Does Dentin Thickness and Aging Affect the Bonding to Dentin?

Objectives: To evaluate the effect of remaining dentin thickness (RDT) and 1-year water storage on microtensile bond strength (µTBS) of self-etch adhesives to bur-prepared dentin.
Methods: Three self-etch adhesives were used: Clearfil SE Bond 2 (SE), Clearfil Universal Bond (CU) and Scotch Bond Universal (SB). The adhesives were applied according to the manufacturer’s instructions on flat dentin surfaces prepared with regular diamond bur. Resin composite blocks were built up. Bonded teeth were stored in distilled water at 37°C for 24-h and sectioned in both directions to obtain resin-dentin beams. Eight teeth (n=8) from each group were tested at 24-h, while the remaining teeth (n=8) were kept in distilled water at 37°C for 1-year testing. Kruskal-Wallis One-way analysis of variances was used to analyze the µTBS data. The correlation between µTBS and remaining dentin thickness (RDT) was evaluated with regression analysis. Fractured surfaces were observed by SEM.
Results: µTBS and RDT showed statistically significant linear relationship (p<0.001) except for SE and CU at 24-hour (p>0.001). The bond strength of SE and CU did not show RDT dependency at 24-hour. In both testing times, SE (24-hour: 55.18±6.40 and 1-year: 41.25±5.06) showed higher bond strength then CU (24-hour: 36.59±5.07 and 1-year: 32.11±4.85) and SB (24-hour: 39.33±6.61 and 1-year: 29.11±5.67). µTBS values significantly decreased after 1-year storage for all materials (p<0.001). At 24-hour and 1-year, the most frequent fracture mode was mixed failure for all groups, but adhesive failure increased after 1-year for all groups.
Conclusions: Remaining dentin thickness and aging in water negatively affected the bond strength of self-etch adhesives to bur-prepared dentin.