Shear Bond Strength of Resin to Amalgam

Amalgam restorations are known for their durability and reliability; however, the grey or black color of these restorations presents an esthetic challenge. Objective: This study evaluated shear bond strength (SBS) of composite bonded to various surfaces in order to determine the feasibility of masking amalgam restorations with composite overlays. Methods: Specimens of human enamel, condensed amalgam and enamel-amalgam junctions were embedded in PMMA and flattened with 400-600 grit sandpaper. Six groups of ten were randomly assigned as A, B, C, D, E, and F. The groups were composite bonded to: enamel (A), highly polished amalgam (B), enamel-amalgam interface (C), sandblasted-amalgam (D), carbide bur-prepared amalgam (E), and sandblasted-enamel-amalgam interface (F). Fifty micron aluminum oxide sandblasting was performed (Microetcher™, Danville, CA). Surfaces were prepared with Amalgam Bond® Plus-system (Parkell, Farmingdale, NY) using base-catalyst-powder following manufacturer directions. Composite cylinders were made using Point 4® (Kerr Corporation, Orange, CA) and Ultradent (Ultradent, South Jordan, UT) mold-setting-system. After 80 second light curing, a shear bond strength test was performed using an Ultradent jig-blade in the Instron® Universal Machine (Canton, MA) at a head speed of 0.5mm/minute. Results: ANOVA indicated significant differences among the groups (p<0.0001). SBS in MPa (Mean/SD) were for A: (24.63/4.19), B: (6.77/3.27), enamel-amalgam interface C: (9.13/2.18), D: 16.82/3.60, E: (9.27/4.03), F: (16.67/4.87). Significant statistical differences were observed between the groups A, D, F and the remaining 3 groups (B), (C), and (E). Conclusion: In vitro test demonstrated that amalgam masking has the strongest SBS on sandblasted and carbide-prepared amalgams and could be an alternative to improve the esthetics of amalgam restorations.