An Evaluation of the Frozen Slab Mixing Technique on the Physical Properties of Certain Dental Cements

Abstract

A method was devised to evaluate the effect of the "frozen slab" mixing technique on the physical properties of a zinc phosphate, zinc silicophosphate, hydrophosphate and polycarboxylate cement. Those properties studied were the setting time, compressive strength, tensile strength and solubility. Standardized mixing procedures were employed using predetermined powder/liquid ratios. Setting and working times were increased for all cements when mixed on glass slabs chilled to -15 c. All cements kept on the cold slab were still unset after 32 minutes. Compressive and tensile strengths were adversely affected by the "frozen slab" technique. All cements gave parallel reductions of the two strengths on the order of 20 percent except the polycarboxylate which exhibited only a 5 percent reduction in tensile strength. The polycarboxylate exhibited the highest tensile strength while its compressive strength was one half the others tested. Solubility samples were prepared and placed in 0.001M acetic acid at pH4. Solutions were changed daily and solubility was determined by the gravimetric method. The solubility of all cement was adversely affected. The zinc silicophosphate exhibited the highest and the polycarboxylate the lowest solubility of the cements tested. It was recommended that cements be mixed above the dew point and multiple mixes be used to ensure optimum physical properties.