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An in-vitro study of the sterilization of titanium dental implants using low intensity UV-radiation
Dental Materials (2005) 21, 756–760
www.intl.elsevierhealth.com/journals/dema
An in-vitro study of the sterilization of titanium dental implants using low intensity UV-radiation D. Jason Rileya,1, Valter Bavastrelloa, Ugo Covanib, Antonio Baroneb, Claudio Nicolinia,b,* a
Fondazione Elba, Via delle Testuggini, Roma, Italy Nanoworld Institute and Biophysics Division, Department of Biophysical M & O Sciences and Technologies, University of Genoa, Corso Europa 30, 16132 Genoa, Italy
b
Received 1 November 2004; accepted 20 January 2005
KEYWORDS Bacteria; Dental implant; Osseointegration; Titanium oxide; Sterilization
Summary Objectives. Commercial titanium dental implants are coated with nanostructured TiO2. The aim of the research reported in this paper was to assess whether the TiO2 at the surface of a dental implant is sufficiently photoactive to eradicate bacteria when illumined with low intensity light. Methods. The photoactivity of dental implants was established by studies of the photoenhanced decomposition of Rhodamine B. In vitro studies to establish the influence of irradiating with UV light an implant that is immersed in a solution containing Escherichia Coli were performed. Results. It was demonstrated that under low UV intensity irradiation, 49 mW cmK2, bacteria are killed at a rate of approximately 650 million per cm2 of implant per minute. Significance. The results indicate that illumination of dental implants with UV light may be a suitable treatment for periimplantitis. Q 2005 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
Introduction Dental implants are today successfully used in dentistry for oral rehabilitation supporting mobile or fixed prostheses. Beside undisturbed osseointegration and an adequate prosthetic design,
* Corresponding author. Tel.: C39 010 35338217; fax: C39 010 35338215. E-mail address: [email protected] (C. Nicolini). 1 Permanent address: School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, United Kingdom.
the clinical success of dental implants could be jeopardized by bacterial infection inducing mucositis or periimplantitis [1–3]. Various methods have been proposed for the treatment of periimplantitis including access flap procedures, the use of locally or systemically administered antimicrobial agents, as well as decontamination of the exposed implant surfaces [4,5]. The eradication of pathogenic microorganisms from implant surfaces is a key step for the successful treatment of a failing implant. Several methods for the cleaning of a failing implant surfaces have been described.
0109-5641/$ - see front matter Q 2005 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.dental.2005.01.010
An in-vitro study of the sterilization of titanium dental implants using low intensity UV-radiation Among others, laser treatment seemed to be effective in terms of bacteria elimination [5–11]. Two strategies have been suggested for laser sterilization of dental implants. In the first, visible or infra-red lasers are employed to give local heating and clean the surface [5,6]. High reflectivity and rapid dissipation of the heat energy by the dental implant means that intense, highpower lasers are required to obtain effective cleaning. It has been reported that illumination with such lasers can lead to damage to the surface of the implant [9–11]. The second method involves sensitizing the implant surface with a dye. The dye, an organic molecule, absorbs laser light and uses the energy to produce highly reactive chemical agents that attack the bacteria. For example, the dye toluidine blue when illumined reacts with oxygen molecules in the atmosphere to produce singlet oxygen, a very reactive species [12]. It has been demonstrated in vitro [7] that toluidine blue, can be adsorbed onto a contaminated implant and subsequent irradiation with laser light leads to re-sterilization. The efficient absorption of light by the dye molecules and the high yield of the photochemical reaction means that efficient sterilization of dye photosensitized implants can be achieved at low laser power. Thus the possibility of laser induced damage to a photosensitized implant during laser induced sterilisation is minimal. However, this method of eradicating pathogenic microorganisms from the surface of implants has not been widely adopted as methods of attaching the photosensitive dye molecules to implant surfaces remain challenging. Commercially pure titanium is used to produce implants owing to its excellent biocompatability. To promote bio-efficacy the surfaces of metal implants are roughened. Grit blasting followed by acid etching or titanium plasma spraying are employed to produce the roughened nanoscale surfaces [13, 14]. Titanium is a very reactive metal that is rendered corrosion resistant, and hence suitable for in vivo applications, by a passive TiO2 layer. Hence dental implants have nanoscale TiO2 at their surface [15,16]. TiO2 is a wide band gap semiconductor [17,18] that produces radicals, O,2, HOO, or OH,, when illuminated with UV light [19,20]. There is evidence that these free radicals, may be successfully employed in redox chemistry, killing bacteria [21–23]. In this study it is considered whether the nanostructured TiO2 layer already present on the surface of commercial dental implants may act as a photosensitizer; absorbing incident radiation and producing reactive chemical species that sterilise the surface.
757
Materials and method Experiments were performed on dental implants supplied by Premium Implant System (Sweden and Martina, Padova, Italy). The implants were 3.75 mm in diameter and had an insertion depth of 8.5 mm. The implants were of commercially pure titanium and had been sand blasted and acid etched to promote osseointegration. All samples were unpacked from their sterile containers immediately prior to use. The photoactivity of the dental implants was verified by studying their effect on the photoinduced degradation of Rhodamine B (Aldrich). Rhodamine B is a dye molecule that reacts with photogenerated oxyradicals. The loss of Rhodamine B may be monitored using UV–visible spectroscopy. A 1.74 mM aqueous solution of Rhodamine B was prepared and the UV spectrum recorded using a JASCO V530 UV–visible spectrometer. Rhodamine B solution was then placed into two cuvettes. To the first cuvette a dental implant was added. Both cuvettes were then placed under illumination from a UV lamp of intensity 49 mW cmK2. To compare the rate of Rhodamine B photodegradation in the presence and absence of dental implants the absorption spectra of both samples were recorded at timed intervals, up to 4 h. The ability of the implants to destroy bacteria when under low intensity UV illumination was monitored in vitro. A bacterial solution (Escherichia Coli) of concentration 8!1010 bacteria/ml was split into three aliquots of volume 25 cm3; into two of the aliquots dental implants, of approximate area 1.2 cm2, were placed. To assess whether the dental implants enhanced photosterilization, one sample containing a dental implant and the sample without a dental implant were placed in an incubator at 37 8C and illuminated with UV light of intensity 49 mW cmK2. To monitor whether the dental implant influenced bacterial population in the absence of light the second sample containing a dental implant was kept in the dark at the same temperature. The concentration of bacteria in all three samples was monitored after 20, 40, 60, 80 min and 17 h. Bacteria populations were determined using a Thoma counting chamber of volume 10K4 ml. Aliquots were diluted by a factor of 104 before being injected into the chamber.
Results The inset in Fig. 1 shows the absorption spectrum of a 1.74 mM solution of Rhodamine B. The change
758
Figure 1 The Rhodamine B concentration as a function of UV illumination time; & in the presence of a TiO2 coated dental implant and , with no implant present. The inset shows the UV-absorption spectrum of Rhodamine B.
in concentration of Rhodamine B under UV illumination was determined by application of the Beer–Lambert law at the peak wavelength, 553 nm. The change in Rhodamine B concentration with UV illumination time is displayed in Fig. 1. There is clearly an accelerated loss of Rhodamine B in the presence of the dental implant, indicating that the TiO2 at the surface of the dental implant is photoactive. The photoinduced sterilization of titania coated dental implants via illumination with UV irradiation is demonstrated in the data plotted in Fig. 2. It is noted that the bacterial populations are shown on a log scale. In control experiments, (a) the bacteria plus implant under no illumination and (b) the illuminated bacteria in the absence of an implant, the population of bacteria increases as a function of time. After a period of 17 h, not shown on the graph, the concentration of bacteria had risen to 880!109/ml in control sample (a) and 128!109/ml in control sample (b). In contrast the bacterial concentration in the sample containing the dental implant that was illuminated fell to 1.6!109/ml in the same time period, i.e. 98% of the bacteria were destroyed.
Discussion The photoreaction between TiO2 and Rhodamine B (RH) under UV–visible radiation is complex [19].
D.J. Riley et al.
Figure 2 The concentration of E. Coli in solution as a function of time; C under UV illumination in the presence of a TiO2 coated dental implant, , in the presence of a dental implant but no illumination and under illumination but in the absence of a dental implant. The lines are plotted as guides to the eye.
Essentially two mechanisms operate in parallel. Absorption of UV radiation by semiconducting TiO2 yields a conduction band electron (eK) and a valence band hole (hC). The photogenerated electron reacts with molecular oxygen to form an O,K which on protonation yields HOO,. The HOO, 2 may be further reduced, via hydrogen peroxide, to a hydoxyl radical. Hydroxyl radicals are also formed by the reaction between water or OHK and the photogenerated holes. The photogenerated oxyradicals may then react with RH to give mineralised products; either, , , RH C fO,K 2 ; HOO or OH g / intermediate//products
ð1Þ
or , , R C hCðTiO2 Þ/ R, C fO,K 2 ; HOO or OH g / intermediate//products
ð2Þ
alternatively the RH may adsorb visible light and then transfer an electron to TiO2. As above, the electron on the TiO2 will react with molecular oxygen to form the (hydr)oxyradicals that breakdown the dye. This second process is termed sensitization. The accelerated loss of Rhodamine B in the presence of the dental implant that is observed in these studies indicates that the TiO2 on the surface of the implant is photoactive.
An in-vitro study of the sterilization of titanium dental implants using low intensity UV-radiation The results with respect to eradication of bacteria indicates that the (hydr)oxyradicals produced at a UV illuminated TiO2 surface will react with and deplete populations of bacteria. To estimate the rate of loss of bacteria at the TiO2 surface it is assumed that initially, when the concentration of bacteria is high, the photoinduced reaction is chemically, and not diffusion, controlled. Analysis of the data indicates that under the low intensity UV illumination employed bacteria were killed at the interface at a rate of approximately 650 million per cm2 of implant per minute.
Conclusions In vitro experiments indicate that dental implants may be sterilized by illumination with UV irradiation. The high rate of loss of bacteria, 800 million per geometric cm2 of implant per minute, suggests that illumination of dental implants with UV light during surgery will be beneficial, reducing incidence of biomaterial centred infections. In vivo experiments to test the effect of UV illumination on long-term patient health and methods of increasing the photoactivity of the TiO2 at the implant surface are in progress.
Acknowledgements The authors thank C. Rando for help monitoring bacterial populations. The Project was supported by a FIRB Grant to the Fondazione Elba and to the Nanoworld Institute and Biophysics Division of the University of Genova by the MIUR on Organic Nanosciences and Nanotechnologies, by a FISR on Nanotechnology by MIUR to Fondazione Elba and by a Grant on Nanotechnology to the Biophysics Division of the University of Genova by Consiglio Nazionale Ricerche of Italy.
References [1] Mombelli A, Van Oosten MAC, Schurch E, Lang NP. The microbiota associated with successful or failing osseointegrated titanium implants. Oral Microbiol Immunol 1987;2: 145–51. [2] Leonhardt A, Berglundh T, Ericsson I, Dahlen G. Putative periodontal pathogens on titanium implants and teeth in experimental gingivitis and periodontitis in beagle dogs. Clin Oral Implant Res 1992;3:112–9.
759
[3] Lindhe J, Berglundh T, Ericsson B, Lijienberg B, Marinello C. Experimental breakdown of periimplant and periodontal tissues. A study in the dog. Clin Oral Implant Res 1992;3: 9–16. [4] Persson LG, Berglundh T, Sennerby L, Lindhe J. Reosseointegration after treatment of peri-implantitis at different implant surfaces. An experimental study in the dog. Clin Oral Implant Res 2001;12:595–603. [5] Kreisler M, Kohnen W, Marinello C, Gotz H, Duschner H, Jansen B, D’Hoedt B. Bactericidal effect of the Er: Yag laser on dental implant surfaces: an in vitro study. J Periodont 2002;73:1292–8. [6] Kreisler M, Kohnen W, Marinello C, Schoof J, Langnau E, Jansen B, D’Hoedt B. Antimicrobial efficacy of semiconductor laser irradiation on implant surfaces. Int J Oral Maxillofac Implants 2003;18:706–11. [7] Dortbudak O, Haas R, Bernhart T, Mailath-Pokorny G. Lethal photosensitization for decontamination of implant surfaces in the treatment of peri-implantitis. Clin Oral Implant Res 2001;12:104–8. [8] Shibli JA, Martins MC, Nociti FH, Garcia VG, Marcantonio E. Treatment of ligature-induced peri-implantitis by lethal photosensitization and guided bone regeneration: a preliminary histologic study in dogs. J Periodont 2003;74: 338–45. [9] Karacs A, Fancsaly AJ, Divinyi T, Peto G, Kovach G. Morphological and animal study of titanium dental implant surface induced by blasting and high intensity pulsed Ndglass laser. Mater Sci Eng C-Biomimetic Supramol Syst 2003; 23:431–5. [10] Swift JQ, Jenny JE, Hargreaves KM. Heat-generation in hydroxyapatite-coated implants as a result of CO2-laser application. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1995;79:410–5. [11] Bereznai M, Pelsoczi I, Toth Z, Turzo K, Radnai M, Bor Z, Fazekas A. Surface modifications induced by ns and sub-ps excimer laser pulses on titanium implant material. Biomaterials 2003;24:4197–203. [12] Matysik J, Alia Bhalu B, Mohanty P. Molecular mechanisms of quenching of reactive oxygen species by proline under stress in plants. Curr Sci 2002;82:525–32. [13] Aparicio C, Gil FJ, Thams U, Munoz F, Padros A, Planell JA. Osseointegration of grit-blasted and bioactive titanium implants: histomorphometry in minipigs. Bioceramics 2004;254-2:737–40. [14] Jayaraman M, Meyer U, Buhner M, Joos U, Wiesmann HP. Influence of titanium surfaces on attachment of osteoblastlike cells in vitro. Biomaterials 2004;25:625–31. [15] Placko HE, Perry W, Mishra S, Lucas LC, Weimer JJ. Surface studies of titanium-based dental implant materials. J Dent Res 1997;76:1514. [16] Placko HE, Mishra S, Weimer JJ, Lucas LC. Surface characterization of titanium-based implant materials. Int J Oral Maxillofac Implants 2000;15:355–63. [17] Ding HM, Ram MK, Nicolini C. Nanofabrication of organic/ inorganic hybrids of TiO2 with substituted phthalocyanine or polythiophene. J Nanosci Nanotechnol 2001;1:207–13. [18] Ding HM, Ram MK, Nicolini C. Construction of organicinorganic hybrid ultrathin films self-assembled from poly (thiophene-3-acetic acid) and TiO2. J Mater Chem 2002;12: 3585–90. [19] Wu TX, Liu GM, Zhao JC, Hidaka H, Serpone N. Photoassisted degradation of dye pollutants V. Self-photosensitized oxidative transformation of Rhodamine B under visible light irradiation in aqueous TiO2 dispersions. J Phys Chem B 1998;102:5845–51.
760 [20] Wu TX, Liu GM, Zhao JC, Hidaka H, Serpone N. Evidence for H2O2 generation during the TiO2-assisted photodegradation of dyes in aqueous dispersions under visible light illumination. J Phys Chem B 1999;103:4862–7. [21] Ohko Y, Utsumi Y, Niwa C, Tatsuma T, Kobayakawa K, Satoh Y, Kubota Y, Fujishima A. Self-sterilizing and self-cleaning of silicone catheters coated with TiO2
D.J. Riley et al. photocatalyst thin films: a preclinical work. J Biomed Mater Res 2001;58:97–101. [22] Tatsuma T, Takeda S, Saitoh S, Ohko Y, Fujishima A. Bactericidal effect of an energy storage TiO2-WO3 photocatalyst in dark. Electrochem Commun 2003;5:793–6. [23] Nicolini C, editor. Biophysics of electron transfer and molecular bioelectronics. New York: Plenum Press; 1997.
www.intl.elsevierhealth.com/journals/dema
An in-vitro study of the sterilization of titanium dental implants using low intensity UV-radiation D. Jason Rileya,1, Valter Bavastrelloa, Ugo Covanib, Antonio Baroneb, Claudio Nicolinia,b,* a
Fondazione Elba, Via delle Testuggini, Roma, Italy Nanoworld Institute and Biophysics Division, Department of Biophysical M & O Sciences and Technologies, University of Genoa, Corso Europa 30, 16132 Genoa, Italy
b
Received 1 November 2004; accepted 20 January 2005
KEYWORDS Bacteria; Dental implant; Osseointegration; Titanium oxide; Sterilization
Summary Objectives. Commercial titanium dental implants are coated with nanostructured TiO2. The aim of the research reported in this paper was to assess whether the TiO2 at the surface of a dental implant is sufficiently photoactive to eradicate bacteria when illumined with low intensity light. Methods. The photoactivity of dental implants was established by studies of the photoenhanced decomposition of Rhodamine B. In vitro studies to establish the influence of irradiating with UV light an implant that is immersed in a solution containing Escherichia Coli were performed. Results. It was demonstrated that under low UV intensity irradiation, 49 mW cmK2, bacteria are killed at a rate of approximately 650 million per cm2 of implant per minute. Significance. The results indicate that illumination of dental implants with UV light may be a suitable treatment for periimplantitis. Q 2005 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
Introduction Dental implants are today successfully used in dentistry for oral rehabilitation supporting mobile or fixed prostheses. Beside undisturbed osseointegration and an adequate prosthetic design,
* Corresponding author. Tel.: C39 010 35338217; fax: C39 010 35338215. E-mail address: [email protected] (C. Nicolini). 1 Permanent address: School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, United Kingdom.
the clinical success of dental implants could be jeopardized by bacterial infection inducing mucositis or periimplantitis [1–3]. Various methods have been proposed for the treatment of periimplantitis including access flap procedures, the use of locally or systemically administered antimicrobial agents, as well as decontamination of the exposed implant surfaces [4,5]. The eradication of pathogenic microorganisms from implant surfaces is a key step for the successful treatment of a failing implant. Several methods for the cleaning of a failing implant surfaces have been described.
0109-5641/$ - see front matter Q 2005 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.dental.2005.01.010
An in-vitro study of the sterilization of titanium dental implants using low intensity UV-radiation Among others, laser treatment seemed to be effective in terms of bacteria elimination [5–11]. Two strategies have been suggested for laser sterilization of dental implants. In the first, visible or infra-red lasers are employed to give local heating and clean the surface [5,6]. High reflectivity and rapid dissipation of the heat energy by the dental implant means that intense, highpower lasers are required to obtain effective cleaning. It has been reported that illumination with such lasers can lead to damage to the surface of the implant [9–11]. The second method involves sensitizing the implant surface with a dye. The dye, an organic molecule, absorbs laser light and uses the energy to produce highly reactive chemical agents that attack the bacteria. For example, the dye toluidine blue when illumined reacts with oxygen molecules in the atmosphere to produce singlet oxygen, a very reactive species [12]. It has been demonstrated in vitro [7] that toluidine blue, can be adsorbed onto a contaminated implant and subsequent irradiation with laser light leads to re-sterilization. The efficient absorption of light by the dye molecules and the high yield of the photochemical reaction means that efficient sterilization of dye photosensitized implants can be achieved at low laser power. Thus the possibility of laser induced damage to a photosensitized implant during laser induced sterilisation is minimal. However, this method of eradicating pathogenic microorganisms from the surface of implants has not been widely adopted as methods of attaching the photosensitive dye molecules to implant surfaces remain challenging. Commercially pure titanium is used to produce implants owing to its excellent biocompatability. To promote bio-efficacy the surfaces of metal implants are roughened. Grit blasting followed by acid etching or titanium plasma spraying are employed to produce the roughened nanoscale surfaces [13, 14]. Titanium is a very reactive metal that is rendered corrosion resistant, and hence suitable for in vivo applications, by a passive TiO2 layer. Hence dental implants have nanoscale TiO2 at their surface [15,16]. TiO2 is a wide band gap semiconductor [17,18] that produces radicals, O,2, HOO, or OH,, when illuminated with UV light [19,20]. There is evidence that these free radicals, may be successfully employed in redox chemistry, killing bacteria [21–23]. In this study it is considered whether the nanostructured TiO2 layer already present on the surface of commercial dental implants may act as a photosensitizer; absorbing incident radiation and producing reactive chemical species that sterilise the surface.
757
Materials and method Experiments were performed on dental implants supplied by Premium Implant System (Sweden and Martina, Padova, Italy). The implants were 3.75 mm in diameter and had an insertion depth of 8.5 mm. The implants were of commercially pure titanium and had been sand blasted and acid etched to promote osseointegration. All samples were unpacked from their sterile containers immediately prior to use. The photoactivity of the dental implants was verified by studying their effect on the photoinduced degradation of Rhodamine B (Aldrich). Rhodamine B is a dye molecule that reacts with photogenerated oxyradicals. The loss of Rhodamine B may be monitored using UV–visible spectroscopy. A 1.74 mM aqueous solution of Rhodamine B was prepared and the UV spectrum recorded using a JASCO V530 UV–visible spectrometer. Rhodamine B solution was then placed into two cuvettes. To the first cuvette a dental implant was added. Both cuvettes were then placed under illumination from a UV lamp of intensity 49 mW cmK2. To compare the rate of Rhodamine B photodegradation in the presence and absence of dental implants the absorption spectra of both samples were recorded at timed intervals, up to 4 h. The ability of the implants to destroy bacteria when under low intensity UV illumination was monitored in vitro. A bacterial solution (Escherichia Coli) of concentration 8!1010 bacteria/ml was split into three aliquots of volume 25 cm3; into two of the aliquots dental implants, of approximate area 1.2 cm2, were placed. To assess whether the dental implants enhanced photosterilization, one sample containing a dental implant and the sample without a dental implant were placed in an incubator at 37 8C and illuminated with UV light of intensity 49 mW cmK2. To monitor whether the dental implant influenced bacterial population in the absence of light the second sample containing a dental implant was kept in the dark at the same temperature. The concentration of bacteria in all three samples was monitored after 20, 40, 60, 80 min and 17 h. Bacteria populations were determined using a Thoma counting chamber of volume 10K4 ml. Aliquots were diluted by a factor of 104 before being injected into the chamber.
Results The inset in Fig. 1 shows the absorption spectrum of a 1.74 mM solution of Rhodamine B. The change
758
Figure 1 The Rhodamine B concentration as a function of UV illumination time; & in the presence of a TiO2 coated dental implant and , with no implant present. The inset shows the UV-absorption spectrum of Rhodamine B.
in concentration of Rhodamine B under UV illumination was determined by application of the Beer–Lambert law at the peak wavelength, 553 nm. The change in Rhodamine B concentration with UV illumination time is displayed in Fig. 1. There is clearly an accelerated loss of Rhodamine B in the presence of the dental implant, indicating that the TiO2 at the surface of the dental implant is photoactive. The photoinduced sterilization of titania coated dental implants via illumination with UV irradiation is demonstrated in the data plotted in Fig. 2. It is noted that the bacterial populations are shown on a log scale. In control experiments, (a) the bacteria plus implant under no illumination and (b) the illuminated bacteria in the absence of an implant, the population of bacteria increases as a function of time. After a period of 17 h, not shown on the graph, the concentration of bacteria had risen to 880!109/ml in control sample (a) and 128!109/ml in control sample (b). In contrast the bacterial concentration in the sample containing the dental implant that was illuminated fell to 1.6!109/ml in the same time period, i.e. 98% of the bacteria were destroyed.
Discussion The photoreaction between TiO2 and Rhodamine B (RH) under UV–visible radiation is complex [19].
D.J. Riley et al.
Figure 2 The concentration of E. Coli in solution as a function of time; C under UV illumination in the presence of a TiO2 coated dental implant, , in the presence of a dental implant but no illumination and under illumination but in the absence of a dental implant. The lines are plotted as guides to the eye.
Essentially two mechanisms operate in parallel. Absorption of UV radiation by semiconducting TiO2 yields a conduction band electron (eK) and a valence band hole (hC). The photogenerated electron reacts with molecular oxygen to form an O,K which on protonation yields HOO,. The HOO, 2 may be further reduced, via hydrogen peroxide, to a hydoxyl radical. Hydroxyl radicals are also formed by the reaction between water or OHK and the photogenerated holes. The photogenerated oxyradicals may then react with RH to give mineralised products; either, , , RH C fO,K 2 ; HOO or OH g / intermediate//products
ð1Þ
or , , R C hCðTiO2 Þ/ R, C fO,K 2 ; HOO or OH g / intermediate//products
ð2Þ
alternatively the RH may adsorb visible light and then transfer an electron to TiO2. As above, the electron on the TiO2 will react with molecular oxygen to form the (hydr)oxyradicals that breakdown the dye. This second process is termed sensitization. The accelerated loss of Rhodamine B in the presence of the dental implant that is observed in these studies indicates that the TiO2 on the surface of the implant is photoactive.
An in-vitro study of the sterilization of titanium dental implants using low intensity UV-radiation The results with respect to eradication of bacteria indicates that the (hydr)oxyradicals produced at a UV illuminated TiO2 surface will react with and deplete populations of bacteria. To estimate the rate of loss of bacteria at the TiO2 surface it is assumed that initially, when the concentration of bacteria is high, the photoinduced reaction is chemically, and not diffusion, controlled. Analysis of the data indicates that under the low intensity UV illumination employed bacteria were killed at the interface at a rate of approximately 650 million per cm2 of implant per minute.
Conclusions In vitro experiments indicate that dental implants may be sterilized by illumination with UV irradiation. The high rate of loss of bacteria, 800 million per geometric cm2 of implant per minute, suggests that illumination of dental implants with UV light during surgery will be beneficial, reducing incidence of biomaterial centred infections. In vivo experiments to test the effect of UV illumination on long-term patient health and methods of increasing the photoactivity of the TiO2 at the implant surface are in progress.
Acknowledgements The authors thank C. Rando for help monitoring bacterial populations. The Project was supported by a FIRB Grant to the Fondazione Elba and to the Nanoworld Institute and Biophysics Division of the University of Genova by the MIUR on Organic Nanosciences and Nanotechnologies, by a FISR on Nanotechnology by MIUR to Fondazione Elba and by a Grant on Nanotechnology to the Biophysics Division of the University of Genova by Consiglio Nazionale Ricerche of Italy.
References [1] Mombelli A, Van Oosten MAC, Schurch E, Lang NP. The microbiota associated with successful or failing osseointegrated titanium implants. Oral Microbiol Immunol 1987;2: 145–51. [2] Leonhardt A, Berglundh T, Ericsson I, Dahlen G. Putative periodontal pathogens on titanium implants and teeth in experimental gingivitis and periodontitis in beagle dogs. Clin Oral Implant Res 1992;3:112–9.
759
[3] Lindhe J, Berglundh T, Ericsson B, Lijienberg B, Marinello C. Experimental breakdown of periimplant and periodontal tissues. A study in the dog. Clin Oral Implant Res 1992;3: 9–16. [4] Persson LG, Berglundh T, Sennerby L, Lindhe J. Reosseointegration after treatment of peri-implantitis at different implant surfaces. An experimental study in the dog. Clin Oral Implant Res 2001;12:595–603. [5] Kreisler M, Kohnen W, Marinello C, Gotz H, Duschner H, Jansen B, D’Hoedt B. Bactericidal effect of the Er: Yag laser on dental implant surfaces: an in vitro study. J Periodont 2002;73:1292–8. [6] Kreisler M, Kohnen W, Marinello C, Schoof J, Langnau E, Jansen B, D’Hoedt B. Antimicrobial efficacy of semiconductor laser irradiation on implant surfaces. Int J Oral Maxillofac Implants 2003;18:706–11. [7] Dortbudak O, Haas R, Bernhart T, Mailath-Pokorny G. Lethal photosensitization for decontamination of implant surfaces in the treatment of peri-implantitis. Clin Oral Implant Res 2001;12:104–8. [8] Shibli JA, Martins MC, Nociti FH, Garcia VG, Marcantonio E. Treatment of ligature-induced peri-implantitis by lethal photosensitization and guided bone regeneration: a preliminary histologic study in dogs. J Periodont 2003;74: 338–45. [9] Karacs A, Fancsaly AJ, Divinyi T, Peto G, Kovach G. Morphological and animal study of titanium dental implant surface induced by blasting and high intensity pulsed Ndglass laser. Mater Sci Eng C-Biomimetic Supramol Syst 2003; 23:431–5. [10] Swift JQ, Jenny JE, Hargreaves KM. Heat-generation in hydroxyapatite-coated implants as a result of CO2-laser application. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1995;79:410–5. [11] Bereznai M, Pelsoczi I, Toth Z, Turzo K, Radnai M, Bor Z, Fazekas A. Surface modifications induced by ns and sub-ps excimer laser pulses on titanium implant material. Biomaterials 2003;24:4197–203. [12] Matysik J, Alia Bhalu B, Mohanty P. Molecular mechanisms of quenching of reactive oxygen species by proline under stress in plants. Curr Sci 2002;82:525–32. [13] Aparicio C, Gil FJ, Thams U, Munoz F, Padros A, Planell JA. Osseointegration of grit-blasted and bioactive titanium implants: histomorphometry in minipigs. Bioceramics 2004;254-2:737–40. [14] Jayaraman M, Meyer U, Buhner M, Joos U, Wiesmann HP. Influence of titanium surfaces on attachment of osteoblastlike cells in vitro. Biomaterials 2004;25:625–31. [15] Placko HE, Perry W, Mishra S, Lucas LC, Weimer JJ. Surface studies of titanium-based dental implant materials. J Dent Res 1997;76:1514. [16] Placko HE, Mishra S, Weimer JJ, Lucas LC. Surface characterization of titanium-based implant materials. Int J Oral Maxillofac Implants 2000;15:355–63. [17] Ding HM, Ram MK, Nicolini C. Nanofabrication of organic/ inorganic hybrids of TiO2 with substituted phthalocyanine or polythiophene. J Nanosci Nanotechnol 2001;1:207–13. [18] Ding HM, Ram MK, Nicolini C. Construction of organicinorganic hybrid ultrathin films self-assembled from poly (thiophene-3-acetic acid) and TiO2. J Mater Chem 2002;12: 3585–90. [19] Wu TX, Liu GM, Zhao JC, Hidaka H, Serpone N. Photoassisted degradation of dye pollutants V. Self-photosensitized oxidative transformation of Rhodamine B under visible light irradiation in aqueous TiO2 dispersions. J Phys Chem B 1998;102:5845–51.
760 [20] Wu TX, Liu GM, Zhao JC, Hidaka H, Serpone N. Evidence for H2O2 generation during the TiO2-assisted photodegradation of dyes in aqueous dispersions under visible light illumination. J Phys Chem B 1999;103:4862–7. [21] Ohko Y, Utsumi Y, Niwa C, Tatsuma T, Kobayakawa K, Satoh Y, Kubota Y, Fujishima A. Self-sterilizing and self-cleaning of silicone catheters coated with TiO2
D.J. Riley et al. photocatalyst thin films: a preclinical work. J Biomed Mater Res 2001;58:97–101. [22] Tatsuma T, Takeda S, Saitoh S, Ohko Y, Fujishima A. Bactericidal effect of an energy storage TiO2-WO3 photocatalyst in dark. Electrochem Commun 2003;5:793–6. [23] Nicolini C, editor. Biophysics of electron transfer and molecular bioelectronics. New York: Plenum Press; 1997.