Effect of Substrate Age and Adhesive Composition on Dentin Bonding

Purpose: To study the effect of dentin age and adhesive composition on the microtensile dentin bond strengths (mu TBS) of five dentin adhesives. Materials and Methods: Sixty extracted caries-free human teeth were assigned to the appropriate age group: less than 21 years of age (<21), 21-40 years of age (21-40), and greater than 40 years of age (>40). For each age group, specimens were randomly divided into five dentin adhesives: (1) Adper Easy Bond (EB, 3M ESPE), a one-step self-etch adhesive; (2) Experimental Adper Easy Bond without the Vitrebond Co-polymer (CP) (EBnoCP, 3M ESPE); (3) Adper Single Bond Plus (SB, 3M ESPE), a two-step etch&rinse adhesive; (4) Experimental Adper Single Bond Plus without CP (SBnoCP, 3M ESPE); and (5) Adper Scotchbond Multi-Purpose (MP, 3M ESPE), a three-step etch&rinse adhesive, as the control group. Specimens were sectioned in X and Y directions and the resulting beams were tested to failure in tension mode at a crosshead speed of 1 mm/min. Statistical analysis was computed using t-test and two-way analysis of variance followed by Fisher least significant difference multiple comparison post hoc test at p < 0.05. Results: The highest mean mu TBS values were obtained in the control group (MP) for all age groups. EB resulted in statistically similar mean mu TBS compared to EBnoCP for all age groups: p = 0.538 for (<21);p = 0.974 for (21-40); and p = 0.909 for (>40). SB resulted in statistically higher mean mu TBS than SBnoCP for all age groups [p<0.009 for (<21); p<0.028 for (21-40); and p<0.041 for (>40)]. MP, the control group, resulted in statistically lower mean mu TBS when applied to the oldest age group (>40) compared to the youngest age group (<21), at p < 0.04. When means were pooled for the variable 'age group,' SB resulted in significantly higher mean mu TBS than SBnoCP at p < 0.009, while EB resulted in statistically similar mean mu TBS compared to EBnoCP (p=0.9). MP resulted in statistically higher mean mu TBS than all other adhesives-SB (p<0.0001), SBnoCP (p<0.0001), EBnoCP (p<0.022), and EB (p <0.046). Conclusions: The substrate age influenced the bonding ability of the three-step etch&rinse adhesive. The presence of a carboxylic-based polymer (CP) enhanced the bonding ability of the two-step etch&rinse adhesive.