Bactericidal effect of Nd:YAG laser irradiation on some endodontic pathogens ex vivo.
OBJECTIVE
To define the role of neodymium:yttrium-aluminum-garnet (Nd:YAG) lasers in root canal disinfection along with a minimally invasive treatment concept.


METHODS
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.
Bergmans
L
L
Department of Conservative Dentistry, Leuven BIOMAT Research Cluster, Leuven, Belgium. lars.bergmans@med.kuleuven.be
Moisiadis
P
P
Teughels
W
W
Van Meerbeek
B
B
Quirynen
M
M
Lambrechts
P
P
D000190:Actinomyces / Q000528:radiation effects; D000538:Aluminum Silicates; D018441:Biofilms / Q000528:radiation effects; D015169:Colony Count, Microbial; D003430:Cross-Sectional Studies; D003786:Dental Pulp Cavity / Q000382:microbiology; D003788:Dental Pulp Diseases / Q000382:microbiology*; D003804:Dentin / Q000382:microbiology; D004203:Disinfection / Q000379:methods; D013293:Enterococcus faecalis / Q000528:radiation effects; D006094:Gram-Positive Bacteria / Q000528:radiation effects*; D006801:Humans; D053685:Laser Therapy; D008855:Microscopy, Electron, Scanning; D009354:Neodymium; D034366:Streptococcus anginosus / Q000528:radiation effects; D013997:Time Factors; D015019:Yttrium
D000538:Aluminum Silicates; D009354:Neodymium; D015019:Yttrium