Biaxial Flexural Strength of Lithium-Based CAD/CAM Dental Glass-Ceramics

Objective: This study aimed to assess and compare the biaxial flexural strength (BFS) and microstructure of lithium-based CAD/CAM ceramics. Material and Methods: Eighty disc-shaped specimens were fabricated from four distinct Lithium-containing CAD/CAM ceramic blocks. Twenty samples were allocated to each category: IPS e.max CAD, GC LiSi Block, CEREC Tessera, and an unbranded ceramic. Universal testing machine equipment facilitated BFS testing in compliance with ISO 6872:2015 standards. Scanning electron microscopy (SEM) alongside energy-dispersive spectroscopy (EDS) techniques were employed for analysis of microstructural properties. One-way ANOVA followed by Tukey's post hoc test comprised the statistical evaluation, with a significance level of α = 0.05. Calculations of the Weibull modulus (m) and characteristic strength (σ₀) determined material reliability. Results: CEREC Tessera showed the highest mean biaxial flexure strength and characteristic strength (biaxial flexure strength: 580.6 ± 208, σ₀ = 659 MPa). GC LiSi Block showed the lowest values (biaxial flexure strength: 351 ± 71 MPa, σ₀ = 381 MPa). Statistically significant differences appeared between GC LiSi Block and the other groups (p < 0.05). No differences appeared among IPS e.max CAD, CEREC Tessera, and the unbranded ceramic (p > 0.05). SEM analysis revealed rod-like lithium disilicate crystals in IPS e.max CAD and the unbranded material, whereas CEREC Tessera and GC LiSi Block exhibited spherical crystals, indicating substantial microstructural variation. Zirconia peaks appeared only in IPS e.max CAD. Conclusions: Differences in biaxial flexure strength and microstructure appeared among the tested ceramics. GC LiSi Block showed the lowest mechanical performance. IPS e.max CAD, CEREC Tessera, and the unbranded material showed similar values. Both research hypotheses gained support. Clinical Significance: All tested ceramics exceeded the ISO 6872:2015 minimum BFS threshold of 300 MPa. This confirms their suitability for single-unit restorations. Unbranded lithium disilicate ceramics provide acceptable mechanical reliability. Their variability in composition and lack of regulatory oversight require caution in clinical applications.