Effect of environmental stress and surface treatment on resin-to-metal bonding

This study compares the bond strength and durability of three metal surface treatments subjected to two types of environmental stress for both short- and long-term exposures. The luting resins Panavia and Comspan were applied to alumina-blasted, non-beryllium, nickel-chromium alloy coupons. Metal surface treatments consisted of either microscopic roughening by electrochemical etching, or one of two types of adhesives: a silanated silica coating (Silicoating) or a phosphate ester monomer (a component in the Panavia liquid). Shear bond strength was determined following short- or long-term exposure to either thermocycling in 6-60 degrees C water (2,672 cycles/7 days or 10,584 cycles/42 days) or storage in 37 degrees C water (7 or 42 days). Three-way ANOVA showed that both the type of environmental stress and the exposure time affected the bond strength of electroetched surfaces, but that only exposure time affected the two chemical adhesives (P < 0.05), regardless of the environmental stress used. In the short-term, the silica/silane coated surfaces produced and maintained the higher shear bond strengths (15.9 +/- 2.3 MPa). However, after 42 days the silica/silane bonds decreased 30% (to 11.3 +/- 2.2 MPa), while the phosphate ester bonds were essentially unchanged (11.4 +/- 3.0 at 4 days, 10.4 +/- 2.2 MPa at 42 days). Electroetched bonds were the weakest and decreased by 18% between 7 and 42 days in water (8.8 +/- 1.2 to 7.2 +/- 3.0 MPa) and 27% after 42 days of thermocycling (7.2 +/- 2.8 to 5.3 +/- 1.8 MPa).