The principal ingredient of modeling plastic is:

 # The principal ingredient of modeling plastic is:
A. Waxes
B. Zinc oxide
C. Aluminium oxide
D. Silicon oxide

The correct answer is A. Waxes.

In general, impression compounds (modelling plastic) are composed of a mixture of waxes, thermoplastic resins, filler, and a coloring agent. Shellac, stearic acid, and gutta-percha are added to improve plasticity and workability. The waxes or resins in the impression compound are the principal ingredients of the matrix. Filler is added to increase the viscosity at temperatures above that of the mouth and to increase the rigidity of the compound at room temperature.

Reference: PHILLIPS’ SCIENCE OF DENTAL MATERIALS, Anusavice, Shen, Rawls, 12th Edition, Page No: 178

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