ELECTROMOTIVE FORCES AND ELECTRIC CURRENTS CAUSED BY METALLIC DENTAL FILLINGS

¹ Department of Physics, University of Oklahoma, Norman, Okla.
² Department of Biochemistry, University School of Medicine, Oklahoma City, Okla.

A critical review of the literature from 1878 to date is presented. The more important experiments are described and the more important conclusions are cited. Certain fallacies are pointed out.

The sources of possible electromotive forces for pairs of metallic fillings and for single fillings are described. The literature survey revealed that neither these e.m.f.'s, nor their resulting currents, had been measured, and that no measurements had been reported from which these e.m.f.'s and currents could have been calculated.

A condenser-ballistic-galvanometer potential-difference meter was developed, with which the electrical potential differences between pairs of metallic fillings could be measured. The scheme for carrying out the measurements and the theory for the calculations are given.

Measurements were made on 213 pairs of fillings in the mouths of 137 subjects. Average values of the results are given in Table I.

A study of these measurements (Part I) led to the conclusion that the electrical resistance associated with a filling is almost entirely concentrated in, and very near, the metal-saliva and metal-bone fluid contacts. This was confirmed in Part II for metal-saliva contacts.

This conclusion made it possible to prove, by use of the well-known principles applying to electric circuits, that the electric current through any metallic filling is virtually independent of the number and kinds of other metallic fillings in that oral cavity, provided that filling is not in contact with any other metallic filling.

This proof, together with the conclusion above, made it possible to develop a method, including the necessary theory, for determining the electromotive force, electrical resistance, and electric current associated with a single metallic filling. The theory calls for the measurement of five potential differences as well as the resistances introduced by an auxiliary electrode and a saliva probe.

A second apparatus for measuring the potential differences was developed: it incorporated a special highly-insulated electrometer tube. A potential measurement with this meter required a closed-circuit time of only a fraction of a second, and only a very small electric charge needed to be furnished by the source of the potential. This meter eliminated intolerable polarization effects.

The experimental procedure is described and the scheme for dealing with the data is given. Results were computed for 78 fillings in the oral cavities of 66 subjects whose ages fell in the range 18 to 30 years. These results are summarized in Table II.

These results are discussed and their relations to other results obtained with the condenser-ballistic-galvanometer meter on 127 fillings in the mouths of 77 persons, are described.