Photodynamic therapy in the
control of oral biofilms
NIKOLAOS S. SOUKOS
& J. MAX GOODSON
Periodontology 2000, Vol. 55, 2011, 143–166
Printed in Singapore. All rights reserved
Microbial
biofilms in the oral cavity are involved in the etiology of various oral
conditions, including caries, periodontal and endodontic diseases, oral malodor,
denture stomatitis, candidiasis and dental implant failures. It is generally
recognized that the growth of bacteria in biofilms imparts a substantial decrease
in susceptibility to antimicrobial agents compared with cultures grown in
suspension (39). It is therefore not surprising that bacteria growing in dental
plaque, a naturally occurring biofilm (127), display increased resistance to
antimicrobial agents (4, 67). Current treatment techniques involve either periodic
mechanical disruption of oral microbial biofilms or maintaining therapeutic
concentrations of antimicrobials in the oral cavity, both of which are fraught
with limitations. The development of alternative antibacterial therapeutic
strategies therefore becomes important in the evolution of methods to control
microbial growth in the oral cavity. The use of photodynamic therapy for
inactivating
microorganisms
was first demonstrated more than 100 years ago, when Oscar Raab (164) reported
the lethal effect of acridine hydrochloride and visible light on Paramecia
caudatum. Photodynamic therapy for human
infections is based on the concept that an agent (a photosensitizer) which
absorbs light can be
preferentially
taken up by bacteria and subsequently activated by light of the appropriate
wavelength (Fig. 1) in the presence of oxygen to generate singlet oxygen and
free radicals that are cytotoxic to microorganisms (Fig. 2). Because of the
primitive molecular nature of singlet oxygen, it is unlikely that microorganisms
would develop resistance to the cytotoxic action. Photodynamic therapy has
emerged as an alternative to antimicrobial regimes and mechanical means in
eliminating dental plaque species as a result of the pioneering work of
Professor Michael Wilson and colleagues (223) at the Eastman Dental Institute,
University College London, UK. In this review, we propose to provide an
overview of photodynamic therapy with emphasis on its current status as an
antimicrobial therapy to control oral bacteria, and review the progress that
has been made in the last 15 years concerning the applications of photodynamic
therapy for targeting biofilm-associated oral infections. Problems and
challenges that have arisen will be identified and discussed. Finally, new
frontiers of antimicrobial photodynamic therapy research will be introduced,
including targeting strategies that may open new opportunities for the maintenance
of bacterial homeostasis in dental plaque, thereby providing the opportunity
for more effective disease prevention and control.
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