EFFECTS OF THERMAL AGEING ON THE MECHANICAL PROPERTIES OF CAD-CAM CERAMIC MATERIALS

This study aimed to evaluate the effect of thermal ageing on the Vickers microhardness, fracture toughness and surface microstructures of four CAD-CAM dental ceramic materials. Specimens of a polymer-infiltrated ceramic network (PICN) (ENA; Vita Enamic), a resin nano-ceramic (CERA; GC Cerasmart), a zirconia-reinforced lithium silicate (ZLS) ceramic (DUO; Celtra Duo), and polycrystalline zirconia (ZIR; IPS e.max ZirCAD) were prepared (n=10). Each test was subjected to a thermocycling process (5 to 55 °C, 20 s, 10,000 cycles). The Vickers microhardness and fracture toughness were measured and re-evaluated after the thermal ageing. Surface microstructures were observed by scanning electron microscopy. Statistical analyses were performed using the paired sample t-test and the Wilcoxon test (α=0.05). ENA and CERA exhibited a decrease in the microhardness after ageing. The microhardness change of ENA was more significant than DUO. ENA, DUO and ZIR showed a decrease in the fracture toughness. The change in the fracture toughness of ZIR was more significant than ENA, CERA, and DUO. ENA and CERA did not exhibit a stable image on the microscopic evaluation. The microhardness and fracture toughness of the CAD-CAM ceramics were influenced by ageing. Clinicians should consider how well the materials they use can adapt to the oral environment and choose the material accordingly.