Influence of water concentration on the etching aggressiveness of self-etch primers to ground primary enamel

The purpose of this study was to investigate the influence of water concentration in self-etch primers on their etching aggressiveness to ground primary human enamel.

Five hydroxylethyl methacrylate/glycerol dimethacrylate phosphate-based experimental self-etch primers with the same pH (1.1) and different water concentrations (0%, 5%, 10%, 20%, or 40%) were formulated. The enamel of primary molars was flattened, and the primers were applied vigorously for 30 seconds. The etching morphology was assessed via scanning electron microscopy. Thirty-seven percent phosphoric acid gel was tested as a positive control.

Increasing etching aggressiveness was associated with increased water content. The etching potential of the anhydrous primer was marginal to none. Primers with 5% and 10% water concentration showed similar etching potentials, producing slight enamel demineralization. The primer with 20% water concentration produced removal of crystals within and around the enamel prisms, with the outline of the prisms being clearly visible. The aggressiveness of the primer with 40% water concentration was more pronounced, with generalized porosity involving the center and periphery of the prisms, with vast surface irregularity. The etching pattern of the phosphoric acid gel was more pronounced than the primer with 20% water concentration, but less aggressive than the primer with 40% water concentration.

Water content has a significant role on the aggressiveness of self-etch primers applied to the ground primary enamel.