Influence of gap width and distance between electrodes on eliminating organic material of the isthmus by high frequency electric current

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Hokkaido University
Background: Root canal disinfection is a critical step for the success of root canal therapy. However, traditional disinfection methods have limitations, and root canal treatment can fail because of the complex root canal system, which includes lateral branches and isthmuses, which are challenging to fully eliminate, leading to persistent bacterial infection. Cauterization is a novel method for disinfecting root canals which conducted a high frequency current that has been found to have several benefits in root canal therapy. Aim: The aim of this in vitro study was to evaluate how the isthmus gap width, distance between electrodes, and duration of high-frequency electrical current application affect the elimination of organic matter in the simulated isthmus inner surfaces. Methodology: Dentin blocks were prepared using bovine roots and immersed in Plank-Rychlo solution for 5 min. A simulated isthmus model was made with gaps of 0.1, 0.2, and 0.3 mm between the two walls with organic layers on the inner surfaces. In addition, two root canals of 0.4 mm diameter and 7 mm depth were prepared at a distance of 2 mm or 5 mm. Isthmus width with root canal distance, including root canal depth, were divided into six groups. The gap width was 0.1 mm for groups 1 and 4, 0.2 mm for groups 2 and 5, and 0.3 mm for groups 3 and 6, and the root canal distance was 2 mm for groups 1, 2, and 3, and 5 mm for groups 4, 5, and 6 mm. The root canals and isthmus were filled with NaClO, #35K files were inserted into the two root canals as electrodes, and a current of 225 V, 520 kHz was applied between the electrodes. Energizing times are 0, 5sec for groups 1,2,5,6, and 0,5,10 sec for groups 3,4, for 0, 5, or 10 seconds. The isthmus model was split, the morphological and elemental analysis of the isthmus inner surface were evaluated by SEM and EDS. Results: By electrification, a flat layer in the isthmus caused by demineralization was removed, and dentin tubules and lava-like surfaces were observed. At these sites, significant decreases in carbon and oxygen and increases in calcium were shown by EDS, resulting a significant difference (p<0.05) in the remaining organic residuals between Group 1 with a narrow isthmus gap of 0.1 mm and a closer root canal distance of 2 mm, and Groups 4 and 5 with a narrow isthmus gap of 0.1 mm and 0.2 mm and farther root canals of 5 mm distance. Groups 3 and 4 had significantly (p<0.05) less organic material remaining after high-frequency conduction for 10 seconds compared to 5 seconds. Increasing the cauterization time removed almost all organic materials. Conclusion: By applying high frequency electricity to the isthmus, it was possible to remove most of the organic matter. The effect varied based on the width of the isthmus gap and distance between the root canals. A narrower isthmus with closer canals had a higher effect from the electricity, and a wider gap between canals farther apart had less effect. More electrification time was needed to completely remove all organic material from wider gaps or farther distances. High frequency current, isthmus gap, cauterization, electrodes distance, organic material.
High frequency current, isthmus gap, cauterization, electrodes distance, organic material.