Efficacy of Self-etching Primers in the Adhesion of 4-META/MMA-TBB Resin Cement to Enamel

The effect of self-etching primer on the adhesion of tri-n-butylborane (TBB)-initiated resin cement to enamel has not been determined. This study evaluated the effectiveness of the self-etching primer by measuring the tensile bond strength between enamel and TBB-initiated methyl methacrylate (MMA) resin containing 4-methacryloxyethyl trimellitate anhydride (4-META). The self-etching primers were an aqueous mixture of 30 wt% methacryloxyethyl phosphate, 35 wt% 2-hydroxyethyl methacrylate, and ferric chloride. The concentration of ferric chloride was varied from 0 to 7 wt%. The bovine enamel surface was treated with self-etching primer for 30 s. After drying, a stainless steel rod was bonded to the enamel using TBB-initiated 4-META/MMA resin cement. The tensile bond strengths were measured after 1 day of immersion in 37°C water and after thermal cycles between 4°C and 60°C. The resin-enamel interface was observed under field-emission scanning electron microscopy (FE-SEM). The self-etching primer containing 5 wt% ferric chloride (Phosmer-5Fe) yielded the highest mean bond strength and significantly higher bond strengths than phosphoric acid etching after 1 day of immersion. After 5000 thermal cycles, the bond strength with Phosmer-5Fe was still significantly higher than that with phosphoric acid etching. FE-SEM images revealed tight bonding between the resin and enamel in the specimens of Phosmer-5Fe primer treatment. The self-etching primer treatment may be an alternative to phosphoric acid etching for the adhesion of TBB-initiated 4-META/MMA resin cement to enamel.