Pretreatment of dentin using colloidal platinum nanoparticles (CPtN) can enhance the bond strength of dentin adhesives. However, the combination of CPtN, which is negatively charged, with cationic monomer-containing adhesive may reduce the antibacterial activity of the original material. Thus, the purpose of this study was to assess the effect of CPtN on the bactericidal activity of two cationic antibacterial monomers, 12-methacryloyloxydodecylpyridinium bromide (MDPB) and methacryloxylethyl cetyl dimethyl ammonium chloride (DMAE-CB). The rapid killing effects of the two monomers against planktonic or attached Streptococcus mutans in the presence or absence of CPtN were examined by viable cell counts. The measurement of minimum inhibitory and bactericidal concentrations demonstrated that CPtN up to 2.5 mM has no antibacterial activity. In the absence of CPtN, rapid killing of both planktonic and attached Streptococcus mutans were achieved by the two cationic monomers. Combination with 0.1 mM CPtN did not reduce the bactericidal effects of the two monomers, indicating that CPtN may be used as a pretreatment with antibacterial adhesives.

OBJECTIVES: We had previously discovered that the flexural and tensile strengths of human dentin were 2-2.4 times greater after being heated to 140°C, and deduced that the generation of higher-density structures and therefore dehydration probably promoted the increased strength. Our test hypotheses were that intertubular dentin, which constitutes a major part of organic components, was selectively affected by heating, and such changes could happen without critical damages to the basic structure of dentin type I collagen. METHODS: Micro-mechanical changes of human dentin by heating at 140°C were investigated by nano-indentation. Chemical changes in dentin collagen after heating were also investigated by X-ray diffraction study, a microscopic Fourier transform infrared (micro-FTIR) and a laser Raman spectroscopic analyses, and a cross-linking analysis by high-performance liquid chromatography. RESULTS: The results of nano-indentation showed that the micro-hardness of intertubular dentin increased after heating at 140°C to 1.8 times more than unheated dentin; on the other hand, peritubular dentin was unchanged. Results of X-ray diffraction showed that the lateral packing of collagen molecules shrank from 13.6±0.3 to 10.6±0.1Å after heating, but the shrinkage reversed to the original after rehydration for seven days. After heating, no substantial chemical changes in the collagen molecules were detected in tests by micro-FTIR or Raman analyses, or by cross-linking analysis. SIGNIFICANCE: These results suggest that intertubular dentin, which contains most of the type I collagen, was selectively affected by heating at 140°C without critical damage to its collagen.

This study evaluated the cytotoxicity of self-etching primers/adhesives by direct contact and dentin barrier tests. The three two-step self-etching systems Clearfil SE Bond (CSE), Clearfil Protect Bond (CPB), Prime&Bond NT/NRC (PB) and one-step self-etching systems Reactmer Bond (RB), Clearfil Tri-S Bond (CTS), and Adper Prompt L-Pop (AP) were examined. In direct contact tests, L929 cells were cultured in the presence of diluted solutions (50, 20, 10, and 1%) of primer/conditioner of adhesive systems. For dentin barrier tests, each system was applied onto 0.5 or 1.5 mm thick human dentin assembled in a simple pulp chamber device and incubated for 24 h at 37°C to make the diffusive components contact the L929 cells placed at the bottom of the chamber. The cytotoxic effects were assessed by MTT assay. Cell culture without application of any primers/adhesives served as the control for both tests. One-way ANOVA and Tukey HSD tests were used for statistical analyses. The direct contact tests demonstrated that CSE and CPB were less toxic than the other materials at all dilutions. In the dentin barrier tests, toxic effects of materials were reduced with an increase in thickness of intervening dentin. CSE and CPB showed less cytotoxicity than the other adhesives (p<0.05) when applied to 0.5 mm-thick dentin, and CSE was the least toxic in the 1.5 mm-dentin group (p<0.05). Dentin thickness positively affected biocompatibility of the tested bonding systems. Two-step self-etching systems with HEMA-based primers were more biocompatible than other self-etching adhesives.

AIMS To investigate the effects of the combined application of an N-acyl homoserine lactone (HSL) analog and antibiotics on biofilms of Porphyromonas gingivalis, a major pathogen of periodontal disease. METHODS AND RESULTS Antibiotics used were cefuroxime, ofloxacin and minocycline. A flow-cell model was used for biofilm formation. Samples were divided into four groups: control, analog-treated, antibiotic-treated and combined application groups. Biofilm cell survival was determined using adenosine triphosphate (ATP) bioluminescence and confocal laser microscopy (CLSM). In the combined application group, the ATP count in biofilm cells was significantly decreased compared with the antibiotic-treated group (Games-Howell test, P < 0·05). A combination of cefuroxime and the analog was most effective against the P. gingivalis biofilm. CLSM observations revealed that the proportion of dead cells was highest in the combined application group. CONCLUSIONS The combined application of the N-acyl HSL analog and antibiotics was effective at reducing the viability of P. gingivalis cells in biofilms. SIGNIFICANCE AND IMPACT OF THE STUDY The combined application of the N-acyl HSL analog and antibiotics may be successful for eradicating infections involving bacterial biofilms, such as periodontitis.

Gerodontology 2011; doi: 10.1111/j.1741-2358.2011.00571.x Clinically acceptable restorations may be a hotbed for cariogenic microbes Objective:  The aim of this study was to investigate the cross-sectional association of dental restorations with salivary cariogenic pathogens among the elderly to establish effective parameters of caries risk for this population. Materials and methods:  Stimulated whole saliva was collected from 289 community-dwelling older adults (66.2 ± 3.9 years old) who had 20 or more teeth. Salivary levels of three cariogenic bacteria (Streptococcus mutans, Streptococcus sobrinus and lactobacilli) were estimated using quantitative polymerase chain reaction (real-time PCR) method. Results:  The mean number of residual teeth was 26.4, and restored teeth with crowns, inlays and composite resin were 7.35, 3.88 and 0.68, respectively. The number of crowns correlated positively with salivary S. mutans, S. sobrinus and lactobacilli. Multiple linear regression analyses showed that the number of restored teeth with crowns was independently associated with salivary S. mutans, S. sobrinus and lactobacilli after controlling for age, gender, number of residual teeth and salivary flow rate. Salivary flow rate was independently associated with salivary S. mutans and lactobacilli. Conclusion:  The number of crowns had an association with salivary levels of cariogenic bacteria, suggesting that this parameter may be a caries risk indicator for the elderly population.

Antibiotic resistance of biofilm-grown bacteria contributes to chronic infections such as marginal and periapical periodontitis, which are strongly associated with Porphyromonas gingivalis. Concurrent azithromycin (AZM) administration and mechanical debridement improve the clinical parameters of periodontal tissue in situ. We examined the in vitro efficacy of AZM against P. gingivalis biofilms. The susceptibility of adherent P. gingivalis strains 381, HW24D1, 6/26 and W83 to AZM, erythromycin (ERY), ampicillin (AMP), ofloxacin (OFX) and gentamicin (GEN) were investigated using a static model. The optical densities of adherent P. gingivalis cells were significantly decreased by using AZM and ERY at sub-MIC compared with controls in all the strains tested, except for the effect of ERY on strain W83. AMP and OFX inhibited P. gingivalis adherent cells at over their MICs, and GEN showed no inhibition in the static model. The effects of AZM and ERY against biofilm cells were investigated using a flow cell model. The ATP levels of P. gingivalis biofilms were significantly decreased by AZM at concentrations below the sub-MICshowever, ERY was not effective for inhibition of P. gingivalis biofilm cells at their sub-MICs. Furthermore, decreased density of P. gingivalis biofilms was observed three-dimensionally with sub-MIC AZM, using confocal laser scanning microscopy. These findings suggest that AZM is effective against P. gingivalis biofilms at sub-MIC levels, and could have future clinical application for oral biofilm infections such as chronic marginal and periapical periodontitis.

Chronological gene expression patterns of biofilm-forming cells are important to understand bioactivity and pathogenicity of biofilms. For Porphyromonas gingivalis ATCC 33277 biofilm formation, the number of genes differentially regulated by more than 1.5-fold was highest during the growth stage (312/2,090 genes), and some pathogen-associated genes were time-dependently controlled.

The cholesterol biosynthetic pathway produces not only sterols but also non-sterol mevalonate metabolites involved in isoprenoid synthesis. Mevalonate metabolites affect transcriptional and post-transcriptional events that in turn affect various biological processes including energy metabolism. In the present study, we examine whether mevalonate metabolites activate PPARγ (peroxisome-proliferator-activated receptor γ), a ligand-dependent transcription factor playing a central role in adipocyte differentiation. In the luciferase reporter assay using both GAL4 chimaera and full-length PPARγ systems, a mevalonate metabolite, FPP (farnesyl pyrophosphate), which is the precursor of almost all isoprenoids and is positioned at branch points leading to the synthesis of other longer-chain isoprenoids, activated PPARγ in a dose-dependent manner. FPP induced the in vitro binding of a co-activator, SRC-1 (steroid receptor co-activator-1), to GST (glutathione transferase)-PPARγ. Direct binding of FPP to PPARγ was also indicated by docking simulation studies. Moreover, the addition of FPP up-regulated the mRNA expression levels of PPARγ target genes during adipocyte differentiation induction. In the presence of lovastatin, an HMG-CoA (3-hydroxy-3-methylglutaryl-CoA) reductase inhibitor, both intracellular FPP levels and PPARγ-target gene expressions were decreased. In contrast, the increase in intracellular FPP level after the addition of zaragozic acid, a squalene synthase inhibitor, induced PPARγ-target gene expression. The addition of FPP and zaragozic acid promotes lipid accumulation during adipocyte differentiation. These findings indicated that FPP might function as an endogenous PPARγ agonist and regulate gene expression in adipocytes.

OBJECTIVES Being able to predict an individual's risks of dental caries would offer a potentially huge natural step forward toward better oral heath. As things stand, preventive treatment against caries is mostly carried out without risk assessment because there is no proven way to analyse an individual's risk factors. The purpose of this study was to try to identify those patients with high and low risk of caries by using Classification and Regression Trees (CART). METHODS In this historical cohort study, data from 442 patients in a general practice who met the inclusion criteria were analysed. CART was applied to the data to seek a model for predicting caries by using the following parameters according to each patient: age, number of carious teeth, numbers of cariogenic bacteria, the secretion rate and buffer capacity of saliva, and compliance with a prevention programme. The risks of caries were presented by odds ratios. Multiple logistic regression analysis was performed to confirm the results obtained by CART. RESULTS CART identified high and low risk patients for primary caries with relative odds ratios of 0.41 (95%CI: 0.22-0.77, p = 0.0055) and 2.88 (95%CI: 1.49-5.59, p = 0.0018) according the numbers of cariogenic bacteria. High and low risk patients for secondary caries were also identified with the odds ratios of 0.07 (95%CI: 0.01-0.55, p = 0.00109) and 7.00 (95%CI: 3.50-13.98, p < 0.0001) according the numbers of bacteria and existing caries. CONCLUSIONS Cariogenic bacteria play a leading role in the incidence of caries. CART proved effective in identifying an individual patient's risk of caries.

The periodontopathogenic bacterium Eikenella corrodens has an N-acetyl-D-galactosamine (GalNAc)-specific lectin, that contributes significantly to the pathogenicity of the bacterium. Recently, we reported that plasmid-mediated genomic recombination enhances the activity of this lectin. In this study, we investigated the effects of genomic recombination on certain virulence factors. Introduction of the recombinase gene resulted in hemolysis and significantly increased bacterial adhesion to epithelial cells. It was suggested that the enhanced adhesion was attributable to increased lectin activity due to genomic recombination, because it was inhibited by the addition of GalNAc. In contrast, invasion of the epithelial cells was remarkably reduced by genomic recombination. Although we assumed that this decrease in invasion resulted from a loss of type-IV pili, the phase variant did not show any decrease in invasion activity. This suggests that type-IV pili do not contribute to the invasive ability of E. corrodens. Our results suggest that genomic recombination enhances the pathogenicity of E. corrodens.