Effect of Nonthermal Atmospheric Plasma on S. mutans Biofilms

Abstract

Aims: Verify the effect of non-thermal atmospheric plasma on biofilms under different conditions. Study Design:  In vitro laboratory, Experimental, Randomized. Place and Duration of Study: Federal University of Ceará, 2 years. Methodology: Biofilms of Streptococcus mutans UA159 were formed on human enamel slabs, submitted to episodes of sucrose exposure for 5 days. The specimens were randomly divided in 2 different experiments; one submitted to daily plasma treatment of biofilms and other submitted to one-time treatment of the biofilms after 5 days. The samples were divided in nine groups as follows: NT (No treatment), CHX (chlorhexidine 0.12%), NaF (sodium fluoride 0.05%), ARG1 (1 minute argon flow), ARG5 (5 minutes argon flow), ARG10 (10 minutes argon flow), PLA1 (1 minute plasma jet), PLA5 (5 minutes plasma jet), PLA10 (10 minutes plasma jet). Results: The groups CHX, ARG 1, ARG 5, ARG 10, PLA1, PLA5, PLA10 significantly reduced the bacterial viability in the daily treated biofilms (p <0.001). The same results were only observed in mature biofilms submitted to one time treatment only for the groups PLA5 and PLA10 (p <0.005). The results showed a reduction in soluble extracellular polysaccharides in CHX, ARG and PLA dairy treatments. The percentage of the superficial hardness loss demonstrated a significant reduction only for the CHX group (p <0.05) in daily treatment. In addition, no statistically significant differences were found between the groups before (p = 0.6978) or after treatments (p = 0.8904) in the mineral profile of the specimens by Raman Spectroscopy. Also, scanning electron microscopy showed no difference in the topographic of the treated enamel surface. Conclusion: Dairy ARG or PLA treatments were effective in reducing the number of viable bacteria and the concentration of water-soluble polysaccharide in the S. mutans biofilms.  For the one-time treatment of mature biofilms only PLA5 and PLA10 treatments were effective. No alteration in the surface of the enamel was observed on tested conditions.