Surface hardness, compressive strength, and abrasion resistance of indirect die stones

Abstract

HE common use of the indirect method in the preparation of inlays, threequarter and full crowns, various bridge forms, and other dental castings, together with the appearance on the market of newer type gypsum products for use as dies, indicates a need for more knowledge of some of the physical properties of the quick-setting artificial stones. In addition, an understanding of the best method of die preparation is necessary in order that the stone may be used to its fullest advantage. Every dentist who includes in his practice gold castings, or other precision techniques requiring dies, should ‘have a thorough knowledge of the factors involved in the fabrication of the die which lead to its improvement. Such a study should enable him, with a minimum of extraneous effort, to produce the most satisfactory stone die obtainable by practical methods. Recently, much has been written about the hydrocolloid technique for use in crown and bridge procedures. Special equipment for taking agar impressions has received widespread recognition, and the accuracy of the material is acclaimed by many dentists as superior to that of other impression materials. This method of impression making, however, requires that the operator use artificial dental stone as a die material inasmuch as no other well-accepted method appears practicable. Amalgam cannot be packed readily into the hydrocolloid impression because of the frailty of the impression material. The hydrocolloid impression cannot be copperplated unless special preparations and extremely careful methods are employed, although some operators have succeeded in accomplishing this. The technique is not a simple one, however, nor can it be done with the equipment generally found in the average dental office. The regular and improved dental stones have been found to be reasonably satisfactory as a die material to be used in conjunction with the hydrocolloid impression materials. In the past, objections have been made to the use of dental