The effect of monolithic zirconia crown dimension on the accuracy of fit

Abstract

This study aimed to investigate the influence of monolithic zirconia crown dimension on the accuracy of marginal and internal fit. Four titanium models with various dimensional preparations were constructed. The general designed characteristics were circumferential deep chamfer finish line, round internal line angle, 12°of total occlusal convergence and 10 mm diameter at the margin. For group 1 and 2, the abutment was designed in order to get 1-mm and 2-mm uniform crown thickness, respectively. For group 3, the abutment was designed to get 1-mm thickness at axial wall and 2-mm thickness at occlusal wall, and, conversely, for group 4, the abutment was designed to get 2-mm thickness at axial wall and 1-mm thickness at occlusal wall. Forty identical external contour crowns were fabricated with Ceramill system (n= 10). Replica technique was used to examine marginal gap, absolute marginal discrepancy and additional 3 locations of internal gap: mid-axial wall, axio-occlusal angle and mid-occlusal area. The data were analysed using One-way ANOVA and Turkey's test at a significance level of 0.05. There were significant differences of gaps at most locations, except axial area (P<.05). The mean ± SD of marginal gaps were 27.9±5.4 μm, 32.8±6.8 μm, 32.6±7 μm and 22.3±4.2 μm for group 1, 2, 3 and 4, respectively. The mean ± SD of absolute marginal discrepancies were 131.5±11.7 μm, 111±15.6 μm, 114.5±15.8 μm and 125.9±9.7 μm for group 1, 2, 3 and 4, respectively. The highest internal gap was found at occlusal area in all groups. The thickness of translucent zirconia crown influenced the marginal and internal fit. Occlusal wall thickness could affect the marginal gap, absolute marginal discrepancy and internal gap despite crown's axial wall thickness. Thicker occlusal wall could result in lesser absolute marginal discrepancy and occlusal internal gap, but greater marginal gap. However, the marginal gap in all groups was obviously, clinically acceptable. Therefore, appropriate occlusal crown thickness should be fabricated to avoid unpredictable stress that affected crown fitness and to prevent the fracture of the crown clinically.