Effect of denture wax-pattern position on radial setting expansion.

Th dynamics of the setting expansion of gypsum-bonded investment is complicated by many variables and not well understood. The purposes of this study were to examine the fluid mechanics of the flow of investment during setting and to determine if the presence of wax patterns influences effective setting expansion. Mesial-occlusal-distal (MOD) inlay wax patterns were invested at six different radial positions and four different axial positions in plastics casting rings. Total expansion was determined by using xeroradiography. Combined results of radial expansion data at different axial and radial locations within casting rings suggest that expansion of gypsum-bonded investment may represent a variant of the laminar flow of a viscous fluid.

The relationship between the fit of MOD inlays and the storage time and conditions of investing.

It has been traditional either to cast invested wax patterns immediately after the investment has set or to store the invested patterns in a humidor for casting later. This study compared the fit of MOD inlays to parent dies after casting immediately following set of the investment, after casting 1 hour following the setting of the investment in air, storage in a humidor for 7 days, and after storage in air for 7 days. The only significant differences in fit were in the group stored in a humidor, and then only at the axiogingival junctions.