Influence of adhesive systems containing different functional monomers on the longevity of bond strength at different dentin depths

This study evaluated the influence of adhesive systems containing different functional monomers on the longevity of bond strength (BS) to superficial (SD) and deep dentin (DD). Thirty molars were sectioned longitudinally, to obtain regions of SD (closest to the dentin-enamel junction) and DD (closest to the pulp chamber). Adhesive systems were applied (n = 10): Clearfil SE Bond (containing 10-MDP), FL-Bond II (containing 4-MET) and OptiBond Universal (containing GPDM). Microcylinders were made of resin composite (Filtek Z250) in SD and DD. After 24 h or 180 days of storage in Simulated Body Fluid (SBF) solution, BS tests were carried out. The fracture mode was evaluated by scores. ANOVA showed that there was no statistically significant difference between the adhesives in terms of BS (p = 0.5156). There was no significant difference between storage times for the three adhesive systems (p = 0.4703). There was a significant interaction between storage time and dentin depth (p = 0.0175), and in the time interval of 24 h, irrespective of the adhesive system, BS was significantly higher in SD than in DD (p < 0.05). In the time interval of 24 h, there was a significant association between the adhesive and the type of failure in SD (p = 0.0085) (Fisher`s Exact test). Under these conditions, only OptiBond Universal showed cohesive failures in dentin (10 %) and mixed failures (15 %). After 180 days of storage, the percentages of early failures in deep dentin were 25.0 % (OptiBond Universal), 16.7 % (Clearfil SE Bond) and 0.0 % (FL-Bond II), with a significant difference between adhesives regarding early failures (p = 0.0410). The adhesive systems showed similar BS at different dentin depths over time, irrespective of the composition of functional monomers. FL Bond II was the only adhesive system that did not show early failures mode in DD within 180 days.