J Korean Dent Sci.  2025 Mar;18(1):1-11. 10.5856/JKDS.2025.18.1.1.

Effect of Occlusal and Margin Design on the Fracture Load of Zirconia-Lithium Disilicate Bi-layered Posterior Crowns: An in Vitro Study

• Kim SH
• Ko KH
• Park CJ
• Cho LR
• Huh YH

• KMID: 2566677
• DOI: http://doi.org/10.5856/JKDS.2025.18.1.1

Abstract

Purpose
The opacity of zirconia sometimes requires a veneering material; thus lithium disilicate, a veneer material with excellent strength, can be used. This study investigated the fracture resistance of zirconia–lithium disilicate (Zr-LS2) bi-layered crowns according to the design of the substructure.
Materials and Methods
Five groups of posterior Zr-LS2 restorations (Zirtooth and Amber LiSi-POZ) were fabricated with different zirconia substructure coverage (control group, groups half occlusal zirconia coverage; 1/2OZ, and three-quarter occlusal zirconia coverage; 3/4OZ) and margin designs (control group, groups collar margin; C-M, and collarless margin; Cl-M). All restorations were cemented with self-adhesive resin cement followed by 24-h water storage and thermocycling (10,000 cycles, 5°C and 55°C). The fracture load was measured, and failure mode analysis, fractography, and elemental analysis were performed. The one-way analysis of variance and Fisher’s exact test were performed for statistical analyses (α=.05).
Results
A significant difference was found in the fracture load of Zr-LS2 restorations according to the zirconia coverage of the occlusal area and margin design (P<.05). Group 3/4OZ was significantly larger than the control group C and 1/2OZ (P<.05). The C-M group had greater fracture loads based on margin design than the control group C and Cl-M (P<.05).
Conclusion
The fracture resistance of posterior Zr-LS2 restorations increased with the zirconia coverage, occlusal thickness, and collar margin.

Keyword

Zirconia; Lithium disilicate; Substructure; Margin; Fracture resistance; Fractography