Biofilm Control Strategies in Dental Health - Antibiofilm Agents: From Diagnosis to Treatment and Prevention - page 292

Fig. 3 Mechanism of
photodynamic therapy. A
photosensitizer is taken up
by bacteria and gets
activated by the appropriate
wavelength. The
photosensitizer transfers the
energy to molecular oxygen
and generates free radicals
that will kill bacteria that
have incorporated the
photosensitizer (Adapted
from Soukos and Goodson
( 2011 ) with permissions)
5.2 Photodynamic Therapy
Photodynamic therapy refers to the use of a chemical compound called a photo-
sensitizer, which absorbs light and is preferentially taken up by bacteria and
subsequently activated by light of the appropriate wavelength in the presence of
oxygen to generate oxygen free radicals that are toxic to microorganisms (Soukos
and Goodson 2011 ) (Fig. 3 ). One of the advantages of using photodynamic therapy
is that, because of the molecular nature of the oxygen free radicals, it is unlikely that
microorganisms will develop resistance to the cytotoxic action of these compounds.
Photodynamic therapy has emerged as an alternative to antimicrobial regimes
designed to complement mechanical methods in eliminating pathogenic compo-
nents of the biofilm. Unlike mechanical methods that do not discriminate which
organisms are removed, photodynamic therapy targets the organisms that take up
the phothosensitizer but not the rest of the biofilm, thus allowing for a more targeted
control of the oral biofilm. For a thorough review of photosensitizers and their
clinical use in oral health, I would address the reader to the review by Soukos and
Goodson on the use of photodynamic therapy to control oral biofilms in disease
(Soukos and Goodson 2011 ).
Several laboratories have demonstrated the susceptibility of cariogenic bacteria,
both in suspension and biofilms, to photodynamic therapy using toluidine blue O or
disulfonated aluminum phthalocyanine (AlPcS2) as photosensitizers. Toluidine
blue O-induced photodynamic therapy was able to achieve a 10-fold reduction of
S. mutans when the organism was embedded in a collagen matrix mimicking
carious dentin or present in decayed teeth (Williams et al. 2004 ). Moreover, the
combined application of photodynamic therapy and casein phosphopeptide-
amorphous calcium phosphate, a compound with established remineralization