Effect of thermal aging on glass-matrix ceramic and resin-matrix ceramic CAD/CAM blocks: flexural strength and Vickers microhardness assessment.

AIM: The present study aimed to evaluate and compare the flexural strength, elastic modulus, and Vickers microhardness values of glass-matrix ceramic and resin-matrix ceramic CAD/CAM blocks, and to examine the differences after thermal aging. MATERIALS AND METHODS: The present in vitro study involved seven different CAD/CAM blocks: Amber Mill (Hassbio, Republic of Korea), Initial LiSi Block (GC, Japan), Celtra Duo (Dentsply Sirona, Germany), Tessera (Dentsply Sirona), IPS e.max CAD (Ivoclar, Liechtenstein), Cerasmart (GC), and Grandio Blocs (Voco, Germany). Bar-shaped samples (1.2 × 4 × 14 mm) for the three-point bending test and rectangular samples (2-mm thickness) for the Vickers microhardness test were prepared using a precision cutting device under water. Half of the samples underwent 50,000 thermal cycles between 5 and 55°C, and the other half were kept in distilled water at 37°C for 24 hours. Flexural strength and elastic modulus values were measured using a universal testing machine, and Vickers microhardness values were measured using a microhardness tester. Statistical analyses were performed using Kruskal-Wallis and Mann-Whitney U tests, with significance set at P 0.05. RESULTS: Tessera showed the highest median values for flexural strength (570 MPa), elastic modulus (66.2 GPa), and Vickers microhardness (717.7) after 24 hours, whereas Cerasmart had the lowest values (flexural strength: 260 MPa; elastic modulus: 12.8 GPa; Vickers microhardness: 99.9). Significant differences were found between the materials' flexural strength, elastic modulus, and Vickers microhardness values after 24 hours and after thermal aging (P 0.001). All materials showed a significant decrease in flexural strength values following thermal aging (P 0.05). CONCLUSIONS: In the selection of CAD/CAM materials, it is critical to consider that mechanical properties vary with structure and tend to change over time due to aging.