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.