ACCURACY OF MACHINE MILLING AND SPARK EROSION WITH A CAD CAM SYSTEM/

A method for manufacturing crowns and fixed partial dentures based on CAD/CAM has been developed as an alternative to the lost wax technique and the casting of an alloy, In this process two steps are included: milling and spark erosion. The computer-assisted design (CAD) relies h eavily on the accuracy of the milling and spark erosion processes to a chieve a clinically acceptable restoration, These two processes must b e able to produce the crown data generated in the CAD files. This stud y evaluated the accuracy of the Procera CAD/CAM system in creating spe cific geometric bodies that were compared with the known dimensions in the CAD files for these bodies, The manufacturing errors of milling ( ellipse +/-6.5 mu m, square +/-3.4 mu m, and cylinder +/-5.8 mu m) and spark erosion (ellipse +/-8.6 mu m and square +/-10.4 mu m) were dete rmined. The accuracy of this manufacturing process demonstrated that t his system was capable of producing a crown with a clinically accepted range for marginal opening gap dimension of less than 100 mu m.