Evaluation of the marginal fit of a CAD/CAM zirconia-based ceramic crown system

To evaluate the marginal fit of zirconia (Zi) CAD/CAM crowns in terms of gap and overhang compared to lithium disilicate (LDS) computer-aided design crowns, as well as the effect of finish line design on marginal accuracy.

Stone dies were acquired from two master metal dies (n = 20 each) with two different finish lines and were scanned to produce digital models. Ceramic crowns (ZS-Ronde Zi, KaVo and IPS e.max CAD LDS, Ivoclar Vivadent) were designed and milled on the resulting 40 dies: 10 Zi-shoulder, 10 Zi-chamfer, 10 LDSshoulder, and 10 LDS-chamfer. Marginal gap and overhang were evaluated at six designated margin locations. The data were obtained, and the influence of material and finish line on the marginal fit of crowns was assessed using two-way analysis of variance and Bonferroni multiple comparisons test (α = .05).

Mean marginal gap and overhang on Zi crowns were 30 ± 14 μm and 79 ± 27 μm for the shoulder, respectively, and were 68 ± 34 μm and 104 ± 34 μm for the chamfer. The corresponding values for LDS crowns were 57 ± 22 μm and 74 ± 29 μm for the shoulder, and 62 ± 12 μm and 59 ± 27 μm for the chamfer. ANOVA revealed that the differences in marginal gap between the two materials were not significant (P > .05), but that the finish line effect and interaction were significant (P < .05). With regard to marginal overhang, significant differences were found between Zi and LDS crowns (P < .05), although the finish line geometries did not show any significant differences (P > .05). LDS crowns showed no differences between shoulder and chamfer margins for gap or overhang (P > .05), whereas significant differences were found in marginal gap between the Zi shoulder and chamfer margins (P lt; .005).

In terms of marginal accuracy, shoulder margins produced smaller marginal gaps compared to chamfers for Zi CAD/CAM crowns.