The production of a dental prosthesis customarily requires the following operations:
casting of an impression; PA0 checking the occlusion after production of a model; PA0 mounting on wax for esthetic review; PA0 fabrication of the metal or resin parts by the lost-wax technique; PA0 checking and polishing; and PA0 introducing the prosthesis into the mouth. PA0 the need to work in the mouth; PA0 delays at least in part caused by the need to transmit materials and information between the dental technician and the dentist and the time required for the various fabrication steps; PA0 the precision of the fabrication is directly related to the skill of the prosthetist; PA0 the possibility of a disagreement or lack of communication between the prosthetist and the dentist; PA0 high cost because of the large amount of manual labor; PA0 the dependence upon materials which can be used in the lost-wax process; and PA0 the large number of invasive procedures required in the mouth of the patient which are time-consuming and may be even painful and uncomfortable for the patient.
This method, which is very old, has a number of disadvantages including:
In application Ser. No. 262,905 there is described a method of producing dental prostheses, especially crowns, wherein, after basic preparation of the stump, an interferometric impression is taken of the implantation zone and the resulting interferogram is subjected to an analog/numerical conversion to produce binary data which is combined with stored data to produce numerical control data. This latter data is ultimately used for the numerical control of a machine tool by which the crown is machined.
Application Ser. No. 485,059 (U.S. Pat. No. 4,611,288) discloses further refinements of these principles, especially having reference to the taking of "optical impressions" of the implantation zone or the oral cavity or pertinent parts thereof, and the use of these impressions for automatically or semiautomatically producing a dental prosthesis. The means for taking such optical impressions and for converting them and appropriate stored data to numerical-control signals are likewise described. Applications Ser. No. 262,905 and Ser. No. 485,059 are hereby incorporated by reference in their entireties.
The method described in the Ser. No. 485,059 comprises preparing a dental region in the mouth of a patient to receive a dental prosthesis including at least one prosthetic tooth, directing nontraumatic waves at this region, collecting reflected waves from this region and converting the reflected waves into numerical information signals representing the shape and dimensions of this region. The mouth of the patient is then scanned to establish at least one plane representing an occlusal surface and planes tangent to a prosthesis to be formed at this region in accordance with the shape of the mouth, existing dentition and maxillary movements.
A prosthesis blank is then selected based upon color and is shaped to form the envelope of the prosthetic tooth based upon these predetermined planes. A prosthesis support is automatically machined based upon the numerical information under numerical control so that the support precisely will fit the mouth region.
The blank is secured to the support to form the prosthesis which is then inserted into the mouth of the patient.