Enhanced removal of Enterococcus faecalis biofilms in the root canal using sodium hypochlorite plus photon-induced photoacoustic streaming: an in vitro study

Abstract

Objective: The purpose of this study was to determine the effectiveness of laser-activated irrigation by photon-induced photoacoustic streaming (PIPS) using Er:YAG laser energy in decontaminating heavily colonized root canal systems in vitro.

Materials and methods: Extracted single-rooted human teeth (n=60) were mechanically and chemically prepared, sterilized, inoculated with Enterococcus faecalis for 3 weeks, and randomly assigned to four groups (n=15): Group I (control, no decontamination), Group II (PIPS+6% NaOCl), Group III (PIPS+saline), and Group IV (6% NaOCl). PIPS settings were all preset to 50 μsec pulse, 20 mJ, 15 Hz, for an average power of 0.3 W. After decontamination, the remaining live microbes from all specimens were collected and recovered via plate counting of the colony-forming units (CFUs). Randomized root canal surfaces were examined with scanning electron microscopy and confocal laser microscopy. Mean variance and Dunnett's t test (post-hoc test) comparisons were used to compare mean scores for the three groups with the control group.

Results: The CFU analysis showed the following measurements (mean±SE): Group I (control), 336.8±1.8; Group II (PIPS+NaOCl), 0.27±0.21; Group III (PIPS+saline), 225.0±21; and Group IV (NaOCl), 46.9±20.29. Group II had significantly lower CFUs than any other groups (p<0.05). Both imaging analyses confirmed levels of remaining bacteria on examined root surfaces.

Conclusions: The use of the PIPS system along with NaOCl showed the most efficient eradication of the bacterial biofilm. It appears that laser-activated irrigation (LAI) utilizing PIPS may enhance the disinfection of the root canal system.

FIG. 1.

A close-up view of the photon-induced photoacoustic streaming (PIPS) tip and its composition, with stripped sheath that helps to propagate the shockwaves in the root canal system (A). Illustration shows how the PIPS is placed in the coronal aspect of access only, not in the canal, and how it delivers the shock waves (B).

FIG. 2.

Scanning electron microscope analysis of root canal surface. (A and B) Group I shows E. faecalis colonies attached to the root canal surface. (C and D) Group II (PIPS+ NaOCl) shows a clean root canal surface. (E and F) Group III (PIPS+saline) shows colonies attached to the root canal surface. (G–I) Group IV (irrigation with NaOCl) shows some colonies and the other image shows no colonies.

FIG. 3.

Confocal scanning laser microscopy analysis of live/dead bacteria on root canal surface. (A) Example of a split-opened tooth sample showing the exposed root canal surface. The box at the mid-root area of the root canal system indicates where the imaging analysis was performed. (B) Negative control sterile tooth samples showing no detectable autofluorescence background. (C–F) Experimental samples with live bacterial biofilms are shown in green fluorescence and the dead bacterial biofilm in red fluorescence. (C) Group I, a control sample with no treatment, the green fluorescence (arrows) indicate live bacteria. (D) A representative sample from Group II (PIPS+NaOCl) showing red fluorescence (arrow) in dentinal tubules indicative of dead bacteria. (E) Group III, (PIPS+saline), the green indicates still live bacteria (marked with arrows) with some red dead bacteria. (F) Group IV, NaOCl with no PIPS, shows the red fluorescence (upper vertical arrow) on the superficial layer with green florescence deeper in dentin tubules (lower horizontal arrow) where NaOCl was unable to penetrate without laser activation.