Effect of photo-activated disinfection on endodontic pathogens ex vivo.

AIM: To test the hypothesis that photo-activated disinfection (PAD) has a bactericidal effect on pathogens inoculated in root canals, with emphasis on biofilm formation/destruction. METHODOLOGY: Root canals of extracted teeth (n = 38) were prepared (size 30, 0.10 taper), autoclaved, divided into three groups and two negative controls inoculated (Streptococcus anginosus, Enterococcus faecalis or Fusobacterium nucleatum) and treated (PAD, laser, dye or positive control) according to a cross-sectional design. Resultant colony-forming unit counts were associated with observations of cell structural changes using environmental scanning electron microscopy (ESEM) on inoculated dentinal surfaces (n = 22, two controls) before (1, 2 and 6 days of incubation) and after treatment with PAD. RESULTS: Treatment of root canals with PAD (15 J) caused a significant reduction of the bacterial load, resulting in a 93.8% kill of S. anginosus (P < 0.0001), a 88.4% kill of E. faecalis (P < 0.05) and a 98.5% kill of F. nucleatum (P < 0.0001), but no sterilization. Laser alone had no significant effect on the load nor did the dye without laser. The ESEM experiment showed that individual cells or monolayers were easily eliminated with PAD. But when biofilms were present (2 and 6 days for E. faecalis, 6 days for S. anginosus), bacterial eradication was substantially reduced in deep layers. CONCLUSIONS: Photo-activated disinfection is not an alternative but a possible supplement to the existing protocols for root canal disinfection as the interaction between light (diode laser) and associated dye (TBO) provides a broad-spectrum effect. Some endodontic pathogens that grow as single-species biofilms, however, are difficult to eradicate.

Bactericidal effect of Nd:YAG laser irradiation on some endodontic pathogens ex vivo.

AIM: To define the role of neodymium:yttrium-aluminum-garnet (Nd:YAG) lasers in root canal disinfection along with a minimally invasive treatment concept. METHODOLOGY: The hypothesis was tested ex vivo that Nd:YAG laser irradiation has a bactericidal effect on endodontic pathogens inoculated in root canals. Resultant colony-forming unit counts were associated with observations of bacterial cell structural changes using conventional scanning electron microscopy (CSEM) and environmental scanning electron microscopy (ESEM) on inoculated dentine surfaces, following indirect and direct Nd:YAG laser irradiation, respectively. RESULTS: The Nd:YAG laser irradiation (1.5 W, 15 Hz, four times for 5 s) of Enterococcus faecalis inoculated canals resulted in a significant reduction (P < 0.05, Wilcoxon signed rank test) of the bacterial load, meaning a 99.7% kill, but no sterilization. The CSEM procedure verified that the extent of radiation damage was in line with the total amount of laser energy applied. After 2 h of incubation and three cycles of indirect laser treatment (i.e. through a 1-mm-thick dentine disc), no morphologically intact bacteria of Actinomyces naeslundii or Streptococcus anginosus were discernible. However, when micro-colonies of S. anginosus and specially biofilms of E. faecalis were present after 2 days, the in situ experiment using ESEM and direct laser treatment showed that bacterial eradication was reduced in deep layers. CONCLUSIONS: The Nd:YAG laser irradiation is not an alternative but a possible supplement to existing protocols for canal disinfection as the properties of laser light may allow a bactericidal effect beyond 1 mm of dentine. Endodontic pathogens that grow as biofilms, however, are difficult to eradicate even upon direct laser exposure.