金銀パラジウム冠の鋳巣に関する実験的研究
スポンサーリンク
概要
- 論文の詳細を見る
Ag-Pd-Au alloy is commonly used for the cast crown and bridge. The occurrence of inner porosities, however, has often been pointed out as one of the disadvantages of this alloy. Although some reports have been issued concerning the porosities in the casting of this alloy, almost all of them have dealt with some simple shaped experimental castings such as rods or plates. However, the shape of the casting might be a primarily important factor affecting the occurrence of porosities. And the shape commonly encountered in the clinical use should be adopted as the shape of test specimens. In the present study, therefore, a frequently found clinical shape (premolar crown) was selected as the test specimen shape. Then the effects of several casting machines and conditions on the size, number and distribution of inner porosities were investigated for the premolar crown cast by usual spruing. There were significant differences in size, number and distribution of the porosities among the four casting methods employed, namely, (1) melted by gas-air flame and cast by centrifugal casting machine, (2) melted by electric furnace in carbon crucible and cast by centrifugal casting machine, (3) melted by electric furnane in carbon crucible and cast by vacuum-pressure casting machine, and (4) melted by induction heating in argon atmosphere and cast by vacuum-pressure casting machine. Large, localized porosities were found near the occlusal surface in the crown cast by centrifugal casting machine. When vacuum-pressure casting machine was used, the porosities were significantly decreased in size and number, and they distributed throughout the whole crown body. Particularly, vacuum-pressure casting combined with induction heating in argon atmosphere brought a marked reduction of porosities. In the case of centrifugal casting combined with gas-air flame melting, the inner porosities were minimized in size and number at the mold temperature of 600℃. No increasing effects of overheating the alloy up to 1, 100℃ were recognized on the porosities as long as the mold temperature was kept at 600℃. When the mold was prepared with phosphate bonded investment instead of gypsum bonded investment, the inner porosities were significantly decreased. It is suggested from this fact that the molten alloy may react with the mold wall of gypsum bonded investment more vigorously than with that of phosphate bonded one to cause more porosities at the elevated temperature. The use of flux was not so effective as ever expected to reduce the porosities in the cast crown of this alloy.
- 九州歯科学会の論文
- 1985-12-25