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Gypsum Products, Dental Waxes, and Impression Materials

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3-30. MODELING PLASTIC--CHARACTERISTICS

a. General. Modeling plastic (modeling composition) is an impression material (thermoplastic type) which can be softened by heat into a soft plastic mass and then hardened by cooling with either a stream of cold water or a blast of air. Modeling plastic is used primarily to make impressions of the edentulous arches (the tooth ridges without teeth).

b. Properties and Materials. Modeling plastic is composed of shellac, talc, and glycerides derived from certain tallow oils. The temperature range at which softening occurs depends upon the proportions of the ingredients contained in the material. Modeling plastic is supplied in cakes, wafers, or sticks, and in various colors to aid in distinguishing between products of different softening (fusing) temperature ranges.

c. Recommended Procedures. Any of the gypsum products can be poured against a modeling plastic impression without the use of a separator. Also, modeling plastic is one of the impression materials against which an amalgam die can be packed. (An amalgam die is a model of a tooth in silver amalgam, used for making an inlay or crown.) Although no separating medium is required in either of these procedures, extreme care must be exercised in drawing the impression material from the cast or die, since both materials are hard and relatively unyielding. Therefore, the modeling plastic is softened in heated water, at 120o F (49o C), and removed gently so that the cast is not damaged.

David L. Heiserman, Editor

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Revised: May 22, 2017