Posteruptive changes of electrical resistance values in fissure enamel of premolars

In studies about 15-25% of the caries-free teeth proved to have as low electrical resistance values as carious teeth, due probably to incomplete enamel maturation. It was the aim of the present prospective clinical study to investigate, if an increase in electrical resistance values could be observed after the eruption of premolars. The electrical resistance measurements were performed in children who were patients of the Dental School of the University of Marburg, Germany. The first measurement was made when a premolar was erupting or when it had erupted within 12 months before. The electrical resistance measurements were repeated every 3-6 months until the 24th posteruptive month. The measuring device consisted of an AC ohmmeter modified by Gente indicating the real component of the impedance and employing a frequency of 500 Hz and an amplitude of about 1 microA. For erupting teeth a mean resistance value of 17+/-15 kohm was computed when the contact fluid had been NaCl (A). The corresponding values were 72+/-51 kohm when distilled water (B) had been applied and 392+/-374 kohm when the initially saliva-coated teeth had briefly been dried (C). The mean resistance values of the premolars increased continuously from the eruption up to the 15th posteruptive month. This observation was independent of the three modes of measuring that had been used. It is concluded that enamel maturation leads to an increase in electrical resistance. To improve accuracy of caries diagnosis with electrical resistance measurements, the posteruptive age of teeth should be taken into account. In addition, electrical resistance measurements offer the opportunity to observe enamel maturation in vivo noninvasively.