Streptococcus Species Biofilm is Inhibited by Cold Atmospheric Plasma Pressure.

Objectives: Less invasive methods for caries treatment are needed to avoid unnecessary loss of dental tissue. Low temperature atmospheric pressure plasma (LTAPP) shows promising antimicrobial activity. The hypothesis is that LTAPP might be an effective and non-invasive tool for the disinfection of carious cavities previous to restoration procedures. The aim of this study is to evaluate the application of LTAPP in the control of multispecies cariogenic biofilms.
Methods: The effective parameters of LTAPP against polymicrobial biofilms composed by Streptococcus gordonii, Streptococcus mutans and Streptococcus sanguinis were established. The microorganisms were activated and incubated at 37 °C for 48h, 5% CO₂. Standardized suspensions were prepared (10⁷ cells/ml) using a spectrophotometer. These suspensions were diluted to 8x10⁶ cells/ml. Equal volumes of standardized suspensions were mixed up. Aliquots of 40 μL of the multi-species inoculum and 160 μl of TSB broth supplemented with 1% sucrose were added to the wells of microdilution plates. Plates were incubated (37°C, 5% CO₂, 48h). After 24h, the biofilm was washed with sterile saline and the culture medium was refreshed. Subsequently, multispecies biofilms were exposed to LTAPP and chlorhexidine digluconate (0.12%) for 1, 3, 5 and 7 min. The number of viable cells were determined by plating method. LTAPP was generated by helium (99.5% purity, 2.0SLM flow rate) and electric discharge (32kHz signal frequency, 1.0W mean power). Non-exposed control was included. Data were analyzed by percentage of reduction/ANOVA.



Results: Reductions (%) in total viable cells counts (86.0±20.0, 79.0±26.0, 87.0±21.0 and 82.0±19.0) were observed after exposure for 1, 3, 5 and 7 min with LTAPP. Additionally, treatment with chlorhexidine provided significant reductions (94.0±15, 99.0±14,99.0±13.0 and 99.0±14.0) after treatment for 1, 3, 5 and 7 min, respectively. Statistically significative reduction in the number of CFU/biofilm was detected (P=0,0001).





Conclusions: Both LTAPP and chlorhexidine showed significant inhibitory effect on cariogenic multispecies biofilms.