Evaluation of Temperature Increase From Joule Heat in Numerical Tooth Model by Applying 500 kHz Current for Apical Periodontitis Treatment—Effect of Applied Voltage and Tooth Conductivity

Abstract

For apical periodontitis treatments, a new method with the insertion of an electrode into the root canal of a tooth and application of a current at 500 kHz to sterilize the area by Joule heat has attracted attention. However, few studies have quantified the temperature increase in the root canal. This study aimed to investigate the basic characteristics of the temperature increase in a simple and standard tooth model when energizing a current at 500 kHz to the numerical tooth model with typical electrical and physical properties. We developed a numerical model of a standard tooth (dentin) and periodontal tissues consisting of an alveolar bone, cortical bone, and gingiva, and physiological saline in a root canal and calculated the temperature increase inside the numerical model by a coupled analysis of current and heat when a voltage was applied across the electrodes. The calculated results for the different applied voltages showed a temperature increase at the apical portion of the root canal, which increased with the applied voltage even for the same total supplied energy. The temperature increase occurred at the apical portion of the root canal as the tooth conductivity decreased. When the tooth conductivity was high, a current passed through the dentin, which led to a decrease in the temperature at the apical portion of the root canal. However, a chemical solution with a higher conductivity in the root canal tended to increase the temperature at the apical portion of the root canal, regardless of the tooth conductivity. More efficient approaches for increasing the spatial and temporal temperature for the tooth model target are needed.

Cauterization of Narrow Root Canals Untouched by Instruments by High-Frequency Current

“…However, during electrical conduction to the root canal, the higher impedance at the apical constriction and in accessory canals where the root canal is narrower means that the thermal energy increases in accordance with Ohm’s law and Joule’s law [ 39 ], generating Joule heat that may result in a large temperature increase. In a numerical simulation, Tarao et al [ 40 ] found that passing a 500 kHz, 60 V electric current through a root canal with an apical foramen 0.4 mm in diameter resulted in a 62 °C increase in the vicinity of the apical foramen after 0.1 s. Accordingly, when apical patency fails because of a ledge, step, or other obstruction, and the uninstrumented root canal is narrow, the current density of a high-frequency electric current increases, and Joule heat is generated, which may make it possible to cauterize the pathogenic factors in the root canal. However, all previous studies of the application of a high-frequency electric current in root canal treatment have used it to heat the tip of the file, and none have investigated its effect at the apical constriction where the temperature increase is the greatest.…”