Mechanical Failure of Amalgam Restorations with Zinc Phosphate and Zinc Oxide/Eugenol Cement Bases

¹ College of Dentistry, Ohio State University, Columbus, Ohio

Laboratory models containing both deep- and shallow-cavity preparations were restored (1) with amalgam alone, (2) with underbases of zinc oxide/eugenol, and (3) with underbases of zinc phosphate cement. For the shallow cavity the underbase was emplaced in a small hemispherical excavation, but for the deep cavity the base formed a continuous layer under the amalgam.

Amalgam restorations with underbases of zinc oxide/eugenol failed under relatively small loads if the underbase covered the entire floor of a deep-cavity preparation. When this same base material was confined to a small hemispherical excavation, however, the load sustained was similar to that sustained by zinc phosphate or of amalgam alone.

With increased depth of the cavity preparation, a general decline in strength of the models was observed, even with amalgam alone, and this decline was extreme with zinc oxide/eugenol as a base material.