Dental health, nutritional status and recent-onset dementia in a Korean community population

Unraveling brain aging through the lens of oral microbiota

The oral cavity is a complex physiological community encompassing a wide range of microorganisms. Dysbiosis of oral microbiota can lead to various oral infectious diseases, such as periodontitis and tooth decay, and even affect systemic health, including brain aging and neurodegenerative diseases. Recent studies have highlighted how oral microbes might be involved in brain aging and neurodegeneration, indicating potential avenues for intervention strategies. In this review, we summarize clinical evidence demonstrating a link between oral microbes/oral infectious diseases and brain aging/neurodegenerative diseases, and dissect potential mechanisms by which oral microbes contribute to brain aging and neurodegeneration. We also highlight advances in therapeutic development grounded in the realm of oral microbes, with the goal of advancing brain health and promoting healthy aging.

Masticatory Function, Sex, and Risk of Dementia Among Older Adults: A Population-Based Cohort Study

BACKGROUND

A decline in masticatory function may indicate brain dysfunction related to dementia, but the relationship between masticatory function and dementia risk remains unclear. This study aimed to investigate whether masticatory function is associated with the risk of cognitive decline and dementia.

METHODS

Data were obtained from the nationwide prospective cohort study of randomly sampled community-dwelling Koreans aged ≥ 60 years. The 5,064 non-demented participants, whose number of chewing cycles per bite was assessed by clinical interview, were followed for 8 years with biennial assessments of cognitive performance and clinical diagnoses of all-cause dementia and Alzheimer's disease (AD). Structural brain magnetic resonance imaging was collected from a subset of cohort participants and their spouses for imaging analyses.

RESULTS

Males who chewed ≥ 30 cycles/bite had faster decline in global cognition and memory function and were at higher risk for incident all-cause dementia (hazard ratio [HR], 2.91; 95% confidence interval [CI], 1.18-7.18) and AD (HR, 3.22; 95% CI, 1.14-9.11) compared to males with less than 10 cycles/bite. Additionally, increased chewing cycles in males were associated with reduced brain volume, particularly in regions involved in compensatory cognitive control of mastication. There was no significant association between chewing cycles and the risk of dementia or brain volume in females.

CONCLUSION

Older men who frequently chew their meals could be considered a notable population at risk for dementia who should be carefully assessed for their cognitive trajectories.

Association between tooth loss-related speech and psychosocial impairment with cognitive function: A pilot study in Hong Kong's older population

BACKGROUND

Tooth loss has been associated with cognitive decline, but the underlying mechanisms involving speech and psychosocial impairment remain unclear.

OBJECTIVES

To investigate the impact of tooth loss-related speech and psychosocial impairment on cognitive function in Hong Kong's older population.

METHODS

Seventy-six Cantonese-speaking participants between the ages of 51-92 were classified into three groups: patients with complete dentures (CD), partially edentulous patients with less than 10 occluding tooth pairs (OU <10), and at least 10 occluding tooth pairs (OU ≥10). Cognitive function was assessed using the Montreal Cognitive Assessment Hong Kong Version, One-minute Verbal Fluency Task and Hayling Sentence Completion Test. Objective and subjective speech assessments were carried out using artificial intelligence speech recognition algorithm and a self-designed speech questionnaire. The impact of tooth loss on psychosocial condition was evaluated by the Reading the Mind in the Eyes Test and a self-designed questionnaire. Statistical analyses (one-way ANOVA, ANCOVA, Kruskal-Wallis test, Spearman correlation test) were performed.

RESULTS

Tooth loss was significantly associated with lower cognitive function (p = .008), speech accuracy (p = .018) and verbal fluency (p = .001). Correlations were found between cognitive function and speech accuracy (p < .0001). No significant difference in tooth loss-related psychosocial impact was found between the three groups.

CONCLUSION

While warranting larger sample sizes, this pilot study highlights the need for further research on the role of speech in the association between tooth loss and cognitive function. The potential cognitive impact of tooth retention, together with its known biological and proprioceptive benefits, supports the preservation of the natural dentition.

Association Between Subjective Masticatory Function and Mild Cognitive Impairment in Older Adults

AIM

This study aimed to examine the effect of subjective masticatory function on the occurrence of mild cognitive impairment (MCI) by analysing the Korean Longitudinal Study of Ageing (KLoSA) data.

METHODS

The study participants were 2954 KLoSA participants aged 60 years or older in the first wave (2006) who had normal cognitive function. The subjective masticatory function was determined using a survey item, and the responses were grouped into 3 categories, ie, good, moderate, and poor. The occurrence of MCI in the 3 groups was followed up until 2020. Cognitive function was assessed based on the Korean Mini-Mental State Examination score. Age, sex, education level, residence, health insurance type, smoking status, drinking status, and the number of chronic diseases were considered as potential confounders. To examine the occurrence of MCI according to subjective masticatory function, Cox proportional hazard regression analysis was performed.

RESULTS

Cox proportional hazard regression models adjusted for confounders yielded the following results: in men, the risk of MCI was higher in those whose subjective masticatory function was moderate and poor, as compared to those with good subjective masticatory function (adjusted hazard ratio [aHR], 1.33; 95% confidence interval [CI], 1.12-1.58; aHR, 1.23; 95% CI, 1.04-1.46). In contrast, in women, subjective masticatory function did not significantly influence the occurrence of MCI (aHR, 1.05; 95% CI, 0.89-1.24; aHR, 1.08; 95% CI, 0.92-1.28).

CONCLUSIONS

This study suggests that poor masticatory function may be a risk factor for MCI in older men.

Periodontitis and brain magnetic resonance imaging markers of Alzheimer's disease and cognitive aging

INTRODUCTION

We examined the association of clinical, microbiological, and host response features of periodontitis with MRI markers of atrophy/cerebrovascular disease in the Washington Heights Inwood Columbia Aging Project (WHICAP) Ancillary Study of Oral Health.

METHODS

We analyzed 468 participants with clinical periodontal data, microbial plaque and serum samples, and brain MRIs. We tested the association of periodontitis features with MRI features, after adjusting for multiple risk factors for Alzheimer's disease/Alzheimer's disease-related dementia (AD/ADRD).

RESULTS

In fully adjusted models, having more teeth was associated with lower odds for infarcts, lower white matter hyperintensity (WMH) volume, higher entorhinal cortex volume, and higher cortical thickness. Higher extent of periodontitis was associated with lower entorhinal cortex volume and lower cortical thickness. Differential associations emerged between colonization by specific bacteria/serum antibacterial IgG responses and MRI outcomes.

DISCUSSION

In an elderly cohort, clinical, microbiological, and serological features of periodontitis were associated with MRI findings related to ADRD risk. Further investigation of causal associations is warranted.

Effects of early tooth loss on chronic stress and progression of neuropathogenesis of Alzheimer's disease in adult Alzheimer's model AppNL-G-F mice

Introduction

Alzheimer's disease (AD), the most common neurodegenerative disease, is characterized by accumulated amyloid-β (Aβ) plaques, aggregated phosphorylated tau protein, gliosis-associated neuroinflammation, synaptic dysfunction, and cognitive impairment. Many cohort studies indicate that tooth loss is a risk factor for AD. The detailed mechanisms underlying the association between AD and tooth loss, however, are not yet fully understood.

Methods

We explored the involvement of early tooth loss in the neuropathogenesis of the adult AppNL-G-F mouse AD model. The maxillary molars were extracted bilaterally in 1-month-old male mice soon after tooth eruption.

Results

Plasma corticosterone levels were increased and spatial learning memory was impaired in these mice at 6 months of age. The cerebral cortex and hippocampus of AD mice with extracted teeth showed an increased accumulation of Aβ plaques and phosphorylated tau proteins, and increased secretion of the proinflammatory cytokines, including interleukin 1β (IL-1β) and tumor necrosis factor α (TNF-α), accompanied by an increased number of microglia and astrocytes, and decreased synaptophysin expression. AD mice with extracted teeth also had a shorter lifespan than the control mice.

Discussion

These findings revealed that long-term tooth loss is a chronic stressor, activating the recruitment of microglia and astrocytes; exacerbating neuroinflammation, Aβ deposition, phosphorylated tau accumulation, and synaptic dysfunction; and leading to spatial learning and memory impairments in AD model mice.

Relationship between oral health and depression: data from the National Health Survey 2016-2017

OBJECTIVE

To evaluate the relationship between oral health status, self-perception of oral health, and depression.

METHODS

This cross-sectional study included 2953 individuals that were ≥ 18 years of age and participated in the Chilean National Health Survey (NHS), 2016-2017. Information on oral, dental, and mental health, and the presence or absence of depressive symptoms was collected. Secondary data analysis was carried out using STATA and included logistic regression models adjusted for sex, age, and educational level. The analyses factored in the expansion weights to estimate representative prevalences of the entire population.

RESULTS

Participants experiencing frequent dental or prosthesis-related discomfort while speaking (OR: 1.57; 95% CI: 1.01-2.43) were related with exhibiting suspected depression. Removable upper denture users were at a higher risk of exhibiting suspected (OR: 2.04; 95% CI: 1.11-3.74) than those not using them. Participants diagnosed with depression in the past 12 months had a similar number of teeth (median = 24) compared to those without depression (median = 25) (OR: 0.99; 95% CI: 0.96-1.02).

CONCLUSION

Experiencing dental or prosthesis-related difficulties in speaking is related to suspected depression or a diagnosis of depression. These findings highlight the importance of developing comprehensive healthcare approaches that consider mental health in the context of oral health.

From teeth to brain: dental caries causally affects the cortical thickness of the banks of the superior temporal sulcus

OBJECTIVES

Dental caries is one of the most prevalent oral diseases and causes of tooth loss. Cross-sectional studies observed epidemiological associations between dental caries and brain degeneration disorders, while it is unknown whether dental caries causally affect the cerebral structures. This study tested whether genetically proxied DMFS (the sum of Decayed, Missing, and Filled tooth Surfaces) causally impacts the brain cortical structure using Mendelian randomization (MR).

METHODS

The summary-level GWAS meta-analysis data from the GLIDE consortium were used for DMFS, including 26,792 participants. ENIGMA (Enhancing NeuroImaging Genetics through Meta Analysis) consortium GWAS summary data of 51,665 patients were used for brain structure. This study estimated the causal effects of DMFS on the surface area (SA) and thickness (TH) of the global cortex and functional cortical regions accessed by magnetic resonance imaging (MRI). Inverse-variance weighted (IVW) was used as the primary estimate, the MR pleiotropy residual sum and outlier (MR-PRESSO), the MR-Egger intercept test, and leave-one-out analyses were used to examine the potential horizontal pleiotropy.

RESULTS

Genetically proxied DMFS decreases the TH of the banks of the superior temporal sulcus (BANSSTS) with or without global weighted (weighted, β = - 0.0277 mm, 95% CI: - 0.0470 mm to - 0.0085 mm, P = 0.0047; unweighted, β = - 0.0311 mm, 95% CI: - 0.0609 mm to - 0.0012 mm, P = 0.0412). The causal associations were robust in various sensitivity analyses.

CONCLUSIONS

Dental caries causally decrease the cerebral cortical thickness of the BANKSSTS, a cerebral cortical region crucial for language-related functions, and is the most affected brain region in Alzheimer's disease. This investigation provides the first evidence that dental caries causally affects brain structure, proving the existence of teeth-brain axes. This study also suggested that clinicians should highlight the causal effects of dental caries on brain disorders during the diagnosis and treatments, the cortical thickness of BANKSSTS is a promising diagnostic measurement for dental caries-related brain degeneration.

Association Between Reduced Posterior Occlusal Contact and Alzheimer's Disease Onset in Older Japanese Adults: Results from the LIFE Study

BACKGROUND

An association between poor oral health and cognitive decline has been reported. Most of these studies have considered the number of teeth as a criterion, only a few studies have analyzed the relationship between occlusal status and Alzheimer's disease (AD).

OBJECTIVE

To elucidate whether posterior occlusal contact is associated with AD, focusing on the Eichner classification, among an older population aged 65 years or older in Japan.

METHODS

This study used monthly claims data of National Health Insurance in Japan from April 2017 to March 2020. The outcome was newly diagnosed AD defined according to ICD-10 code G30. The number of teeth was estimated by dental code data, and occlusal contact was divided into three categories, namely A, B, and C, according to the Eichner classification. Multivariate Cox proportional hazards models were used to analyze the association between a new diagnosis of AD and the Eichner classification.

RESULTS

A total of 22,687 participants were included, 560 of whom had newly diagnosed AD during a mean follow-up period of 12.2 months. The AD participants had a lower proportion of Eichner A and a higher proportion of Eichner C. After adjusting for covariates, hazard ratios (95% confidence intervals) with Eichner B and C were 1.34 (1.01-1.77) and 1.54 (1.03-2.30), respectively.

CONCLUSION

In older people aged≥65 years old, reduced posterior occlusal contact as well as tooth loss have an impact on AD. This study emphasizes the importance of paying attention to occlusal contacts to reduce the risk of AD.

The relationships between mastication and cognitive function: A systematic review and meta-analysis

Masticatory function such as chewing is expected to modify human cognitive function, and/or the possibility of improving cognitive function is also predicted. This systematic review investigated whether masticatory function affects cognitive function for older/young adults. Full articles written in English from January 2000 to April 2022 were collected using PubMed and Cochrane Library. Target outcomes were cognitive function test scores, cognitive processing speed (reaction time), and masticatory function. For each research question, two independent reviewers conducted the search and screening, data extraction, quality assessment, and risk of bias assessment. The reviewers resolved any disagreements by discussion. From 226 articles retrieved, 20 were included in this review. Older adults with lower scores on the cognitive function test had lower masticatory performance, lower chewing ability, chewing difficulty, and decreased number of teeth. An increased risk of cognitive impairment was found in older adults with masticatory dysfunction. For young adults, gum chewing significantly reduced the processing speed of cognitive tasks compared to no gum chewing. Although most of the evidence included had a low level of evidence and a high risk of bias because of the research designs, the results still suggest that mastication may be a factor in improving cognitive function.

Tooth loss and the risk of cognitive decline and dementia: A meta-analysis of cohort studies

Introduction

Epidemiological studies have shown that tooth loss may be associated with an increased risk of cognitive decline and dementia. However, some results do not show a significant association. Therefore, we performed a meta-analysis to evaluate this association.

Methods

Relevant cohort studies were searched in PubMed, Embase, Web of Science (up to May 2022), and the reference lists of retrieved articles. The pooled relative risk (RR) and 95% confidence intervals were computed using a random-effects model (CI). Heterogeneity was evaluated using the I 2 statistic. Publication bias was evaluated using the Begg's and Egger's tests.

Results

Eighteen cohort studies met the inclusion criteria. Original studies with 356,297 participants with an average follow-up of 8.6 years (ranging from 2 to 20 years) were included in this study. The pooled RRs of tooth loss on dementia and cognitive decline were 1.15 (95% CI: 1.10-1.20; P < 0.01, I 2 = 67.4%) and 1.20 (95% CI: 1.14-1.26; P = 0.04, I 2 = 42.3%), respectively. The results of the subgroup analysis showed an increased association between tooth loss and Alzheimer's disease (AD) (RR = 1.12, 95% CI: 1.02-1.23) and vascular dementia (VaD) (RR = 1.25, 95% CI: 1.06-1.47). The results of the subgroup analysis also showed that pooled RRs varied by geographic location, sex, use of dentures, number of teeth or edentulous status, dental assessment, and follow-up duration. None of the Begg's and Egger's tests or funnel plots showed evidence of publication bias.

Discussion

Tooth loss is associated with a significantly increased risk of cognitive decline and dementia, suggesting that adequate natural teeth are important for cognitive function in older adults. The likely mechanisms mostly suggested include nutrition, inflammation, and neural feedback, especially deficiency of several nutrients like vitamin D.

Poor Oral Health as a Risk Factor for Dementia in a Swedish Population: A Cohort Study with 40 Years of Follow-Up

BACKGROUND

Whether poor oral health is associated with dementia risk remains unclear.

OBJECTIVE

We conducted a cohort study of 14,439 participants who were followed up for up to 40 years in Uppsala County, central Sweden, aiming to explore the association between poor oral health, namely the number of tooth loss, dental plaque status, and oral mucosal lesions, and the risk of dementia.

METHODS

We used Cox proportional hazards regression model to derive cause-specific hazard ratios (HR) and corresponding 95% confidence intervals (CI), while adjusting for baseline potential confounders as well as a time-varying covariate, Charlson's Comorbidity Index score.

RESULTS

Dementia risk was substantially higher among those with a higher number of tooth loss; compared to the group with tooth loss 0-10, the HRs were 1.21 (95% CI: 1.02, 1.42), 1.17 (95% CI: 0.97, 1.40), and 1.30 (95% CI: 1.09, 1.54) respectively for groups with increasing number of tooth loss. There was some evidence of dose-risk association in this study, with a HR of 1.10 (1.04, 1.18) comparing adjacent groups (ptrend = 0.001). In a stratified analysis by attained age, tooth loss was more pronouncedly associated with the risk of dementia onset before age 80 (those with 21-32 versus 0-10 lost teeth, HR = 1.82, (95% CI: 1.32, 2.51); HR = 1.22 (95% CI: 1.10, 1.35) comparing adjacent groups, ptrend < 0.001).

CONCLUSION

In summary, there are some indications that poor oral health, as indicated by more tooth loss, is positively associated with an increased risk of dementia, especially for dementia onset before age 80.

With Teeth, Broken, or Fixed: The Challenges of Linking Periodontitis, Neuroepidemiology, and Biomarkers of Disease

Periodontitis is a chronic inflammatory, bacterially-driven disease of the tooth-supporting tissues that shares several risk factors and elements of host response with Alzheimer's disease and related dementias (ADRD). Epidemiological studies have identified relatively consistent associations between adverse oral health conditions and ADRD. In this issue of the journal, a large study from the UK Biobank further explores these relationships along with MRI cognitive biomarkers. Despite its strength due to the large sample size, challenges in the study of periodontitis and neuroepidemiology markers include potential sampling bias, appropriate assessment of exposures, and the possibility of reverse causality.

The Effect of a Masticatory Muscle Training Program on Chewing Efficiency and Bite Force in People with Dementia

Until now, no study has investigated the effects of masticatory muscle training on chewing function in people with dementia. This study aimed to investigate whether physiotherapeutic exercises for the masticatory muscles have an influence on chewing efficiency and bite force in people with dementia. In a clinical trial with stratified randomization subjects were assigned to three groups based on the Mini Mental State Examination (MMSE: group 1—28–30, group 2—25–27, group 3—18–24). Each group was divided into an experimental (ExpG, intervention) and control group (ConG, no intervention). As intervention a Masticatory Muscle Training (MaMuT) (part 1: three physiotherapeutic treatments and daily home exercises, part 2: daily home exercises only) was carried out. Chewing efficiency and bite force were recorded. The MaMuT influenced the masticatory performance regardless of the cognitive state. Bite force increased in ExpG 1 and 2. Without further training, however, the effect disappeared. Chewing efficiency increased in all ExpG. After completion of the training, the ExpG 2 and 3 showed a decrease to initial values. Subjects of ExpG 1 showed a training effect at the final examination, but a tendency toward the initial values was observed. ExpG 3 seemed to benefit most from the physiotherapeutic exercises in terms of improving chewing efficiency by the end of the intervention phase. ExpG 1 showed the greatest gain in bite force. The MaMuT program is a potential method of improving masticatory performance in people with cognitive impairment or dementia when used on a daily basis.

Dementia and the Risk of Periodontitis: A Population-Based Cohort Study

Dementia and Alzheimer's disease (AD) are proposed to be comorbid with periodontitis (PD). It is unclear whether PD is associated with dementia and AD independent of confounding factors. We aimed at identifying the relationship between the longitudinal risk of developing PD in a cohort of patients with dementia and AD who did not show any signs of PD at baseline. In this retrospective cohort study, 8,640 patients with dementia without prior PD were recruited, and 8,640 individuals without dementia history were selected as propensity score-matched controls. A Cox proportional hazard model was developed to estimate the risk of developing PD over 10 y. Cumulative probability was derived to assess the time-dependent effect of dementia on PD. Of the 8,640 patients, a sensitivity test was conducted on 606 patients with AD-associated dementia and 606 non-AD propensity score-matched controls to identify the impact of AD-associated dementia on the risk for PD. Subgroup analyses on age stratification were included. Overall 2,670 patients with dementia developed PD. The relative risk of PD in these patients was significantly higher than in the nondementia group (1.825, 95% CI = 1.715 to 1.942). Cox proportional hazard models showed that patients with dementia were more likely to have PD than individuals without dementia (adjusted hazard ratio = 1.915, 95% CI = 1.766 to 2.077, P < 0.0001, log-rank test P < 0.0001). The risk of PD in patients with dementia was age dependent (P values for all ages <0.0001); younger patients with dementia were more likely to develop PD. The findings persisted for patients with AD: the relative risk (1.531, 95% CI = 1.209 to 1.939) and adjusted hazard ratio (1.667, 95% CI = 1.244 to 2.232; log-rank test P = 0.0004) of PD in patients with AD were significantly higher than the non-AD cohort. Our findings demonstrated that dementia and AD were associated with a higher risk of PD dependent of age and independent of systemic confounding factors.

Tooth Loss, Denture Use, and Cognitive Impairment in Chinese Older Adults: A Community Cohort Study

BACKGROUND

Evidence regarding the associations of tooth loss and denture use with incident cognitive impairment is inconclusive in older adults, and few prospective studies have examined the potential interaction between tooth loss and denture use in these specific populations.

METHODS

Data were assessed from 17 079 cognitively normal older adults aged ≥65 years, participating in the Chinese Longitudinal Healthy Longevity Survey. The outcome of interest was cognitive impairment (assessed by the Chinese version of Mini-Mental State Examination). The number of natural teeth and status of denture use were collected by a structural questionnaire.

RESULTS

A total of 6456 cases of cognitive impairment were recorded during 88 627 person-years of follow-up. We found that compared with participants with 20+ teeth, those with 10-19, 1-9, and 0 teeth had increased risks of incident cognitive impairment (p-trend < .001). Participants without dentures also had a higher risk of incident cognitive impairment, compared with those who wore dentures. Effect modification by denture use was observed (p-interaction = .010). Specifically, among those without dentures, the adjusted hazard ratio (95% confidence interval) for participants with 10-19, 1-9, and 0 teeth were 1.19 (1.08, 1.30), 1.28 (1.17, 1.39), and 1.28 (1.16, 1.41), respectively, as compared to those with 20+ teeth. In contrary, among denture users, detrimental effect was only observed among those with 0 teeth (hazard ratio 1.14, 95% confidence interval: 1.16, 1.41).

CONCLUSIONS

In Chinese older adults, maintaining 20+ teeth is important for cognitive health; denture use would attenuate the detrimental effects of tooth loss, especially for partial tooth loss, on cognitive impairment.

The Role of Chronic Infection in Alzheimer's Disease: Instigators, Co-conspirators, or Bystanders?

PURPOSE OF REVIEW

Herein, we provide a critical review of the clinical and translational research examining the relationship between viral and bacterial pathogens and Alzheimer's disease. In addition, we provide an overview of the biological pathways through which chronic infection may contribute to Alzheimer's disease.

RECENT FINDINGS

Dementia due to Alzheimer's disease is a leading cause of disability among older adults in developed countries, yet knowledge of the causative factors that promote Alzheimer's disease pathogenesis remains incomplete. Over the past several decades, numerous studies have demonstrated an association of chronic viral and bacterial infection with Alzheimer's disease. Implicated infectious agents include numerous herpesviruses (HSV-1, HHV-6, HHV-7) and various gastric, enteric, and oral bacterial species, as well as Chlamydia pneumonia and multiple spirochetes.

SUMMARY

Evidence supports the association between multiple pathogens and Alzheimer's disease risk. Whether these pathogens play a causal role in Alzheimer's pathophysiology remains an open question. We propose that the host immune response to active or latent infection in the periphery or in the brain triggers or accelerates the Alzheimer's disease processes, including the accumulation of amyloid-ß and pathogenic tau, and neuroinflammation. While recent research suggests that such theories are plausible, additional longitudinal studies linking microorganisms to Aß and phospho-tau development, neuroinflammation, and clinically defined Alzheimer's dementia are needed.

Dose-Response Meta-Analysis on Tooth Loss With the Risk of Cognitive Impairment and Dementia

OBJECTIVES

To quantify the dose-response associations between tooth loss and risk of cognitive impairment and dementia.

DESIGN

Longitudinal studies that examined the association between tooth loss and cognitive function were systematically searched on 6 databases through March 1, 2020. The study adhered to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) reporting guidelines. Risk estimates were pooled using random-effects models. The dose-response associations were assessed using generalized least squares spline models.

SETTING AND PARTICIPANTS

Adults from community, institution, outpatient or in-hospital were included in the meta-analysis.

MEASURES

Cognitive impairment and dementia were defined by neuropsychological tests, diagnostic criteria, or medical records. Tooth loss was self-reported or assessed by clinical examinations.

RESULTS

Fourteen studies were entered into the meta-analysis, including 34,074 participants and 4689 cases with diminished cognitive function. Participants with more tooth loss had a 1.48 times higher risk of developing cognitive impairment [95% confidence interval (CI) 1.18-1.87] and 1.28 times higher risk of being diagnosed with dementia (95% CI 1.09-1.49); however, the association was nonsignificant for participants using dentures (relative risk = 1.10, 95% CI 0.90-1.11). Eight studies were included in the dose-response analysis, and data supported the use of linear models. Each additional tooth loss was associated with a 0.014 increased relative risk of cognitive impairment and 0.011 elevated relative risks of dementia. Edentulous participants faced a 1.54 times higher risk of cognitive impairment and a 1.40 times higher risk of being diagnosed with dementia.

CONCLUSIONS AND IMPLICATIONS

Moderate-quality evidence suggested tooth loss was independently associated with cognitive impairment and dementia; risk of diminished cognitive function increased with incremental numbers of teeth lost. Furthermore, timely prosthodontic treatment with dentures may reduce the progression of cognitive decline related to tooth loss.

The Association of Periodontitis and Alzheimer's Disease: How to Hit Two Birds with One Stone

Alzheimer's disease (AD) is the leading cause of cognitive impairment in the elderly. Recent evidence suggests that preventive interventional trials could significantly reduce the risk for development of dementia. Periodontitis is the most common dental disease characterized by chronic inflammation and loss of alveolar bone and perialveolar attachment of teeth. Growing number of studies propose a potential link between periodontitis and neurodegeneration. In the first part of the paper, we overview case-control studies analyzing the prevalence of periodontitis among AD patients and healthy controls. Second, we survey observational libraries and cross-sectional studies investigating the risk of cognitive decline in patients with periodontitis. Next, we describe the current view on the mechanism of periodontitis linked neural damage, highlighting bacterial invasion of neural tissue from dental plaques, and periodontitis induced systemic inflammation resulting in a neuroinflammatory process. Later, we summarize reports connecting the four most common periodontal pathogens to AD pathology. Finally, we provide a practical guide for further prevalence and interventional studies on the management of cognitively high-risk patients with and without periodontitis. In this section, we highlight strategies for risk control, patient information, dental evaluation, reporting protocol and dental procedures in the clinical management of patients with a risk for periodontitis and with diagnosed periodontitis. In conclusion, our review summarizes the current view on the association between AD and periodontitis and provides a research and intervention strategy for harmonized interventional trials and for further case-control or cross-sectional studies.

Association between number of teeth and Alzheimer's disease using the National Database of Health Insurance Claims and Specific Health Checkups of Japan

Associations of numbers of teeth present and of missing teeth with Alzheimer’s disease were cross-sectionally analyzed using the National Database of Health Insurance Claims and Specific Health Checkups of Japan. Dental care claims data of patients aged 60 years or older diagnosed with periodontitis (n = 4,009,345) or missing teeth (n = 662,182) were used to obtain information about the numbers of teeth present and of missing teeth, respectively, and they were combined with medical care claims data including the diagnosis of Alzheimer’s disease. Numbers of teeth present and of missing teeth excluding third molars were calculated using the dental formula in the claims for periodontitis and missing teeth, respectively, and categorized into three groups each. Percentages of subjects treated for Alzheimer’s disease with 20–28, 10–19, and 1–9 teeth present were 1.95%, 3.87%, and 6.86%, respectively, in patients diagnosed as having periodontitis, and those treated for Alzheimer’s disease with 1–13, 14–27, and 28 missing teeth were 2.67%, 5.51%, and 8.70%, respectively, in patients diagnosed as having missing teeth. Logistic regression models using treatment for Alzheimer’s disease as an outcome variable and adjusting for age and sex showed that odds ratios (95% confidence intervals) for patients with 10–19 and 1–9 teeth (reference: 20–28 teeth) were 1.11 (1.10–1.13) and 1.34 (1.32–1.37), respectively, (p<0.001), in patients diagnosed as having periodontitis, and odds ratios (95% confidence intervals) for patients with 14–27 missing teeth and 28 missing teeth (reference: 1–13 missing teeth) were 1.40 (1.36–1.44) and 1.81 (1.74–1.89), respectively, (p<0.001), in patients diagnosed as having missing teeth. In conclusion, the results of the present study using Japanese dental claims data showed that older people visiting dental offices with fewer teeth present and a greater number of missing teeth are more likely to have Alzheimer’s disease.

Lozenges with probiotic strains enhance oral immune response and health

OBJECTIVE

Probiotics participate in regulating oral microbiota and reducing the prevalence of oral diseases; however, clinical research on probiotics is insufficient. Therefore, in this study, we performed in vitro screening of potential oral protective probiotic strains and then evaluated the clinical efficacy of the selected strains on maintaining oral health.

MATERIALS AND METHODS

Fifty healthy individuals were recruited and randomly assigned into the placebo group and probiotics group, which included three strains of probiotics, Lactobacillus salivarius subs. salicinius AP-32, Lactobacillus paracasei ET-66, and Lactobacillus plantarum LPL28. Each group was blindly administered placebo or probiotics for four weeks.

RESULTS

Next-generation sequencing results showed that the oral microbiota of Lactobacillus salivarius in the oral cavity were significantly increased in subjects supplemented with mixed probiotic lozenges. The anti-bacterial activities of viable probiotics were observed within two weeks. Both IgA levels and Lactobacillus and Bifidobacterium abundances in the oral cavity were significantly increased in the experimental groups, along with a reduced formation of plaque. Most participants reported that their oral health conditions and intestinal symptoms had improved.

CONCLUSIONS

Overall, our clinical study suggests that oral probiotic lozenges may enhance oral immunity, modulate oral microbiota, and improve oral health.

Oral dysfunctions and cognitive impairment/dementia

With global increases in the aging population, the number of patients with dementia is greatly increasing, which has become a big social problem. Many studies have shown strong associations between oral disorders and systemic disorders, such as diabetes, arthritis, sepsis, aspiration pneumonia, arteriosclerosis, bacterial endocarditis, and other cardiovascular diseases. Similarly, numerous cross-sectional studies showed that patients with dementia usually have poor oral conditions and tooth loss. These have long been considered as a result of difficulty with oral care due to impaired cognitive function, memory, and physical ability in patients with dementia. Indeed, even in patients with mild cognitive impairment, oral care becomes insufficient owing to decreases in spontaneity of grooming and finger dexterity. However, recent studies have shown that tooth loss and occlusal dysfunction may affect brain function and trigger the onset of dementia found in neurodegenerative diseases including Alzheimer's disease. In this review, we highlight the relationships among aging, oral dysfunction, and the development of dementia. Increasing evidence suggests that oral dysfunction is not only a result of dementia in the elderly people, but could also be a causative factor for the onset of dementia.

The association between mastication and mild cognitive impairment in Korean adults

Currently, a few of studies revealed that there is an association between mastication and cognitive impairment. There is no study of Korean adult representative samples in relation to mastication and cognitive decline. This study was to investigate the relationship between mastication and mild cognitive impairment in Korean adults.A population-based cross-sectional study was conducted in which a total of 7029 subjects (2987 men and 4042 women) over 45 years old were surveyed from the Korea Longitudinal Study on Aging (KLoSA), Round 5th survey. Logistic regression analysis was performed for the study data controlling for confounding factors such as age, gender, education, income, smoking, drinking, exercise, wearing denture, and the number of chronic diseases.Decreased chewing function is associated with mild cognitive impairment (odds ratio [OR] = 3.24, 95% confidence interval [CI] = 2.67-3.93) after controlling for confounding variables. In the participants who did not wear dentures, the reduction of chewing function was strongly correlated with mild cognitive impairment (OR = 3.97, 95% CI = 3.11-5.08).Mastication was associated with mild cognitive impairment. To prevent cognitive decline, health specialists should pay more attention to the decline of the mastication in people without dentures.

Loss of Functional Dentition is Associated with Cognitive Impairment

BACKGROUND

Although tooth loss is known to increase the risk of cognitive impairment and dementia, few studies have investigated the association between functional teeth including rehabilitated lost teeth and cognitive functionObjective:We investigated the associations of the numbers of functional teeth and functional occlusal units with cognitive impairment and cognitive function in late life.

METHODS

The current study was conducted as a part of the Korean Longitudinal Study on Cognitive Aging and Dementia (KLOSCAD), a community-based elderly cohort study. We analyzed 411 participants who have agreed with the additional dental exam. Geriatric psychiatrists and neuropsychologists administered the Consortium to Establish a Registry for Alzheimer's disease Assessment Packet Clinical and Neuropsychological Assessment Battery to all participants, and dentists examined their dental status.

RESULTS

Higher number of functional teeth (OR = 0.955, 95% CI = 0.914-0.997, p = 0.037) and higher number of functional occlusal units (OR = 0.900, 95% CI = 0.813-0.996, p = 0.042) were associated with lower odds of cognitive impairment. When we analyzed these relationships separated by the location of teeth, only the numbers of functional teeth (OR = 0.566, 95% CI = 0.373-0.857, p = 0.007) and functional occlusal units (OR = 0.399, 95% CI = 0.213-0.748, p = 0.004) in the premolar area were associated with lower odds of cognitive impairment.

CONCLUSION

Loss of functional teeth and functional occlusal units (especially in the premolar region) were associated with increased cognitive impairment.

Oral microbiota and Alzheimer's disease: Do all roads lead to Rome?

Alzheimer's disease (AD) is a progressive neurodegenerative pathology affecting milions of people worldwide associated with deposition of senile plaques. While the genetic and environmental risk factors associated with the onset and consolidation of late onset AD are heterogeneous and sporadic, growing evidence also suggests a potential link between some infectious diseases caused by oral microbiota and AD. Oral microbiota dysbiosis is purported to contribute either directly to amyloid protein production, or indirectly to neuroinflammation, occurring as a consequence of bacterial invasion. Over the last decade, the development of Human Oral Microbiome database (HOMD) has deepened our understanding of oral microbes and their different roles during the human lifetime. Oral pathogens mostly cause caries, periodontal disease, and edentulism in aged population, and, in particular, alterations of the oral microbiota causing chronic periodontal disease have been associated with the risk of AD. Here we describe how different alterations of the oral microbiota may be linked to AD, highlighting the importance of a good oral hygiene for the prevention of oral microbiota dysbiosis.

Tooth Loss-associated Cognitive Impairment in the Elderly: A Community-based Study in Japan

Objective Dementia is a major cause of disruption for a healthy life expectancy in Japan. It has been suggested that the number of teeth is a modifiable risk factor for cognitive impairment and dementia. We therefore examined the possible association between the cognitive function and the number of natural and artificial teeth in community-dwelling Japanese elderly individuals. Methods Among the participants in our prospective, community-based study, 210 elderly individuals (103 men and 107 women; 78.1±4.9 years; mean age±standard deviation) underwent both dental examinations and a Mini-Mental State Examination (MMSE), as well as various medical checkups, in 2016 and 2017. Results The number of natural teeth was significantly associated with an individual's MMSE score. The percentage of cognitively normal subjects (MMSE scores: 27-30) decreased significantly with a decrease in the number of natural teeth. Among the MMSE items, the calculation ability was significantly and independently associated with the number of natural teeth. Regression was calculated as the predicted score of MMSE =21+0.3× (years of schooling) +0.1× (number of natural teeth). Among individuals with 19 or fewer natural teeth, those who had a total of 20 teeth or more, including both natural and artificial teeth, had significantly higher MMSE scores than those who had 19 or fewer natural and artificial teeth combined. Conclusion The number of natural teeth was significantly associated with the cognitive function, especially the calculation ability, and the use of artificial teeth was associated with the preservation of the cognitive function in community-dwelling elderly individuals.

Tooth loss causes spatial cognitive impairment in rats through decreased cerebral blood flow and increased glutamate

OBJECTIVE

The loss of teeth not only causes damage to oral function but also is associated with cognitive impairment. Previous studies have reported that chewing can increase CBF, and CBF plays an important role in cognitive function. Whether the loss of teeth can lead to cognitive impairment by reducing CBF is unclear. This study aimed to investigate the changes in CBF, glutamate concentration, the expression of neuronal apoptosis-relatedBax/Bcl-2 and Caspase-3 mRNA and pyramidal cells in the hippocampus, as well as behavioral changes after tooth loss in rats.

DESIGN

Twelve weeks after the extraction of all maxillary molars in rats, their spatial learning and memory were tested by the Morris water maze, the CBF was detected by ASL-MRI and glutamate concentration was detected by HPLC; the expression of neuronal apoptosis-related Bax/Bcl-2 and Caspase-3 mRNA and the number of pyramidal cells in the CA1 region were also measured.

RESULTS

Rats with tooth loss exhibited spatial cognitive impairment in the Morris water maze, decreased CBF, increased glutamate levels andBax/Bcl-2 and Caspase-3 mRNA expression in the hippocampus; the number of pyramidal cells in the CA1 region were also reduced.

CONCLUSIONS

These findings suggest that the loss of teeth causes spatial cognitive impairment in rats and that the underlying mechanism might be associated with a decrease in CBF and an increase in the glutamate level in the hippocampus.

The effect of missing teeth on dementia in older people: a nationwide population-based cohort study in South Korea

Background

To determine the effect of missing teeth on the risk of dementia onset among individuals who received tooth extractions and those who did not, based on the number of missing teeth.

Methods

We selected individuals who had not been diagnosed or treated for dementia between 2002 to 2011 from the National Health Insurance Service-Elderly Cohort Database (NHIS-ECD). We divided participants into two cohorts, a tooth extraction and non-extraction cohort, based on tooth loss from 2002 to 2011. After propensity score matching, there were 104,903 individuals in each cohort, and we included a total of 209,806 individuals in this study. Each cohort was grouped by sex, age, residential area, health insurance eligibility, income level, history of dental caries, history of periodontal treatment, and number of extracted teeth. We analyzed the relationship between dementia onset and these variables using logistic regression analysis.

Results

Individuals with tooth loss had a higher risk for dementia than those without tooth loss (odds ratio [OR] = 1.18; 95% confidence interval [CI]: 1.146–1.215). Regarding the incidence of dementia, the OR increased as the number of missing teeth and age increased, and the OR was higher for women (OR = 1.33; 95% CI: 1.286–1.367) than for men, and this difference was statistically significant (P < 0.01). The incidence of dementia decreased with periodontal treatment (OR = 0.96; 95% CI: 0.932–0.992) and increased with dental caries (OR = 1.07; 95% CI: 1.035–1.101).

Conclusions

These results suggest that it is important to delay tooth loss and preserve the stable remaining teeth to help prevent dementia.

Electronic supplementary material

The online version of this article (10.1186/s12903-019-0750-4) contains supplementary material, which is available to authorized users.

Retrograde transport of masseter muscle-derived neprilysin to hippocampus

Although the effects of neprilysin (NEP), also called CD10, on the clearance of Alzheimer's disease (AD)-associated amyloid-β (Aβ) have been reported, NEP is not made in the brain, and the mechanism for the transport of NEP to the brain has not been investigated. Our hypothesis is that muscle packages NEP in exosomes in response to a neuromuscular signal and sends it to the brain via retrograde axonal transport. The masseter muscle (MM) and the trigeminal nerve (TGN) are good candidates for this mechanism by virtue of their proximity to the brain. The aim of this study was to trace the NEP protein from the MM, through the TGN, and to the hippocampus (HPC) in muscle contraction models in vitro and in vivo. NEP expression in mouse tissue lysates was analyzed by RT-PCR and Western blot. Four-week-old mice were perfused to remove blood NEP contamination. The MM expressed substantial levels of NEP protein and mRNA. On the other hand, a remarkably high level of NEP protein was measured in the TGN in the absence of mRNA. NEP protein, without the corresponding mRNA, was also detected in the HPC. These results suggested that the MM derived NEP was taken up by the TGN, which in turn permitted NEP access to the central nervous system and within it the HPC. When the MM was induced to contract by electric stimulation in freshly euthanized mice, NEP protein decreased in the MM in a stimulus time-dependent manner, while that in the TGN and the HPC increased sequentially. Furthermore, NIR-labeled exosomes tracked along the same route. Finally, carbachol induced secretion of exosomal NEP in C2C12-derived myotube cells. These results support our hypothesis that MM-derived NEP is transported along the TGN to reach the HPC following electrical or cholinergic stimulation.

Tooth Loss Is Associated With Increased Risk of Dementia and With a Dose-Response Relationship

Objective: Both tooth loss and dementia are age-related and frequently-occurring diseases. Increasing attention has been given to explore the pathogenesis related to oral-brain function disorders. The present study was performed to evaluate the association between tooth loss and dementia through a dose-response meta-analysis. Methods: Relevant cohort studies were searched from online databases up until June 20, 2018, which examined the association between tooth loss and the risk of dementia. Literature selection according to inclusion and exclusion criteria, as well as data extraction from included studies were completed independently by two reviewers. Data syntheses in this meta-analysis were performed using Stata 12.0 software. Results: A total of 8 cohort studies were included, containing a total of 14,362 samples and 2,072 dementia patients. The result of the meta-analysis indicated that patients with tooth loss faced a 1.34 times greater risk of developing dementia (RR = 1.34,95% CI = 1.19-1.51). The result from this dose-response meta-analysis in a linear model, suggested that every missed tooth might increase the risk of dementia by 1.01 times (RR = 1.01, 95%CI = 1.00-1.02). Further subgroup analyses pointed out that tooth loss patients without dentures may have a higher risk of dementia than those with dentures (with denture: RR = 0.98, 95% CI = 0.87-1.10; without denture: RR = 1.53, 95% CI = 1.19-1.97); at the same time, the study design, study area and education level of the study participants, might also have some effect on the results. Conclusions: Tooth loss may be a risk factor for the development of dementia. In addition, there is a dose-response relationship with the increase of missing teeth.

Tooth loss as a risk factor for dementia: systematic review and meta-analysis of 21 observational studies

BACKGROUND

Tooth loss is suggested to be associated with an increased risk of dementia in many studies. But the relationship between tooth loss and dementia is not yet fully understood. This systematic review and meta-analysis aimed to determine the relative effect of tooth loss on dementia risk.

METHODS

An electronic search of PubMed, Scopus, Embase, and Web of Knowledge was conducted in March 2018 to identify relevant observational studies with the English language restriction. Studies were included if they assessed the relationship between tooth loss and risk of dementia. Study quality was detected by the modified Downs and Black scale. Odds risks (ORs) were pooled using a random-effects model in the crude model.

RESULTS

The literature search initially yielded 1574 articles, and 21 observational studies published between 1994 and 2017 were finally included for the analyses. The crude results with random-effects model showed that patients with multiple tooth loss had higher incidence of dementia (OR 2.62, 95% CI 1.90-3.61, P < 0.001, I² = 90.40%). The association remained noted when only adjusted results were pooled from 18 studies (OR 1.55, 95% CI 1.41-1.70, P = 0.13, I² = 28.00%). Meta-regression analysis showed that study design explained about 16.52% of heterogeneity in the crude model. The overall quality rating scores of studies ranged from 11 to 16.

CONCLUSIONS

Findings from this review evidenced that tooth loss is positively associated with an increased risk of dementia in adults. Future well-designed longitudinal researches examining the direct and indirect relationship between tooth loss and dementia risk are encouraged.

Association between tooth loss and cognitive impairment in community-dwelling older Japanese adults: a 4-year prospective cohort study from the Ohasama study

BACKGROUND

Numerous prospective studies have investigated the association between the number of remaining teeth and dementia or cognitive decline. However, no agreement has emerged on the association between tooth loss and cognitive impairment, possibly due to past studies differing in target groups and methodologies. We aimed to investigate the association between tooth loss, as evaluated through clinical oral examinations, and the development of cognitive impairment in community-dwelling older adults while considering baseline cognitive function.

METHODS

This 4-year prospective cohort study followed 140 older adults (69.3% female) without cognitive impairment aged ≥65 years (mean age: 70.9 ± 4.3 years) living in the town of Ohasama, Iwate Prefecture, Japan. Cognitive function was evaluated with the Mini-Mental State Examination (MMSE) in baseline and follow-up surveys. Based on a baseline oral examination, the participants were divided into those with 0-9 teeth and those with ≥10 teeth. To investigate the association between tooth loss and cognitive impairment, we applied a multiple logistic regression analysis adjusted for age, sex, hypertension, diabetes, cerebrovascular/cardiovascular disease, hypercholesterolemia, depressive symptoms, body mass index, smoking status, drinking status, duration of education, and baseline MMSE score.

RESULTS

In the 4 years after the baseline survey, 27 participants (19.3%) developed cognitive impairment (i.e., MMSE scores of ≤24). Multiple logistic regression analysis indicated that participants with 0-9 teeth were more likely to develop cognitive impairment than those with ≥10 teeth were (odds ratio: 3.31; 95% confidence interval: 1.07-10.2). Age, male gender, and baseline MMSE scores were also significantly associated with cognitive impairment.

CONCLUSIONS

Tooth loss was independently associated with the development of cognitive impairment within 4 years among community-dwelling older adults. This finding corroborates the hypothesis that tooth loss may be a predictor or risk factor for cognitive decline.

Dental deafferentation and brain damage: A review and a hypothesis

In the last few decades, neurobiological and human brain imaging research have greatly advanced our understanding of brain mechanisms that support perception and memory, as well as their function in daily activities. Knowledge of the neurobiological mechanisms behind the deafferentation of stomatognathic systems has also expanded greatly in recent decades. In particular, current studies reveal that the peripheral deafferentations of stomatognathic systems may be projected globally into the central nervous system (CNS) and become an associated critical factor in triggering and aggravating neurodegenerative diseases. This review explores basic neurobiological mechanisms associated with the deafferentation of stomatognathic systems. Further included is a discussion on tooth loss and other dental deafferentation (DD) mechanisms, with a focus on dental and masticatory apparatuses associated with brain functions and which may underlie the changes observed in the aging brain. A new hypothesis is presented where DD and changes in the functionality of teeth and the masticatory apparatus may cause brain damage as a result of altered cerebral circulation and dysfunctional homeostasis. Furthermore, multiple recurrent reorganizations of the brain may be a triggering or contributing risk factor in the onset and progression of neurodegenerative conditions such as Alzheimer's disease (AD). A growing understanding of the association between DD and brain aging may lead to solutions in treating and preventing cognitive decline and neurodegenerative diseases.

Tooth loss is associated with accelerated cognitive decline and volumetric brain differences: a population-based study

Tooth loss has been related to cognitive impairment; however, its relation to structural brain differences in humans is unknown. Dementia-free participants (n = 2715) of age ≥60 years were followed up for up to 9 years. A subsample (n = 394) underwent magnetic resonance imaging at baseline. Information on tooth loss was collected at baseline, and cognitive function was assessed using the Mini-Mental State Examination at baseline and at follow-ups. Data were analyzed using linear mixed effects models and linear regression models. At baseline, 404 (14.9%) participants had partial tooth loss, and 206 (7.6%) had complete tooth loss. Tooth loss was significantly associated with a steeper cognitive decline (β: -0.18, 95% confidence interval [CI]: -0.24 to -0.11) and remained significant after adjusting for or stratifying by potential confounders. In cross-sectional analyses, persons with complete or partial tooth loss had significantly lower total brain volume (β: -28.89, 95% CI: -49.33 to -8.45) and gray matter volume (β: -22.60, 95% CI: -38.26 to -6.94). Thus, tooth loss may be a risk factor for accelerated cognitive aging.

Periodontal disease severity in subjects with dementia: A systematic review and meta-analysis

BACKGROUND AND OBJECTIVE

Despite clinical trials and reviews attempt to assess a possible relationship between dementia and periodontal disease, no meta-analysis has been performed and this issue remains undetermined. The aim of this study is to conduct a systematic review and meta-analysis to assess severity of periodontitis in subjects with dementia.

METHODS

The search was conducted in Pubmed, Embase/MEDLINE. Two independent reviewers extracted data and assessed the risk bias (Newcastle-Ottawa scale). Meta-analyses were performed using the means of probing depth (PD) and clinical attachment loss (CAL) in patients with or without dementia. The mean difference were analyzed (P ≤ 0.05).

RESULTS

Fourteen studies were included in the systematic review. In the qualitative analysis, most studies reported higher prevalence of periodontal disease in dementia patients. The studies had low risk of bias and two meta-analyses were performed for each parameter, including or not a cross-sectional study. The meta-analyses including the cross-sectional study demonstrated significant association between dementia and periodontal disease (mean difference: PD = 1.41; CAL = 1.40, P < 0.05), however, it wasn't confirmed when the cross-sectional study was removed (1.25 mm, P < 0.22) and CAL (1.20 mm, P < 0.22).

CONCLUSION

Although the qualitative analysis have suggested worse periodontal conditions in dementia patients, due to different study types and the high heterogeneity among them, the meta-analysis does not support the association between dementia and severity of periodontal disease.

Effects of Tooth Loss and the Apolipoprotein E ɛ4 Allele on Mild Memory Impairment in the Fujiwara-kyo Study of Japan: A Nested Case-Control Study

Background: Several studies have suggested that periodontal disease can exacerbate the pro-inflammatory status of the brain. Tooth loss is one of the alternative evaluation indices of periodontal disease. There are few data on the relationship between tooth loss and memory impairment, depending on the apolipoprotein E (APOE) ɛ4 genotype.

Objective: To determine if tooth loss is associated with mild memory impairment (MMI) and if this association is modified by the presence of the APOEɛ4 allele.

Methods: A nested case-control study was conducted from 2007 to 2012 in Japan. Five hundred and thirty-seven Japanese subjects aged 65 years and over who were cognitively intact at baseline were analyzed. MMI at follow-up was evaluated.

Results: The median number of teeth at baseline was significantly lower in MMI participants (n = 179) than in controls (n = 358) (MMI: median 21.0, interquartile range 10.0–25.0 versus controls: 24.0, 14.0–27.0). After adjustment for demographics, vascular risk factors, and APOEɛ4 allele, the multivariate adjusted odds ratio (OR) of ≤8 teeth was 1.97 (95% confidence interval [CI], 1.13–3.44) compared to 25–32 teeth. Participants with both the presence of at least 1 APOEɛ4 allele and ≤8 teeth had a higher risk of MMI compared with those with neither (OR, 2.82; 95% CI, 1.15–6.91). Those with either risk factor alone did not have a higher risk of MMI.

Conclusions: A lower number of teeth is related to risk of MMI. This may be primarily true for those individuals with an APOEɛ4 allele.

Association between residual teeth number in later life and incidence of dementia: A systematic review and meta-analysis

Background

It has been suggested that tooth loss in later life might increase dementia incidence. The objective of this analysis is to systematically review the current evidence on the relationship between the number of remaining teeth and dementia occurrence in later life.

Methods

A search of multiple databases of scientific literature was conducted with relevant parameters for articles published up to March 25th, 2017. Multiple cohort studies that reported the incidence of dementia and residual teeth in later life were found with observation periods ranging from 2.4 to 32 years. Random-effects pooled odds ratios (OR) and 95% confidence intervals (CI) were estimated to examine whether high residual tooth number in later life was associated with a decreased risk of dementia. Heterogeneity was measured by I². The Grading of Recommendations Assessment, Development, and Evaluation (GRADE) system was used to assess the overall quality of evidence.

Results

The literature search initially yielded 419 articles and 11 studies (aged 52 to 75 at study enrollment, n = 28,894) were finally included for analysis. Compared to the low residual teeth number group, the high residual teeth number group was associated with a decreased risk of dementia by approximately 50% (pooled OR = 0.483; 95% CI 0.315 to 0.740; p < 0.001; I² = 92.421%). The overall quality of evidence, however, was rated as very low.

Conclusion

Despite limited scientific strength, the current meta-analysis reported that a higher number of residual teeth was associated with having a lower risk of dementia occurrence in later life.

Electronic supplementary material

The online version of this article (10.1186/s12877-018-0729-z) contains supplementary material, which is available to authorized users.

Functional determinants of dietary intake in community-dwelling older adults: a DEDIPAC (DEterminants of DIet and Physical ACtivity) systematic literature review

Objective

The identification of determinants of dietary intake is an important prerequisite for the development of interventions to improve diet. The present systematic literature review aimed to compile the current knowledge on individual functional determinants of dietary intake in community-dwelling older adults.

Design

A systematic search was performed in PubMed, Scopus, Web of Science and the Cochrane Library. Titles, abstracts and full texts were screened according to predefined inclusion and exclusion criteria. Studies were included when focusing on dietary intake as an outcome and on chemosensory, oral, cognitive or physical function as a determinant.

Setting

Community.

Subjects

Older adults at least 65 years old without acute or specific chronic diseases.

Results

From initially 14 585 potentially relevant papers, thirty-six were included. For chemosensory, cognitive and physical function only a few papers were found, which reported inconsistent results regarding the relationship to dietary intake. In contrast, oral function was extensively studied (n31). Different surrogates of oral function like dental status, number of teeth, bite force or chewing problems were associated with food as well as nutrient intakes including fibre. As all except six studies had a cross-sectional design, no causal relationships could be derived.

Conclusions

Among functional determinants of dietary intake oral factors are well documented in older adults, whereas the role of other functional determinants remains unclear and needs further systematic research.

Oral inflammation and infection, and chronic medical diseases: implications for the elderly

Oral diseases, such as caries and periodontitis, not only have local effects on the dentition and on tooth-supporting tissues but also may impact a number of systemic conditions. Emerging evidence suggests that poor oral health influences the initiation and/or progression of diseases such as atherosclerosis (with sequelae including myocardial infarction and stoke), diabetes mellitus and neurodegenerative diseases (such as Alzheimer's disease, rheumatoid arthritis and others). Aspiration of oropharyngeal (including periodontal) bacteria causes pneumonia, especially in hospitalized patients and the elderly, and may influence the course of chronic obstructive pulmonary disease. This article addresses several pertinent aspects related to the medical implications of periodontal disease in the elderly. There is moderate evidence that improved oral hygiene may help prevent aspiration pneumonia in high-risk patients. For other medical conditions, because of the absence of well-designed randomized clinical trials in elderly patients, no specific guidance can be provided regarding oral hygiene or periodontal interventions that enhance the medical management of older adults.

The Effect of Number of Teeth and Chewing Ability on Cognitive Function of Elderly in UAE: A Pilot Study

Cognitive decline is one of the major causes of disability among the aging population. The aim of this study was to explore the relationship between oral health parameters (number of teeth, chewing ability, and presence of a denture) and cognitive function in the elderly across the UAE. Fifty persons (age ≥ 60; 71.26 ± 10.23) were enrolled in the study. Cognitive status was assessed using the standardized mini-mental state examination (SMMSE) and accordingly, cognitively normal subjects scoring ≥24 were considered as the control group and cognitively impaired individuals scoring ≤23 were considered as the low scoring group. Chewing ability was examined, number of teeth was noted, and demographical data was collected. The results of this pilot study showed that individuals with low SMMSE scores were significantly less educated (P < 0.01) and had fewer number of remaining teeth (P < 0.05) and impaired chewing ability (P < 0.05). These results demonstrate a significant link between the number of teeth, chewing ability, and cognitive function. However, this pilot study had its limitations and was the first of its kind in the UAE and Gulf region; therefore, future research addressing the limitations is needed to further explore this association.

Oral Health in Low-Income Older Adults in Korea

Oral diseases among older adults are prevalent and a major public health problem, but public attention regarding this matter is quite limited. Many older adults experience limited access to oral care services. The study aimed to describe characteristics of oral health conditions, perceived oral health status, and oral health practices and to examine factors related to living status and accessibility to dental health care among 9,660 low-income older adults living in a suburban city in Korea. Approximately 42% of low-income older adults lived alone; 68% perceived their oral health as either excellent or good; and 31% reported difficulty accessing dental services. Lack of accessibility to oral care services was significantly more common in older adults with low incomes, living alone, having poor oral conditions, poor self-perceived oral health, and poor tooth-brushing behavior. Strategies to promote access to dental care services for underserved older adults should be developed to prevent further oral problems and their impact on overall health conditions.

Cognitive Ability as a Determinant of Socioeconomic and Oral Health Status among Adolescent College Students of Bengaluru, India

INTRODUCTION

Levels of oral health and economic status are unequally distributed throughout the population. Inequality has multiple causes and that the effect of Socio Economic Status (SES) and demographic factors, on oral health is mediated through several factors. Association between cognitive ability and oral health had been demonstrated in older age groups but adolescents and younger adults have received relatively little attention in this field.

AIM

To establish the role of cognitive ability as a determinant of SES and oral health status among adolescent college students of Benagluru, Karnataka, India.

MATERIALS AND METHODS

A cross-sectional study was conducted among 1000 adolescents aged 17-19 years. Six government and six private first grade colleges were selected by multi-stage random sampling. Cognitive ability was assessed using digit symbol substitution test and digit span test. Dental caries and periodontal status were recorded by extent of bleeding, presence of calculus, periodontal pockets, loss of attachments using Community Periodontal Index, decayed, missing and filled teeth surfaces using Decayed, Missing, Filled Teeth and Surfaces Index. SES status was assessed using Kuppuswamy scale. Chi-square test was used to check the association of cognitive ability with oral health indicators and SES status. Regression analysis was performed to assess the effect of cognitive ability on oral health indicators after adjusting for SES and effect of SES status on oral health indicators after adjusting for indicators of cognitive ability.

RESULTS

Significant association and negative correlation between cognitive ability and indicators for oral health was seen in the regression models. Cognitive ability attributed for nearly 30% changes in the indicators for oral health after adjusting for SES and SES attributed for nearly 25% variance in indicators for oral health after adjusting for cognitive ability.

CONCLUSION

There is a potential role of cognitive ability in SES and oral health.

Association between tooth loss and cognitive decline: A 13-year longitudinal study of Chinese older adults

OBJECTIVES

To examine the association between the number of teeth remaining and cognitive decline among Chinese older adults over a 13-year period.

DESIGN

A large national longitudinal survey of Chinese older adults.

SETTING

The Chinese Longitudinal Healthy Longevity Survey (CLHLS) (1998-2011).

PARTICIPANTS

A total of 8,153 eligible participants aged 60+ interviewed in up to six waves.

MEASUREMENTS

Cognitive function and teeth number were measured at each interview. Cognitive function was measured by the Mini-Mental Status Examination (MMSE). Number of natural teeth was self-reported. Individuals with severe cognitive impairment were excluded. Covariates included demographic characteristics, adult socioeconomic status characteristics, childhood socioeconomic status, health conditions, and health behaviors. Linear mixed models were applied in the analysis.

RESULTS

The mean teeth number at baseline was 17.5(SD = 0.1), and the mean of baseline cognitive function was 27.3(SD = 0.0). Cognitive function declined over time (β = -0.19, P < .001) after controlling covariates. But, regardless of time, more teeth were associated with better cognitive function (β = 0.01, P < .001). The interaction of teeth number and time was significant (β = 0.01, P < .001), suggesting that the participants who had more teeth showed a slower pace of cognitive decline over time than those with fewer teeth after controlling for other covariates.

CONCLUSION

This study showed that tooth loss was associated with cognitive decline among Chinese older adults. Further studies are needed to examine the linkages between cognitive decline and oral health status using clinical examination data.

Association between mastication and cognitive status: A systematic review

PURPOSE

A substantial number of elderly people suffer from cognitive impairment and dementia, which are considered to have various risk factors, including masticatory dysfunction; however, the association between mastication and cognition is inconclusive. The objectives of this systematic review were to provide an overview of the literature on (1) the association between mastication and cognitive function and (2) the association between mastication and dementia incidence, in elderly people.

MATERIALS AND METHODS

Searches were conducted on five electronic databases (PubMed, EMBASE, CINHL, Cochrane Library, and Pro Quest) and publications were selected that met the following criteria: published between 2005 and 2015, written in English, and assessed associations between mastication and cognitive function, cognitive decline and dementia among population over 40 years old. The included publications were analyzed for study design, main conclusions, and strength of evidence by two reviewers who screened all abstracts and full-text articles, abstracted data and performed quality assessments by using a critical appraisal tool.

RESULTS

A total of 33 articles (22 cross-sectional, and 11 prospective cohort studies) were evaluated. Poorer mastication was associated with lower cognitive function in 15 of the 17 cross-sectional studies and steeper decline in 5 of the 6 prospective studies. Poorer mastication was one of significant risk factors for having dementia or mild memory impairment (MMI) in 4 of 5 cross-sectional studies and for the incidence of dementia or MMI in 4 of 5 prospective studies.

CONCLUSIONS

Most studies point to a positive association between mastication and cognitive function, including dementia among elderly people.