Recovery of Acid Production in Streptococcus mutans Biofilms after Short-Term Fluoride Treatment.

Fluoride is commonly used as an ingredient of topical oral hygiene measures. Despite the anti-acidogenic activities of fluoride against cariogenic biofilms, the recovery of the biofilms from fluoride damage is unclear. Herein, we investigated the recovery of acid production in Streptococcus mutans biofilms after short-term or during periodic 1-min fluoride treatments. For this study, 46-hour-old S. mutans biofilms were treated with fluoride (0-2,000 ppm F-) for 1-8 min and then incubated in saliva for 0-100 min. The 74-hour-old biofilms were also periodically treated with the fluoride concentration during biofilm formation (1 min/treatment). Changes in acidogenicity and viability were determined via pH drop and colony-forming unit assays, respectively. In this study, acid production after a 1-min fluoride treatment was recovered as saliva incubation time increased, which followed a linear pattern of concentration dependence (R = 0.99, R2 = 0.98). The recovery pattern was in a biphasic pattern, with an initial rapid rate followed by a second slow recovery. Furthermore, recovery from fluoride damage was retarded in a concentration-dependent manner as treatment time increased. In periodic 1-min fluoride treatments, acid production in the biofilms was not diminished during the non-fluoride treatment period; however, it was reduced in a concentration-dependent manner during the fluoride treatment period. The viability of the biofilm cells did not change, even at high fluoride concentrations. Collectively, our results suggest that brief fluoride treatment does not sustain anti-acidogenic activity against S. mutans in biofilms since the damage is recoverable with time.

Difference in formation of a dental multi-species biofilm according to substratum direction.

OBJECTIVES: The aim of this study was to investigate the difference in dental biofilm formation according to substratum direction, using an artificial biofilm model. METHODS: A three-species biofilm, consisting of Streptococcus mutans, Streptococcus oralis, and Actinomyces naeslundii, was formed on saliva-coated hydroxyapatite (sHA) discs oriented in three directions: downward (the discs placed in the direction of gravity), vertical (the discs placed parallel to the direction of gravity), and upward (the discs placed in opposite direction of gravity). The biofilms at 22 h and 46 h of age were analyzed using microbiological and biochemical methods, fluorescence-based assays, and scanning electron microscopy to investigate difference in bacterial adhesion, early and mature biofilm formation. RESULTS: The biofilms formed in the upward direction displayed the most complex structure, with the highest number and biovolume of bacteria, as well as the lowest pH conditions at both time points. The vertical and downward directions, however, had only scattered and small bacterial colonies. In the 22-h-old biofilms, the proportion of S. oralis was similar to, or slightly higher than, that of S. mutans in all directions of substratum surfaces. However, in the 46-h-old biofilms, S. mutans became the dominant bacteria in all directions, especially in the vertical and upward directions. CONCLUSIONS: The direction of the substratum surface could impact the proportion of bacteria and cariogenic properties of the multi-species biofilm. Biofilms in an upward direction may exhibit a higher cariogenic potential, followed by those in the vertical and downward directions, which could be related to gravity.

Ionic liquid-immobilized silica gel as a new sorbent for solid-phase extraction of heavy metal ions in water samples.

In the current study, we have developed a solid-phase extraction (SPE) method with novel C18-alkylimidazolium ionic liquid immobilized silica (SiO2-(CH2)3-Im-C18) for the preconcentration of trace heavy metals from aqueous samples as a prior step to their determination by inductively coupled plasma mass spectrometry (ICPMS). The material was characterized by Fourier-transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TGA), Energy-Dispersive X-ray Spectroscopy (EDS), and Brunauer-Emmett-Teller (BET) analysis. A mini-column packed with SiO2-(CH2)3-Im-C18 sorbent was used for the extraction of the metal ions complexed with 1-(2-pyridylazo)-2-naphthol (PAN) from the water sample. The effects of pH, PAN concentration, length of the alkyl chain of the ionic liquid, eluent concentration, eluent volume, and breakthrough volume have been investigated. The SiO2-(CH2)3-Im-C18 allows the isolation and preconcentration of the heavy metal ions with enrichment factors of 150, 60, 80, 80, and 150 for Cr3+, Ni2+, Cu2+, Cd2+, and Pb2+, respectively. The limits of detection (LODs) for Cr3+, Ni2+, Cu2+, Cd2+, and Pb2+ were 0.724, 11.329, 4.571, 0.112, and 0.819 µg L-1, respectively with the relative standard deviation (RSD) in the range of 0.941-1.351%.

Dentist Job Satisfaction: A Systematic Review and Meta-analysis.

OBJECTIVES: Because of the heterogeneous nature of the evidence regarding dentists' job satisfaction, an overview was necessary to examine dentists' level of job satisfaction and to determine related work environmental factors. MATERIALS AND METHODS: A literature search was conducted using preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines. Electronic database searches of PubMed/MEDLINE, EMBASE, and Web of Science were performed until March 1, 2020. Two independent authors collected data and assessed the methodological quality of primary studies using the Newcastle Ottawa Scale. RESULTS: Nine studies were included from the 1987 initially retrieved. Among the included studies, 5 exhibited a neutral level of satisfaction and originated from China, South Korea, Egypt, and the United States, and 3 studies from Canada, Lithuania, and the United States showed a high level of satisfaction. Only 1 study did not report the mean job satisfaction score. According to bias evaluation, 9 studies were considered low risk. CONCLUSION: The findings showed that dentists were satisfied with their jobs at a moderate to high level, and specialists were more satisfied than general dentists. Regarding work environmental factors, the 6 most satisfied factors were patient relationships, respect, delivery of care, staff, professional relationship, and professional environment. Five of the least satisfied factors were personal time, stress, income, practice management, and professional time. However, longitudinal studies would be required to identify changes in these factors. Further studies should be performed in middle- and low-income countries using the Dentist Satisfaction Survey, including stress evaluation.

Tailoring chemical compositions of biodegradable mesoporous organosilica nanoparticles for controlled slow release of chemotherapeutic drug.

Biodegradable periodic mesoporous organosilica nanoparticles (B-PMO) are an outstanding nanocarrier due to their biodegradability and high drug load capacities. The present study describes a synthesis of a phenylene-containing tetrasulfide based B-PMO, named P4S. The incorporation of aromatic phenylene groups into the framework creates a strong interaction between nanoparticles (NPs) with aromatic rings in the cordycepin molecules. This results in the low release profile under various conditions. In addition, the replacement of this linker slowed the degradation of nanoparticles. The physicochemical properties of the nanoparticles are evaluated and compared with a biodegradable ethane-containing tetrasulfide based PMO and a non-degradable MCM-41. The biodegradability of P4S is also demonstrated in a reducing environment and the 100 nm spherical nanoparticles completely decomposed within 14 days. The porous structure of P4S has a high loading of hydrophilic cordycepin (approximately 731.52 mg g-1) with a slow releasing speed. The release rates of P4S NPs are significantly lower than other materials, such as liposomes, gelatin nanoparticles, and photo-crosslinked hyaluronic acid methacrylate hydrogels, in the same solution. This specific release behavior could guarantee drug therapeutic effects with minimum side-effects and optimized drug dosages. Most importantly, according to the in vitro cytotoxicity study, cordycepin-loaded P4S NPs could retain the toxicity against liver cancer cell (HepG2) while suppressed the cytotoxicity against normal cells (BAEC).

Synthesis of 5-hydroxymethylfurfural from monosaccharides catalyzed by superacid VNU-11-SO4 in 1-ethyl-3-methylimidazolium chloride ionic liquid.

Superacid VNU-11-SO4, a modified metal-organic framework by post-synthetic treatment with a sulfuric acid solution, has been considered as a promising heterogeneous catalyst in the isomerization of glucose to fructose and further dehydration to form 5-hydroxymethylfurfural (HMF) due to its possession of both Lewis and Brønsted acid sites. In this work, we focused on using VNU-11-SO4 for the optimization of the conversion of fructose and glucose into HMF using an ionic liquid as a green solvent. The highest yields of HMF from glucose and fructose could be obtained in 28% (140 °C, 8 h) and 86% (110 °C, 3 h), respectively, with the use of VNU-11-SO4 catalyst in 1-ethyl-3-methylimidazolium chloride ionic liquid. Recycling examination of the catalyst showed only a slight decrease in the HMF yield, implying its potential industrial application in biomass transformation.

Difference in virulence and composition of a cariogenic biofilm according to substratum direction.

The aim of this study was to investigate the difference in composition and virulence of Streptococcus mutans biofilms according to substratum direction. S. mutans biofilms (46-h-old) were formed on three different saliva-coated hydroxyapatite (sHA) disc direction groups: downward (discs placed in the direction of gravity), vertical (discs placed parallel to gravity direction), and upward (discs placed opposite to gravity). The 46-h-old biofilms on sHA discs in the upward direction showed the highest biofilm accumulation, colony forming unit (CFU) count, and extracellular polysaccharide (EPS) amount, followed by those in the vertical and downward directions. In the confocal laser scanning microscopy (CLSM) study, the biofilms in the upward direction also showed the highest bacterial count (live or dead cells) and EPS biovolume. Scanning electron microscopy (SEM) analysis confirmed the microbiological and biochemical results. In addition, biofilm density and acid production were higher in the upward direction than those in the other directions. Our findings suggest that substratum direction, which might be related to gravity, strongly influences the formation and virulence of cariogenic biofilms and subsequent initiation of dental caries. Collectively, the differences in the formation and virulence of cariogenic biofilms are related to the direction of tooth surface (occlusal surfaces of mandibular teeth > proximal surfaces > occlusal surfaces of maxillary teeth).

Functional Relationship between Sucrose and a Cariogenic Biofilm Formation.

Sucrose is an important dietary factor in cariogenic biofilm formation and subsequent initiation of dental caries. This study investigated the functional relationships between sucrose concentration and Streptococcus mutans adherence and biofilm formation. Changes in morphological characteristics of the biofilms with increasing sucrose concentration were also evaluated. S. mutans biofilms were formed on saliva-coated hydroxyapatite discs in culture medium containing 0, 0.05, 0.1, 0.5, 1, 2, 5, 10, 20, or 40% (w/v) sucrose. The adherence (in 4-hour biofilms) and biofilm composition (in 46-hour biofilms) of the biofilms were analyzed using microbiological, biochemical, laser scanning confocal fluorescence microscopic, and scanning electron microscopic methods. To determine the relationships, 2nd order polynomial curve fitting was performed. In this study, the influence of sucrose on bacterial adhesion, biofilm composition (dry weight, bacterial counts, and water-insoluble extracellular polysaccharide (EPS) content), and acidogenicity followed a 2nd order polynomial curve with concentration dependence, and the maximum effective concentrations (MECs) of sucrose ranged from 0.45 to 2.4%. The bacterial and EPS bio-volume and thickness in the biofilms also gradually increased and then decreased as sucrose concentration increased. Furthermore, the size and shape of the micro-colonies of the biofilms depended on the sucrose concentration. Around the MECs, the micro-colonies were bigger and more homogeneous than those at 0 and 40%, and were surrounded by enough EPSs to support their structure. These results suggest that the relationship between sucrose concentration and cariogenic biofilm formation in the oral cavity could be described by a functional relationship.