Heat Generation and Temperature Increase in the Root during Electromagnetic Apical Treatment

Research Article

J Dent & Oral Disord. 2020; 6(1): 1125.

Heat Generation and Temperature Increase in the Root during Electromagnetic Apical Treatment

Tominaga T1*, Tada E1,2, Takahira K1,3 and Sugaya T2

¹Department of Tominaga Dental Clinic, Shimohonjo Akinokami Seto Naruto, Japan

²Department of Periodontology and Endodontology, Hokkaido University, Japan

³Department of Management and Information Science, Shikoku University, Japan

*Corresponding author: Toshihiko Tominaga, Department of Tominaga Dental Clinic, Shimohonjo Akinokami Seto Naruto, Japan

Received: February 03, 2020; Accepted: February 24, 2020; Published: March 02, 2020


The temperature increase due to high-frequency energization reduces bacterial viability. However, the harmful effects of overheating of the periodontal tissues during a root canal procedure are a matter of concern. Therefore, we examined the heat generation and temperature increase in an active electrode on the intracanal and root surfaces by energization and to develop a novel endodontic treatment system using high-frequency current. K-file #10–40/.02 T was inserted into an egg white at several insertion depths. The current flow was energized with 510-kHz frequency at the maximum output of 15.5 W for 1.0 s, and coagulation was evaluated. K-file was inserted at 2.0 mm on the crown side from the apical foramen of a mandibular anterior tooth, followed by energizing ten times. The temperatures of the intracanal and root surfaces were measured at the portion by a thermocouple Type-K TC-K-F-0.1-WP (HAYASHI DENKO Corp., Tokyo, Japan). The results were statistically analyzed. A uniform coagulated layer was created on the tip portion of the K-file when the insertion depth was up to 3.0 mm. The intracanal temperature of a mandibular anterior tooth increased up to 40.8°C–45.1°C during the 1st energization. However, the root surface temperature increased by 7.1°C–7.8°C, with temperature increase per one energization being ‹0.5°C if the time interval was ›3.0 s during the subsequent energization. In the electromagnetic apical treatment system developed based on these results, the efficient generation of Joule heat and energization were possible without harmful effects on the periodontal tissue.

Keywords: Electromagnetic apical treatment; High-frequency current; Heat generation; Temperature increase; Root canal treatment


The primary etiological cause of periapical periodontitis are preexisting substances in the root canal such as bacteria and/or their products, infected tooth or pulp debris [1-3]. Howeverachieving perfect disinfection by chemomechanical preparation is difficult owing to the root canal’s complex anatomical morphology [4,5]. Recently, a diode laser or pulsed Nd: YAG laser has been utilized [6-8]. However, such laser devices need to be improved further so that they can exhibit the crucial difficulty of directing appropriate radiation onto the curved root canal [9,10]. Although various medications show effective bactericidal actions [11,12]. There are concerns regarding the appearance of the antibiotic-resistant DNA [13,14].

To energize high-frequency current, the current density is increased at the tip and the Joule heat is produced. Substances inside the root canal or the root canal itself could be cauterized and sterilized by the Joule heat [15]. Note that the bactericidal action of the electrical energy has been investigated previously [16-19]. The bactericidal effect by electric current is known as the electricidal effect [16,17]. Whereas a similar effect along with an antimicrobial agent is defined as the “bioelectric effect [18,19]. Among the proposed theories on the bactericidal mechanism, electric current has been reported to enhance antimicrobial agents’ functions against the bacteria within the biofilm. The sole application of direct current is to exfoliate the biofilm from the surface layer [16]. However, the bactericidal effect of high-frequency current is owing to the mechanical action against the exopolysaccharide matrix. Thus, the weakening of the tissue membrane is possible by vibrating the biofilms under the current flow [17]. Assumptions such as the physical removal of biofilms by air bubbles owing to electrolysis or enhanced sensitivity owing to temperature increase within the biofilms have been previously reported [16].

In our previous study [20,21]. We applied high-frequency current against the gram-positive bacteria Streptococcus mutans, Staphylococcus intermedius, and Enterococcus faecalis and the gramnegative bacteria Fusobacterium nucleatum and Porphyromonas gingivalis; our results indicated a remarkable bactericidal effect against all types of bacteria. Moreover, the production quantity of inflammatory cytokines produced from the human monocyte cell line THP-1 cell stimulated by S. mutans was measured and found that S. mutans treated by an electric conduction controlled the production of inflammatory cytokines at the same level as S. mutans that was heattreated at 100°C for 10 min; hence, the pathogenicity of S. mutans was confirmed to be effectively inactivated. Simultaneously, the gingipain activity inhibitory action of P. gingivalis was also recognized.

Therefore, we assume that these effects are involved for effectively treating the infection source in the uninstrumented area. The traceability of electric current traveling in the intricate morphology of the root canals can be excellent; thus, its permeability in the curved or constricted root canal is expected to be high. Nevertheless, overheating owing to the high-frequency current may increase the risk of harmful effects on the periodontal tissue. Therefore, we measured the heat produced by energization around the K-file and evaluated temperature changes on the intracanal and root surfaces.

Materials and Methods

The Electromagnetic Apical Treatment (EMAT) device

The high-frequency treatment device (J. MORITA MFG. Corp., Kyoto, Japan) is monopolar and is composed of the electrosurgical main unit, active electrode, and counter electrode. The electro unit is characterized by the maximum output power of 15.5 W, the output discrete wave of 50-70 ms, and the frequency of 510 kHz.

Evaluation of coagulation by the joule heat

Energization method: As a heat-sensitive substance, according to a previously used method [22,23] an egg white was placed into a polystyrene Sample cup (5 ML, SANPLATEC Corp., Osaka, Japan) with 18.0 mm diameter and 35.0 mm depth. K-file #10–40/.02T (MANI Inc. Utsunomiya, Japan) was used as the active electrode, whereas a stainless steel wire of 1.30 mm (TOMY Inc., Tokyo, Japan) was used as the counter electrode. The current flow was energized for 1.0 s.

To investigate the influence of K-file based on its depth, K-file #10–40/.02T was inserted into the egg white every 1.0 mm from 1.0 to 16.0 mm in depth. To evaluate the Joule heat derivation aspect inside the root canal and to examine influences based on the Apical Foramen (AF) diameter, three types of Endo Training-Bloc (J 02 Taper, Dentsply MAILLFER Corp., NY, USA) with AF diameter/ taper degree of #15/.02T, #30/.02T, and #60/.02T were installed in the Sample cup 5 ML. The egg white was placed into the Sample cup 5 ML and into the root canal. K-file #10/.02T was inserted into the root canal and energized the same way as above. The current effective value at each K-file was measured using an oscilloscope (MIXED SIGNAL OSCILLOSCOPE DLM2054, Yokogawa Test & Measurement Corp., Tokyo, Japan) (Figure 1).