Efeito do plasma de baixa temperatura em biofilmes maduros de Streptococcus mutans: estudo in vitro

Abstract

Currently available antimicrobial agents are not effective against mature oral biofilms. This work aimed to evaluate the effect of low temperature argon plasma in the control of mature biofilms formed on human dental enamel. Additionally, the effect of irradiation on this enamel underlying the biofilm was also verified. UA159 Streptococcus mutans biofilms were formed on the human enamel blocks using culture medium supplemented with yeast extract and incubated at 37°C in a 5% CO2 partial atmosphere for five days. On the 5th day, the specimens were submitted to one of the following treatments: ST (no treatment), NaF (0.05% sodium fluoride solution for ten minutes), CHX (chlorhexidine solution 0.12% for ten minutes), ARG1 (argon flux for one minute), ARG5 (argon flux for five minutes), ARG10 (argon flux for ten minutes), PLA1 (plasma for one minute), PLA5 (plasma for five minutes) and PLA10 (plasma for ten minutes). The biofilm was collected to be analyzed for bacterial viability (through counts of CFU and confocal laser microscopy) and the amount of extracellular polysaccharides (colorimetric analysis). Part of the blocks were submitted to the surface microhardness test, Raman spectroscopy and scanning electron microscopy (SEM). Plasma treatment showed a significant reduction in the viability of S. mutans biofilms, with a statistically significant difference between the control groups and the PLA5 and PLA10 test groups. As regards the analysis of the soluble and insoluble polysaccharides of the extracellular matrix, differences were observed only between the chlorhexidine group and the groups of plasma application in the soluble polysaccharides. In Confocal Laser Microscopy, the application of the argon and plasma flux was sufficient to generate visible changes in 2dimensions (2D). The loss of hardness (%SML) was statistically similar between the groups. In Raman microscopy, there was no statistical difference between the groups submitted to the different treatments. SEM showed homogeneous and smooth regions in the enamel. In conclusion, the PBT applied for 5 and 10 minutes was effective in reducing the mature S. mutans biofilm without damaging the surface of the enamel under treated biofilm.