Abstract
Introduction: Photodynamic inactivation of bacteria (PIB) may be a supportive antimicrobial approach for use in endodontics, but sufficient activation of photosensitizers (PS) in root canals is a critical point. Therefore, aim of this study was to evaluate the ability of PS absorbing blue (TMPyP) or red light (Methylene Blue; MB) for light activation through human dental hard and simulated surrounding tissue to inactivate root canal bacteria.Methods: A tooth model was fabricated with a human premolar and two molars in an acrylic resin bloc simulating the optical properties of a porcine jaw. The distal root canal of the first molar was enlarged to insert a glass tube (external diameter 2 mm) containing PS and stationary-phase Enterococcus faecalis. Both PS (10 μM) were irradiated for 120 s with BlueV (20 mW/cm2; λem = 400–460 nm) or PDT 1200L (37.8 mW/cm2; λem = 570–680 nm; both: Waldmann Medizintechnik), respectively. Irradiation parameters ensured identical numbers of photons absorbed by each PS. Three setups were chosen: irradiating the glass pipette only (G), the glass pipette inside the single tooth without (GT) and with (GTM) simulated surrounding tissues. Colony forming units (CFU) were evaluated. Transmission measurements of the buccal halves of hemisected mandibular first molars were performed by means of a photospectrometer.Results: PIB with both PS led to reduction by ≥ 5 log10 of E. faecalis CFU for each setup. From transmission measurements, a threshold wavelength λth for allowing an amount of light transmission for sufficient activation of PS was determined to be 430 nm.Conclusion: This study can be seen as proof of principle that light activation of given intra-canal PS from outside a tooth may be possible at wavelengths ≥ 430 nm, facilitating clinical application of PIB in endodontics.
Highlights
Photodynamic inactivation of bacteria (PIB) may be a supportive antimicrobial approach for use in endodontics, but sufficient activation of photosensitizers (PS) in root canals is a critical point
The PS molecule is converted into an excited state from where there are two reaction mechanisms: type I mechanism describes the transfer of charge to a substrate or molecular oxygen resulting in reactive oxygen species (ROS) such as hydroxyl radicals and superoxide ions
PIB with TMPyP inactivated E. faecalis by 6.5 log10 as compared to corresponding untreated control PS–L, regardless whether the glass tube only (G) was irradiated or the glass tube inserted in the single tooth (GT) or the whole tooth model (GTM; Figure 3A)
Summary
Photodynamic inactivation of bacteria (PIB) may be a supportive antimicrobial approach for use in endodontics, but sufficient activation of photosensitizers (PS) in root canals is a critical point. PIB Light-Activation through Dental Tissues dressings are used for enhancing disinfection and dissolution of pulpal soft tissue or suppressing inflammation, e.g., based on calcium hydroxide (Mohammadi et al, 2012) or as combined corticosteroid-antibiotic pastes (e.g., Ledermix, Odontopaste; (Athanassiadis et al, 2007) Most of these substances exhibit evident disadvantages, such as potential development of resistances in bacteria (Arias and Murray, 2009), risk of drug hypersensitivity (Kawashima et al, 2009), or biocompatibility problems (Schmalz, 2014), vague duration of action (Hecker et al, 2013), inactivation by organic compounds (Abouassi et al, 2014), or esthetic limitations due to staining of teeth (Kim et al, 2000). Type II mechanism describes the direct transfer of energy to molecular oxygen with generation of the highly reactive singlet oxygen (1O2;Wainwright, 1998; Schweitzer and Schmidt, 2003)
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