INFLUENCE OF PORCELAIN FIRING AND CORE THICKNESS ON MARGINAL GAP OF CAD/CAM AND PRESSABLE ALL-CERAMIC CROWNS (IN-VITRO STUDY)

Abstract

Statement of Problem: Marginal gap is important for the long-term success of all-ceramic restorations, the marginal accuracy of different manufacturing techniques and core thicknesses must be considered. Purpose: This study compared marginal gap of CAD/CAM and heat-pressed ceramic cores with different thicknesses before and after veneering porcelain application. Materials and Methods: A standard die was prepared. Sixty resin dies were duplicated. Samples were divided into two groups, Group I: samples were fabricated by CAD/CAM, Group II: samples were fabricated by heat pressing. Each group was divided into three subgroups: Subgroup 1: cores of 0.3 mm. thickness, Subgroup 2: cores of 0.5 mm. thickness, Subgroup 3: full contoured crowns were manufactured by characterization technique. marginal gap was measured at core stageand after veneering porcelain firings using a microscope . Results: Marginal gaps of CAD/CAM samples in all subgroups were higher than pressable(P˂0.05), A significant increase in the marginal gap was observed after porcelain firing, Full contour crowns recorded the lowest marginal gap(58.54±9.1, 32.76±8.5) followed by 0.5mm.( 66.7±8.4, 40.06±4.1) while 0.3mm. thickness recorded the highest value (81.14±12.3, 47.96±7.15). Significant difference in pre-firing and post firing gap values in 0.3mm. thickness(P=0.001), while in 0.5mm. thickness and full contour there were no significant difference (P=0.657 and 0.88 respectively). no statistically significant difference in mean marginal gap between 0.5 mm. and 0.3mm. at both pre-firing and post-firing. Conclusion: Marginal gap were all within the clinically acceptable range. Marginal gap increased after porcelain firing. for esthetic reasons, 0.3mm core thickness can be used instead of 0.5mm.