sprue
Pronunciation: /spruː/
A wax or plastic rod attached to a wax pattern to create a channel through which molten metal flows into a casting mould during the lost-wax casting process.
Full Definition
In dental laboratory casting technique, the sprue is a wax or pre-formed plastic former attached to the wax pattern before the investment is poured. When the mould is heated, the sprue burns out along with the wax pattern, leaving a channel (the sprue hole) through which molten alloy is forced into the mould cavity. Sprue design—including its diameter, length, direction, and attachment point—has a significant effect on casting accuracy and the incidence of porosity. Editors working on dental casting protocols must retain precise terminology: 'sprue' refers to the former; after casting, the residual metal rod is called the 'sprue button' or 'button.'
Usage
Usage note: Do not use 'sprue' to refer to the residual cast metal rod; that element is the 'sprue button.' Maintain this distinction in procedural texts.
In Context
- "The technician attached a 2.5 mm wax sprue to the occlusal surface of the pattern before investing." — Casting Protocol
- "After burnout, a clean sprue channel was visible in the investment mould, indicating successful elimination of the wax." — Laboratory Procedure Manual