Efficient Sterilization for Infected-dentin and Biofilm Models with Peroxynitric Acid

Objectives: Peroxynitric acid (PNA: HOONO₂) was recently found to be a main substance of plasma sterilization. We are now advancing PNA-sterilization as a novel approach to non-invasive caries treatment. In this presentation, high performance of PNA-sterilization is demonstrated using infected-dentin and biofilm models.
Methods: Chemicals; PNA solution was synthesized by mixing hydrogen peroxide and nitrous acid, and the pH was adjusted to 3.5 by adding citrate buffer just before use. For controls buffer solution only and inactivated PNA solution were prepared.
Infected-dentin model; Root of extracted human teeth was decalcified with lactic acid (pH 2.3) for 2 days. The root was autoclaved and immersed in bacteria suspension (10^7-8 CFU/mL) of Streptococcus mutans (ATCC25175) in culture medium for 7 days.
Sterilization test: Infected-dentin model was treated with each solution for 10 seconds (n = 7). Before and after the treatment, bacteria were recovered from each sample using sterilized round burs (φ = 0.8 mm). The recovered dentin was suspended in BHI medium to determine the CFU/bur.
The results were statistically analyzed with Wilcoxon signed-rank test (α = 0.01).
Biofilm model test: S. mutans alone or its mixture with Candida albicans were cultured to form biofilm. Each solution was applied on the biofilm for 30 seconds. Metabolic activity of the viable bacteria in the biofilm were monitored using a REDOX indicator.
Results: In the infected-dentin model, the count of viable bacteria was 10^5-6 CFU/bur before the application of solutions. The application of PNA statistically decreased the count to detection limit (< 2.5 CFU/bur), while the application of control solutions did not change the counts.
In the biofilm model, PNA revealed a high-performance of sterilization capability.
Conclusions: PNA demonstrated a high efficiency to sterilize both infected-dentin and biofilm models. Therefore, PNA application is considered to be a promising non-invasive way to treat caries.