Effect of primers containing N-methylolacrylamide or N-methylolmethacrylamide on dentin bond durability of a resin composite after 5 years

Abstract

Objectives: The effect of experimental dentin primers containing N-methylolacrylamide (MEAA) or N-methylolmethacrylamide (MEMA) on bond durability of a resin composite (Photo Clearfil A) with a bonding agent (Clearfil Photo Bond) to bovine dentin was investigated. Methods: The etching agents were 10% maleic acid (10% MA), 10% phosphoric acid (10% PA) and 10% citric acid–3% ferric chloride (10–3 solution). Water solutions of 35% hydroxyethyl methacrylate (HEMA), 50% MEAA or 30% MEMA were used as dentin primers. The etched dentin was pre-treated with the dentin primers for 30 s. The resin composite systems were applied in a Teflon tube positioned onto pre-treated dentin surfaces. After water immersion for 1 day and 5 years, the shear bond strengths were measured. The amounts of calcium dissolved with etching agents were measured using atomic absorption spectrometry. The thicknesses of hybrid layers at the dentin–resin interfaces treated with 6 mol/l HCl and 1% NaOCl were measured using scanning electron microscopy. Results: The bond strengths of the specimens (Controls) without primers to dentin etched with 10% MA and 10–3 solution significantly decreased after immersion in water for 5 years ( p<0.05) while other bond strengths did not decrease. The bond strengths of the composites to MEMA- and MEAA-primed dentin were significantly higher than that of the control after 1 day, regardless of the types of etching agents ( p<0.05). The 5 year bond strengths of the composites to HEMA-, MEMA- and MEAA-primed dentin were significantly higher than that of the control, regardless of the types of etching agents ( p<0.05). The 1 day and 5 year bond strengths of the composite to MEAA-primed dentin were significantly higher than those of the composites to HEMA-primed dentin, regardless of the types of etching agents ( p<0.05). The highest amount (182.3±8.0 μg/cm 2) of dissolved calcium was determined for the pre-treatment with 10% PA, followed by that (152.0±6.9 μg/cm 2) with 10% MA and that (140.1±2.8 μg/cm 2) with 10–3 solution ( p<0.05). The hybrid layer thicknesses (approximately 1 μm) for 10–3 solution were thinner than those (approximately 2 μm) for others after HCl immersion. For the controls, the hybrid layers after NaOCl immersion become narrower or disappeared. The main fracture pattern of specimens was a mixture of resin–dentin interface failure and dentin cohesive fracture after the bond test. Conclusions: MEAA solution was more effective in improving the bond strength of the controls to etched dentin than was HEMA after 1 day and 5 years. Clearfil Photo Bond created good hybrid dentin layers which could resist NaOCl-attack and showed good dentin bond durability when dentin primers were used, regardless of the type of etching agent.