For dental ceramic restorations, the manufacturing process presumes a high temperature sample heating treatment process, more than 1,000 degrees C for applied aesthetic veneer and glazer. The present study presents and analyzes a comparative survey for two dental ceramics regarding the link between the heating treatment and reported cases of fractures and failure (delamination) of ceramic core. Two different dental ceramics samples were investigated: alumina based ceramic, respectively zirconia based ceramic materials. For zirconia based ceramic, changes concerning monoclinic (M) and tetragonal (T) crystalline phases occur and peak intensity variation from x-ray diffraction patterns are observed during heating process. For alumina based ceramic, the crystalline structure is less affected by the heating process but a different grain size and orientation were noticed during/after heating treatment. Both of them are affecting the strength and fracture toughness of the dental ceramic core.