Spatial changes occurring in fixed partial dentures made as one-piece castings

U se of base metal alloys to make the metal framework of ceramic veneered crowns and fixed partial dentures has created the need for technical modification in procedures previously applied to gold base ceramic alloys. Making one-piece metal castings for multipleunit fixed partial dentures is one of the more notable technical modifications, since in preand postsoldering procedures it has been difficult to achieve a strong, dependable solder joint in the base metal framework. Thus, one specific problem is assessing the degree of dimensional accuracy in casting a one-piece base metal fixed partial denture. Studies on casting accuracy for single crowns1-4 and multiple-unit fixed partial dentures5-* reported marginal discrepancies after cast specimens were returned to dies of origin. In general, these investigations determined casting accuracy by observing the closeness by which the margin(s) of castings and margin(s) of dies could be brought into apposition. Suffert and Mahler’ suggested that inherent surface roughness of the casting influenced fit and that this variable could create confusion in making an assessment of casting fit. This study was designed to establish a method of assessing the dimensional changes occurring at the margins of a multiple-unit fixed partial denture. The distances between specific precast (wax stage) and postcast (metal stage) points on abutment crown margins were recorded in conjunction with alterations in the expansion of investment material. Comparisons of these measurements provided an evaluation of the accuracies of the castings.