Fracture strength of Class II amalgam restorations condensed over protective bases

Abstract

A protective base, serving as a substitute for dentin, guards the pulp against thermal, electrical, chemical, and mechanical injury. In addition, a medicated base promotes the formation of reparative dentin. All bases should possess sufficient strength to resist the forces of condensation of dental amalgam or gold foil’; in addition, they must resist the stresses of mastication. The most important physical requirement of a base is its ability to resist condensation forces.” A cement base needs to resist more than 170 p.s.i. to preclude fracture and displacement resulting from condensation3 Zinc oxide and eugenol cement (ZOE) lacks the necessary strength when compared to zinc phosphate cement in Class I and II amalgam restorations.‘+ The recommendation that two or more layers of varnish be applied to cavity walls has added another factor to base techniques.” When tested, the varnish failed to alter the strength of cylindrical specimens of amalgam.7 A previous report discussed pertinent factors which relate to the physical problems of protective bases5 The class of preparation, the size of the cavity, and whether or not the line angles are created in dentin relate to the physical needs of a base. The views in that report agreed with earlier discussions of this problem.P. :’ Calcium hydroxide, protected with zinc oxide and eugenol cement (ZOE), may suffice for small bases, but larger areas require zinc phosphate cement, These concepts and other clinical practices have, in part, been investigated. and the results are described in this report.