[in Japanese]

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Recently, the influences of biofilm have been focused on as serious problems in various fields such as biomaterial sciences and environmental engineering. Oral biofilm, generally called "dental plaque", is also regarded as a direct causative pathogen of dental caries and periodontal disease in dentistry. Therefore, it is indispensable to control biofilm for the prevention and improvement of oral diseases. In this study, a parallel plate flow-cell system using automated image analysis with a new algorithm was developed to enumerate initial biofilm formation. The aim of this study was to observe the properties and capabilities of the flow-cell system using human saliva-induced bacterial cells. In addition, the effects of salivary treatment of bacterial cells and the substratum (slide glass) on bacterial deposition were examined in consideration of the clinical oral state. It was found that the flow-cell system was useful to quantify initial bacterial deposition in real time. Five repetitions of each experiment indicated that the error levels (coefficient of variation) of the initial deposition rate J_0 values were within 24.6% for untreated glass plates, 34.5% for saliva-treated glass plates, 17.4% for saliva-treated cells, and 31.9% for saliva-treated glass plates and cells. It was shown that the initial adhesion of bacterial cells decreased specifically by saliva treatment of glass plates (t-test : p<0.05). In contrast, it was indicated that the initial adhesion of bacterial cells increased remarkably by saliva treatment of bacterial cells (t-test : p< 0.005). It was concluded that initial biofilm formation using human saliva-induced bacterial cells can be examined quantitatively by the parameter J_0 derived from the flowcell system of this study, and that saliva treatment of bacterial cells and the substratum strongly influences initial biofilm formation.

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The purpose of this study was to investigate the prevalence of dry mouth, and its association with dietary habits and related factors. A total of 143 girls at a junior high school (13-15 years old) and 854 girls at a senior high school (16-18 years old) participated in the present study. The prevalence of dry mouth among junior and senior high school students was 37.1% and 51.6%, respectively, which was significantly different (p<0.01). Multiple logistic regression analysis showed a significant association of age (OR=1.77, senior high school students), eating less than 3 times/day (OR=1.53, sometimes or always), eating fast foods (OR=1.55, sometimes or always), stuffy nose (OR=2.00, sometimes or always), mouth breathing (OR=1.55, sometimes or always), and stress (OR=2.02, sometimes or always) with subjective symptoms of dry mouth. These results suggested that subjective symptoms of dry mouth are affected according to increasing age, dietary habits, stuffy nose, mouth breathing, and stress.

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Various kinds of canned and bottled drinks or beverages (soft drinks, sports drinks, milk-containing beverages, juices, carbonated drinks, etc.) are easily available from vending machines, convenience stores, and supermarkets at any time. Excessive consumption of these drinks or beverages may cause systemic diseases such as diabetes mellitus. In view of dental health, we examined the potential risk of 62 popular drinks to induce dental caries by evaluating four factors : initial pH, titration amount of alkali for neutralization, acid productivity, and adhesive insoluble glucan synthesis induced by Streptococcus sobrinus. Then, we proposed radar chart models by integrating the scores obtained from the evaluations. All of the carbonated drinks, sports drinks, fruit and vegetable juices, and milk-containing beverages possessed a pH below 5.5, which is supposed to be the critical point of enamel decalcification. A large amount of alkali was required to neutralize such drinks and beverages, especially fruit and vegetable juices. The drinks except natural water, non-sugar tea and coffee drinks also showed a lower pH than the critical point after 2-h incubation at 37°C with S. sobrinus. Half of the investigated drinks induced adhesive insoluble glucan synthesis, which is responsible for biofilm formation on tooth surfaces. After evaluation of the radar charts, all drinks were categorized into four characteristic patterns. Using the radar charts, we could easily differentiate weakly cariogenic drinks such as non-sugar tea and natural water from other strongly cariogenic ones. Drinks containing sucrose were categorized as strongly cariogenic. These results suggest that we should be aware of the potential risk of popular drinks to induce dental caries, and also that radar charts on the cariogenicity of drinks are useful for recognizing their characteristics.

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We concluded an in vitro study using quantitative light-induced fluorescence to evaluate how mucin and the application of topical fluoride affected enamel demineralization. Bovine enamel specimens were mounted on acrylic rods and polished. The enamel samples were immersed in non-mucin-containing, and three different mucin-containing (0.29, 0.87, and 2.70 mg/ml) demineralizing solutions. Each demineralization group was then divided into three subgroups based on the type of fluoride application : control (no application), fluoride dentifrice, or APF-gel. The lesions were quantified with parameter ΔQ (total mineral loss from the lesions), ΔF (average fluorescence loss), and the demineralized area. We found that the addition of mucin in the controls reduced demineralization by half. Mucin and fluoride dentifrice further decreased demineralization, while the application of APF-gel virtually eliminated demineralization. We concluded that the combination of mucin and the application of fluoride controlled the demineralization of tooth enamel.

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