Round ringless mold and triangular spoke sprue

A mold assembly for dental investment casting, comprising:

• a round casing made of resilient plastic material, having opposite open ends, the casing having an inner surface defining a casing volume and a lower collar separated from the inner surface by a shoulder;
• a round base made of resilient plastic material and including a neck having an outer surface extending along the axis of the casing for frictional engagement with the collar, the base including a hub extending along the axis, a floor portion extending radially between the hub and the neck, the neck including an upper ring shaped surface with a circular sighting bead on said ring shaped surface for defining an imaginary cylindrical surface in said casing when said base and casing are fictionally engaged with each other;
• and
• a sprue having a post engaged with said hub and a ring connected to said post and extending into said casing when said casing and said base are fictionally engaged with each other, said ring being within said imaginary cylindrical surface.