Longitudinal Changes of Electrical Impedance in Teeth (in vitro)

Electrical impedance has been used for quantitative assessment of occlusal caries in vitro, as well as in vivo, in several studies with different devices. It is not known to what extent in vitro measurements are comparable to those performed in vivo, or what changes will be perceived after extraction, and introduced during preservation in the storage medium. Objectives: The aim of this study was to determine the electrical impedance in teeth, in vivo, after extraction, and during storage, in order to find out whether in vitro measurements are comparable to those performed in vivo, and for how long the teeth could be stored without changes in readings. Methods: The material consisted of 12 test subjects admitted for treatment at the School of Dentistry, Huddinge, Sweden, with one tooth in varying health condition with planned extraction therapy. The inclusion criteria were teeth that were sound or had carious lesions confined to the enamel or the dentine. The electrical impedance was measured with the Electrical Caries Monitor (ECM IIb) device in vivo, before extraction, directly after extraction, and then in vitro, once every hour for twelve hours. Measurements were then repeated day 2, after 1 week, and then after 2, 3, 4, 6, 8, 12, 20, 36, 68 weeks, and finally after 6 years. The teeth were stored in saline, saturated with thymol, during the experimental period. Results: A repeated measures ANOVA was used to determine changes in reading over time. The results showed a significant change over time, p<0.05, from pre-extraction to 6 years. Conclusion: It was concluded that there were changes in readings over a time period of one year, but in a clinical perspective, the changes were minor. However, if teeth are stored in 6 years, the readings could change clinically significantly to a higher reading.