Effects of pH, ionic strength, and applied voltage on migration of dental monomers in an organic matrix

The application of an electric field has been shown to positively influence the bonding of dentin bonding systems (DBS) by improving adhesive impregnation into dentin. However, the mechanism responsible for this phenomenon has not been completely elucidated. The aim of this study was to clarify the effects of pH, matrix ionic strength, and applied voltage on the migration of commonly used DBS monomers in a model matrix (agarose gel).

Some common monomers examined were bis-GMA (2,2-bis[4-(2-hydroxy-3-methacryloyloxy propoxy) phenyl] propane); HEMA (2-hydroxyethyl methacrylate); 2-MP (bis[2-(methacryloyloxy) ethyl] phosphate); TCDM [di(hydroxyethyl methacrylate) ester of 5-(2,5,-dioxo tetrahydrofurfuryl)-3-methyl-3-cyclohexenyl-1,2-dicarboxylic acid]; and TEGDMA (triethylene glycol dimethacrylate). Agarose gels poured into a horizontal 10-well electrophoretic cell were used to mimic the collagen fibrils of the dentin organic matrix. The role of pH, matrix ionic strength, and voltage on monomer migration was assayed by modifying the experimental conditions.

Results of experiments performed at pH 3.1, 6.3, 8.5, and 12.3; at low, medium, and high ionic strength; and at 50 and 100 V clearly showed that DBA monomer migration toward both the anode and the cathode can be affected by each of these parameters.

Migration of acrylic monomers toward the anode or cathode can be achieved as desired by selective choice of pH, ionic strength, and applied voltage. Additional studies are needed to evaluate the synergistic effects of DBS monomer blends on migration in an electric field.