Effect of venting on cast gold full crowns

Abstract

I t would be highly desirable if the marginal opening of a crown could be reduced significantly by venting the crown before cementation without making any other alteration of the casting. Both electrochemical milling and etching require a long time. Also, the equipment that is necessary to do the electrochemical milling is not generally available to the practitioner. Although stripping can be done with aqua regia, the amount of gold removed by the process is at best an estimate and the process is time-consuming. Therefore, a procedure that can be accomplished at the chair, with a minimum of time and equipment, would help dentists to improve the marginal adaptation of full-crown castings. In 1966, a study’ was made to determine the type of margin of a cast gold restoration that would be acceptable to experienced dentists. The results showed that interproximal margins from 34 microns up to 119 microns were acceptable. This study underlines the difficulties involved in using an explorer and radiographs to evaluate a subgingival margin after cementation of a cast restoration. One of the most common causes of failure of any cast restoration is the solubility of the luting agent used to cement the restoration.’ Because the rate of marginal washout is related to the amount of exposed cement at the margin, anything that can be done to reduce the amount of marginal opening will increase the restoration’s chance for success. Several factors can influence the marginal opening of a crown after cementation. Of these factors, the consistency of the mixed cement and the contour of the preparation are important considerations, but the failure of the cemented crown to go completely to place on the prepared tooth is also a common source of error. One result of incomplete seating is an increased amount of exposed cement at the margins.