Shear Bond Strength of Resin Cement to Saliva-Contaminated Metal Alloys after Various Surface Treatments

Abstract

The bonding ability of resin cement to metal alloys of conventional dental restorations is critical for the retention and long-term survival rate. Contaminated saliva during try-in process which is resistant to simple water rinsing could reduce bond strength. Surface treatment before cementation might have an important role in optimizing resin-metal bond strength. The purpose of this study was to study the effect of surface pretreatment on the shear bond strength of dental base metal alloys after saliva contamination using a self-adhesive resin cement. Forty dental wax patterns (7-mm diameter) were made and cast with dental base metal alloy (Argeloy N.P. (V)). Cast metal specimens were embedded in PVC tube using self-curing acrylic resin and then flattened with 600-grit silicon carbide paper. PVC tube holders were specifically designed for the shear bond strength test device. Forty resin composite specimens were prepared in plastic mold (diameter of 3 mm and depth of 3 mm). The resin composite specimens were treated with sandblasting. Fifty-μm aluminum oxide particle was blasted for 10 seconds from the distance of approximately 5 mm perpendicular to the bonding surface. Metal alloy specimens were immersed in artificial saliva for 1 minute and rinsed with water-spray for 15 seconds. The specimens were also air-dried for 15 seconds. Specimens were divided into four groups, which received one of the following surface treatments: (1) No surface treatment (Control), (2) 37% phosphoric acid, (3) 37% phosphoric acid and then rinsed with 70% ethyl alcohol, and (4) 70% ethyl alcohol. After rinsing and drying, the resin composite specimens were cemented with Panavia SA Cement (Kuraray Noritake Dental Inc., Okayama, Japan) at the center of metal alloy specimens followed by the manufacturer’s instruction. Before testing, the specimens were stored in distilled water at 37oC for 24 hours. For testing, specimens were dried and mounted to universal testing machine (EZ-S, Shimadzu Co., Kyoto, Japan) at the crosshead speed of 1 mm/minute. Failure loads was recorded in Newton (N) and then analyzed to Mega Pascal (MPa). The highest shear bond strength was observed for group 2 and 3. The failure mode in all the materials was adhesive failure which occurred at the resin-metal interface. Within the limitations of this study, phosphoric acid was effective in removing saliva contamination and enhancing bond strength at the resin-dental base metal interface.