The development of a new 3D scanning system (PRECISCAN) is described which can crucially improve the CAD/CAM process. Stone replicas of preparations are measured without physical contact using an optical sensor. After mounting into the scanner's special jig, up to 14 prepared teeth and one jaw cast can be digitized fully automatically in one measuring session, requiring no further operator steps. Additionally, the preparation border is detected automatically. By spatial correlation of the prepared teeth to the jaw cast, even data sets for bridges or larger prosthodontic constructions can be produced. Within a z-range of 3.5 cm, the accuracy is about 11 um.