Dental erosion caused by acidic damage is becoming a more common disease in daily life. We investigated the influence of different kinds of acid, pH values, and immersion times on dental erosion, as measured by the micro hardness (Knoop hardness) of human enamel. Lactic, acetic, and citric acids were selected because they are generally contained in soft drinks. The pH values chosen were 2.5, 3.0, and 3.5, corresponding to the values of many soft drinks. In this study, human enamel samples were immersed in 10 different solutions consisting of each of the 3 acids at each of the 3 pH values and distilled water. After being immersed in these solutions for 15, 30, 60, 120, and 180 minutes, these samples were rinsed with distilled water, dried in air, and measured for Knoop hardness. The Knoop hardness measurements were analyzed using 3-way repeated-measures ANOVA and the Bonferroni multiple-comparison method with the factors being the 3 kinds of acid, 3 different pH values, and 5 different immersion times.
 As a result, the acids and immersion times were significant factors affecting Knoop hardness, and there was a significant interaction between them. In addition, there was a significant difference in Knoop hardness among the 3 pH values under certain conditions.
 These results suggest that the Knoop hardness of human enamel is changed not only by the pH value, but also by the acid type and immersion time on food intake, and it depends on the properties of acids (such as pK_a values).
 In conclusion, regarding the consumption of soft drinks, promoting further oral health awareness would be very helpful for encouraging people to give more consideration to the acid content and type of their soft drink-consuming habits.

View full abstract

 A food education support program to improve masticatory ability was developed, and its efficacy was examined in this study. The food education support program consisted of instruction in oral health by a dental hygienist at the start, and then eating and consciously chewing a special doughnut with a chewy texture (trade name: "Chewin' Donuts!" (Kekkou Kamigotae-aru Donatsu®), manufactured by Shiraho Tanpaku Co., Ltd.), which is made of soymilk, soy pulp, and liquid konjak, once daily for 7 days.
 Subjects were 81 high-school students enrolled in the general course of a public high school. Consent was obtained from both the school principal and individual students. At the start and end of the program, direct masticatory ability was measured as the amount of eluted sugar using chewing gum, and indirect masticatory ability was also measured as the occlusal area, average and maximum occlusal pressures, and occlusal force using Dental Prescale® 50H Type R. Furthermore, awareness of mastication, eating behavior, and lifestyle were studied with a self-completed questionnaire and changes before and after the program were examined.
 The results showed that the amount of eluted sugar in male and female students was 63.0±6.3 and 56.5±7.3% before the program and 65.7±8.6 and 59.2±9.0% at the end of the program, respectively; the amount had significantly improved in both male and female students at the end of the program. For indirect masticatory ability, the average and maximum occlusal pressures and occlusal force in male students and the occlusal force in female students had significantly improved at the end of the program. In addition, masticatory behavior and awareness had both significantly improved after the program.
 Therefore, it was suggested that the food education support program implemented in this study was an effective method for supporting the improvement of the masticatory ability of high-school students.

View full abstract

 The aim of this cross-sectional study was to examine factors associated with the eruption pattern of the second molars, and whether this pattern affects periodontal disease and dental caries of the first molars in university students.
 Of 2,303 first-year students who underwent a general health examination at Okayama University in April 2013, 2,205 students volunteered to receive an oral examination. After we excluded 273 participants who were ≥20 years old and had provided incomplete data in their questionnaires, data from 1,932 students (1,124 males, 808 females), accounting for 83.9% of all first-year students, aged 18 and 19 years were analyzed. We examined their oral health status including malocclusion, total number of decayed, missing, and filled teeth, the Simplified Oral Hygiene Index, Community Periodontal Index, percentage of bleeding on probing (%BOP), and eruption pattern of the second molars. Students completed a selfreported questionnaire including items of experience of orthodontic treatment. For statistical analysis, the t-test, chi-square test, and multivariate logistic regression analysis were performed.
 The percentages of participants with at least one unerupted and partially erupted second molar were 0.9 and 12.4%, respectively.
 According to logistic regression analysis, the presence of abnormality on eruption of the second molars (unerupted and/or partially erupted) was significantly correlated with malocclusion (p<0.001) in both males and females. On the right side of the mandible, the percentage of BOP was significantly higher for a first molar adjacent to a partially erupted second molar. In conclusion, malocclusion was related to the eruption pattern of the second molars, and the presence of partially erupted mandibular second molars was related to the presence of BOP in the mesial first molars in the Japanese university students.

View full abstract

 We analyzed the regional inequality in dental caries prevalence, factors that may influence the existence of caries such as lifestyle, and risk factors involving 4,047 three-year-old children (2,055 boys and 1,992 girls) who lived in 14 cities in Kanagawa Prefecture, where the prefectural government conducted the Prefecture Resident Survey on the Actual Oral Health Situation in 2011.
 As a result, regional inequality in caries prevalence was observed among the 14 cities (chi-square test, p<0.001). We also recognized regional inequality in the intake of chewy foods, the habit of eating meals while watching TV or a video, the intake of sweet snacks, intake of sweet drinks, and the use of fluoride dentifrice as risk factors of caries. The risk factors showing a significant odds ratio affecting caries in all 14 cities obtained from a logistic-regression analysis were: the sex, birth order, habit of eating a meal while watching TV or a video, intake of sweet snacks, intake of sweet drinks, and toothbrushing by their guardians. Significant odds ratios such as "birth order" were provided as a risk factor, but no risk factor was detected in five other cities based on a logistic-regression analysis in each city. The items for which a significant difference was recognized were characteristic in each city, unlike in the results of the total of 14 cities.
 It was shown that regional inequality in caries prevalence existed among 14 the cities in Kanagawa Prefecture, and the risk factors were characteristic according to each city based on this study. However, it was thought that the order of favorable or unfavorable factors such as lifestyle with the regional inequality was not reflected in the order of the caries prevalence rate. It is necessary to analyze the background of these factors and utilize the results to educate each community, with the aim to reduce regional inequality in caries prevalence in three-year-old children in the future.

View full abstract

Abstract in Japanese

View full abstract

Abstract in Japanese

View full abstract