding resin was not significantly different with that at the baseline for 4, 23 and 37 degrees C groups, but there was a significant decrease observed in hardness for TS stored at 37 degrees C, compared to that at the baseline. The pH of both self-etching materials decreased when they were stored at 37 degrees C.
Conclusion: Storage time and temperature significantly affected the bond strength of both materials through the time dependent hydrolysis and other changes that are likely to occur in the water-containing self-etching agents at high temperatures.