CHARACTERIZATION OF NON UNIFORM VENEER LAYER THICKNESS DISTRIBUTION ON CURVED SUBSTRATE ZIRCONIA CERAMICS USING X-RAY MICRO-TOMOGRAPHY

摘要

The fabrication process of bi-layer ceramics requires a temperature change from sintering to room temperature. Residual stresses created as a result of thermal expansion coefficient mismatch may be sufficiently large to influence failure. Theoretical models predict residual stress as a function layer thickness. The scale and to some extent the geometry changes during the firing process. In the case of complex geometries like dental crowns. micro-X-ray tomography is a unique non-destructive technique for layer thickness measurement. A method of developing a finite mesh model of real components involving complex geometries has been developed through the use of X-ray micro-tomography. This method computes the minimum distance between two triangulated surfaces constructed from tomography data. For each vertex of one surface, it computes the closest point on the other surface. The veneer layer thickness distribution was combined with residual stress curves advancing our understanding of the lower limit threshold of thickness in dental restoration design. An important observation is the significant range in predicted residual stress in the veneer top surface from a tensile stress of 80 MPa to a compressive stress of-70 MPa as the thickness increased to 0.5 mm.