Alternative acid-functional monomer and its pH influence on the enamel

Abstract

Purpose: The aim of this study was to synthesize an alternative acidic monomer (polypropylene glycol phosphate methacrylate – Poly-P) to constitute experimental two-step self-etch adhesive systems and to evaluate its influence on the pH and microshear bond strength ( SBS) to enamel. Methods and materials: Four primers containing Poly-P (10, 15, 30 or 50wt%), 2-hydroxyethyl methacrylate (HEMA), ethanol, and water were prepared, which were allocated in two subgroups according to an adjusted (buffered) or non-adjusted (non-buffered) pH. One experimental control and one commercial (ClearfillTM SE Bond) references were used. SBS protocol was performed at human enamel, followed by mechanical testing (EMIC). Scanning Electron Microscopy (SEM) was performed after each primer application. Data was analyzed by One-Way Kruskall–Wallis and Student-Newman–Keuls tests (p<0.05) and by linear regression predictive models. Results: As greater the Poly-P content, the lower the primer’s pH. Buffered groups showed lower SBS values than non-buffered groups. Groups with Poly-P content equal or higher than 30wt% showed similar SBS results when compared to the controls. SEM images demonstrated that only primers with high Poly-P content (30 and 50wt%) etched enamel in a more evidenced Type 1 (prisms exposure) etching pattern. Conclusion: The pH of the primer was directly influenced by the concentration of acidic monomer, which directly affected the enamel bond strength results. Poly-P is a potential monomer to be used in the formulation of self-etch dental adhesive systems.