Final Expansion of Plaster

¹ Department of Oral Diagnosis and Oral Medicine, Hebrew University-Hadassah School of Dental Medicine, Jerusalem, Israel

The onset, duration, rate, and magnitude of setting expansions of one gypsum product were compared under different conditions of restraint. Specimens were set normally or hygroscopically in a mercury bath or in tinfoil- or plastic-lined troughs. The final setting times were the same for all combinations. Both internal and external restraints altered the rates, and thus the magnitude. of expansion during all stages of setting. Conditions affecting the rate of restraint, in decreasing order, were tinfoil, plastic film, and mercury.