In Vitro Efficacy of Ultrasonic Debridement with Adjunctive St. John’s Wort on Multispecies Dental Biofilms

Background and Objectives: The use of St. John’s wort (Hypericum perforatum) in periodontal therapy remains underexplored despite its anti-inflammatory, antimicrobial, and potential osteoregenerative effects. This was the first study aiming to determine the in vitro efficacy of ultrasonic debridement combined with a H. perforatum extract against dental biofilms. Materials and Methods: A multispecies biofilm model comprising Streptococcus mutans, Porphyromonas gingivalis, Fusobacterium nucleatum, and Tannerella forsythia was established on bovine dentin discs. Biofilms were treated with saline solution (control), ultrasonic debridement alone, ultrasonic debridement combined with H. perforatum extract (0.5%), and ultrasonic debridement combined with chlorhexidine (0.12%). Biofilm biomass was quantified with the crystal violet assay, and total viable counts were determined by colony-forming unit (CFU) analysis. Quantitative PCR was used to assess the genomic load of P. gingivalis. Biofilm architecture and bacterial viability were further examined using confocal laser scanning microscopy (CLSM). Results: Ultrasonic debridement combined with H. perforatum extract significantly reduced biofilm biomass compared to saline irrigation (p < 0.001) and ultrasonic debridement alone (p < 0.01). Similar reductions were observed for viable bacterial counts and P. gingivalis genomic load. The antimicrobial effect of the plant extract was comparable to that of chlorhexidine, with only minor differences in efficacy. Confocal microscopy confirmed marked disruption of biofilm architecture and decreased bacterial viability following treatment with the plant extract. Conclusions: Within the limitations of this in vitro model, H. perforatum extract demonstrated measurable antibiofilm activity when used as an adjunct to ultrasonic debridement. These findings provide proof-of-concept evidence supporting the antimicrobial potential of this plant-derived extract under controlled laboratory conditions. Further preclinical studies and well-designed clinical investigations are required to determine its therapeutic relevance in periodontal treatment.