Influence of the concentration of ions and foramen diameter on the accuracy of electronic root canal length measurement--an experimental study.

Investigations on the concentration of cations in human pulp have shown that pathological changes in the pulp lead to changes in the concentration of ions in the tissue. Consequently, its electrophysiological characteristics are changed, which affects the accuracy of electronic root canal length measurements (ERCLMs). The aim of this study was to examine the effect of concentrations of Na+, K+, and Ca2+ cations in medium within the canal and around the tooth, and also foramen diameter, on the accuracy of ERCLMs. The model comprised 21 extracted single-rooted human teeth divided into two experimental groups and one control group, with seven teeth each. Two aqueous solutions of different concentrations of NaCl, KCl, and CaCl2 were mixed with agar. The concentrations of Na+, K+, and Ca2+ corresponded to the results of analyses performed by atomic spectrophotometry on the extirpated human pulps. Agar containing cations was injected into the root canal prepared with a foramen diameter of 0.25 mm. In the control group, the teeth were then completely immersed in agar of the same concentration of cations as the agar inside the canal. In the first experimental group (group 1), the concentration of ions was higher inside the canal, compared with the concentration outside the canal. In the second experimental group (group 2), the order of concentrations was inverse. In all three groups, ERCLMs was performed in the previously described model. Then, the size of the apical foramens was enlarged and ERCLMs repeated at foramen diameters of 0.45 mm and 0.70 mm diameters, respectively. Results indicate that at 0.25 diameters, the most accurate measurements were taken when the concentrations of ions inside the canal were higher than outside the canal (Xdif = 1.39 +/- 1.21 mm) (group 1). At diameters of 0.45 and 0.70 mm, no significant differences were found (p < 0.05) between the experimental groups (error amounted to Xdif = 6.27 +/- 1.47 mm). In the control group measurement, error increased with enlargement of the foramen.