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Gypsum Products, Dental Waxes, and Impression Materials

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3-27. MIXING AND SETTING TIME

The polysulfide base and its chemical reactor are both furnished as pastes that are packaged in separate tubes. The silicone base is also a paste that is packaged in tubes. Its chemical reactor may be either a paste or a bottled liquid. With both types, the proportions and the method of spatulation recommended by the manufacturer must be followed exactly. The bases and the chemical reactors are of different colors. They must be spatulated together until no streaks remain. Undermixing will prevent material from polymerizing evenly and overmixing will increase both the set and the strain pattern, but especially the set. Increased relative humidity and temperature tend to shorten both setting and mixing time, particularly for the polysulfide type. The chemical reactor is necessary to polymerize the material. It is often called an accelerator because the setting time may be shortened by increasing the amount used. It does not change the structure of the materials as does the accelerator used with gypsum products. Varying the amount of chemical reactor is the only method of changing the setting time of the silicone type.

David L. Heiserman, Editor

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Revised: May 22, 2017