Meanwhile, yttrium-stabilized zirconia (YSZ) is the most important material for dental prosthetics. Doping with Y2O3 aims at stabilizing tetragonal ZrO2 at low temperatures and avoiding monoclinic and rhombohedral modifications. The integrity of the initial phase composition is important for mechanical stability, surface roughness and optical properties. Nevertheless, common machining procedures such as grinding and sandblasting, spur YSZ's tendency to phase transformation. XRD helps to quantify this effect, but the information is neither depth resolved nor going beyond the sample surface. Electron microscopy can provide this information, but sample preparation by FIB and exposure of the observed regions can itself influence the phase composition. Diffraction tomography provides exactly the required conditions and information. Based on the results of these experiments, we will present adjusted parameters for grinding and sandblasting in favor of optimal properties.