The main objective of this study will be to evaluate the influence of different forms of controlled surface defects in the fatigue behavior and lifetime of the lithium disilicate glass-ceramic. This study will be divided into two parts, in silico and in vitro. Lithium disilicate glass-ceramic blocks will be used to form bar-shaped specimens for the step-stress fatigue test. All specimens will be divided into 3 experimental groups (n = 20) according to the format and location of the controlled defect: GC - None; GE1 - Spherical defect in surface; GP1 - Sharp defect in surface. In order to evaluate the morphology, size and position of the introduced defects and surface roughness of the lithium disilicate a scanning electron microscopy (SEM) and 3D optical profilometry analysis of the specimens will be performed prior to the fatigue test. The fatigue test will be performed by the step-stress method for each experimental group (n = 15). A 4-point flexural strength test bar-shaped specimen will be modeled in CAD and it will be exported to CEA software to simulate a Static Structural Analysis using the finite element method. Lifetime estimates and probability of failure of lithium disilicate at stress levels of 50 or 100 MPa will be performed using Weibull's statistics (± = 0.05). Additionally, Spearman or Pearson correlations (± = 0.05) will be performed between dimension and positioning of the controlled defects information with the flexural strength and fatigue of the experimental groups. A qualitative SEM analysis of the fracture surfaces of all specimens to locate the fracture origin and details of the crack propagation will be performed.
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