Adhesion of 4-META / MMA-TBB Resin to Ground Enamel Treated with Self-etching Primer Containing Amino Acid Methacrylate

The effect of self-etching primer on the adhesion of tri-n-butylborane (TBB)-initiated resin to enamel has not been fully determined. We prepared a self-etching primer containing amino acid methacrylate, and evaluated the effectiveness of the self-etching primer for the adhesion of TBB-initiated 4-methacryloxyethyl trimellitate anhydride (4-META)/methyl methacrylate (MMA) resin to ground enamel. Methacryloyloxy tyrosine (MTY) was prepared by reacting methacryloyl chloride and L-tyrosine in trifluoroacetic acid. An original self-etching primer containing an aqueous mixture of MTY, 35 wt% 2-hydroxyethyl methacrylate (HEMA), and 3 wt% ferric chloride was designed. Three strengths of MTY (5%, 10%, and 20%) were tested. The bovine enamel surface was treated with the self-etching primer for 30 s. After drying, a stainless steel rod was bonded to the enamel using TBB-initiated 4-META/MMA resin. The tensile bond strength was measured after 1-day immersion in water at 37°C. The self-etching primer containing 20 wt% MTY (20MTY) yielded a significantly higher bond strength of 13.2 ± 2.8 MPa than the self-etching primer containing 5 wt% and 10 wt% MTY. This value was not significantly different from that with phosphoric acid etching. Field-emission scanning electron microscopy revealed that 20MTY treatment produced no distinct dissolution pattern on enamel. Tight bonding between the resin and enamel was clearly observed. Our original self-etching primer containing 20 wt% MTY, 35 wt% HEMA, and 3 wt% ferric chloride was effective for obtaining strong adhesion of 4-META/MMA-TBB resin to enamel compatible with phosphoric acid etching.