Chemical disinfection of oral biofilms often leaves biofilm structures intact. This study aimed to examine whether the residual structure promotes secondary bacterial adhesion. Streptococcus mutans biofilms generated on resin-composite disks in a rotating disc reactor were disinfected completely with 70% isopropyl alcohol, and were again cultured in the same reactor after resupplying with the same bacterial solution. Specimens were subjected to fluorescence confocal laser scanning microscopy, viable cell counts and PCR-Invader assay in order to observe and quantify secondarily adhered cells. Fluorescence microscopic analysis, particularly after longitudinal cryosectioning, demonstrated stratified patterns of viable cells on the disinfected biofilm structure. Viable cell counts of test specimens were significantly higher than those of controls, and increased according to the amount of residual structure and culture period. Linear regression analysis exhibited a high correlation between viable and total cell counts. It was concluded that disinfected biofilm structures favored secondary bacterial adhesion.

The mouthrinses tested showed different levels of biofilm penetration. The essential oil rinse was superior to other rinses by all three of the in vitro measurements performed.

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：The aims of this study were to evaluate the penetration ability and antimicrobial efficacy of an alcohol-free mouth rinse (Listerine ® Natural Care; N), newly developed to reduce the irritative property and improve the mouthfeel of Listerine ® , using artificially developed Streptococcus mutans biofilms. As test mouth rinses, Listerine ® Zero (Z), Listerine ® Fresh Mint (F) and an alcohol-free chlorhexidine gluconate-containing mouth rinse (CHG) were investigated. S. mutans biofilms were grown on glass-based dishes for 24 h under