JAC Advance Access originally published online on June 27, 2005
Journal of Antimicrobial Chemotherapy 2005 56(2):324-330; doi:10.1093/jac/dki232
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Susceptibility of Streptococcus mutans biofilms to photodynamic therapy: an in vitro study
1 Department of Microbiology and Immunology, Dental School of Piracicaba, State University of Campinas, 901 Limeira Av., Piracicaba, São Paulo, Brazil; 2 Laser Center Department, Dental School of Camilo Castelo Branco University, 584 Carolina Fonseca Street, São Paulo, Brazil; 3 Division of Microbial Diseases, Eastman Dental Institute, UCL, 256 Gray's Inn Road, London WC1X 8LD, UK
Received 8 February 2005; returned 5 May 2005; revised 13 May 2005; accepted 2 June 2005
* Corresponding author. Tel: +44-20-7915-1050; Fax: +44-20-7915-1127; E-mail: J.Pratten{at}eastman.ucl.ac.uk
Objectives: The purpose of this study was to evaluate the antimicrobial effect of toluidine blue O (TBO), in combination with either a helium/neon (HeNe) laser or a light-emitting diode (LED), on the viability and architecture of Streptococcus mutans biofilms.
Methods: Biofilms were grown on hydroxyapatite discs in a constant depth film fermentor fed with artificial saliva that was supplemented with 2% sucrose four times a day, thus producing a typical ‘Stephan pH curve’. Photodynamic therapy was subsequently carried out on biofilms of various ages with light from either the HeNe laser or LED using energy densities of between 49 and 294 J/cm2.
Results: Significant decreases in the viability of S. mutans biofilms were only observed when biofilms were exposed to both TBO and light, when reductions in viability of up to 99.99% were observed with both light sources. Overall, the results showed that the bactericidal effect was light dose-dependent and that older biofilms were less susceptible to photodynamic therapy. Confocal laser scanning microscopy images suggested that lethal photosensitization occurred predominantly in the outermost layers of the biofilms.
Conclusions: Photodynamic therapy may be a useful approach in the treatment of dental plaque-related diseases.
Keywords: dental plaque , caries , Stephan curve , light-emitting diode , biofilm structure
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