Chlorhexidine markedly potentiates the oxidants scavenging abilities of Candida albicans.

The oxidant scavenging ability (OSA) of catalase-rich Candida albicans is markedly enhanced by chlorhexidine digluconate (CHX), polymyxin B, the bile salt ursodeoxycholate and by lysophosphatidylcholine, which all act as detergents facilitating the penetration of oxidants and their intracellular decomposition. Quantifications of the OSA of Candida albicans were measured by a highly sensitive luminol-dependent chemiluminescence assay and by the Thurman's assay, to quantify hydrogen peroxide (H2O2). The OSA enhancing activity by CHX depends to some extent on the media on which candida grew. The OSA of candida treated by CHX was modulated by whole human saliva, red blood cells, lysozyme, cationic peptides and by polyphenols. Concentrations of CHX, which killed over 95 % of Candida albicans cells, did not affect the cells' abilities to scavenge reactive oxygen species (ROS). The OSA of Candida cells treated by CHX is highly refractory to H2O2 (50 mM) but is strongly inhibited by hypochlorous acid, lecithin, trypan blue and by heparin. We speculate that similarly to catalase-rich red blood cells, Candida albicans and additional catalase-rich microbiota may also have the ability to scavenge oxidants and thus can protect catalase-negative anaerobes and facultative anaerobes cariogenic streptococci against peroxide and thus secure their survival in the oral cavity.

The effects of in vitro fluoride mouth rinse on the antibacterial properties of orthodontic cements.

OBJECTIVES: To investigate the ability of orthodontic cements to regain their antibacterial effect after aging for 1 month, followed by 2 weeks of fluoride 'recharging' through daily fluoride rinse. MATERIALS AND METHODS: Four orthodontic cements were tested: composite resin-based materials (Transbond XT and Transbond Plus), a conventional glass ionomer cement (CX Plus) and dual-cured resin-reinforced glass ionomer cement (Fuji ORTHO LC) by direct contact test. After polymerization and a 30-day aging process, the samples were rinsed daily with 0.05% NaF solution for 14 days. Twenty-four hours after the last fluoride rinse, Streptococcus mutans cells (approximately 1 x 10(6) ) were placed on the surface of each sample for 1 h at 37°C to establish direct contact. Bacterial growth was monitored for 24 h by temperature-controlled spectrophotometry. Similar experiments were conducted after aging for 48 h and 72 h after the last fluoride rinse. One-way anova, two-way anova, and Tukey's multiple comparison test were applied to the data. RESULTS: Twenty-four hours after the last fluoride rinse, the resin-modified glass ionomer and the glass ionomer showed potent antibacterial properties, whereas the composite-based material Transbond XT encouraged bacterial growth. After 72 h, only Fuji Ortho LC maintained its bacteriostatic properties while all the other tested materials showed no antibacterial activity. CONCLUSIONS: Fourteen days daily fluoride rinse temporarily revives the antibacterial properties of the resin-modified glass ionomer cement and glass-ionomer-based cement.

Light therapy: complementary antibacterial treatment of oral biofilm.

Conventional antibacterial treatment fails to eradicate biofilms associated with common infections of the oral cavity. Unlike chemical agents, which are less effective than anticipated, owing to diffusion limitations in biofilms, light is more effective on bacteria in biofilm than in suspension. Effectiveness depends also on the type and parameters of the light. We tested the phototoxic effects of non-coherent blue light (wavelengths, 400-500 nm) and CO(2) laser (wavelength, 10.6 µm), which have different mechanisms of action on the oral bacterium Streptoccocus mutans, in biofilm and on tooth enamel. Exposure of S. mutans in biofilm to blue light had a delayed effect on bacterial viability throughout the biofilm and a sustained antibacterial effect on biofilm newly formed by previously irradiated bacteria. A synergistic antibacterial effect between blue light and H(2)O(2) may enhance the phototoxic effect, which involves a photochemical mechanism mediated by reactive oxygen species (ROS) formation. The effect of CO(2) laser irradiation on the viability of S. mutans in biofilm on enamel samples appeared to be higher in the deep layers, due to heating of the enamel surface by the absorbed energy. Biofilms do not interfere with the chemical changes resulting from irradiation, which may increase the enamel's resistance to acid attack.

Effect of sublethal CO2 laser irradiation on gene expression of streptococcus mutans immobilized in a biofilm.

Streptococcus mutans colonizing on tooth surfaces is one of the major causative agents of human dental caries. Despite numerous studies conducted on lasers and oral tissue interactions, little is known about the effect of laser energy on S. mutans gene expression in a biofilm form. The aim of this study was to investigate the effect of sublethal energies of CO(2) laser on biofilm and gene expression of the oral bacteria S. mutans immobilized in biofilm. S. mutans biofilm was irradiated with CO(2) laser. Vitality and construction of the biofilm were observed by confocal laser scanning microscopy and scanning electron microscopy. The effect of laser irradiation on gene expression was evaluated by DNA microarray. CO(2) laser irradiation had a dose effect on the viability of S. mutans immobilized in biofilm. A nonsignificant lethal effect was observed at 31 J/cm(2) while at higher energy of 70 and 144 J/cm(2) an antibacterial effect was recorded. The mode of antibacterial action seems to be from the inner layers toward the outer layer of the biofilm, indicating the influence of the surface on the killing effect. At 31 J/cm(2), microarray analysis indicated a moderate effect on S. mutans gene expression due to CO(2) laser irradiation, mainly down-regulating genes related to bacterial stress response. In conclusion, laser irradiation at sublethal energy had an effect on gene expression of S. mutans.

[Hi-tech trends in future dentistry--part A: computerized technologies].

Growing knowledge and information in the field of dentistry has had a great impact on dental education, management and practice. A prominent change is the digital revolution, which presents new computed technologies and accessible means of communication for sharing written and visual information. Biotechnology, yet another innovated field, will change dentistry even further. This article presents dental innovations forwarded by Israeli Hi-Tech companies. An overview of some advances in technology in the field of dentistry is presented. Part of the described technologies is in R&D phase, part is under preliminary clinical evaluation, and a few have undergone short-term clinical studies. Part A of the article discusses the application of computerized imaging systems to educational purposes, diagnostics and treatment; part B presents other diagnostic and therapeutic technologies.

[Hi-tech trends in future dentistry--Part B: diagnostic and therapeutic technologies].

The technology advance and the growing amount of knowledge had a great impact on dental practice for the last decade. The prominent change began with digital revolution presenting new computed technologies and accessible communicational means for sharing literal and imaging information. Following toward the coming biotechnological revolution, dentistry will be even further changed. This article presents dental innovations of Israeli Hi-Tech companies, sorted into two groups. Part A of the article discussed the area of computed imaging systems for educational purposes, diagnostic and treatment. While part B presents other diagnostic or therapeutic technologies. However, because some of the described technologies are still on their R&D (Research and Development) phases, they are not commercialized yet in the market.

Effect of the ArF excimer laser on human enamel.

Human enamel surface was irradiated with ArF excimer laser and examined under light microscopy and scanning electron microscopy (SEM). Enamel surface was irradiated at three different areas with different energy fluences. It is demonstrated that the ArF excimer laser causes ablation of the calcified hard enamel tissue. Ablation curves were measured. There was no significant difference found in the etch depth between the three different areas of enamel surface. The morphology of the irradiated areas seen under the SEM was found to be dependent on energy fluence. It changed with increase in energy fluence from being etched to forming a smooth, fused, glaze-like surface and then at very high energy fluences producing a rough surface. The influence of the laser irradiation was confined to the irradiated area only, with no visible heat damage to the surroundings. These results suggest that excimer laser could be applied in a controlled and defined manner for tooth enamel treatments in dentistry.