Polypropylene glycol phosphate methacrylate as an alternative acid-functional monomer on self-etching adhesives

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 also to evaluate its influence on the pH and microshear bond strength (μSBS) to enamel.

Primers containing Poly-P (10, 15, 30 or 50wt.%), HEMA, ethanol, and water were prepared and allocated in subgroups according to a buffered or non-buffered pH. One experimental control and one commercial (Clearfill™ SE Bond) references were used. μSBS protocol was performed at human enamel, followed by mechanical testing. Scanning electron microscopy (SEM) was performed after each primer application. Data was analysed by one-way Kruskal-Wallis and Student-Newman-Keuls tests (p<0.05) and by linear regression predictive models.

As greater the Poly-P content, the lower the primer's pH. Buffered groups showed lower μSBS values than non-buffered groups. Groups with Poly-P content equal or higher than 30wt.% showed similar μSBS results when compared to the controls. SEM images demonstrated that primers with high Poly-P content etched enamel with prisms exposure.

The pH of the primer was directly influenced by the concentration of acidic monomer, which directly affected the adhesion to enamel. Both the acidity and the type of acid-functional monomer present in the adhesive influenced the bond strength results.

Poly-P synthesis was easy and effective, and considering the good bond strength results obtained, this acid-functional monomer may be potentially used in the formulation of self-etch dental adhesive systems.