[Radiographic evaluation of 12% Au-Ag-Pd alloy cast lower denture plates constructed by dental student as a laboratory exercise].

We evaluated 12% Au-Ag-Pd alloy cast lower denture plates prepared by dental students in laboratory exercises for casting defects. First, we determined the most suitable exposure conditions for nondestructive radiographic test of 12% Au-Ag-Pd alloy. Subsequently, 130 plates were nondestructively evaluated by radiography under the most suitable exposure conditions. In radiographic testing using X-Omat RP films (Eastman Kodak Co.) and X-Omatic Fine Screen (Eastman Kodak Co.), the most suitable exposure conditions involved a target-to-film distance of 1.9 m, tube voltage of 148 Kvp, tube current of 10 mA, and exposure time of 1.5 sec. Preliminary radiographic examination of artificial casting defects revealed semispherical defects in the diameter of 0.25 mm in 1.6 mm-thick 12% Au-Ag-Pd alloy plates and detects of 0.26 mm in 2.4 mm thick plates. In the 130 cast plates, 56 casting defects were detected. These defects were found at the left webbing part in 40 (30.8%), right webbing part in 36 (27.7%), lingual bar in 7 (5.4%), I-bar in 4 (3.0%), and at other regions of the metal frames in 3 (2.3%) cases. These results indicate that nondestructive radiographic testing is as effective in detection of casting defects in 12% Au-Ag-Pd alloy cast plates as it is in Co-Cr and Ni-Cr alloy plates. This method was also found to be effective in evaluation of the practice metal frames constructed by dental students.