Effect of caries-affected dentin hardness on the shear bond strength of current adhesives

The aim of this study was to evaluate the microshear bond strength of three current adhesives to normal and caries-affected dentin, and to examine the correlation between dentin nanoindentation hardness and bond strength.

Nanoindentation hardness of dentin and microshear bond strength of Clearfil SE Bond, Clerafil Tri-S Bond (Kuraray Medical) and Single Bond (3M ESPE) were measured on caries-affected and normal dentin. Modes of fracture for the bonding tests and the resin/dentin interfaces were observed using SEM. Data were analyzed at a statistical significance level of p < 0.05.

Significantly lower hardness values were recorded for caries-affected dentin compared to normal dentin. Two-way ANOVA showed that bonding material, type of dentin, and the interactions of these two factors had significant effects on bond strength. A significant correlation was found between dentin hardness and microshear bond strength. However, ANCOVA analysis revealed that the effect of dentin type was not only due to the mechanical properties of dentin. One-way ANOVA with Tukey's HSD test revealed that the mean bond strength of normal dentin with Tri-S Bond was significantly lower than that with SE Bond and Single Bond; however, bond strengths to caries-affected dentin showed no significant difference between the three adhesives.

All three adhesives showed lower bond strength to caries-affected dentin than to normal dentin. The differences between adhesives were not significant with caries-affected dentin as the bonding substrate. Dentin mechanical properties are not the only factors responsible for lower bond strength to caries-affected dentin.