The combination of optical 3D-sensing, CAD/CAM and reverse engineering offers new opportunities for medical diagnosis and therapy, as well as for art conservation. We report our activities on the fields of dental CAD/CAM, face surgery, restoration, and others. We will discuss essential problems and solutions, specifically addressing the physical and technological limits for these applications. One example is that speckle noise limits the dynamical range of optical sensors to about 5000: 1, but a good visualization needs a dynamical range of 100000: 1 . A technical (and commercial) limitation of rapid prototyping is the high cost that prevents mass production. As a consequence, for those "real" applications mentioned above, we do not need only optical 3D-sensors that work at the limits given by physics, we need as well perfect surface reconstruction techniques to automatically smooth the sensor data, without destruction of edges. We have to register many views, automatically, and to visualize the data. The processing chain is only complete with effective technology for rapid prototyping, such as fused deposition modeling or laser sintering.