Antimicrobial efficacy of sodium hypochlorite and hyper-pure chlorine dioxide in the depth of dentin tubules in vitro

Abstract

Objectives: The study aimed to compare the antibacterial effect of a novel disinfectant, hyper-pure chlorine dioxide (hClO₂) to sodium hypochlorite (NaOCl) in various depths of dentin tubules.

Materials and methods: The distal root of the extracted lower molars was infected artificially with Enterococcus faecalis. The control group was rinsed with saline, and the test groups were irrigated with either 5% NaOCl or 0.12% hClO₂. The longitudinally split teeth were stained by viability stain. The coronal third of the root was scanned with a confocal laser scanning microscope. The fluorescent intensities were measured, and the percentage of dead bacteria was calculated at depths up to 950 μm along the dentin tubules. The effect of penetration depth, irrigants, and their interaction on antimicrobial efficacy was determined by the linear mixed model.

Results: The percentage of dead bacteria was higher both in the NaOCl (45.1 ± 2.3%, p < 0.01) and in the hClO₂ (44.6 ± 3.8%, p < 0.01) irrigant groups compared to saline (23 ± 4.5%); however, there was no difference between them. The percentage of killed bacteria was not correlated with the depths in any group (p = 0.633).

Conclusions: Our results suggest that the functional penetration depth of NaOCl is at least 2-3 times more than published to date. There is no difference in disinfection effectiveness along the dentin tubules between NaOCl and hClO₂ until at least the measured 950 μm. However, both were only able to eradicate the intratubular bacteria partially.

Clinical relevance: Hyper-pure ClO₂ could be used as an alternative or final adjuvant irrigant in endodontic treatment.

Keywords: Antimicrobial effectiveness; Chlorine dioxide; Confocal laser scanning microscopy; Disinfection; Enterococcus faecalis; Sodium hypochlorite.

Fig. 1

The distance intervals selected from the root canal surface in a confocal laser scanning microscopy image. Live bacteria are shown on the left in green after being stained by SYTO9. Dead bacteria are shown on the right in red after being stained by Propidium Iodide (PI). A white line outlines the root canal border

Fig. 2

Representative confocal laser scanning microscopy images of live and dead bacterial staining in the investigated groups. Samples in the first absolute control group (A and B) were kept sterile. Samples in the second absolute group (C and D) were inoculated but not irrigated. Groups with irrigation were a saline group (E and F), a NaOCl group (G and H), and a hClO₂ (I and J). The upper row (A, C, E, G, I) shows SYTO9 staining of live bacteria, fluoresced in green. The lower row (B, D, F, H, J) shows Propidium Iodide (PI) staining of dead bacteria fluoresced in red. The white line outlines the root canal border

Fig. 3

The penetration depth of irrigant solutions. Significance was not calculated because the slope of the linear equations showed that the ‘depth’ factor had no influence on the % of dead bacteria

Fig. 4

 A. The relationship between the penetration depth of irrigants measured from the root canal surface and the percentage of killed bacteria.B. The mean effect of irrigants on the percentage of dead bacteria. Error bars indicate 95% confidence intervals. Slopes are almost parallel to the x-axis, indicating an insignificant effect of “depth”. The significant difference between the test (NaOCl and hClO₂) and saline groups are indicated by an asterisk. * p < 0.01