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

The kinetics of the exothermic setting reaction of zinc phosphate dental ce ment can be successfully investigated by conduction calorimetry. The primar y objective of this study is to examine the effects arising from the additi on of various additives to the liquid and calcination of cement powder. The rate of heat evolution versus time shows the occurrence of merely one maxi mum. In the case of unmodified orthophosphoric acid a sharp peak occurs ear ly 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, an d ensure sufficient working time in the surgery in this way. The peak of he at evolution broadens and shifts due to the formation of an amorphous react ion product. When the ingredients of the cement powder are calcined at suff icient temperature the reactivity is further reduced, The setting time prov es to be sensitive to changes in specific surface area of cement powder. Th e observed effects are discussed in terms of chemical reactions taking plac e during setting, (C) 1999 Elsevier Science B.V. All rights reserved.