Objective: The purpose of this study was to evaluate 2 thione primers and 3 resin adhesives for enhancement of bonding strength to a silver-palladium-copper-gold alloy. Method and Materials: Two different sized disk specimens (10- and 8-mm diameter by 2.5-mm thick) were prepared from a silver-palladium-copper-gold alloy (Castwell M.C. 12, GC). The specimens were airborne-particle abraded with 50-µm-grain alumina, conditioned either with a thiouracil primer (Metaltite, Tokuyama Dental) or with a triazine dithione primer (V-Primer, Sun Medical), and then bonded with 1 of 3 acrylic resins: a benzoyl peroxide–amine redox-initiated resin adhesive (Multi-Bond, Tokuyama Dental) or a tri-n-butylborane–initiated resin adhesive (Super-Bond C&B and Super-Bond Quick, Sun Medical). For each adhesive, unprimed specimens were prepared as experimental controls. Shear bond strength was determined after thermocycling (100,000 cycles). Results: Use of primers significantly (P < .05) enhanced the bond strength of specimens in all adhesives. Irrespective of the type of primer, the strength of Multi-Bond adhesive was significantly (P < .05) lower than that of Super-Bond C&B and Super-Bond Quick adhesives. The strength of the 2 tri-n-butylborane–initiated adhesives did not differ significantly (P > .05). The mean strength of the Super-Bond C&B adhesive was 40.4 MPa with Metaltite and 37.8 MPa with V-Primer; that of Super-Bond Quick adhesive was 40.9 MPa with Metaltite and 36.5 MPa with V-Primer. Conclusion: Use of thione primers effectively enhanced the strength of the bond to the silver-palladium-copper-gold alloy. Furthermore, the combinations of primers and tri-n-butylborane–initiated adhesives were found to be more efficient for bonding. (Quintessence Int 2006;37:395–399)

Key words: initiator system, resin adhesive, shear bond strength, silver-palladium-copper-gold alloy, thermocycling, thione primer