Objectives: To test the hypothesis that photomechanical waves generated with a high pulse laser can enhance the penetration of a photoactive compound into oral microbial biofilms enabling their photodestruction. Methods: Biofilms of Actinomyces naeslundii and saliva-derived multispecies biofilms were developed on human enamel slabs and agar surfaces in 96-well plates. The photomechanical waves were generated by ablation of a target with a Q-switched ruby laser and launched into the biofilms in the presence of 25-50mg/ml methylene blue. Then the biofilms were irradiated with red light at 665 nm. After illumination, adherent bacteria were scraped and spread over the surface of blood agar plates. Survival fractions were calculated by counting bacterial colonies. Microbial analysis was performed via a colony lift method and a DNA checkerboard assay using whole genomic probes to 40 oral microorganisms. Results: Confocal scanning laser microscopy revealed that a single photomechanical wave was sufficient to induce up to a 50-70% increase in the penetration depth of methylene blue into the biofilms. This enabled their photodestruction (90-99% killing) after photodynamic therapy. Conclusions: This study provides evidence that the synergism of photomechanical waves and photodynamic therapy is a novel research strategy for effective eradication of periodontal biofilms that can be utilized for prevention or control of periodontitis. Supported by NIDCR (RO1-DE-14360).

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