Exposure of Streptococcus mutans and Streptococcus sanguinis to blue light in an oral biofilm model.

The potential anti-cariogenic effect of blue light was evaluated using an oral biofilm model. Two species, Streptococcus mutans and Streptococcus sanguinis, were cultivated ex vivo on bovine enamel blocks for 24 h, either separately or mixed together, then exposed to blue light (wavelengths 400-500 nm) using 112 J/cm2. Twenty four or 48 h after exposure to light the biofilm structure and biomass were characterized and quantified using SEM and qPCR, respectively. Bacterial viability was analyzed by CLSM using live/dead bacterial staining. Gene expression was examined by RT-qPCR. After exposure to light, S. mutans biomass in mono-species biofilm was increased mainly by dead bacteria, relative to control. However, the bacterial biomass of S. mutans when grown in mixed biofilm and of S. sanguinis in mono-species biofilm was reduced after light exposure, with no significant change in viability when compared to control. Furthermore, when grown separately, an upregulation of gene expression related to biofilm formation of S. mutans, and downregulation of similar genes of S. sanguinis, were measured 24 h after exposure to blue light. However, in mixed biofilm, a downregulation of those genes in both species was observed, although not significant in S. mutans. In conclusion, blue light seems to effectively alter the bacterial biomass by reducing the viability and virulence characteristics in both bacterial species and may promote the anti-cariogenic balance between them, when grown in a mixed biofilm. Therefore, exposure of oral biofilm to blue light has the potential to serve as a complementary approach in preventive dentistry.

Effects of Er:YAG laser on bacteria associated with titanium surfaces and cellular response in vitro.

This in vitro study examined (a) the anti-bacterial efficacy of a pulsed erbium-doped yttrium aluminum garnet (Er:YAG) laser applied to Streptococcus sanguinis or Porphyromonas gingivalis adhered to either polished or microstructured titanium implant surfaces, (b) the response of osteoblast-like cells and (c) adhesion of oral bacteria to titanium surfaces after laser irradiation. Thereto, (a) bacteria adhered to titanium disks were irradiated with a pulsed Er:YAG laser (λ = 2,940 nm) at two different power settings: a lower mode (12.74 J/cm(2) calculated energy density) and a higher mode (63.69 J/cm(2)). (b) After laser irradiation with both settings of sterile titanium, disks were seeded with 10(4) MG-63 cells/cm(2). Adhesion and proliferation were determined after 1, 4, and 24 h by fluorescence microscopy and scanning electron microscopy. (c) Bacterial adhesion was also studied on irradiated (test) and non-irradiated (control) surfaces. Adhered P. gingivalis were effectively killed, even at the lower laser setting, independent of the material's surface. S. sanguinis cells adhered were effectively killed only at the higher setting of 63.69 J/cm(2). Laser irradiation of titanium surfaces had no significant effects on (b) adhesion or proliferation of osteoblast-like MG-63 cells or (c) adhesion of both oral bacterial species in comparison to untreated surfaces. An effective decontamination of polished and rough titanium implant surfaces with a Er:YAG laser could only be achieved with a fluence of 63.69 J/cm(2). Even though this setting may lead to certain surface alterations, no significant adverse effect on subsequent colonization and proliferation of MG-63 cells or increased bacterial adhesion was found in comparison to untreated control surfaces.

Photoactivated disinfection (PAD) in endodontics: an in vitro microbiological evaluation.

PURPOSE: The objective of the present study was the in vitro evaluation by MTT test of the antimicrobial effect of photoactivated disinfection (PAD) and, comparatively, of a conventional 5.25% NaOCl irrigating solution. METHODS: Enterococcus faecalis, Streptococcus mutans and Streptococcus sanguis strains were selected for the test. Freshly extracted single-rooted human teeth were endodontically treated, inoculated with bacterial strains and then divided into different groups, each of them treated with PAD, with PAD plus 0.5% NaOCl solution, with TBO, with PAD for longer time and with 5% NaOCl solution (positive control). RESULTS: The results were significantly different among the various groups, and for Enterococcus faecalis, Streptococcus mutans and Streptococcus sanguis. PAD applied for a longer time (in respect to manufacturer's instructions) or PAD associated to 5% NaOCl showed the significantly higher antibacterial effects.

Bactericidal effects of different laser systems on bacteria adhered to dental implant surfaces: an in vitro study comparing zirconia with titanium.

OBJECTIVES: The purpose of this study was to examine in vitro the anti-bacterial efficacy of two different laser systems (CO(2) and diode) applied to Streptococcus sanguinis or Porphyromonas gingivalis cells in suspensions or adhered to zirconia or titanium dental implant materials, with two different surfaces each. MATERIALS AND METHODS: Bacteria were irradiated at two different power settings with either a CO(2) (lambda=10,600 nm) or a diode laser (lambda=810 nm). The lower mode is used clinically (for CO(2) 100 J/cm(2), diode 50 J/cm(2)) and the higher may alter the materials' surface (for CO(2) 1200 J/cm(2), diode 150 J/cm(2)). After irradiation, the number of viable bacteria was determined by culture. RESULTS: Planktonic cells of both species were more resistant to the laser irradiations than bacteria that adhered to surfaces. Adhered P. gingivalis were effectively killed at both wavelengths lambda=10,600 and 810 nm even at the lower settings, independent of the material. S. sanguinis cells that adhered to either zirconia surface were effectively killed by the CO(2) laser at the lower setting of 100 J/cm(2). However, the higher settings of both lasers were needed to reduce S. sanguinis that adhered to titanium surfaces. The CO(2) laser at the lower setting and the diode laser at the higher setting effectively reduced the viability of S. sanguinis or P. gingivalis that adhered to zirconia surfaces. CONCLUSIONS: Under irradiation conditions known not to alter zirconia implant surfaces in vitro, both CO(2) laser (100 J/cm(2)) and the diode laser (150 J/cm(2)) effectively reduced the viability of adhered S. sanguinis or P. gingivalis.

Sensitivity of oral bacteria to 254 nm ultraviolet light.

AIM: To explore the sensitivity of bacteria commonly found in root canals to 254 nm ultraviolet (UV) light, either as individual cells or as participants of a bacterial multilayer. METHODOLOGY: The sensitivity of oral bacteria, as individual cells, to UV light was tested by subjecting plates streaked with bacteria to 254 nm UV, at a fluence of 1-20 mJ cm(-2). An experimental model was designed to produce a bacterial multilayer and to study absorption of UV light by bacteria in an outer layer and its effect on the elimination of bacteria in the inner layer. RESULTS: Direct exposure to relatively low doses of UV light (2-7 mJ cm(-2)) effectively eliminated all bacterial strains tested. Furthermore, an Enterococcus faecalis strain, partially resistant to a 24 h exposure to calcium hydroxide, was effectively eliminated within several seconds of exposure to UV light (P < 0.001). UV was absorbed by a multilayer of bacteria. When 4 bacterial cells microm(-2) were present in the light path, the UV light dose had to be increased by a factor of x10 to achieve 100% elimination of the bacteria in an inner layer. CONCLUSIONS: The application of UV light to eliminate endodontic pathogens may be possible. Nevertheless, its absorbance by outer layers of bacteria should be considered and the UV light dose adapted accordingly.

Bactericidal effect of the Er:YAG laser on dental implant surfaces: an in vitro study.

BACKGROUND: The aim of the in vitro study was to examine the bactericidal effect of an Er:YAG laser on common dental implant surfaces. METHODS: Seventy-two titanium platelets with 3 different surfaces--sandblasted and acid-etched (SA), titanium plasma-sprayed (TPS), and hydroxyapatite-coated (HA)--were incubated with a suspension of Streptococcus sanguinis (ATCC 10556). Irradiation at pulse energies of 60 and 120 mJ and a frequency of 10 pps was performed on a computer-controlled XY translation stage. After laser treatment the specimens were sonicated and the bacterial growth examined by counting colony forming units on blood agar plates. Temperature elevations during irradiation were investigated using K-type thermocouples. Laser treated implant surfaces were analyzed by means of electron microscopy. RESULTS: Compared to non-irradiated specimens, mean bacterial reductions of 99.51% (SA), 98.39% (HA), and 99.6% (TPS) at a pulse energy of 60 mJ and 99.92% (SA), 99.85% (HA), and 99.94% (TPS) at 120 mJ were calculated. At these laser parameters, no excessive temperature elevations or morphological implant surface alterations were detected. CONCLUSIONS: Even at low energy densities, the Er:YAG laser has a high bactericidal potential on common implant surfaces. Clinical studies are justified to evaluate the applicability and efficacy of the Er:YAG laser in the treatment of peri-implantitis.

Comparative evaluation of antibacterial effects of Nd:YAG laser irradiation in root canals and dentinal tubules.

The antibacterial effects of the Nd:YAG laser on contaminated root canals and dentinal tubules were observed as the aim of this study. The samples were inoculated with Streptococcus sanguis (NCTC 7853) and Prevotella intermedia (NCTC 93336), and the effects of Nd:YAG laser were tested on these teeth. The specimens were lased with 1.8 W and 2.4 W Nd:YAG laser for 30 s, and the presence of bacteria in tubules was observed under light microscopy. The 1.8 W laser sterilized the tubules in 86.3% of sections inoculated with S. sanguis, whereas 2.4 W laser sterilized in 98.5% of the sections. Both laser powers sterilized all samples inoculated with P. intermedia. The scanning electron microscopic observations supported the light microscopic findings.

Er:YAG and alexandrite laser radiation propagation in root canal and its effect on bacteria.

OBJECTIVE: The objective of this study was to compare the bactericidal effect of the Er:YAG (wavelength 2.94 microm) and the Alexandrite (wavelength 0.75 microm) laser radiation. The spreading laser energy in the surrounding hard dental tissues round the root canal was evaluated and the bactericidal effect of both these different laser wavelengths was analyzed. SUMMARY BACKGROUND DATA: The use of a laser to clean and shape the root canal space is the latest method used for cleaning of root canals. The interest in laser endodontics was concentrated on the possibility to extirpate the contents of the root canal, to sterilize and to "melt" the walls of the root canals. The previous reports were performed with CO2, excimer, argon, Nd:YAG, Ho:YAG, and Er:YAG lasers. METHODS: Er:YAG laser system (2.94 microm, energy 100 mJ or 300 mJ, repetition rate 1 Hz, 30 pulses) and alexandrite laser system (0.75 microm, energy 250 mJ, repetition rate 1 Hz, 30 pulses) were prepared and three experimental arrangements were used during the measurements. First the energy transport through the tooth tissue was observed (frontal and side experimental setups) and then, the bactericidal effect was evaluated. RESULTS: It was demonstrated that due to the absorption in the hydroxyapatite and water content in the dentin, the Er:YAG laser radiation is fully absorbed in the root canal wall. This direct influence of the radiation could be expected only close to the sapphire tip. It was found that the tissue, which was not directly affected by the laser radiation, cannot be disinfected by the subablative effect of Er:YAG laser radiation. In the second part of the experiment the real bactericidal effect of Er:YAG ablative energy (300 mJ) could be observed. It was also shown that the alexandrite laser radiation with a wavelength of 0.75 microm spreads through the canal system space and leaks into the surrounding tooth tissues. Both lasers have bactericidal effect. CONCLUSIONS: The pulsed Er:YAG and alexandrite lasers can be efficiently used for killing dental bacteria but the spreading of their radiation in the tooth tissues are different.

Bactericidal efficacy of carbon dioxide laser against bacteria-contaminated titanium implant and subsequent cellular adhesion to irradiated area.

BACKGROUND AND OBJECTIVE: The aim of this study was to assess CO2 laser ability to eliminate bacteria from titanium implant surfaces. The changes of the surface structure, the rise in temperature, and the damage of connective tissue cells after laser irradiation were also considered. STUDY DESIGN/MATERIALS AND METHODS: Streptococcus sanguis and Porphyromonas gingivalis on titanium discs were irradiated by an expanded beam of CO2 laser. Surface alteration was observed by a light, and a scanning electron, microscope. Temperature was measured with a thermograph. Damage of fibroblastic (L-929) and osteoblastic (MC3T3-E1) cells outside the irradiation spot and adhesion of the cells to the irradiated area were also estimated. RESULTS: All the organisms (10(8)) of S. sanguis and P. gingivalis were killed by the irradiation at 286 J/cm2 and 245 J/cm2, respectively. Furthermore, laser irradiation did not cause surface alteration, rise of temperature, serious damage of connective tissue cells located outside the irradiation spot, or inhibition of cell adhesion to the irradiated area. CONCLUSION: CO2 laser irradiation with expanded beam may be useful in removing bacterial contaminants from implant surface.

Sensitization of oral bacteria in biofilms to killing by light from a low-power laser.

Biofilms of Streptococcus sanguis, Porphyromonas gingivalis, Fusobacterium nucleatum and Actinobacillus actinomycetemcomitans were prepared on the surfaces of agar plates and a number of compounds were screened for their ability to sensitize bacteria in these biofilms to killing by light from a 7.3 mW Helium/Neon (He/Ne) laser. Toluidine blue O and methylene blue enabled detectable killing of all four target organisms after exposure to He/Ne light for 30 s. Aluminium disulphonated phthalocyanine, haematoporphyrin HCl and haematoporphyrin ester were effective photosensitizers of only some of the target organisms. These findings suggest that lethal photosensitization may be an effective means of eliminating periodontopathogenic bacteria from dental plaque.

Sensitization of oral bacteria to killing by low-power laser radiation.

Twenty-seven compounds were screened for their ability to sensitize Streptococcus sanguis to killing by light from a 7.3-mW Helium/Neon (HeNe) laser. Bacteria were mixed with various concentrations of the test compounds, spread over the surfaces of agar plates, and then exposed to light from the HeNe laser for various time periods. The plates were then incubated and examined for zones of inhibition. Those compounds found to be effective photosensitizers were then tested against Porphyromonas gingivalis, Actinobacillus actinomycetemcomitans, and Fusobacterium nucleatum. Toluidine blue O, azure B chloride, and methylene blue at concentrations of 0.005% (wt/vol) were effective photosensitizers of all four species, enabling killing of bacteria following exposure to laser light for only 30 s.

Bactericidal action of carbon dioxide laser radiation in experimental dental root canals.

The ability of a carbon dioxide laser to sterilize the root canal of human teeth has been investigated. Three oral bacteria, Streptococcus sanguis, Streptococcus mutans, and Actinomyces viscosus, and three other bacteria, Bacillus cereus, Staphylococcus aureus, and Pseudomonas aeruginosa were used as experimental organisms. Exposure of cells on glass slides to laser radiation showed there was little difference in the exposure required to kill these six organisms. Complete recovery of bacteria from the root canal was initially a problem and was only achieved when bacterial manipulations and removal were carried out in rapid succession, within 5 min of inoculation. However, the geometry of the instrumented canal and the laser alignment were major factors in achieving consistent cell death of oral bacteria in the root canals. Using sets of 10 teeth, four repeated exposures of 10 W for 1 s was found to sterilize 4 or more of the teeth.

Recombination-deficient Streptococcus sanguis.

A UV-sensitive derivative was obtained from Streptococcus sanguis Challis. The organism could be transformed with a number of small streptococcal plasmids at frequencies equal to, or 1 logarithm below, the transformation frequencies for the parent organism. However, transformation with chromosomal DNA was greatly impaired in the UV-sensitive derivative.

Effects of bactericidal treatments on bacterial adherence and dental plaque formation.

In vivo plaque formation was significantly reduced when tooth surfaces were subjected to topical applications of iodine (0.2% I2 in 2.0% KI) twice daily for 3 d. Similarly, in vivo plaque formation was significantly reduced on enamel surfaces that were subjected to ultraviolet irradiation. Control experiments indicated that neither ultraviolet irradiation nor iodine treatment interfered with mechanisms for bacterial apposition to dental plaque. The results are interpreted to suggest that plaque grows in mass primarily by the division and multiplication in situ by plaque bacteria, not by a continued apposition of salivary microbes.