RESIDUAL-STRESS MEASUREMENTS OF COMPUTER-AIDED DESIGN COMPUTER AIDED MANUFACTURING (CAD-CAM) MACHINED DENTAL CERAMICS/

Residual stress analysis is becoming more important in terms of unders tanding the strength and fatigue behaviour of ceramic materials. The r esidual stresses after computer aided design/computer aided manufactur ing (CAD/CAM) machining according to dental practice were analysed for two different kinds of dental ceramics, a feldspathic porcelain and a glass-ceramic. A mechanical strain gauge element was used to measure the deformation of dental test inlays during material removal by etchi ng the surface of the sample. From these data the residual stress dept h profile could be calculated for crystalline as well as amorphous mat erials. The strain gauge results were compared to X-ray diffraction da ta. The depth profile of the residual stress for both ceramics showed compressive stress at the surface of the machined ceramics, changing t owards tensile stress at a depth of 10 to 15 mu m from the surface. Ce ramics with pronounced plastic deformation behaviour in CAD/CAM machin ing revealed higher residual stresses as well as a more distinct stres s anisotropy in terms of grinding direction.