The effect of novel mercapto silane systems on resin bond strength to dental noble metal alloys

Self-assembled monolayers of thiols (RSH), which are key elements in nanoscience and nanotechnology, have been used to link a range of materials to planar gold surfaces or gold nanoparticles. In this study, the adhesive performance of mercapto silane systems to dental noble metal alloys was evaluated in vitro and compared with that of commercial dental primers. Dental gold-palladium-platinum (Au-Pd-Pt), gold-palladium-silver (Au-Pd-Ag), and palladium-silver (Pd-Ag) alloys were used as the bonding substrates after air-abrasion (sandblasting). One of the following primers was applied to each alloy: (1) no primer treatment (control), (2) three commercial primers: V-Primer, Metal Primer II, and M.L. Primer, and (3) two experimental silane primer systems: 2-step application with 3-mercaptopropyltrimethoxysilane (SPS) (1.0 wt%) and then 3- methacryloxypropyltrimethoxysilane (MPS) (1.0 wt%), and a silane blend consisting of SPS and MPS (both 1.0 wt%). Composite resin cylinders with a diameter of 2.38 mm were bonded to the surfaces and irradiated for 40 sec using a curing light. After storage in water at 37 - C for 24 h, all the bonded specimens were thermocycled 5000 times before the shear bond strength test. Regardless of the alloy type, the mercapto silane systems (both the 2-step and blend systems) consistently showed superior bonding performance than the commercial primers. Contact angle analysis of the primed surfaces indicated that higher resin bond strengths were produced on more hydrophilic alloy surfaces. These novel mercapto silane systems are a promising alternative for improving resin bonding to dental noble metal alloys.