Introduction
The search for alternative direct-filling materials to replace silver amalgam, is intensifying. Despite assurances of relative safety, there is continuing controversy over the use of a restorative material containing mercury, and concern about the discharge of amalgam waste. A metallic alternative containing gallium, instead of mercury, was suggested as early as 1928 in Germany, and has been under development since 1956 [McComb, 1998]. The first gallium alloy (in 1956) for dental purposes alloyed liquid gallium with powders of Ta, Cr, Mo, In, Co, Ni, Au and some Cu –Sn alloys. Waterstrat formulated Ga –Pd –Sn alloys and found their strength and setting expansion to be acceptable [Dunne et al , 2005].
Two types of Gallium containing alloys became available for clinical use, those containing palladium at 9% (Gallium Alloy GF, Tokurike Honten, Japan) or 2% Gallium GFII and palladium-free alloys namely Galloy (Southern Dental Industries, Bayswater, Australia). Many studies have been performed to evaluate and develop gallium restorative alloys[Horasawa et al, 1999, Shaini,et al, 2001, Hero, et al, 1997, Dunne ,et al,2000 ].Unfortunately, studies with the 9% palladium alloy indicated poor clinical performance with marked discolouration, surface roughness and marginal breakdown. The performance of the reformulated Gallium GFII in laboratory studies was superior, exhibiting fewer defects associated with corrosion, but the setting expansion was much greater than that exhibited by silver amalgam.