The role of functional monomers in bonding to enamel: Acid–base resistant zone and bonding performance

Abstract

Objectives To investigate the effects of two functional monomers on caries-inhibition potential and bond strength of two-step self-etching adhesive systems to enamel. Methods Clearfil SE Bond and similar experimental formulations different in the functional monomer were used. Four combinations of primer and bonding agents were evaluated: (1) Clearfil SE Bond which contains MDP in both primer and bonding (M–M); (2) Clearfil SE Bond primer and Phenyl-P in bonding (M–P); (3) Phenyl-P in primer and Clearfil SE Bond bonding (P–M); (4) Phenyl-P in primer and bonding (P–P). Ground buccal enamel surfaces of human sound premolars were treated with one of the systems and the bonded interface was exposed to an artificial demineralising solution (pH 4.5) for 4.5 h, and then 5% NaOCl with ultrasonication for 30 min. After argon-ion etching, the interfacial ultrastructure was observed using SEM. Micro-shear bond strength to enamel was measured for all groups and results were analysed using one-way ANOVA and Turkey's HSD, while failure modes were analysed by chi-square test. Results An acid–base resistant zone (ABRZ) was found with all adhesive systems containing MDP either in primer or bond; however, ultramorphology and crystallite arrangement in the ABRZ were different among groups. P–P was the only group devoid of this protective zone. Micro-shear bond strength in M–M was significantly higher than those in M–P, P–M and P–P, while the latter three were not different from each other. Failure modes were significantly different ( p < 0.05). Conclusions Functional monomers in two-step self-etching systems influence both the bonding performance and the formation of ABRZ on enamel.