Self-etch Adhesives on Enamel and Dentin: Dynamic pH and Wettability

Objective: Effectiveness of self-etch adhesives (SE-Ad) is still inadequate despite the rapid progress made in adhesive bonding of direct restorations since the 90s. Clinical outcome of SE-Ad can depend on the dental tissue to which they are applied, enamel or dentin, and on their technology, single-bottle or two-bottle. As an objective of this study, two influential factors on the performance of SE-Ad, pH and wettability, were tested directly on enamel and dentin, before and after light-curing.

Materials and Methods: Two SE-Ad systems, Scotchbond-SE and Prompt L-Pop (3M-ESPE), were applied following manufacturer instructions on glass/control, bovine cut enamel, and dentin. pH vs time was measured with a custom-made system based on a flat-surface pH-electrode and special software. pH was measured before, while the adhesive was reacting with dental tissues, and after light-curing. Dynamic wettability of the adhesives on enamel and dentin after light-curing was determined by measuring contact-angles (DM-CE1) of ultrapure water (WCA) and hydrophobic resin (RCA) of Filtek-Z250 (3M-ESPE) composite using the sessile-drop method. ANOVA-Tables with post-hoc Tukey's test were used for statistical analysis.

Results: Some relevant results obtained: 1) pH-values were higher on dentin than on enamel regardless of the SE-Ad, before and after curing. This indicates water from dentin has a higher buffering effect than Ca ions released from mineralized tissues while being etched. 2) No significant differences in WCA were found between the two adhesives. RCA on SE-Ad applied on dentin were higher than those on enamel (Figure). Water on the adhesive surface after interacting with dentin may explain this response.

Conclusion: Significant differences in pH and wettability of two SE-Ad on enamel and dentin, before and after curing, were demonstrated by using custom-made equipment. The data obtained from these tests can be valuable in the determination of critical factors for the clinical performance of SE-Ad.