Investigation of Cavity-sealing Properties of Zinc Phosphate Cement

¹ West Virginia University School of Dentistry, Morgantown, West Virginia

This investigation was designed to determine the rate of penetration of a dye solution through the margins of cavities restored with zinc phosphate cement under standardized conditions in vitro.

Buccal and lingual cavities were prepared in 57 freshly extracted maxillary and mandibular molars and were restored with zinc phosphate cement. The crowns of these teeth were immersed in an aqueous solution of 0.20 per cent methyl violet and 11 per cent glycerin, kept at constant body temperature. A mixture such as this took into account the increased viscosity of saliva over that of aqueous dyes.

At every hour up to and including 18 hours, 3 experimental teeth were removed and their cavities observed under a microscope for dye penetration. It was found that this dye solution had traveled to the base of a 2-mm.-deep cavity at a somewhat faster rate along the gingival wall than along the occlusal. The average rate of penetration along the dentin of the gingival wall was 0.218 mm. per hour, whereas the average rate along the enamel of the occlusal wall was only 0.134 mm. per hour.

A coating of 11 per cent glycerin on the surface of these teeth, before immersion in the dye, was capable of slowing down the capillary attraction of the dye for only a short period of time.

Incubation of these teeth from the time they were filled until the time they are examined definitely increased this rate of penetration.

The manner in which these teeth were preserved, following their extraction, also was a determining factor in this rate of penetration. Storage solutions containing highly viscous fluids decreased this rate of dye penetration, especially along the dentin walls of the cavities.

An increase in the concentration of the dye from 0.20 to 1.00 per cent did not cause a change in the results. Other aqueous dye solutions in a 0.20 per cent concentration, having nearly the same physical and chemical properties as methyl violet, did not alter the rate of penetration. Alcoholic dye solutions, however, increased the rate of dye penetration so much that it was uncontrollable and should not have been used in such a test.