[A study on the outer shape of full cast crown. 1. Au-Pd-Ag alloy]

Recently, as the result of much research, cast crowns with a very accurate fit are being produced, and even on the clinical level satisfactory results have been achieved. Few reports, however, have been made on the outer shapes of full cast crowns and no clear results have been obtained in this field of research. In a previous report a newly developed apparatus and method were introduced by means of which the outer shapes of wax patterns and the casting made from them can be compared and evaluated, and the apparatus and method were shown to be very accurate. In the present study, the difference in the shapes of wax patterns and castings made from them was investigated using 12% Au-Pd-Ag alloy, the alloy used for restorations as stipulated by the National Health Insurance. Also, dry and wet asbestos was used to see if this affected the shape of the castings. The results are given below: 1. When day asbestos was used, the casting were the same size as the wax patterns at the marginal areas but became smaller towards the occlusal surface. The upper surface of the castings were lower than the wax patterns, being much closer to the occlusal surface itself. 2. When the asbestos was immersed in water before using it, the diameter of the casting above the marginal area was even smaller but at the occlusal surface the height of the casting was almost the same as the wax pattern. 3. It appears that better results may be obtained by using dry asbestos because of the possibility of reducing the space between the cast crown and occlusal surface of the tooth.