Adherence of investment to Au–Pd–Ag alloy using a vacuum–argon pressure casting machine

Objective. The removal of adhered investment material from marginal metal surfaces represents a possible risk of poor marginal adaptation. The aim of this work was to evaluate the effects of argon on investment adherence to the casting surface and on the alloy surface microstructure. Methods. A die of stainless steel was used. 10 wax copings were cast by vacuum–argon pressure, while 10 copings by vacuum–air pressure using a Combilabor CLG-77 A in a graphite crucible; supply was direct with curved sprues of empty set 3.5 mm. The alloy used was Herabond. After coarse investment, removal of all specimens were investigated with scanning electron microscopy and semi-quantitative digital densitometry. Results. The specimens cast under vacuum–argon pressure showed less amount of investment adhered (unpaired t test of grouped specimens, difference 2.896×105 pixel; p=0.002) while the grain size on the casting surface increased significantly p=0.000 (difference 5.968 (μm). Significance. Vacuum–argon pressure supply during casting reduces the investment adherence to the metal surface, and increases the packing density and size of the grains, especially on the casting surface. These minimize the risk of marginal distortions due to casting cleaning procedures and facilitate the finishing and polishing procedures.