Factors Affecting The Setting Time of Zinc Oxide-Eugenol Impression Materials: The Influence of Humidity and Temperature to The Reaction Velocity

Zinc oxide-eugenol paste are widely used in clinical dentistry, principally forimpression of non-undercut edentulous ridges, or bite taking materials. However it has beenrealized by those who use these paste that different products, direction for mixing, or differentconditions for mixing, have different characteristics. An experiment have been made to observe the influence of different conditions for mixingto the setting time. Zinc oxide-eugenol impression pastes were mixed in accordance with the manufacturer'sinstruction when supplied. The condition for mixing was at temperature of 15±1, 20±1, 25±1, 30+1° and at humidity of 40±5, 70±5, 90±5%. The setting time (a initial settingtime, a final setting time) was defined in the A.D.A. specification No.16. The following results were obtained. 1. A higher temperature and humidity shortened the initial setting time of all paste. 2. A higher temperature and humidity shortened slightly the time interval between a initialand a final setting time of all paste. 3. In clinical use, sample C is better than other ones, so that a setting time of the sampleis property for impression making.