Electrochemical Properties of Human Dental Enamel

Abstract

DESPITE numerous findings that intact enamel is permeable in certain circumstances to various dyes, radioactive tracers and other chemically identifiable substances¹, the ionic-sieve behaviour of enamel demonstrated as long ago as 1929 by Klein and Amberson² has been largely ignored. Their work could have an important bearing on the whole problem of ionic transport through enamel in vivo, and its chemical stability, so a more systematic study of membrane phenomena associated with enamel has been undertaken. The selectivity to ionic transport of enamel caps of sound human teeth, enamel sections and membranes prepared from a synthetic hydroxyapatite powrder in a poly (methyl methacrylate) matrix has been investigated by e.m.f. measurements of concentration cells using KCl, NaCl and CaCl₂ solutions at pH. 7.4 and 25° ± 1° C. The technique for mounting the teeth and measuring the cell e.m.f. has been described in the literature³. The concentration of the electrolyte was maintained at 0.100 M on one side of the cell and on the other side varied in steps from 0.100 M to 0.002 M. All cell e.m.f.s were measured under equilibrium conditions as assessed by the constancy of the e.m.f. over a period of days. The establishment of equilibrium conditions on changing from one salt solution to another was protracted; following the replacement of CaCl₂ solutions by KCl solutions, for example, the average time to re-establish equilibrium was of the order of 8 weeks.