An evaluation of the effects and interactions of several factors upon the cementation of cast metal crowns

Abstract

This study evaluates the effects and interactions of cements, cement space, seating forces, marginal designs and bite materials on crown seating upon cementation. Two stainless steel dies of 6 mm crown preparations with 10 degree axial tapers were used. Both were designed with 1 mm wide shoulders, one with a simple shoulder, the other, a shoulder with a 65 degree bevel. Ten impressions (Impregum, Premier) were made from each die and poured in die stone (Super-Die, Whip Mix). Four coats of die-spacer (Tru-Fit, Taub.) were painted on 5 dies of each type. The dies were divided into 4 groups as follows: spacer; B: shoulder, no die-spacer; A: shoulder, with die­ C: shoulder-bevel, with die-spacer; D: shoulder-bevel, waxed up on all dies and cast no die-spacer. Crowns were in Rexillium (Rx Jeneric). Before and after cementation, the seating of crowns on metal dies was measured with a micrometer (Starrett). Comparisons were made between zinc phosphate cement (Mizzy, Fleck's) and ionomer cement (Ketac-Cem, Premier) under 2 seating forces (5 and 30 pounds) in an Instron machine using an orangewood stick (Aidaco, Interstate) or the E-Z-bite (Gingipak). Five pairs of dead flat metal disks (2 mm thick, 11 mm in diameter) were also used to test the cement film thickness attributable to the use of the above-mentioned cements, seating forces, and bite materials. The use of ANOVA and Newman Keuls tests revealed that die-spacer, heavy force (30 pounds), glass ionomer cement (Ketac-Cem) all significantly improve crown seating upon cementation. Die-spaced shoulder­ bevel preparations yielded superior crown seating when 30 pounds of force or ionomer cement (Ketac-Cem) were used. Orangewood stick and E-Z-bite were equivalent in effectiveness.