The effect of investment material and ceramming regime on the surface roughness of two castable glass–ceramic materials

Objective: To assess the surface roughness ( R a) of two castable glass–ceramic materials, cast using four different investment materials and employing different ceramming regimes. Methods: Forty discs, each 12 mm diameter and 2 mm thick were produced from two castable glass–ceramic materials, one a glass ionomer derivative based on 1.5SiO 2–1Al 2O 3–0.53P 2O 5–1CaO–0.67CaF 2 (LG112), the other a fluorcanasite material based on 0.60SiO 2–0.05K 2O–0.10Na 2O–0.15CaO–0.10CaF 2 (SG3). The discs were made using four dental investments, two gypsum-bonded (Whip-Mix Cristobalite (WMC), Degussa California (DC)) and two phosphate-bonded (Fujivest Super (FS), Techceram Glass (TG)). A Ni–Cr metal/ceramic alloy (Wiron 99) was also used as a control. Each investment was used to produce 10 discs for each glass–ceramic material, five left in the as-cast, glass state, the other five cerammed. Ceramming was carried out either within the investment mold or after de-vesting from the investment mold. The discs had their surface roughness values measured using a stylus, surface contact measuring instrument. Results: For the Ni–Cr alloy the phosphate-bonded investments produced discs significantly smoother than those produced by the two gypsum-bonded investments ( p0.05), with the WMC investment producing the smoothest discs ( p