Effect of 4-MET on bond strength and penetration of monomers into enamel.

The effect of 4-[2-(methacryloyloxy)ethoxycarbonyl]phthalic acid (4-MET) in self-curing acrylic resin initiated by BPO-amine on the bond strength to etched enamel was studied. Scanning electron microscopic (SEM) observations of resin-enamel interfaces were carried out to elucidate the bonding mechanism and the effect of 4-MET on the adhesion. 4-MET, which has both hydrophilic and hydrophobic groups, increased the bond strength of self-curing acrylic resin to etched enamel and improved the bonding stability. SEM pictures strongly suggested that 4-MET promoted interpenetration of monomers into enamel prism peripheries and their polymerization therein resulted in excellent adhesion to etched enamel.