Introduction
A cast crown begins as a wax copy, the wax pattern. Its shape is transferred exactly into metal, so the wax-up decides the crown's contours, contacts and occlusion. The aim is to rebuild the lost anatomy and function without harming the supporting tissues, with forces spread evenly.
Two occlusal schemes
In the tripod contact the cusp tip itself never touches, so it wears very little, and forces run along the long axis of the tooth.
Instruments
The PKT kit (P.K. Thomas) has five instruments:
Heat the shank about 1 cm from the tip in the flame for 2–3 seconds, never the tip itself. Wax flows away from the hottest part: heat the shank and a drop flows off the tip; heat the tip and the wax runs up the shank.
Inlay casting wax
- Main ingredient: paraffin, 40–60%.
- Plus dammar resin, carnauba, ceresin or candelilla wax to raise the melting point; it must be hard at room temperature.
- Coloured in four shades (yellow, red, green, blue) so that each step stands out. Single-colour waxing hides fine detail.