A dental Computer-aided design (CAD)/Computer-aided manufacturing (CAM) system forms a custom dental preparation guide for guiding a dental tool that alters a shapes a tooth structure to which a custom prosthetic dental item is to be attached. The system acquires an optical measurement and an x-ray of at least one dental structure. The system correlates the acquired optical measurement and the x-ray to form a model of the at least one dental structure. The system generates a model of a reduced tooth structure based on the model of the at least one dental structure. The system also provides at least one dental preparation guide based on the model of the reduced tooth structure.
