Yoshihiro Shimazaki

Bacterial diversity in saliva and oral health-related conditions: the Hisayama Study

This population-based study determined the salivary microbiota composition of 2,343 adult residents of Hisayama town, Japan, using 16S rRNA gene next-generation high-throughput sequencing. Of 550 identified species-level operational taxonomic units (OTUs), 72 were common, in ≥75% of all individuals, as well as in ≥75% of the individuals in the lowest quintile of phylogenetic diversity (PD). These “core” OTUs constituted 90.9u2009±u20096.1% of each microbiome. The relative abundance profiles of 22 of the core OTUs with mean relative abundances ≥1% were stratified into community type I and community type II by partitioning around medoids clustering. Multiple regression analysis revealed that a lower PD was associated with better conditions for oral health, including a lower plaque index, absence of decayed teeth, less gingival bleeding, shallower periodontal pockets and not smoking, and was also associated with tooth loss. By contrast, multiple Poisson regression analysis demonstrated that community type II, as characterized by a higher ratio of the nine dominant core OTUs, including Neisseria flavescens, was implicated in younger age, lower body mass index, fewer teeth with caries experience, and not smoking. Our large-scale data analyses reveal variation in the salivary microbiome among Japanese adults and oral health-related conditions associated with the salivary microbiome.

Distinct composition of the oral indigenous microbiota in South Korean and Japanese adults

A comparison of national surveys on oral health suggested that the population of South Korea has a better periodontal health status than that of Japan, despite their similar inherent backgrounds. Here, we investigated differences in oral bacterial assemblages between individuals from those two countries. To exclude potential effects of oral health condition on the microbiota, we selected 52 Korean and 88 Japanese orally healthy adults (aged 40–79 years) from the participants of two cohort studies, the Yangpyeong study in South Korea and the Hisayama study in Japan, and compared the salivary microbiomes. The microbiota of the Japanese individuals comprised a more diverse community, with greater proportions of 17 bacterial genera, including Veillonella, Prevotella, and Fusobacterium, compared to the microbiota of the Korean individuals. Conversely, Neisseria and Haemophilus species were present in much lower proportions in the microbiota of the Japanese individuals than the Korean individuals. Because higher proportions of Prevotella and Veillonella and lower proportions of Neisseria and Haemophilus in the salivary microbiome were implicated in periodontitis, the results of this study suggest that the greater proportion of dysbiotic oral microbiota in the Japanese individuals is associated with their higher susceptibility to periodontitis compared to the Korean individuals.

Tooth loss and metabolic syndrome in middle-aged Japanese adults.

AIMnMetabolic syndrome is associated with periodontal disease and dental caries; however, little attention has been given to the association between metabolic syndrome and tooth loss, which is the endpoint of these two diseases. This study examined this association in middle-aged adults over a 5-year period.nnnMETHODSnA retrospective study was performed in 2107 participants (1718 males and 389 females) aged 35-60xa0years who underwent annual dental check-ups, to evaluate tooth loss and metabolic components, including obesity, elevated triglycerides, blood pressure, fasting glucose, and reduced high-density lipoprotein. Logistic regression analysis was performed to evaluate the association between metabolic syndrome (≥3 components) at the baseline examination and tooth loss.nnnRESULTSnOver a 5-year period, 10.8% of the participants lost at least one tooth. Compared to those with no metabolic components, participants with ≥3 components had an increased risk of tooth loss (odds ratioxa0=xa01.54; 95% confidence interval: 1.01-2.37), adjusting for age, gender, dental caries experience, attachment loss, oral hygiene status, number of teeth, tooth brushing frequency, smoking, and occupational status.nnnCONCLUSIONSnMetabolic syndrome was associated with the incidence of tooth loss among middle-aged adults.

Risk Factors for Reduced Salivary Flow Rate in a Japanese Population: The Hisayama Study

The purpose of this study was to determine distinct risk factors causing reduced salivary flow rate in a community-dwelling population using a prospective cohort study design. This was a 5-year follow-up survey of 1,377 community-dwelling Japanese individuals aged ≥40 years. The salivary flow rate was evaluated at baseline and follow-up by collecting stimulated saliva. Data on demographic characteristics, use of medication, and general and oral health status were obtained at baseline. The relationship between reduced salivary flow rate during the follow-up period and its predictors was evaluated after adjustment for confounding factors. In a multivariate logistic regression model, higher age and plaque score and lower serum albumin levels were significantly associated with greater odds of an obvious reduction in salivary flow rate (age per decade, odds ratio [OR] = 1.25, 95% confidence interval [CI] = 1.03–1.51; serum albumin levels <4u2009g/dL, OR = 1.60, 95% CI = 1.04–2.46; plaque score ≥1, OR = 1.53, 95% CI = 1.04–2.24). In a multivariate linear regression model, age and plaque score remained independently associated with the increased rate of reduced salivary flow. These results suggest that aging and plaque score are important predictors of reduced salivary flow rate in Japanese adults.

Impact of Oral Commensal Bacteria on Degradation of Periodontal Connective Tissue in Mice

BACKGROUNDnInnate and adaptive immunosurveillance mechanisms in response to the normal commensal bacteria can affect periodontal innate defense status. However, it is still unclear how commensal bacteria contribute to the inflammatory responses of junctional epithelium (JE) and periodontal connective tissue (PCT). The aim of the present study is to investigate the contribution of commensal bacteria on inflammatory responses in JE and PCT in mice.nnnMETHODSnThe periodontal tissue of germ-free (GF) and specific-pathogen-free (SPF) mice were compared at age 11 to 12 weeks (n = 6 per group). In this study, the number of neutrophils and expression of intercellular adhesion molecule (ICAM)-1, fibroblast growth factor receptor (FGFR)-1, matrix metalloproteinase (MMP)-1, and MMP-8 within the JE and the PCT are evaluated. The collagen density was also determined in PCT stained with picrosirius red (PSR). PSR staining combined with or without polarized light microscopy has been used to assess the organization and maturation of collagen matrix.nnnRESULTSnIn the present findings, the area of JE in SPF mice was significantly greater than that in GF mice (P <0.05). In addition, the JE and PCT in SPF mice showed greater migration of neutrophils and higher expression of ICAM-1, FGFR-1, MMP-1, and MMP-8 than those in GF mice (P <0.05). Furthermore, the density of collagen in PCT in SPF mice was lower compared to GF mice (P <0.05).nnnCONCLUSIONnThese results indicate that commensal bacteria induced a low-grade inflammatory state in JE and that such conditions may contribute to degradation of collagen in PCT in mice.

Assessment of oral malodor and tonsillar microbiota after gargling with benzethonium chloride

The oropharyngeal area can be a source of halitosis. However, the relationship between healthy tonsillar microbiota and halitosis is poorly understood. We conducted a pilot clinical study to clarify the effect of gargling with an antiseptic agent on tonsillar microbiota in patients with halitosis. Twenty-nine halitosis patients who did not have otolaryngologic disease or periodontitis were assigned randomly to one of three groups: benzethonium chloride (BZC) gargle; placebo gargle; no gargle. Concentrations of volatile sulfur compounds (VSCs) in mouth air, the organoleptic score (ORS) and tongue-coating score (TCS) were measured before and after testing. Tonsillar microbiota were assessed by detection of periodontal pathogens, and profiling with terminal-restriction fragment length polymorphism (T-RFLP) analysis and sequencing of 16SrRNA clone libraries for taxonomic assignment. Gargling with BZC reduced the concentrations of methyl mercaptan and hydrogen sulfide and the ORS, but did not affect the TCS or prevalence of periodontal pathogens. T-RFLP analyses and 16SrRNA clone sequencing showed a tendency for some candidate species to decrease in the test group. Although gargling of the oropharyngeal area with an antiseptic agent can reduce oral malodor, it appears that tonsillar microbiota are not influenced greatly. (J Oral Sci 58, 83-91, 2016).

Oral health for an ageing population: the importance of a natural dentition in older adults

Despite progress in dentistry, tooth loss in old age is still a reality, even more so in long-term-care residents. However, recent trends indicate that natural teeth are lost later in life. Functional decline and age-related pathologies have to be considered in oral health care for this vulnerable population. Retaining and restoring teeth and oral function in elders is important. Tooth loss significantly impairs masticatory performance, which cannot be fully restored by prosthodontic means. Hence an unconscious change in food intake occurs, often involving malnutrition and withdrawal from common meals. Poor oral appearance and bad breath may further impede social activities. Although a chewing activity may be beneficial for cognitive function, natural teeth can present a considerable risk for fragile elders, in whom aspiration of biofilm can lead to pneumonia and death. The presence of natural teeth is also correlated with higher life expectancy, but socio-economic confounding factors have to be considered. When evaluating oral health in the elderly population, standards and priorities for reporting oral health outcome measures have to be defined. Anatomical indicators such as the number of natural teeth or the presence of prostheses might be one option for reporting. However, functional indicators such as masticatory performance and patient-centred outcome measures may be more relevant. In conclusion, there is an overwhelming body of evidence that maintaining a healthy natural dentition in old age is beneficial from a structural, functional and psycho-social point of view.

Exploration of bacterial species associated with the salivary microbiome of individuals with a low susceptibility to dental caries

ObjectiveDental caries is caused by acidogenic plaque microbiota formed on saliva-bathed tooth surfaces, in which multiple organisms act collectively to initiate and expand a cavity. We explored bacterial species associated with the salivary microbiome of individuals with low susceptibility to dental caries.Materials and methodsThe bacterial composition of saliva from 19 young adults was analyzed using barcoded pyrosequencing of the 16S rRNA gene; we compared 10 caries-experienced (CE) and nine caries-free (CF) individuals.xa0Axa0quantitative PCR assay of salivaxa0from 139 orally healthy adults aged 40–59xa0years was carried outxa0to confirm the result obtained by pyrosequencing analysis.ResultsThe microbiomes of CF individuals showed more diverse communities with a significantly greater proportion of the genus Porphyromonas. Among operational taxonomic units (OTUs) corresponding to the genus Porphyromonas, the OTU corresponding to P. pasteri was the most predominant and its relative abundance in CF individuals was significantly greater than in CE individuals (Pxa0<xa00.001, Wilcoxon rank sum test). A quantitative PCR assay of saliva confirmed that the amounts of P. pasteri were significantly higher in individuals with lower caries experience (filled teeth <15, nxa0=xa067) than in those with higher caries experience (filled teeth ≥15, nxa0=xa072) (Pxa0<xa00.001, Student’s t test).ConclusionThese results revealed an association between a greater abundance of P. pasteri and lower susceptibility to dental caries.Clinical relevanceP. pasteri may be a bacterial species that could potentially be used as a marker for maintaining a healthy oral microbiome against dental caries.

Descriptive study of dental injury incurred by junior high school and high school students during participation in school sports clubs

AIMnStudents often injure their teeth during participation in school-based sports clubs. This study examined the frequencies and types of dental injuries sustained at school sports clubs and compared the risk of dental injury among different sports.nnnMETHODSnBased on injury statistics from the Japan Sport Council of the junior high schools and high schools in seven prefectures during fiscal year 2006, the risk of dental injury was estimated using a rate ratio (RR) by calculating the ratio of occurrence of dental injury under various circumstances.nnnRESULTSnThe RRs of exercise-related dental injury for boys and girls in junior high school were 0.7 (P < 0.001) and 1.3 (P < 0.05), respectively, and for those in high school were 2.6 (P < 0.001) and 2.7 (P < 0.001), respectively. In junior high school, softball (RR = 7.7) for boys and handball (RR = 3.9) for girls commonly led to dental injuries. In high school, Japanese-style wrestling (RR = 18.5) and rugby (RR = 7.3) for boys and handball (RR = 6.5) for girls had high risks for dental injury. Crown fracture was the predominant dental injury among boys and girls attending both junior high school and high school. The proportion of alveolar fracture was higher in school sports clubs than outside school sports clubs among high school boys. Contact or limited-contact sports had significantly higher risks for dental injuries than did noncontact sports.nnnCONCLUSIONnThe results of this study suggest that teachers and administrators at schools should pay attention to the risk of dental injury among students participating in high-risk sports.

Age-related changes of CD4+ T cell migration and cytokine expression in germ-free and SPF mice periodontium

OBJECTIVEnIncreasing age is a potential risk factor for periodontal tissue breakdown, which may be affected by commensal flora. The aim of this study evaluated age-related changes in CD4+ T cells, C-C chemokine ligand 5 (CCL5), interleukin (IL)-17A, and receptor activator of nuclear factor-kappa B ligand (RANKL) expression using germ-free (GF) and conventionally reared (SPF) mice.nnnDESIGNnGF and SPF mice at 8 (nu202f=u202f6/group) and 22 weeks old (nu202f=u202f6/group) were used. Immunohistochemical analyses were performed to determine the effects of aging on protein expression in periodontal tissues. Age-related changes in alveolar bone were quantified using micro-CT analysis.nnnRESULTSnSPF mice, but not GF mice, showed an age-related increase in alveolar bone loss (Pu202f<u202f0.01). SPF mice at 22 weeks of age increased expression of CD4+ T cells, CCL5, IL-17A, and RANKL compared to those at 8 weeks of age in connective tissue and alveolar bone surface (Pu202f<u202f0.01). Furthermore, there was increased CD4+ T cells, which were co-expressed with IL-17A and RANKL in SPF mice at 22 weeks of age. On the other hand, the GF mice did not show any significant differences in CD4+ T cells, CCL5, IL-17A and RANKL expression between the two age groups.nnnCONCLUSIONSnSPF mice induced an age-related increase in CD4+ T cells co- expressed with IL-17A and RANKL, with occurring alveolar bone loss. In contrast, GF mice did not show age-related changes in CD4+ T cell migration and cytokine expression.