Applications of conduction calorimetry to the setting reaction of zinc phosphate dental cement

The kinetics of the exothermic setting reaction of zinc phosphate dental cement can be successfully investigated by conduction calorimetry. The primary objective of this study is to examine the effects arising from the addition of various additives to the liquid and calcination of cement powder. The rate of heat evolution versus time shows the occurrence of merely one maximum. In the case of unmodified orthophosphoric acid a sharp peak occurs early after onset of mixing due to the formation of crystalline alpha-hopeite. Commercial cement liquids contain aluminum and zinc. From the calorimetric curves it has been found that these cations act as a setting retarders, and ensure sufficient working time in the surgery in this way. The peak of heat evolution broadens and shifts due to the formation of an amorphous reaction product. When the ingredients of the cement powder are calcined at sufficient temperature the reactivity is further reduced, The setting time proves to be sensitive to changes in specific surface area of cement powder. The observed effects are discussed in terms of chemical reactions taking place during setting, (C) 1999 Elsevier Science B.V. All rights reserved.