Evaluation of Anti-biofilm Effects of High-frequency Waves In vitro

Objectives: Refractory apical periodontitis (RAP) refers to apical periodontitis that fails to resolve after root canal treatment (RCT) is performed. It has been reported that RAP was caused by extradicular biofilms. High-frequency waves (HFW) was reported to have bactericidal effect against planktonic bacteria. So, we think of applying HFW to periapical lesion for treating RAP. The purpose of this study was to evaluate the anti-biofilm effect of HFW in vitro.
Methods: Enterococcus faecalis SS497, Streptococcus mutans 10449, Fusobacterium nucleatum 1436, Porphyromonas gingivalis 381 and Prevotella intermedia ATCC 25611 were used for this study. For HFW irradiation, electro-surgical unit system was used. The biofilm was formed on a hydroxyapatite (HA) disc which had been treated with saliva. HA discs were immersed in 2 ml of bacterial solution and incubated under anaerobic conditions for biofilm formation. After preparation of the biofilm on the HA disc, the disc was washed with sterile saline. A #10 stainless steel K-file as the active electrode was inserted in the centre of the HA disc in the irradiated group. Each disc was irradiated with HFW is different output settings (35V, 100V). The effect of HFW irradiation on biofilm were evaluated by confocal laser scanning microscopy (CLSM) observation and ATP assay.
Results: At 35V, the irradiated group showed no effect in most of the species tested, however, at 100V, the irradiated group showed a tendency to decrease biofilms compared with the control.
Conclusions: These results showed the possibility that HFW at higher voltages have the anti-biofilm effect. So it might be useful as a nonsurgical treatment for refractory apical periodontitis. (This work was supported by JSPS KAKENHI Grant Numbers JP17K17129, JP17K17131, JP17K17133 and JP19K18994.)