The Antimicrobial Effect of a Low-Frequency Square Wave Compared to Chlorhexidine

Abstract

Background/Objectives: Oral health is critical for overall health, particularly in hospitalized patients whose weakened physical state can lead to oral changes, such as dry mouth and gingivitis due to anxiety and stress. Neglected oral hygiene can lead to infections and systemic complications. This study aims to evaluate the antibacterial efficacy of low-frequency square-wave positive voltage electrical stimulation compared to chlorhexidine and to assess its potential as a next-generation solution for preventing hospital-acquired infections. Methods: Sixty-three tooth specimens were randomly assigned to seven groups, including various concentrations of chlorhexidine and electrical stimulation with or without brushing. Biofilm formation was induced using saliva from healthy donors and standard strains of Streptococcus mutans and Aggregatibactor actinomycetemcomitans. Bacterial colony-forming units (CFU) and absorbance changes were measured post-treatment. Results: Significant reductions in CFU counts were observed in both the chlorhexidine and electrical stimulation groups compared to the control, with the 5V2H group showing superior antibacterial efficacy over 0.12% chlorhexidine. Chlorhexidine-treated specimens demonstrated a dose-dependent response and minimal bacterial presence, while electrical stimulation showed effectiveness but with re-growth observed after 4 h. Scanning electron microscopy revealed substantial biofilm on untreated and electrically stimulated specimens, whereas chlorhexidine-treated specimens exhibited minimal bacterial presence. Conclusions: Intermittent electrical stimulation shows promise as an alternative to chlorhexidine for oral hygiene management in critical care settings, though an optimization of electrical parameters is necessary for sustained effects. This approach could reduce hospital-acquired infections by providing an effective, non-chemical method for maintaining oral hygiene.

Keywords: Schumann resonance; biofilms; chlorhexidine; extremely low frequency electromagnetic fields; oral hygiene.

Figure 1

A square wave generator with a continuous positive voltage offset of 0.7 V.

Figure 2

Bacterial CFU counts after treatment.

Figure 3

Bacterial growth curve after treatment.

Figure 4

Biofilm formation process on the specimen.

Figure 5

SEM image of the biofilm on the specimen after chlorhexidine treatment. The CHX0.5 group shows a greater reduction in bacterial colonies compared to the CHX0.12 group, and the group that underwent brushing shows biofilm removal with bacterial deformation observed (arrow). (CHX0.12: Immersion in 0.12% chlorhexidine; CHX0.12B: Immersion in 0.12% chlorhexidine and brushing; CHX0.5: Immersion in 0.5% chlorhexidine; CHX0.5B: Immersion in 0.12% chlorhexidine and brushing).

Figure 6

SEM image of biofilm on the specimen after electric stimulation. Partial bacteria were removed. (5V2H: A low-frequency square wave AC at 7.83Hz was applied to the specimen at 5V for 2 h.; 5V2HB: 5V2H with brushing).

Figure 7

SEM image of bacteria detached from specimen after treatment. In the CHX0.12 group, the bacteria were observed to detach in clusters, whereas in the 5V2H group, they detached individually or only parts of the biofilm were detached. (CHX0.12: Immersion in 0.12% chlorhexidine; 5V2H: A low-frequency square wave AC at 7.83 Hz was applied to the specimen at 5 V for 2 h).