Does plasma irradiation improve shear bond strength of acrylic resin to cobalt–chromium alloy?

Objectives. Plasma treatment leads to surface modification such as the improved wettability of dental materials. Studies have suggested that plasma treatment may bring about an improvement in the shear bond strength between cobalt–chromium alloy and self-curing acrylic resin. Methods. Forty-eight cobalt–chromium alloy specimens were randomly divided into four groups (each of the groups consisted of 12 specimens); air abrasion, adhesive primer, adhesive primer after air abrasion, or after plasma irradiation. A self-curing acrylic resin, 2 mm thick and 3.6 mm in diameter, was processed on all specimens before storage in distilled water at 37 °C for 24 h. Shear bond strength values were determined at a crosshead speed of 0.5 mm/min. Data was statistically analyzed using Schefféʹs test. Results. Adhesive primer clearly increased the shear bond strength compared with air abrasion (p<0.05). The synergy of air abrasion and adhesive primer greatly increased the shear bond strength, showing a five-fold increase over air abrasion, or one and a half-fold over adhesive primer. A similar tendency in increase was observed in the adhesive primer after plasma treatment, but to a lower degree. Adhesive primer after plasma treatment showed half the shear bond strength of the treatment of adhesive primer after air abrasion (p<0.05). Moreover, adhesive primer after plasma treatment showed a lower shear bond strength than adhesive primer alone although the difference was not statistically significant. Significance. Plasma treatment does not improve adhesion between cobalt–chromium alloy and self-curing acrylic resin.