Age-related changes in ac-impedance spectroscopy studies of normal human dentine: further investigations.

One of the age-related changes occurring in dentine structure is the formation of peritubular dentine on the inner walls of dentinal tubules leading to complete closure of tubules. Ac-impedance is safe, fast and non-invasive technique. In the last decade, the popularity of the technique has increased in dental research. Several investigators have used the technique to detect tooth cracks and caries. The results of in vitro studies showed that ac-impedance technique was more advanced for caries detection than visual and radiographic methods. However, other studies demonstrated that the accuracy of impedance measurements can be affected by many factors such as remineralization after tooth eruption. A study has been published on effect of age on impedance measurements by the authors for two age groups by employing ac-impedance spectroscopy. Therefore, the aim of this study was to demonstrate the importance of this technique by conducting further investigations on dentine samples of wider age groups. Dentine samples were prepared from extracted sound third molars of known patient age. The ac-impedance measurements were carried out over a wide range of frequency. After performing all electrical measurements, dentine samples were examined under SEM to correlate the electrical measurements with their structure. Impedance measurements showed that there were differences in impedance between young and old dentine. One-way ANOVA of the means of resistance and capacitance for all age groups (20, 25, 30, 40 and 50 years old dentine) revealed a significant difference (ANOVA, P < 0.0001) as a function of age. Applying Tukey's post hoc test, to the same data showed that this difference was due to the 50 years old dentine for resistance and was due to the 40 and 50 years old dentine for capacitance which were statistically different to all other groups. SEM investigation of dentine samples showed that young dentine is characterized by open dentinal tubules distributed all over the sample while in old dentine most dentinal tubules were occluded by peritubular dentine. It is believed that this peritubular deposition is responsible for differences in impedance measurements. In spite of increasing use of electrical techniques to understand electrical properties of teeth, it is clear from this study that local structural variations have a marked influence.

Age-related changes in cyclic voltammetry and potentiodynamic studies of normal human dentine.

Impedance spectroscopy is one of the non-destructive techniques used by researchers to measure electrical resistance of biological tissues and ceramics. The purpose of this study is to investigate the voltage-current (V-I) characteristics of sound human dentine from young and old teeth, using cyclic voltammetry and potentiodynamic techniques. Dentine samples were prepared from freshly extracted sound third molars. After electrical measurements, dentine samples were characterized using scanning electron microscopy (SEM). Cyclic voltammetric measurements showed that variation of current through sample as a function of applied voltage is linear for dry samples of both age groups. However, for wet samples V-I characteristic were found to be different. The resistivity of dry young dentine is greater than that of old dentine in dry environment, whereas, it was found to be opposite for wet dentine samples. Using the same voltage sweep in potentiodynamic measurements dry samples display similar traces to controls suggesting that the dry dentine acts as an insulator. The number of dentinal tubules and their diameter has been found to decrease with increasing age. We propose that these changes determine the changes in electrical characteristics of sound human dentine. In spite of increasing use of electrical techniques to understand electrical properties of teeth, it is clear from this study that local structural variations and environment have a marked influence. Therefore, this baseline data needs to be considered in any future study or clinical application.