The Effects of Photodynamic Therapy in Oral Biofilms - Antibiofilm Agents: From Diagnosis to Treatment and Prevention - page 438

viral diseases, the lack of commitment of some patients to complete the treatment
and the widespread use of antibiotics in animal feed only exacerbate the problem by
repeatedly selecting more resistant strains (Harrison and Svec 1998 ). Worldwide,
the inexorable growth of multiresistant bacteria has resulted in a great effort by
researchers to find alternative therapies for which microorganisms do not easily
develop resistance (Dai et al. 2009 ).
Reports of photodynamic therapy (PDT) date from the time of the Egyptian
civilisation through ingestion of plants (containing psoralens, furo [3,2-g] coumarin
or 6-hydroxy-5-benzofuran-acrylic acid δ -lactone) and sunlight to treat diseases
such as vitiligo (Simplicio et al. 2002 ) and psoriasis. Ancient documents found in
India and China also describe the use of PDT (Simplicio et al. 2002 ; Ochsner
1997a ). In 1900, Oscar Raab, Ludwig-Maximillian University, Munich, described
the lethal action of the dye acridine and light on Paramecium , a unicellular
organism that causes malaria (Sternberg and Dolphin 1998 ;K¨bler et al. 2001 ;
Pervaiz 2001 ; Malik et al. 2010 ).
The German physician Friedrich Meyer-Betz pioneered the development of
studies on phototherapy irradiation (PRT) with porphyrin in 1913. He observed
that skin inoculation with 200 mg haematoporphyrin had no effect, but when the
inoculated skin was exposed to light, the subjects developed photosensitivity that
lasted for a few months (Simplicio et al. 2002 ).
John Toth, product manager of Medical Devices Corp Cooper/Cooper
Lasersonics, confirmed the chemical effect of therapy using photosensitisers and
an argon laser; he wrote the first study to rename this therapy photodynamic
therapy. Currently, photodynamic therapy is used to treat various cancers and
infectious diseases (Dougherty and Marcus 1992 ; Lui and Anderson 1992 ; Ackroyd
et al. 2001 ).
2 Photodynamic Therapy
Photodynamic therapy is an effective alternative treatment for localised microbial
infections but also for oral ulcers and chronic infections (Wainwright and Crossley
2004 ). In dentistry, there is ongoing research into the treatment of periodontal
disease with photodynamic therapy as a beneficial method and complementary
treatment to conventional methods (Walker 1996 ; Manch-Citron et al. 2000 ;
Feres et al. 2002 ; Malik et al. 2010 ). Photodynamic therapy has emerged as a
new non-invasive therapeutic method to treat infections caused by various bacteria,
fungi and viruses (Jori et al. 2006 ).
Combining the use of a photosensitising substance and light to antibiotic treat-
ment is referred to as antimicrobial photodynamic therapy (APT), as illustrated in
Fig. 1 . This therapeutic modality illustrates an important fact: without repeated
applications, there is no selective pressure for resistant bacteria, so microbial
resistance is not developed (Wainwright and Crossley 2004 ). Due to the