Journal of Biological Sciences and Medicine
Journal home page: www.jbscim.com∗ Corresponding author
Email address: prabha0502@rediffmail.com (Dr. Chandra Prabha)
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Review Article
Open Access
Photodynamic Therapy in Periodontics: A Review
Chandra Prabha1,* and Surendra Man Shrestha2
1
Sardar Patel Post Graduate Institute of Dental and Medical Sciences, Lucknow, India
2
Department of Periodontics and Oral Implantology, People’s Dental College and Hospital, Tribhuvan University, Kathmandu, Nepal
Received 20 December 2015; Accepted 28 December 2015; Available online 31 December 2015
Abstract
The use of photodynamic therapy has been encouraged as one of the substitutes to antimicrobial agents for suppressing subgingival species and for treatment of periodontitis. Bacteria loaded with dense biofilms such as those encountered in dental plaque or peri implant surfaces are becoming resistant due to the injudicious use of antibiotics, recently. The present review elucidates the evolution and use of photodynamic therapy with the emphasis on application of photosensitizing dyes and their excitation by visible lights that enables effective killing of periodontopathogens.
Keywords: Microbial resistance; Photodynamic therapy; Photosensitizers; Antibiotics
Introduction
The presence of bacterial species, particularly the periodontopathogenic species on the tooth or root surface is major cause of gingivitis or periodontitis (Kolenbrander 2000; Page et al. 1997; Chen 2001). It is well accepted that mechanical removal of dental biofilms is basis of any adjunctive periodontal therapy as microbial biofilms in the oral cavity involved in etiology of various oral conditions including caries, periodontal and endodontic disease, oral malodour, denture stomatitis, candidiasis and dental implant failures (Singh et al. 2014; Cortelli et al. 2014). In general, it is recognised that the growth of bacteria in biofilms imparts a substantial decrease in susceptibility to antimicrobial agents compared with culture growth in suspension (Soukos and Goodson 2011; Silva et al. 2012; Bjarnsholt et al. 2013; Singh et al. 2014). Therefore, dental plaque, a naturally occurring biofilm (Marsh 2005), display increased resistance to antimicrobial agents (Anderson and Toole 2008; Fux et al. 2005). Currently,
various treatment modalities with least possible side effects have been increasingly searched. Local and systemic administration of antibiotics may lead to resistance, gastrointestinal and other disorders besides patient compliance which is often an added problem (Pallasch 2003; Quirynen et al. 2003; Rodrigues et al. 2004).
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History
The use of photodynamic therapy for inactivating microorganisms was first demonstrated more than 100 years ago, in 1900 when Oscar Rabb (Rabb 1900) reported the lethal effects of acridine hydrochloride and visible light on
Paramecia caudatum. PDT was introduced
in medical therapy in 1904, as the light induced inactivation of cells, microorganisms or molecules (Von Tappeiner and Jodlbauer 1904). In 1913, Friedrich Meyer Betz, the German physician performed the pioneering study which was at first called Photo-radiation Therapy with porphyrins. He tested the effect of hematoporphyrins on his own skin (Moan and Peng 2003). It was John Toth who acknowledged the photodynamic chemical effect of therapy with early clinical argon due lasers and wrote the first white paper renaming the therapy as photodynamic therapy. Thomas Dougherty formed international photodynamic association in 1986. PDT was first approved by drug and food administration in 1999 to treat precancerous skin lesions on face and scalp (Babilas et al. 2005). The photodynamic therapy in curing human infections is based on the conception that an agent which absorbs light known as a photosensitizer, is preferentially taken up by bacteria and subsequently photon of light; a molecule of the photosensitizer is activated by light of the appropriate wavelength in the presence of oxygen to generate oxygen and free radicals that are cytotoxic to microorganisms (De Melo et al. 2013). Because of the primitive molecular nature of singlet oxygen, it is unlikely that microorganisms would develop resistance to the cytotoxic action (Soukos and Goodson 2011). Photodynamic therapy has emerged as an alternative to antimicrobial regimes and mechanical means in eliminating dental plaque of species owing to the ground-breaking work of Professor Michael Wilson
and colleagues (Wilson 1993) at the Eastman Dental Institute, University College London, UK.
Principles
behind
the
photo
dynamic therapy
PDT is based on the principle that a photoactivable substance (photosensitiser) binds to the target cell can be activated by light of suitable wavelength. During this process, free radicals are formed (among them singlet oxygen) which then produce an effect that is toxic to the cells. For bactericidal effect on the cells, the respective photosensitiser needs to have selectivity for prokaryotic cells. Some authors have reported the possibility of lethal photosensitisation of bacteria in vivo
and in vitro (Martinetto et al. 1986; Wilson 1993; De Simone 1999; Bertoloni et al. 1992).
By irradiation with light in visible spectrum, the dye (photosensitizer) is excited to its triplet state, the energy of which is transferred to molecular oxygen. The product formed is highly reactive singlet oxygen capable of reacting with biological systems and destroying them, while only the first excited state with energy of 94 kj/mol (22kcal/mol) above the ground state is important, the second excited state does not react. The bactericidal effect of photo- dynamic therapy can be explained by two potential, but different, mechanisms- one is DNA damage and the other is the damage caused to the cytoplasmic membrane of the bacteria by cytotoxicity (Bertoloni et al. 1992).
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photosensitizer at ground state are activated to highly energized triplet state. The extended life of triplet state enables the interaction of excited photosensitiser that leads to generation of cytotoxic species produced during PDT. Two different pathways are followed by the triplet state photosensitizer involving Type I and Type II reactions-
Type I reactions
Type I reaction involves the hydrogen atom abstraction or electron transfer reaction between the excited state of photosensitizer and an organic substrate molecule of the cells which produces free radical and radical ions. These free radical species are generally highly reactive and interact with endogenous molecular oxygen to produce highly reactive oxygen species such as superoxide, hydroxyl radicals and hydrogen peroxide that harm cell membrane integrity causing irreparable biological damage (Rajesh et al. 2011; Khurana et al. 2014).
Type II reaction
In type II reaction, the triplet state photosensitizer reacts with oxygen to produce an electronically excited singlet oxygen which can interact with a large number of biological substrate as a result of its high chemical reactivity inducing oxidative damage and damaging the cell membrane and cell wall (Foote et al.1991; Sharman et al. 1999). Microorganisms that are killed by singlet oxygen includes viruses, bacteria, protozoa and fungi. Sites of initial cell damage from PDT are closely related to the localization of photosensitizer. Thus, the reaction takes place in limited space, leading to a localized response and making it ideal for application at localized sites without affecting distant molecules, cells or organs (Moan et al. 1991; Peng et al. 1996).
A schematic diagram of mechanisms involved during Type I and Type II reactions in photodynamic therapy is presented in Fig 1.
Photosensitizers
More than 400 compounds are known with photosensitizing properties including dyes, drugs, cosmetics, chemicals and many natural substances (Santamaria et al. 1972). Most of the sensitizers used for medical purposes belong to the following basic structures:
1. Trycyclic dyes with different meso atoms, acridine orange, proflavine, riboflavin, methylene blue, fluorescein, eosin, erythrosine, rose Bengal.
2. Tetrapyrroles, porphyrins and derivatives, chlorophyll, phylloerythrin, phthalocynins. 3. Furocoumarins, psoralen and its
methoxy derivatives- xanthotoxin, bergaptene.
Based on the advantages and characteristics of anti-microbial photodynamic therapy, it has been anticipated that periodontal and peri-implant diseases are potential targets of this novel antimicrobial photo-chemotherapy. Antimicrobial photodynamic therapy is expected to resolve the difficulties and problems of conventional antimicrobial therapy and can work as an adjunctive to conventional mechanical treatments.
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Fig 1. The schematic representation of Type I and Type II reactions in photodynamic therapy (Adapted from Khurana et al. 2014).
After exposure to light, the activated photosensitizer during excited triplet state, tracks either of the two pathways. Type I pathway includes electron- transfer reactions from the photosensitizer triplet state by the participation of a substrate to produce radical ions which reacts with oxygen to produce cytotoxic species. Type II pathway includes energy transfer from the photosensitizer triplet state to the ground state molecular oxygen (triplet) to produce excited state singlet oxygen, which oxidizes biological molecules.
hv= photon energy; PS= photosensitizer.
technical simplicity of the method and the high effectiveness of bacterial killing, the use of antimicrobial photodynamic therapy in the treatment of periodontal and peri-implant diseases has extensively studied. The bactericidal effect of antimicrobial photo-dynamic therapy on periodontal pathogens has been demonstrated in several basic studies. In the early 1990s, Dobson & Wilson showed that low-level helium–neon laser irradiation with toluidine blue O or methylene blue was effective for killing P.
gingivalis, F. nucleatum, A.
actinomycetemcomitans and S. sanguinis. In comparison with other photosensitizers, toluidine blue O and methylene photosensitizers, toluidine blue O and methylene blue prove to be more effective for killing periodontal pathogens in antimicrobial photodynamic therapy (Wilson et al.1993). These authors also revealed that the most effective bactericidal effect was achieved with the combination of toluidine blue O and a helium–neon laser in a supragingival biofilm model study (Wilson M Dobson et al.1995). Bhatti et al. 2002 demonstrated that the optimal
concentration of toluidine blue O to kill P. gingivalis was 12.5 lg⁄ ml with helium–
neon laser irradiation. In addition, they revealed, by transmission electron microscopic examination, that the bactericidal effect of light-activated toluidine blue O against P. gingivalis was caused by disruption of the outer membrane proteins of the bacteria. Additionally, it has been indicated that in the presence of methylene blue, the wavelength of 632.8 nm (helium neon) laser and 665 and 830 nm (diode) have a high bactericidal effect on periodontal pathogens (Chan and Lai 2002).
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against subgingival plaque biofilm that comprised both gram positive and gram negative bacteria. They demonstrated that the bacteria present in deep layers of biofilm were killed by extensive penetration of the photosensitizer into the biofilm following antimicrobial photodynamic therapy. In black pigmented bacteria, the endogenous porphyrins present on bacteria may also act as photosensitizer. It seems that antimicrobial photodynamic therapy not only kills the bacteria but may also lead to the detoxification of endotoxins because it has been demonstrated that LPS stimulate the production of pro-inflammatory cytokines by mono nuclear cells (Kennedy et al. 1990). Consequently, PDT may possibly inactivate endotoxins such as lipopolysaccharides by decreasing their biological activity.
Use of antimicrobial PDT in
treatment of peri-implant disease
It has been proven by the treatment of peri-implantitis that complete eradication of causative bacteria is responsible for development of periodontal disease and disinfection or detoxification of peri implant pockets are essential to achieve effective healing with regeneration of lost bone around the affected implants (Mombelli. 1992, 1987). In one of the examples of in vitro study carried out by Hass et al (1997), the efficacy of antimicrobial PDT was examined in killing bacteria associated with Peri-implantitis such as A. actinomycetemcomitans, P. gingivalis or Provetella intermedia which adhered to titanium plates with different surface characterstics. Plates were incubated with those bacteria and subjected to four different treatments - (i) PDT (toluidine blue O + diode laser) (ii) no treatment (iii) laser light alone (iv) toluidine blue O alone. None of the plates subjected to PDT showed bacterial growth of any of the micro-organisms. While in the other treatment groups, all the three species of
bacteria were detected after treatment. The scanning electron microscopic analysis revealed that antimicrobial PDT led to bacterial cell destruction without damage to the titanium surface.
Adverse effects
PDT has a potential of phototoxic or photoallergic unwanted side effects (Kubler et al. 2002). There can be impairment of benign oral flora which may lead to the overgrowth of single resistant species (Roberts et al. 2002). In order to avoid phototoxic reactions, it is more important to stain selectively the target leaving out the gingival mucosa or tongue. Burning sensation stinging or prickling is common complain experienced during PDT (Lui et al. 1993; Kalker et al 2002). It usually occurs in early part of light exposure. A clinically obvious scar is rarely observed. The histological evidence of scarring is evident (Fink et al 1998). Hyperpigmentation or hypopigmentation can occasionally be seen in treated areas and resolves within six months.
Conclusion
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Conflicts of interest
All contributing authors declare no conflicts of interest.
Acknowledgements
The authors would like to thank the Professors of the People’s Dental College, Tribhuvan University for providing necessary assistance and guidance.
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