33. Wax modeling of tooth crowns. Wax addition modeling technique. Wax compounds and instruments.
Explains wax pattern modelling for cast crowns, comparing cusp–marginal ridge and cusp–fossa occlusal schemes in a table and noting the tripod contact. Covers the PKT kit's five instruments and how to heat them, the composition and four colours of inlay casting wax, and a step-by-step wax addition technique using colour-coded layers with an illustrated upper premolar. Closes with a note on adapting the wax-up for older patients.
Topic 33 of 75 in the MU Sofia syllabus for Preclinics of Dental Prosthetics (Dental Medicine, Year 2). The free AceMed note covers it in 5 sections, about 279 words (3 min of reading), with 13 flashcards.
In this note
Introduction
Two occlusal schemes
Instruments
Inlay casting wax
Wax addition technique
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.
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