Treatment of Dental Plaque Biofilms using Photodynamic Therapy

BACKGROUND: Photodynamic therapy (PDT) is a treatment modality involving a dye that is activated by exposure to light of a specific wavelength in the presence of oxygen to form oxygen species causing localised damage to microorganisms. AIM: To determine the most effective bactericidal incubation and irradiation times of erythrosine-based PDT, using a tungsten filament lamp, on in vivo- formed dental plaque biofilms. MATERIALS AND METHODS: The study was a two-phase randomised controlled study consisting of in-vitro and in-situ phases. Phase-1 aimed to determine the most appropriate incubation-time using erythrosine(220μM) based-PDT on lactobacillus species grown in-vitro. Phase-2 was conducted on 18-healthy adult participants wearing intraoral appliances with human enamel slabs to collect dental plaque samples in two separate periods for use in arm-1 and arm-2. For phase-2, accumulated dental plaque samples were tested under different experimental conditions; a) Control-1 (No erythrosine, no light); b) Control-2 (+Erythrosine, no light); c) Treatment-1 (+Erythrosine, +15min continuous light); d) Treatment-2 (+Erythrosine, +30sec light pulses for 5- times separated by 1min dark periods). Incubation-times of 15min and 2min were used in arm-1 and arm-2, respectively; as adapted from the previous pilot study and phase-1. Following treatment, percentage reduction of total bacterial counts were compared between the different groups. Additionally, Confocal Laser Scanning Microscopy(CLSM) was used to investigate the effect of PDT on in vivo-formed plaque biofilms. RESULTS: Significant reductions in the percentage of total bacterial counts (~93-95%) of in vivo-formed biofilms were found when using either 2min or 15min incubation-times and applying 15min continuous light. Whereas, when applying fractionated light, there was more cell death when 15min incubation-time was used (~91%) compared with the 2min incubation-time (~64%). CLSM results supported these findings. CONCLUSION: Improving the clinical usefulness of PDT by reducing its overall treatment time seems to be promising and effective in killing in vivo- formed dental plaque biofilms.