Aims The aim of this study was to investigate the effects of tea catechin epigallocatechin gallate (EGCg) on established biofilms and biofilm formation by Porphyromonas gingivalis, a major pathogen of periodontal disease. Methods and Results Biofilm cell survival was measured using adenosine triphosphate (ATP) bioluminescence. In the presence of EGCg, the ATP level in cells of established biofilms was significantly decreased compared to the controls (P < 0·0001). Transmission electron microscopy revealed that EGCg damaged the cell membrane and cell wall of P. gingivalis. Confocal laser‐scanning microscopy revealed that the proportion of dead cells was higher in biofilms treated with EGCg. Moreover, the effects of subminimal inhibitory concentrations (MICs) of EGCg on P. gingivalis biofilm formation were dose‐dependent (P < 0·0001). Conclusion Our results suggest that EGCg destroys established P. gingivalis biofilms and inhibits biofilm formation. Significance and Impact of the Study Development of chemical control agents against oral biofilms is necessary, because oral biofilms can be only removed using mechanical debridement. This article indicates that EGCg may represent a novel antibiofilm agent that prevents infections involving bacterial biofilms such as periodontitis.

Root canal treatment is performed to treat apical periodontitis, and various procedures and techniques are currently used. Although animal models have been used in the developmental research of root canal treatment, little of this research has used small animals such as rats, because of their small size. In this study, root canal treatment was performed on the rat mandibular first molar, which had four root canals, using a microscope, and the therapeutic effect was evaluated bacteriologically, radiologically and histopathologically. By performing root canal treatment, the level of bacteria in the mesial root of the treated teeth was reduced by 75% compared with the control. Additionally, the volume of the periapical lesions of the treated teeth as measured by micro-computed tomography decreased significantly 2 weeks after the root canal treatment when compared with the control. Histological evidence of healing was observed in the treatment group 8 weeks after root canal treatment. These results suggest that a root canal treatment model using rats can be used in developmental research for novel methods of root canal treatment.

Antibiotic resistance of biofilm-grown bacteria contributes to chronic infections, such as marginal and periapical periodontitis, which are strongly associated with Porphyromonas gingivalis . Concurrent azithromycin (AZM) administration and mechanical debridement improve the clinical parameters of periodontal tissue in situ . We examined the in vitro efficacy of AZM against P. gingivalis biofilms. The susceptibilities of adherent P. gingivalis strains 381, HW24D1, 6/26, and W83 to AZM, erythromycin (ERY), ampicillin (AMP), ofloxacin (OFX), and gentamicin (GEN) were investigated using a static model. The optical densities of adherent P. gingivalis cells were significantly decreased by using AZM and ERY at sub-MIC levels compared with those of the controls in all the strains tested, except for the effect of ERY on strain W83. AMP and OFX inhibited P. gingivalis adherent cells at levels over their MICs, and GEN showed no inhibition in the static model. The effects of AZM and ERY against biofilm cells were investigated using a flow cell model. The ATP levels of P. gingivalis biofilms were significantly decreased by AZM at concentrations below the sub-MICs; however, ERY was not effective for inhibition of P. gingivalis biofilm cells at their sub-MICs. Furthermore, decreased density of P. gingivalis biofilms was observed three-dimensionally with sub-MIC AZM, using confocal laser scanning microscopy. These findings suggest that AZM is effective against P. gingivalis biofilms at sub-MIC levels and could have future clinical application for oral biofilm infections, such as chronic marginal and periapical periodontitis.