Nano-scale mechanical behavior of pre-crystallized CAD/CAM zirconia-reinforced lithium silicate glass ceramic

This paper reports on the mechanical behavior of pre-crystallized CAD/CAM zirconia-reinforced lithium silicate glass ceramic (ZLS) using nanoindentation with a Berkovich diamond tip and in situ scanning probe microscopy (SPM). The indentation contact hardness, the elastic modulus, and the elasticity and plasticity of the material were determined using the Oliver-Pharr method, the Sakai model and the Meyer's law at peak loads of 2.5-10 mN and a loading rate of 0.5 mN/s. The load-displacement curves at all applied loads indicate that ZLS deformed plastically without fracture. The discrete discontinuities in the load-displacement curves might have arisen from the shear plane activation for plastic deformation. The measured hardness and elastic modulus were load-independent (ANOVA, p > 0.05), in ranges of 8.17 +/- 1.23 GPa to 9.86 +/- 1.24 GPa and 98.55 +/- 7.38 GPa to 105.78 +/- 9.98 GPa, respectively. The resistance to plasticity of ZLS significantly showed a second-order polynomial load relationship or a power law load dependency. Meanwhile, both the elastic and plastic displacements also significantly revealed power law load dependencies. However, the elastic and plastic deformation components were load-independent. Increased indentation loads resulted in significant decreases in the normalized elastic strain energy (p < 0.05) accompanied by significant increases in the normalized indentation absorbed energy (p < 0.05). The equivalent elasticity and plasticity of ZLS during indentation occurred at 7.5 mN. The outcomes of this study provide insights into fabrication and mechanical functions of ZLS restorations, particularly facilitating abrasive machining in dental CAD/CAM processing in the ductile regime.