Effect of Thermal Aging on Glass Matrix Ceramic and Resin Matrix Ceramic CAD/CAM Blocks: Flexural Strength and Vicker's Microhardness Assessment.

Background: This study aimed to evaluate and compare the flexural strength, elastic modulus, and Vicker's microhardness values of glass matrix ceramic and resin matrix ceramic CAD/CAM blocks, and to examine the differences after thermal aging.

Methods: This in vitro study involved seven different CAD/CAM blocks: Amber Mill (Hassbio, Korea), LiSi (GC, Japan), Celtra Duo (Dentsply Sirona, Germany), Tessera (Dentsply Sirona, Germany), IPS e.max CAD (Ivoclar, Liechtenstein), Cerasmart (GC, Japan), and Grandio Blocs (VOCO, Germany). Bar-shaped samples (1.2x4x14mm) for the three-point bending test and rectangular samples (2mm-thickness) for the Vicker's microhardness test were prepared using a precision cutting device under water. Half of the samples underwent 50,000 thermal cycles between 5-55°C, while the other half were kept in distilled water at 37°C for 24 hours. Flexural strength/FS and elastic modulus/EM values were measured using a universal testing machine, and Vicker's microhardness/VHN 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 FS (570 MPa), EM (66.2 GPa), and VHN (717.7) after 24 hours, whereas Cerasmart had the lowest values (FS: 260 MPa; EM: 12.8 GPa; VHN: 99.9). Significant differences were found between the materials' FS, EM, and VHN values after 24 hours and after thermal aging (p<0.001). All materials showed a significant decrease in FS values following thermal aging (p<0.05).

Conclusion: 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.