THE EFFECT OF TEMPERATURE ON THE RATE OF SETTING OF PLASTER OF PARIS

¹ Materials Research Laboratory, Australian College of Dentistry, Melbourne, Australia

The setting times of 6 dental plasters have been determined at temperatures ranging between 10° and 100°C. There is an appreciable decrease in setting time as the temperature of the environment is raised from 10°C. to about 30°C. Over the range 30 to 50°C. the setting rate is practically constant and is a maximum for the whole temperature range. At temperatures above 50 to 60°C. the setting times begin to increase again, and with slow setting plasters the retardation becomes quite marked at 70°C. At temperatures above 80°C. all plasters become very slow setting, and at 90°C. there may be little or no evidence of setting at five to six hours. No setting occurs at 100°C. Some explanations of the observed phenomena are offered.