Effects of Ultrasound-Mediated Treatments on Dental Biofilm Attachment and Viability

Dental biofilms are responsible for the majority of oral cavity diseases (e.g., caries, periodontitis and gingivitis). In this work, we evaluate the effects of therapeutic ultrasound on a Streptococcus mutans biofilm model. The research aim is to assess whether therapeutic ultrasound can be implemented in standard practice for the treatment and prevention of oral infections.

Streptococcus mutans biofilms were grown on a tooth-mimicking substrate and subsequently exposed to chlorhexidine (CHX) and therapeutic ultrasound treatments. We examined the effects of low duty cycle (1%) 0.5 MHz ultrasound treatment at varying peak negative pressures (0.75-3.00 MPa) and CHX concentrations (0.025, 0.050 and 0.100 % w/V), both in the presence and absence of lipid-coated gas microbubbles.

Ultrasound treatment was effective at removing biofilm, particularly at peak negative pressures exceeding 2.25 MPa and in the presence of lipid-coated microbubbles as cavitation nuclei. Ultrasound exposure also resulted in improved bactericidal action of low-concentration CHX (0.050% w/V).

We demonstrated that 0.5 MHz therapeutic ultrasound treatment can be used for the mechanical removal of a fully formed and mechanically robust Streptococcus biofilm model. Although the ultrasound treatment alone did not reduce bacterial cell viability, its combination with low concentrations of CHX improved the antimicrobial treatment outcomes.