title: Sensitivity of oral bacteria to 254 nm ultraviolet light.
abstract: OBJECTIVE
  To explore the sensitivity of bacteria commonly found in root canals to 254 nm ultraviolet (UV) light, either as individual cells or as participants of a bacterial multilayer.
  
  
  METHODS
  The sensitivity of oral bacteria, as individual cells, to UV light was tested by subjecting plates streaked with bacteria to 254 nm UV, at a fluence of 1-20 mJ cm(-2). An experimental model was designed to produce a bacterial multilayer and to study absorption of UV light by bacteria in an outer layer and its effect on the elimination of bacteria in the inner layer.
  
  
  RESULTS
  Direct exposure to relatively low doses of UV light (2-7 mJ cm(-2)) effectively eliminated all bacterial strains tested. Furthermore, an Enterococcus faecalis strain, partially resistant to a 24 h exposure to calcium hydroxide, was effectively eliminated within several seconds of exposure to UV light (P < 0.001). UV was absorbed by a multilayer of bacteria. When 4 bacterial cells microm(-2) were present in the light path, the UV light dose had to be increased by a factor of x10 to achieve 100% elimination of the bacteria in an inner layer.
  
  
  CONCLUSIONS
  The application of UV light to eliminate endodontic pathogens may be possible. Nevertheless, its absorbance by outer layers of bacteria should be considered and the UV light dose adapted accordingly.
authors.affiliation: Department of Oral Biology, The Goldschleger School of Dental Medicine, Tel Aviv University, Tel Aviv, Israel. metzger@post.tau.ac.il
authors.forename: Z
authors.initials: Z
authors.lastname: Metzger
authors.forename: M
authors.initials: M
authors.lastname: Dotan
authors.forename: H
authors.initials: H
authors.lastname: Better
authors.forename: I
authors.initials: I
authors.lastname: Abramovitz
mesh_terms: D000042:Absorption; D001419:Bacteria / Q000528:radiation effects*; D002126:Calcium Hydroxide / Q000494:pharmacology; D015169:Colony Count, Microbial; D003786:Dental Pulp Cavity / Q000382:microbiology*; D013293:Enterococcus faecalis / Q000187:drug effects / Q000528:radiation effects; D016967:Fusobacterium nucleatum / Q000528:radiation effects; D007778:Lactobacillus / Q000528:radiation effects; D016966:Porphyromonas gingivalis / Q000528:radiation effects; D012387:Root Canal Filling Materials / Q000494:pharmacology; D013298:Streptococcus sanguis / Q000528:radiation effects; D014466:Ultraviolet Rays
chemical_list: D012387:Root Canal Filling Materials; D002126:Calcium Hydroxide