Curcumin is a polyphenol found in the rhizome of turmeric which has potential in oral care applications for the prevention of periodontal disease. In a previous study, a curcumin solution dissolved in dimethyl sulfoxide (DMSO) was used to evaluate the growth inhibitory effect against Porphyromonas gingivalis (P. gingivalis). However, due to its low level of safety, DMSO cannot be formulated into oral care products. In this study, the influences of different solvents on the growth inhibitory effect and their causes were investigated with curcumin dissolved in DMSO or dihydric alcohols.

  To confirm the growth inhibitory effect, curcumin was dissolved in DMSO or dihydric alcohols and added to the liquid culture medium. P. gingivalis was cultured anaerobically, and the turbidity (OD₆₀₀) of the medium was measured at the start of culture and after 6 to 36 hours. In addition, the growth inhibitory effect of curcumin dissolved in dihydric alcohols was determined by the presence or absence of turbidity in the medium after 36 hours of culture. In order to confirm the amount of curcumin dissolved in the solution, the curcumin solution was centrifuged followed by quantitative analysis of curcumin contained in the supernatant with HPLC.

  The growth inhibition rates of curcumin dissolved in 0.1 and 1% DMSO were 77.5 and 79.1% and those dissolved in 0.1 and 1% propylene glycol were 40.8 and 56.8%, respectively. The differences in the growth inhibitory effect were considered to be due to differences in the amount of dissolved curcumin. Other studied solvents (e.g. butylene glycol and isoprene glycol) showed similar trends to propylene glycol.

  To confirm the results further, the increase of the propylene glycol concentration was investigated. Differences due to solvents were confirmed; the amounts of curcumin dissolved in 0.1 and 1% DMSO was 1.7 were 2.5 µg/mL, and those in 0.1, 1, 5, and 10% propylene glycol were 0.4, 0.7, 2.2, and 2.7 µg/mL, respectively. From the results, effective growth inhibition is expected with a 10% dihydric alcohol concentration, which dissolves the same amount of curcumin as DMSO.

  Since dihydric alcohols are safe, they may be useful as solvents when formulating curcumin into oral care products.

 A new item named “chewing ability” was added to the Japanese specific health checkup questionnaire in 2018. Although the Ministry of Health, Labour and Welfare has released chewing ability data by prefecture, there have been no reports on the factors influencing regional differences. The purpose of this study was to examine prefectural differences in self-reported chewing ability and related socio-demographic factors for men and women aged 40–59 years. Those who selected “Sometimes it is difficult to chew due to dental problems” or “I can hardly chew” on the questionnaire were considered to have chewing difficulty. Regional differences in chewing difficulty were observed across sex and age groups. For example, among women aged 40–44 years, chewing difficulty varied from 7.1 to 14.0%, reveling that chewing difficulty rates differed by about two times among prefectures. Once these differences were identified, we investigated socio-demographic factors associated with chewing difficulty using publicly available government data for each prefecture. For men, greater chewing difficulty was associated with the divorce rate; the decayed, missing, and filled teeth (DMFT) index among 12-year-olds; and heart disease death rates, whereas university enrollment was associated with lower chewing difficulty. Among women, the divorce rate and caries prevalence in 18-month- and 3-year-olds were associated with higher rates of chewing difficulty, whereas university enrollment, number of secondary industry workers, and number of general clinics were associated with lower rates of chewing difficulty. These findings suggest that socio-economic factors and dental caries experience in children may influence self-reported chewing difficulty at the community level. Based on the results of this ecological study, it is necessary to further investigate this relationship through individual-level research.

  The aim of this study was to show the associations among oral health beliefs, oral health behaviors, and number of teeth in older people. Oral examinations and questionnaire surveys were conducted involving 600 older people aged ≥ 70 years living in Niigata City in 1998. The questionnaire items were scored to measure the participants’ oral health beliefs and behaviors, and a logistic simple regression analysis was used to define the relationship between them. Furthermore, we conducted a final evaluation of the associations among the number of teeth as the target variable and oral health beliefs and behaviors. Then, we prepared three ordinal logistic regression models that combined or seperately treated beliefs and behaviors as covariates. Logistic simple regression analysis showed a significant correlation between oral health behavior and belief scores. Furthermore, ordinal logistic regression analysis showed a significant correlation between the number of teeth and oral health behaviors. These results indicate the inter-relation between oral health behaviors and beliefs. Moreover, they suggest the possibility that better oral health behaviors increase the number of remaining teeth in old age.