ABSTRACT
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.
Subject(s)
Biofilms/radiation effects , Dental Pulp Cavity/radiation effects , Disinfection/methods , Laser Therapy/methods , Dental Pulp Cavity/microbiology , Disinfection/instrumentation , Enterococcus faecalis/isolation & purification , Enterococcus faecalis/radiation effects , Fusobacterium nucleatum/isolation & purification , Fusobacterium nucleatum/radiation effects , Humans , Streptococcus anginosus/isolation & purification , Streptococcus anginosus/radiation effectsABSTRACT
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.
Subject(s)
Dental Pulp Diseases/microbiology , Gram-Positive Bacteria/radiation effects , Laser Therapy , Actinomyces/radiation effects , Aluminum Silicates , Biofilms/radiation effects , Colony Count, Microbial , Cross-Sectional Studies , Dental Pulp Cavity/microbiology , Dentin/microbiology , Disinfection/methods , Enterococcus faecalis/radiation effects , Humans , Microscopy, Electron, Scanning , Neodymium , Streptococcus anginosus/radiation effects , Time Factors , YttriumABSTRACT
Throughout the years, various methods have been adopted to investigate bacteria involved in root canal infection and apical periodontitis. This paper reviews the most commonly used microscopic techniques and discusses their possibilities, limitations and sample preparation. In particular, a recently developed variant of scanning electron microscope (SEM), referred to as environmental SEM (ESEM), is highlighted due to its potential impact across the diverse field of biomaterials research. The performance of this ESEM technique for bacterial observation of endodontic pathogens was illustrated by a practical approach. The paper concludes with a discussion on the possible use of ESEM for testing endodontic treatment modalities under environmental conditions in situ.