Marginal Penetration of Dental Restorations by Different Radioactive Isotopes

¹ University of Illinois College of Dentistry, Chicago, and Veterans Administration Hospital, Hines, Illinois

This investigation was designed to compare the marginal penetration of most of the filling materials in common clinical use, employing a variety of radioactive isotopes under standardized conditions in vitro.

Class V cavities were prepared in 147 freshly extracted human teeth and were restored with either silver amalgam, cast gold inlay, gold foil, acrylic resin, silicate cement, red copper cement, copper amalgam, zinc oxide-eugenol, zinc phosphate cement, or temporary stopping. Unfilled cavities were used as controls.

The experimental teeth were immersed in the isotope solutions (10-30 µc/ml) for a 24-hour period. A series of different isotopes was used in this study rather than a single tracer, since preliminary studies showed that the charge on the ion and its chemical affinity greatly influenced its adsorption on the surface of the filling material and on the tooth surface, as well as its penetrability through the margins of the restorations. The following radioactive compounds were selected on the basis of ionic charge and chemical activity: Na₂S³⁵O₄, Na₃P³²O₄, Na²²Cl, Rb⁸⁶Cl₂, and Ca⁴⁵Cl₂. Ground sections were prepared and multiple autoradiographs were obtained under standardized conditions.

All fillings showed some degree of marginal penetration to one or more of the tracers used. A single order of marginal permeability could not be established, since the order of penetration varied somewhat with different isotopes. In general, the metallic restorations were superior to the non-metallic restorations under the conditions of this experiment. The behavior of the cement restorations was very variable, and the order of marginal penetration among silicate cement, zinc phosphate cement, and zinc oxide-eugenol could be reversed by the use of different isotopes. It is concluded that the ionic charge and chemical reactivity of the ion, as well as the physical and chemical nature of the restorative material, influence the depth of marginal penetration by the isotope.