Marginal Gap and Fracture Strength of Hybrid, Zirconia-Reinforced, and Virgilite-Reinforced CAD/CAM Ceramic Crowns

This in vitro study evaluated the vertical marginal gap and fracture strength of four CAD/CAM (computer-aided design/computer-aided manufacturing) ceramic materials: a hybrid ceramic (Vita Enamic, Vita Zahnfabrik; VE), zirconia-reinforced lithium silicate (Vita Suprinity, Vita Zahnfabrik; VS), Virgilite-containing lithium disilicate (Cerec Tessera, Dentsply Sirona; CT), and using lithium disilicate (IPS e.max CAD, Ivoclar; Emax) as a control.

A standardized all-ceramic crown preparation was conducted on a first maxillary premolar tooth. The prepared tooth was duplicated into 40 epoxy resin dies, allocated into four groups (n = 10) according to the four ceramic materials tested. The crowns' marginal gaps were measured using a metallurgical microscope. Cementation of the crowns was done using a self-adhesive resin cement, then tested to failure under a single load using a universal testing machine. The results were statistically analyzed with one-way ANOVA (analysis of variance) and post-hoc Tukey's honest significant difference tests.

VS crowns demonstrated significantly higher (p < 0.001) marginal gap (80.14 ± 7.64 µm) than the other materials, VE (55.56 ± 7.20 µm), CT (58.20 ± 5.22 µm), and Emax (60.13 ± 3.63 µm), whereas VE (1,002.8 ± 78.9 N) showed significantly lower (p < 0.001) fracture strength value than CT (1,850 ± 90 N), Emax (1761.6 ± 101 N), and VS (1633.5 ± 149.5 N).

All tested materials exhibited clinically acceptable marginal gaps and fracture strength values that exceeded the maximum reported masticatory forces. CT exhibited the highest fracture strength, while VE showed the lowest marginal gap. CT's superior fracture strength and excellent marginal fit highlight its suitability for mechanically challenging posterior restorations while maintaining marginal integrity.