Questionnaire survey on the satisfaction of SimEx dental education system.

Background/purpose: The SimEx is dental training system that applies new technology in a computerized dental simulator. The purpose of this study was to understand the usability satisfaction of the SimEx dental education and evaluation system by dental students and dentists at Tohoku University. Materials and methods: In this study, the Tohoku University IRB execution number was 2020-3-33. The number of subjects accepted was 59 at Tohoku University and divided into 4 groups based on years of clinical experience (Group A: 0 years; Group B: 1-2 years; Group C: 2-5 years; Group D: at least 5 years), and a total of 58 usability questionnaires were collected. Subjects completed the SimEx Usability Satisfaction Questionnaire after operating the SimEx (EPED Inc., Kaohsiung, Taiwan) course, which contained 16 questions. Results: Among the 58 questionnaires collected by Tohoku University, there were 19 undergraduate students (4th∼6th grade), 12 post-graduate students, 14 residents, and 13 dentists. Significant differences between Group A and Group B, and between Group A and Group D were found (P < 0.05). The same results were obtained for the "experience satisfaction index". In the items where significant differences were found, longer clinical experience tended to result in lower scores. Conclusion: From these results, we can conclude that the SimEx education and evaluation system facilitates students' self-learning, and this system is very useful for continued study and clinical skill training for dentists, especially for students and junior dentists with high usability satisfaction.

In situ detection of endogenous proteolytic activity and the effect of inhibitors on tooth root surface.

OBJECTIVES: The aim of this study was to clarify the distribution and activity of proteolytic enzymes and examine the inhibitory effects of various substances on this proteolytic activity on tooth root surfaces in situ. METHODS: Disk-shaped bovine tooth root samples were partly pretreated in acid solution (50 mM lactic acid buffer, pH 4.0) for 48 h. The fluorescence intensity of samples was detected with fluorescent substrate solution for collagenase and gelatinase using a stereoscopic fluorescence microscope for 60 min. The acid-pretreated and non-acid-pretreated root samples were treated with chlorhexidine (CHX), sodium fluoride (NaF), epigallocatechin gallate (EGCG), and calcium hydroxide (Ca(OH)2) for 10 min, and silver diamine fluoride (SDF) for 10, 30, and 60 s. These samples were immersed in the fluorescence substrate solution at pH 7.0, and the fluorescence intensity of samples was detected. The fluorescence intensity was calculated using analysis software. RESULTS: Gelatinase activity was detected in root samples. Gelatinase activity of the acid-pretreated side was significantly higher than that of the non-acid-pretreated side (1.63 times) at 60 min. CHX, EGCG, Ca(OH)2, and SDF decreased the gelatinase activity of root samples, while NaF had no effect. CONCLUSIONS: Gelatinase activity was detected from the root in situ and it was increased by acid-pretreatment. CHX, EGCG, Ca(OH)2, and SDF inhibited gelatinase activity. CLINICAL SIGNIFICANCE: Substances that inhibit proteolytic activity found in this research method will be useful for root caries prevention.

Profiling of the microbiota of breast milk before and after feeding with an artificial nipple.

OBJECTIVES: Breast milk is a valuable and useful source of nutrition; however, surplus milk is routinely discarded for hygiene reasons despite an unclear scientific basis. Here, we profiled the microbiota of expressed breast milk before and after feeding with an artificial nipple and examined the bacterial survival in breast milk stored at 4 °C. METHODS: Eleven mother-baby pairs were included in the study. Samples of expressed breast milk were collected before and after feeding with an artificial nipple and examined both immediately (0 h) and after storage for 3 and 12 h at 4 °C. Each sample was inoculated onto a blood agar plate and incubated anaerobically and aerobically at 37 °C. Genomic DNA was extracted from individual bacterial colonies, which were identified by 16S rRNA gene sequencing. RESULTS: Before feeding, the bacterial counts at 0 and 12 h were (1.4 ± 1.6) × 105 colony-forming units (CFU)/mL and (1.4 ± 0.6) × 105 CFU/mL, respectively. Staphylococcus (47.7% and 41.9%, respectively), Cutibacterium (20.7% and 36.0%, respectively), and Streptococcus (16.1% and 6.6%, respectively) were identified among the samples. In contrast, after feeding, the bacterial counts at 0 and 12 h were (2.7 ± 1.7) × 105 CFU/mL and (2.1 ± 2.5) × 105 CFU/mL, respectively. Staphylococcus (30.1% and 37.4%, respectively), Cutibacterium (11.7% and 31.7%, respectively), and Streptococcus (41.5% and 25.2%, respectively), were identified among the samples. CONCLUSIONS: Bacteria were present in the breast milk before feeding. Although the main component of the microbiota shifted from Staphylococcus to Streptococcus species after feeding, these results suggest that surplus expressed breast milk may be preserved safely in a refrigerator for at least 12 h after feeding with an artificial nipple.

Profiling of the microbiota in the remaining sports drink and orange juice in plastic bottles after direct drinking.

OBJECTIVES: The survival of bacteria in the sports drink and orange juice remaining in and at the mouth of bottles after direct drinking was examined after immediately drinking and incubation at 37 °C for 24 h. METHODS: Nine healthy participants were asked to drink approximately 100 mL of a plastic bottled sports drink or orange juice. The samples were cultured anaerobically at 37 °C for 7 days. Genomic DNA was extracted from the resulting individual colonies, and bacterial species were identified using 16 S rRNA gene sequencing. RESULTS: The mean amount of bacteria in the remaining sports drink and orange juice, immediately after drinking, were (1.6 ± 2.3) × 103 colony-forming units (CFU)/mL and (2.9 ± 3.3) × 103 CFU/mL, respectively. Additionally, bacteria recovered from the mouths of the sports drink and orange juice bottles were (2.5 ± 5.5) × 104 CFU/mL and (5.8 ± 2.4) × 103 CFU/mL, respectively. Oral bacteria, such as Streptococcus, Actinomyces, Neisseria, and Rothia were found to be transferred in the sports drink and orange juice, and the bacteria were scarcely detected after incubation at 37 °C for 24 h. CONCLUSIONS: The bacterial levels differed significantly from the previously reported levels in bottled tea 24 h after drinking, suggesting that remaining drinks with low pH levels can be preserved for a longer period.

Microbiota profiles on the surface of non-woven fabric masks after wearing.

This study aimed to characterize commensal microbiota on the skin before and after wearing masks, and to characterize the microbiota on the surface of used masks after 1 week of drying. From the 13 human subjects (age range, 19-26 years), mean bacterial concentrations of (6.1 ± 11.0) × 105 and (1.0 ± 1.4) × 106 colony-forming units (CFU)/mL were recovered from the skin of the buccal areas wiped with a sterile cotton swab before and after wearing non-woven fabric masks for 8 h, respectively. Furthermore (3.4 ± 4.9) × 104 CFU/mL of bacteria were recovered from the mask surfaces. The bacteria contained in the masks, which consisted mainly of Cutibacterium acnes and Staphylococcus epidermidis/aureus, virtually disappeared after drying the masks indoors for 1 week.

A water-soluble glass-based temporary restorative resin inhibited bacteria-induced pH reductions at the bacteria-material interface.

This study aimed to evaluate the inhibitory effects of a water-soluble glass based temporary restorative resin (WSG-TRR) on bacteria-induced pH reductions at the bacteria-material interface. Each material (WSG-TRR, glass-ionomer cement, resin composite and conventional temporary restorative resin) was fixed to the bottom of the well of the experimental apparatus. The well was filled with pelleted cells of Streptococcus mutans, and the pH at the bacteria-material interface was monitored using a miniature pH electrode. The concentration of ions released from WSG-TRR and the effect of fluoride and zinc ions on bacteria-induced pH reduction was evaluated. The buffering capacities of WSG-TRR and WSG were also evaluated. At 90 min after the glucose addition, WSG-TRR exhibited the highest pH (5.29±0.12). Fluoride ion was detected at the interface between bacteria and WSG-TRR. Moreover, WSG were found to confer high buffering capacity. A WSG-TRR reduced bacteria-induced pH reductions at the bacteria-material interface.

Profiling of Microbiota at the Mouth of Bottles and in Remaining Tea after Drinking Directly from Plastic Bottles of Tea.

It has been speculated that oral bacteria can be transferred to tea in plastic bottles when it is drunk directly from the bottles, and that the bacteria can then multiply in the bottles. The transfer of oral bacteria to the mouth of bottles and bacterial survival in the remaining tea after drinking directly from bottles were examined immediately after drinking and after storage at 37 °C for 24 h. Twelve healthy subjects (19 to 23 years of age) were asked to drink approximately 50 mL of unsweetened tea from a plastic bottle. The mouths of the bottles were swabbed with sterile cotton, and the swabs and the remaining tea in the bottles were analyzed by anaerobic culture and 16S rRNA gene sequencing. Metagenomic analysis of the 16S rRNA gene was also performed. The mean amounts of bacteria were (1.8 ± 1.7) × 104 colony-forming units (CFU)/mL and (1.4 ± 1.5) × 104 CFU/mL at the mouth of the bottles immediately after and 24 h after drinking, respectively. In contrast, (0.8 ± 1.6) × 104 CFU/mL and (2.5 ± 2.6) × 106 CFU/mL were recovered from the remaining tea immediately after and 24 h after drinking, respectively. Streptococcus (59.9%) were predominant at the mouth of the bottles immediately after drinking, followed by Schaalia (5.5%), Gemella (5.5%), Actinomyces (4.9%), Cutibacterium (4.9%), and Veillonella (3.6%); the culture and metagenomic analyses showed similar findings for the major species of detected bacteria, including Streptococcus (59.9%, and 10.711%), Neisseria (1.6%, and 24.245%), Haemophilus (0.6%, and 15.658%), Gemella (5.5%, and 0.381%), Cutibacterium (4.9%, and 0.041%), Rothia (2.6%, and 4.170%), Veillonella (3.6%, and 1.130%), Actinomyces (4.9%, and 0.406%), Prevotella (1.6%, and 0.442%), Fusobacterium (1.0%, and 0.461%), Capnocytophaga (0.3%, and 0.028%), and Porphyromonas (1.0%, and 0.060%), respectively. Furthermore, Streptococcus were the most commonly detected bacteria 24 h after drinking. These findings demonstrated that oral bacteria were present at the mouth of the bottles and in the remaining tea after drinking.

Profiling system of oral microbiota utilizing polymerase chain reaction-restriction fragment length polymorphism analysis.

OBJECTIVES: Profiling of oral microbiota has traditionally been performed using conventional methods. These methods are relatively time-consuming and labor-intensive. Metagenomic analysis of oral microbiota using high-speed next-generation sequencing is a highly promising technology. However, it is expensive. This study sought to develop a simple and cost-effective profiling method for oral microbiota using 16S rRNA gene polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis of PCR-amplified 16S ribosomal RNA genes. METHODS: Oral isolates of 59 bacterial species from human saliva, including Streptococcus, Actinomyces, and Veillonella, were cultured anaerobically on CDC Anaerobe 5% sheep blood agar plates. Genomic DNA was extracted from single colonies and 16S rRNA genes were PCR-amplified using the 27F and 1492R universal primers. The PCR products were purified and characterized by single digestion with HpaII restriction endonuclease. 16S rRNA gene sequences were obtained from the GenBank database, and the expected restriction profiles were compared with the RFLP patterns obtained from agarose gel electrophoresis. RESULTS: Sixty-five RFLP patterns were obtained from 27 genera and 59 species. The expected fragment sizes of these species were calculated based on GenBank 16S rRNA gene sequences. Fifty-nine patterns were obtained from the analysis of GenBank sequences. The RFLP patterns produced with HpaII distinguished many oral bacterial species. RFLP patterns enabling identification of oral bacteria were generated. The 16S rRNA gene PCR-RFLP analysis did not require expensive equipment and reagents and was cost-effective. CONCLUSION: PCR-RFLP analysis based on 16S rRNA genes could be an alternative method for oral microbiota analysis in smaller laboratories.

Bacterial concentration and composition in liquid baby formula and a baby drink consumed with an artificial nipple.

OBJECTIVES: To clarify the characteristics and growth of bacteria that may infiltrate liquid baby formula during feeding and after storage for more than 3 h, the transfer of oral bacteria through artificial nipples, and bacterial survival in liquid baby formula and a baby drink were examined immediately after drinking and after storage at 4 °C for 12 h and 24 h. METHODS: Thirteen human subjects (aged 19-24 years) were asked to drink approximately 50 mL of liquid baby formula and a baby drink, via the artificial nipple of a baby bottle. Samples of the remaining liquid after storage at 4 °C for 12 h and 24 h were inoculated onto blood agar plates and incubated anaerobically at 37 °C for 7 days. Genomic DNA was extracted from individual colonies, and the bacterial species were identified by 16S rRNA gene sequencing. RESULTS: The mean concentrations of bacteria in the liquid baby formula were (2.6 ± 2.8) × 104 and (4.1 ± 6.6) × 104 colony-forming unit/mL after storage at 4 °C for 12 h and 24 h, respectively. Streptococcus (43.2%), Veillonella (9.3%), and Schaalia (8.2%) species were recovered from the remaining liquid baby formula after storage at 4 °C for 12 h. In contrast, no bacteria were detected in the remaining baby drink after storage at 37 °C for 24 h. CONCLUSIONS: The levels of bacteria immediately after drinking and after storage at 4 °C for 12 h or 24 h were similar, suggesting that remaining liquid baby formula may be preserved safely in a refrigerator for more than 3 h.

Electrochemical evaluation of the hydrogen peroxide- and fluoride-induced corrosive property and its recovery on the titanium surface.

PURPOSE: This study aimed to elucidate the effects of hydrogen peroxide (H2O2) and sodium fluoride (NaF) on titanium surfaces under conditions mimicking those encountered during dental treatment. METHODS: Titanium samples were immersed in artificial saliva (AS), 1M H2O2, 1M H2O2 with catalase, 1000ppmF NaF, 1M H2O2 with 1000ppmF NaF, or 9000ppmF NaF (9000ppmF NaF: pH 5.3, other solutions: pH 6.5) for 3min. The electrochemical properties of the titanium samples were analyzed before and after the immersion procedures using a potentiostat. The amounts of titanium eluted into each solution were measured using inductively coupled plasma mass spectrometry. The post-immersion color changes (ΔE*ab) and gloss values of the titanium samples were determined using spectrophotometry. Moreover, the solution-treated titanium samples were subsequently immersed in AS and analyzed electrochemically at 1, 2, 3, 4, 6, 8, and 24h. RESULTS: The immersion of titanium in any of the solutions except 1000ppmF NaF caused significant increases in corrosive and passive currents and significant reductions in polarization resistance. No titanium elution or color changes were observed, except when 9000ppmF NaF was used. After immersion in AS, the electrochemical properties of all of the titanium samples, except the 9000ppmF NaF-treated samples, recovered within 24h. CONCLUSIONS: One M H2O2 and 1000ppmF NaF can be used alone or in combination in the clinical setting without causing significant titanium corrosion because the corrosive properties they induce is reversible. However, highly concentrated acidic fluorides can cause irreversible corrosion.

Profiling of microbiota in liquid baby formula consumed with an artificial nipple.

It is suspected that oral bacteria are transferred to the liquid baby formula through the artificial nipple and multiply in the bottle after feeding. In the present study, in order to understand the influence of bacteria on liquid baby formula after feeding, the transfer of oral bacteria through artificial nipples and their survival in liquid baby formula were examined immediately after drinking as well as after storage at 4°C for 3 h. Four healthy human subjects (20-23 years old) were asked to drink liquid baby formula (Aptamil®, ca. 50 mL) from baby bottles using artificial nipples. Samples of the liquid baby formula (immediately after drinking and 3 h later) were inoculated onto blood agar plates and incubated anaerobically at 37°C for 7 days. Salivary samples from each subject and 6 newborn infants were also cultured. Genomic DNA was extracted from individual colonies, and bacterial species were identified by 16S rRNA gene sequencing. The mean amounts of bacteria (CFU/mL) were (3.2 ± 3.0) ×104 and (3.4 ± 3.3) ×104 immediately after drinking and 3 h later, respectively. Streptococcus (41.6 and 40.5%), Actinomyces (24.3 and 21.5%) and Veillonella (16.2 and 11.0%) were recovered from the samples immediately after drinking and 3 h later, respectively. On the other hand, Streptococcus (38.9%), Actinomyces (17.1%), Neisseria (9.1%), Prevotella (6.9%), Rothia (6.9%) and Gemella (5.1%) were predominant in the saliva of adult subjects, and Streptococcus (65.2%), Staphylococcus (18.5%), Gemella (8.2%) and Rothia (5.4%) were predominant in the saliva of infant subjects. From these findings, oral bacteria, e.g., Streptococcus, Gemella and Rothia, were found to transfer into the liquid baby formula through artificial nipples, and the bacterial composition in the remaining liquid baby formula was found to resemble that of human saliva. The bacterial levels were similar between immediately after drinking and when stored at 4°C for 3 h, suggesting that the remaining liquid baby formula may be preserved in a refrigerator for a specified amount of time.

Sodium fluoride and silver diamine fluoride-coated tooth surfaces inhibit bacterial acid production at the bacteria/tooth interface.

OBJECTIVES: This study aimed to evaluate whether coating tooth surfaces with sodium fluoride (NaF) or silver diamine fluoride (SDF) inhibits bacteria-induced pH reductions at the bacteria/tooth interface. METHODS: Specimens of coronal enamel (CE) or root dentin (RD) were prepared. The surfaces of the specimens were treated with 2% NaF or 38% SDF solution. Some specimens were aged for 1 week after being treated. A tooth specimen was fixed to the bottom of the well of the experimental apparatus. A miniature pH electrode was placed on the specimen and the well was filled with Streptococcus mutans (SM) cells. The pH was monitored after the addition of 0.5% glucose. SM cells were recovered from the wells, and the amounts of lactate, calcium, fluoride, and silver were measured. RESULTS: The fluoride-treated tooth specimens exhibited significantly higher pH values than the untreated controls, irrespective of the tooth substrate at 120 min (CE: NaF 4.62 ± 0.06 vs 4.34 ± 0.10 and SDF 5.23 ± 0.29 vs 4.44 ± 0.16, RD: NaF 5.10 ± 0.11 vs 4.54 ± 0.33 and SDF 6.65 ± 0.47 vs 4.64 ± 0.39). The SDF-coated RD specimens released the greatest amounts of fluoride (103.3 ± 48.1 nmol/well) and silver (70.4 ± 36.9 nmol/well), while they exhibited significantly lower lactate production and decalcification (calcium release) than the control samples (lactate: 4.0 ± 0.7 vs 7.4 ± 0.3 mmol/l, calcium: 2.2 ± 0.4 vs 3.7 ± 0.5 µg/ml). This antimicrobial effect was weakened by 1 week's aging, while the acid resistance of the fluoride-treated surfaces seemed to increase with aging. CONCLUSIONS: Fluoride-treated tooth surfaces inhibit bacterial acid production at the bacteria/tooth interface. The SDF-coated RD had the strongest inhibitory effect. CLINICAL SIGNIFICANCE: Coating RD with SDF could help to prevent root caries.

Inhibitory effect of resin composite containing S-PRG filler on Streptococcus mutans glucose metabolism.

OBJECTIVES: Resin composites containing surface pre-reacted glass-ionomer (S-PRG) fillers have been reported to inhibit Streptococcus mutans growth on their surfaces, and their inhibitory effects were attributed to BO33- and F- ions. The aim of this study was to evaluate S. mutans acid production through glucose metabolism on resin composite containing S-PRG fillers and assess inhibitory effects of BO33- and F- on S. mutans metabolic activities. METHODS: The pH change through S. mutans acid production on experimental resin composite was periodically measured after the addition of glucose. Inhibitory effects of BO33- or F- solutions on S. mutans metabolism were evaluated by XTT assays and measurement of the acid production rate. RESULTS: The pH of experimental resin containing S-PRG fillers was significantly higher than that of control resin containing silica fillers (p < 0.05). OD450 values by XTT assays and S. mutans acid production rates significantly decreased in the presence of BO33- and F- compared with the absence of these ions (p < 0.05). CONCLUSIONS: pH reduction by S. mutans acid production was inhibited on resin composite containing S-PRG fillers. Moreover, S. mutans glucose metabolism and acid production were inhibited in the presence of low concentrations of BO33- or F-. CLINICAL SIGNIFICANCE: BO33- or F- released from resin composite containing S-PRG fillers exhibits inhibitory effects on S. mutans metabolism at concentrations lower than those which inhibit bacterial growth.

Corrosive effects of fluoride on titanium under artificial biofilm.

PURPOSE: This study aimed to investigate the effect of sodium fluoride (NaF) on titanium corrosion using a biofilm model, taking environmental pH into account. METHODS: Streptococcus mutans cells were used as the artificial biofilm, and pH at the bacteria-titanium interface was monitored after the addition of 1% glucose with NaF (0, 225 or 900ppmF) at 37°C for 90min. In an immersion test, the titanium samples were immersed in the NaF solution (0, 225 or 900ppm F; pH 4.2 or 6.5) for 30 or 90min. Before and after pH monitoring or immersion test, the electrochemical properties of the titanium surface were measured using a potentiostat. The amount of titanium eluted into the biofilm or the immersion solution was measured using inductively coupled plasma mass spectrometry. The color difference (ΔE*ab) and gloss of the titanium surface were determined using a spectrophotometer. RESULTS: After incubation with biofilm, pH was maintained at around 6.5 in the presence of NaF. There was no significant change in titanium surface and elution, regardless of the concentration of NaF. After immersion in 900ppm NaF solution at pH 4.2, corrosive electrochemical change was induced on the surface, titanium elution and ΔE*ab were increased, and gloss was decreased. CONCLUSIONS: NaF induces titanium corrosion in acidic environment in vitro, while NaF does not induce titanium corrosion under the biofilm because fluoride inhibits bacterial acid production. Neutral pH fluoridated agents may still be used to protect the remaining teeth, even when titanium-based prostheses are worn.

pH Response and Tooth Surface Solubility at the Tooth/Bacteria Interface.

Evaluating the physiochemical processes at the tooth surface/bacteria interface is important for elucidating the etiology of dental caries. This study aimed to compare the mineral solubility and protein degradation of coronal enamel (CE) and root dentin (RD), and investigate the involvement of dissolved components in bacteria-induced pH changes using a model of tooth/bacteria interface. An experimental apparatus forming a well was made of polymethyl methacrylate, and a bovine tooth (CE or RD) specimen was fixed at the bottom of the well. A miniature pH electrode was placed on the tooth, and Streptococcus mutans NCTC 10449 cells, grown in 0.5% glucose-containing complex medium, were packed into the well. The pH at the tooth/S. mutans interface was monitored continuously for 120 min after the addition of 0.5% glucose at 37°C. S. mutans cells were recovered from the wells, and the amounts of lactate and calcium were measured using a portable lactate meter and a fluorescent dye, respectively. Proteolytic activity was also evaluated fluorometrically. The pH of the RD/S. mutans interface was significantly higher than that of the CE/S. mutans interface (30 min: 6.37 ± 0.12 vs. 6.18 ± 0.11, 60 min: 6.08 ± 0.14 vs. 5.66 ± 0.27, 90 min: 5.49 ± 0.24 vs. 5.14 ± 0.22, p < 0.05). Greater amounts of calcium were dissolved from RD (3.19 ± 0.74 µg/mL) than from CE (1.84 ± 0.68 µg/mL; p < 0.05), while similar amounts of lactate were produced. Proteolytic activity was not detected at any of the interfaces. These results indicate that RD is more soluble to bacteria-induced acidification than CE. This method can contribute to the evaluation and development of caries-preventive materials.

PCR-dipstick DNA chromatography for profiling of a subgroup of caries-associated bacterial species in plaque from healthy coronal surfaces and periodontal pockets.

The onset of plaque-mediated disease, including dental caries and periodontal diseases, is highly associated with compositional change of the resident microflora from the ecological perspective. As specific bacterial profiles have been linked to different disease stages, microbial compositional measurements might therefore have great value for clinical diagnosis. Previously we have reported a dry-reagent strip biosensor-PCR-dipstick DNA chromatography, which utilized molecular recognition of oligonucleotides and biotin-streptavidin, and the optical property of colored microspheres, for semiquantifying a five-membered subgroup of caries-associated bacterial species in supragingival plaque from healthy coronal surfaces of teeth. The present study aimed to evaluate this technique's ability to differentiate microflora by comparing the subset profiles. Sixteen subgingival plaque specimens were pooled from periodontal pockets and analyzed for the composition of Streptococcus mutans, Streptococcus sobrinus, Scardovia wiggsiae, Actinomyces sp. and Veillonella parvula. Detection frequencies, relative abundance of each bacterial species, and the five-membered bacterial profiles were compared between supra- and subgingival groups. The supragingival plaque harbored significantly more of the tested species and higher amount of Actinomyces sp. and V. parvula. In subgingival plaque, the predominance was obscured, since several highly overlapped profiles were found at comparable frequencies. Thus, PCR-dipstick DNA chromatography using the same plaque sample enabled simultaneous profiling of multiple species at species level and facilitated discrimination between anticipated different microflora, making this technique a promising chair-side microbiota profiling method.

Effect of fluoride-releasing restorative materials on bacteria-induced pH fall at the bacteria-material interface: an in vitro model study.

OBJECTIVES: Inhibition of bacterial acid production by dental restorative materials is one of the strategies for secondary caries prevention. This study aimed to evaluate the effect of fluoride-releasing restorative materials on bacteria-induced pH fall at the bacteria-material interface. METHODS: Four fluoride-releasing restorative materials, glass-ionomer cement (GIC), resin-modified glass-ionomer cement (RMGIC), resin composite (RC) and flowable resin composite (FRC) were used. Each specimen was immersed in potassium phosphate buffer at pH 7.0 for 10min and 4 weeks, and in potassium acetate buffer at pH 5.5 for 4 weeks. An experimental apparatus was made of polymethyl methacrylate and had a well with restorative materials or polymethyl methacrylate (control) at the bottom. The well was packed with cells of Streptococcus mutans, and the pH at the interface between cells and materials was monitored using a miniature pH electrode after the addition of 1% glucose for 90min, and the fluoride released into the well was quantified using a fluoride ion electrode. RESULTS: The pH of GIC (4.98-5.18), RMGIC (4.77-4.99), RC (4.62-4.75) and FRC (4.54-4.84) at 90min were higher than that of control (4.31-4.49). The fluoride amounts released from GIC were the highest, followed by RMGIC, RC and FRC, irrespective of immersion conditions. Saliva coating on materials had no significant effect. CONCLUSIONS: The fluoride-releasing restorative materials inhibited pH fall at the bacteria-material interface. The degree of inhibition of pH fall seemed to correspond to the amount of fluoride detected, suggesting that the inhibition was due to the fluoride released from these materials. CLINICAL SIGNIFICANCE: A little amount of fluoride actually released from the fluoride-releasing materials may have caries preventive potential for oral bacteria.

Fluoride-sensitivity of growth and acid production of oral Actinomyces: comparison with oral Streptococcus.

Actinomyces are predominant oral bacteria; however, their cariogenic potential in terms of acid production and fluoride sensitivity has not been elucidated in detail and compared with that of other caries-associated oral bacteria, such as Streptococcus. Therefore, this study aimed to elucidate and compare the acid production and growth of Actinomyces and Streptococcus in the presence of bicarbonate and fluoride to mimic conditions in the oral cavity. Acid production from glucose was measured by pH-stat at pH 5.5 and 7.0 under anaerobic conditions. Growth rate was assessed by optical density in anaerobic culture. Although Actinomyces produced acid at a lower rate than did Streptococcus, their acid production was more tolerant of fluoride (IDacid production 50 = 110-170 ppm at pH 7.0 and 10-13 ppm at pH 5.5) than that of Streptococcus (IDacid production 50 = 36-53 ppm at pH 7.0 and 6.3-6.5 ppm at pH 5.5). Bicarbonate increased acid production by Actinomyces with prominent succinate production and enhanced their fluoride tolerance (IDacid production 50 = 220-320 ppm at pH 7.0 and 33-52 ppm at pH 5.5). Bicarbonate had no effect on these variables in Streptococcus. In addition, although the growth rate of Actinomyces was lower than that of Streptococcus, Actinomyces growth was more tolerant of fluoride (IDgrowth 50 = 130-160 ppm) than was that of Streptococcus (IDgrowth 50 = 27-36 ppm). These results indicate that oral Actinomyces are more tolerant of fluoride than oral Streptococcus, and bicarbonate enhances the fluoride tolerance of oral Actinomyces. Because of the limited number of species tested here, further study is needed to generalize these findings to the genus level.

Effects of a coating resin containing S-PRG filler to prevent demineralization of root surfaces.

The purpose of this study was to evaluate the ability of a coating material containing the surface pre-reacted glass-ionomer (S-PRG) filler to protect the root from demineralization in vitro. The proprietary coating resin containing the S-PRG filler (PRG Barrier Coat) was applied to human root dentin and immersed in acid buffer at pH 4.5 for 3 d. Demineralization was evaluated by micro-CT scanning and the dentin-material interface observed by scanning electron microscopy. The ability of the coating resin to modify acid production by Streptococcus mutans was investigated by monitoring pH using an ion-sensitive field-effect transistor pH electrode. Application of PRG Barrier Coat produced a coating layer with the thickness of approximately 200 µm and completely inhibited demineralization. The bacteria-induced pH fall at the material surface was significantly inhibited. We conclude that S-PRG fillercontaining coating resin may be an effective material for protecting exposed root from both chemical and biological challenges.