Pits on inner surfaces of cast gold crowns

Abstract

A total of over 500 castings were made with the hygroscopic water-added technique. In these castings studies were made of the sprue gauge, length, and direction, single or double sprues, pressure of casting machine, amount of gold, and flaring of the sprues as they affect the appearance of pits and voids on the inner surface of gold crowns. It was found that, in general, pits and voids would appear more often in bicuspid full crowns than in other types of single castings. Increasing the casting pressure, amount of gold, and sprue diameter (up to a certain point) and employing proper sprue direction and length tend to reduce the number or eliminate completely these pits. Flaring of the sprue is as important as any other factor just mentioned. Flaring of the sprue may act in the same way as placing a small reservoir very close to the wax pattern, and/or it may facilitate the flow of molten gold into the cavity. In either case it will help to eliminate some of the pits and voids that appear on the inner surface of gold castings. Since this laboratory study was made, extensive clinical experience in the University of Michigan, School of Dentistry clinic, by junior and senior dental students, gives further support to the results obtained from this investigation.