Evaluation of experimental phosphate and sulfur-based primer bonding to metal casting alloys

The aim of this study was to evaluate the effect of three experimental primers prepared with synthesized phosphorous and sulfur monomers (HEMA-P, ETMA and the mixture of HEMA-P/ETMA) on bonding to nickel–chromium (NiCr), silver–palladium (AgPd) and silver–gold (AgAu) metal alloys. The specimens were treated with experimental primers: HEMA-P, ETMA, HEMA-P/ETMA and Alloy Primer (Kuraray Noritake Dental Inc., Okayama, Japan) was used as commercial reference. Resin cement cylinders were built-up after application of tested primers on different alloy surfaces. Samples were stored in distilled water at 37 °C for 24 h before being subjected to shear bond tests using a mechanical testing machine. Shear bond strength (SBS) was recorded in MPa. Failure modes were classified under magnification as adhesive and mixed failure. Data were submitted to a two-way ANOVA and Student–Newman–Keuls׳ test. The statistically highest shear bond strength was observed with commercial primer to the AgPd alloy while the lowest value was shown with commercially available primers and experimental HEMA-P/ETMA to the NiCr alloy ( p<0.05). There was a predominance of adhesive failure, with the exception of commercially available primer, for which mixed failures were predominant. It could be concluded that formulations of metal primers containing HEMA-P or ETMA primers should be considered for use in the bonding protocol of NiCr alloys.