Effect of thione primers on bonding of noble metal alloys with an adhesive resin

Objectives: The purpose of the current study was to evaluate the effects of two metal conditioners on the bond durability of an adhesive resin joined to noble metal alloys by comparing pre- and post-thermocycling bond strengths. Methods: Two different sizes of disk specimens (10 and 8 mm in diameter by 2.5 mm thickness) were prepared from silver–indium (Ag–In–Zn, Salivan), silver–palladium–copper–gold (Ag–Pd–Cu, Castwell M.C.12), metal–ceramic gold (Au–Pt–Pd, Degudent-Universal), metal–ceramic palladium (Pd–Ga–Co, PTM 88), type IV gold (type IV, Casting Gold) alloys, and pure silver (pure Ag). The specimens were air-abraded with 50-μm grain sized alumina, conditioned either with a thiouracil primer (Metaltite) or with a thione–phosphate primer (Alloy Primer), then bonded with an adhesive resin (Super-Bond Opaque). Shear bond strengths were determined both before and after repeated thermocycling (4°C and 60°C, 1 min each, 100,000 cycles). The results were compared by analysis of variance and post-hoc multiple comparison intervals. Results: The average post-thermocycling bond strengths in MPa (n=8) generated with the thiouracil primed and thione–phosphate primed groups, respectively, were: 3.4 and 5.8 for the Ag–In–Zn alloy, 40.4 and 37.7 for the Ag–Pd–Cu alloy, 26.4 and 33.5 for the Au–Pt–Pd alloy, 27.4 and 36.6 for the Pd–Ga–Co alloy, 40.2 and 40.3 for the type IV alloy, and 37.3 and 32.4 for the pure Ag. The Ag–In–Zn alloy exhibited significantly lower bond strength than the other alloys, whereas the Ag–Pd–Cu and type IV alloys exhibited the greatest magnitude of bond strength for both primers (p<0.05). Conclusions: It can be concluded that the combined use of either of the two thione primers and the adhesive resin is effective for bonding the metal/alloys examined, with the exception of the Ag–In–Zn alloy.