Association between Tooth Loss and Alzheimer's Disease in a Nested Case-Control Study Based on a National Health Screening Cohort

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.

Cognitive decline in Sprague-Dawley rats induced by neuroplasticity changes after occlusal support loss

BACKGROUND

Tooth loss is closely related to cognitive impairment, especially affecting cognitive functions involving hippocampus. The most well-known function of the hippocampus is learning and memory, and the mechanism behind is neuroplasticity, which strongly depends on the level of brain-derived neurotrophic factor (BDNF). While research has delved into the possible mechanisms behind the loss of teeth leading to cognitive dysfunction, there are few studies on the plasticity of sensory neural pathway after tooth loss, and the changes in related indicators of synaptic plasticity still need to be further explored.

METHODS

In this study, the bilateral maxillary molars were extracted in Sprague-Dawley rats of two age ranges (young and middle age) to establish occlusal support loss model; then, the spatial cognition was tested by Morris Water Maze (MWM). Quantitative real-time PCR (qPCR) and Western Blotting (WB) were used to detect BDNF, AKT, and functional proteins (viz., PSD95 and NMDAR) of hippocampal synapses. Golgi staining was used to observe changes in ascending nerve pathway. IF was used to confirm the location of BDNF and AKT expressed in hippocampus.

RESULTS

MWM showed that the spatial cognitive level of rats dropped after occlusal support loss. qPCR, WB, and IF suggested that the BDNF/AKT pathway was down-regulated in the hippocampus. Golgi staining showed the neurons of ascending sensory pathway decreased in numbers.

CONCLUSION

Occlusal support loss caused plastic changes in ascending nerve pathway and induced cognitive impairment in rats by down-regulating BDNF and synaptic plasticity.

Association of dietary inflammation with tooth loss and cognitive decline in older adults from cross-sectional data: The moderated role of albumin

OBJECTIVE

Growing evidence suggests a potential connection between tooth loss and cognitive function in recent years. Increasing studies have focused on their inter-relationship, however, the underlying mechanism has yet to be fully elucidated. Few studies have considered the role of dietary inflammation and serum albumin in the association between tooth loss and cognitive function. Therefore, the aim of this study was to explore the role of dietary inflammation and serum albumin in the association between tooth loss and cognitive impairment.

METHODS

A sample of 1,009 US adults from the National Health and Nutrition Examination Survey (NHANES) provided data on oral condition, cognitive function, dietary intake, and serum tests. The association between tooth loss (exposure variable) and cognitive function (outcome variable) was assessed by linear regression. Furthermore, a moderated mediation model was established to examine the influence of dietary inflammation on the association between tooth loss and cognitive tests, and the visualization of the moderating effect of serum albumin concentration was displayed through the Johnson-Neyman curve.

RESULTS

Participants with impaired dentition had worse cognitive function and a higher Dietary Inflammation Index (DII). DII was highly correlated with Immediate Recall Test (IR), Animal Fluency Test (AFT), and Digit Symbol Substitution Test (DSST), which mediated 16.46 %, 14.41 % and 11.28 % of the effect between tooth loss and cognitive functions. Additionally, the relationship between DII and DSST was moderated by serum albumin concentration.

CONCLUSION

Tooth loss was associated with cognitive function which was affected by pro-inflammatory dietary patterns and serum albumin level.

CLINICAL SIGNIFICANCE

This study presents evidence for dentists that dietary pattern change due to tooth loss plays a role in cognitive deterioration, which can also be moderated by serum albumin level. Therefore, the preservation of natural teeth is important for cognitive function, especially in an immunocompromised population with decreased serum albumin concentrations.

Treponema denticola Has the Potential to Cause Neurodegeneration in the Midbrain via the Periodontal Route of Infection-Narrative Review

Alzheimer's disease (AD) is a neurodegenerative disease and the most common example of dementia. The neuropathological features of AD are the abnormal deposition of extracellular amyloid-β (Aβ) and intraneuronal neurofibrillary tangles with hyperphosphorylated tau protein. It is recognized that AD starts in the frontal cerebral cortex, and then it progresses to the entorhinal cortex, the hippocampus, and the rest of the brain. However, some studies on animals suggest that AD could also progress in the reverse order starting from the midbrain and then spreading to the frontal cortex. Spirochetes are neurotrophic: From a peripheral route of infection, they can reach the brain via the midbrain. Their direct and indirect effect via the interaction of their virulence factors and the microglia potentially leads to the host peripheral nerve, the midbrain (especially the locus coeruleus), and cortical damage. On this basis, this review aims to discuss the hypothesis of the ability of Treponema denticola to damage the peripheral axons in the periodontal ligament, to evade the complemental pathway and microglial immune response, to determine the cytoskeletal impairment and therefore causing the axonal transport disruption, an altered mitochondrial migration and the consequent neuronal apoptosis. Further insights about the central neurodegeneration mechanism and Treponema denticola's resistance to the immune response when aggregated in biofilm and its quorum sensing are suggested as a pathogenetic model for the advanced stages of AD.

Locus Coeruleus Dysfunction and Trigeminal Mesencephalic Nucleus Degeneration: A Cue for Periodontal Infection Mediated Damage in Alzheimer's Disease?

Alzheimer's disease (AD) is a leading neurodegenerative disease with deteriorating cognition as its main clinical sign. In addition to the clinical history, it is characterized by the presence of two neuropathological hallmark lesions; amyloid-beta (Aβ) and neurofibrillary tangles (NFTs), identified in the brain at post-mortem in specific anatomical areas. Recently, it was discovered that NFTs occur initially in the subcortical nuclei, such as the locus coeruleus in the pons, and are said to spread from there to the cerebral cortices and the hippocampus. This contrasts with the prior acceptance of their neuropathology in the enthorinal cortex and the hippocampus. The Braak staging system places the accumulation of phosphorylated tau (p-tau) binding to NFTs in the locus coeruleus and other subcortical nuclei to precede stages I-IV. The locus coeruleus plays diverse psychological and physiological roles within the human body including rapid eye movement sleep disorder, schizophrenia, anxiety, and depression, regulation of sleep-wake cycles, attention, memory, mood, and behavior, which correlates with AD clinical behavior. In addition, the locus coeruleus regulates cardiovascular, respiratory, and gastrointestinal activities, which have only recently been associated with AD by modern day research enabling the wider understanding of AD development via comorbidities and microbial dysbiosis. The focus of this narrative review is to explore the modes of neurodegeneration taking place in the locus coeruleus during the natural aging process of the trigeminal nerve connections from the teeth and microbial dysbiosis, and to postulate a pathogenetic mechanism due to periodontal damage and/or infection focused on Treponema denticola.

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.

Electrical impedance tomography for titration of positive end-expiratory pressure in acute respiratory distress syndrome patients with chronic obstructive pulmonary disease

Background

Chronic obstructive pulmonary disease (COPD) is one of most common comorbidities in acute respiratory distress syndrome (ARDS). There are few specific studies on the appropriate ventilation strategy for patients with ARDS comorbid with COPD, especially regarding on positive end-expiratory pressure (PEEP) titration.

Methods

To compare the respiratory mechanics in mechanical ventilated ARDS patients with or without COPD and to determine whether titration of PEEP based on electrical impedance tomography (EIT) is superior to the ARDSnet protocol. This is a single center, perspective, repeated measure study. ARDS patients requiring mechanical ventilation who were admitted to the intensive care unit between August 2017 and December 2020 were included. ARDS patients were divided according to whether they had COPD into a COPD group and a non-COPD group. Respiratory mechanics, gas exchange, and hemodynamics during ventilation were compared between the groups according to whether the PEEP level was titrated by EIT or the ARDSnet protocol.

Results

A total of twenty-seven ARDS patients including 14 comorbid with and 13 without COPD who met the study eligibility criteria were recruited. The PEEP levels titrated by EIT and the ARDSnet protocol were lower in the COPD group than in the non-COPD group (6.93 ± 1.69 cm H₂O vs. 12.15 ± 2.40 cm H₂O, P < 0.001 and 10.43 ± 1.20 cm H₂O vs. 14.0 ± 3.0 cm H₂O, P < 0.001, respectively). In the COPD group, the PEEP level titrated by EIT was lower than that titrated by the ARDSnet protocol (6.93 ± 1.69 cm H₂O vs. 10.43 ± 1.20 cm H₂O, P < 0.001), as was the global inhomogeneity (GI) index (0.397 ± 0.040 vs. 0.446 ± 0.052, P = 0.001), plateau airway pressure (16.50 ± 4.35 cm H₂O vs. 20.93 ± 5.37 cm H₂O, P = 0.001), dead space ventilation ratio (48.29 ± 6.78% vs. 55.14 ± 8.85%, P < 0.001), ventilation ratio (1.63 ± 0.33 vs. 1.87 ± 0.33, P < 0.001), and mechanical power (13.92 ± 2.18 J/min vs. 15.87 ± 2.53 J/min, P < 0.001). The cardiac index was higher when PEEP was treated by EIT than when it was titrated by the ARDSnet protocol (3.41 ± 0.50 L/min/m² vs. 3.02 ± 0.43 L/min/m², P < 0.001), as was oxygen delivery (466.40 ± 71.08 mL/min/m² vs. 411.10 ± 69.71 mL/min/m², P = 0.001).

Conclusion

Titrated PEEP levels were lower in patients with ARDS with COPD than in ARDS patients without COPD. In ARDS patient comorbid with COPD, application of PEEP titrated by EIT was lower than those titrated by the ARDSnet protocol, which contributed to improvements in the ventilation ratio, mechanical energy, cardiac index, and oxygen delivery with less of an adverse impact on hemodynamics.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-022-04201-y.

Periodontal health, cognitive decline, and dementia: A systematic review and meta-analysis of longitudinal studies

BACKGROUND

Emerging evidence indicates that poor periodontal health adversely impacts cognition. This review examined the available longitudinal evidence concerning the effect of poor periodontal health on cognitive decline and dementia.

METHODS

Comprehensive literature search was conducted on five electronic databases for relevant studies published until April 2022. Longitudinal studies having periodontal health as exposure and cognitive decline and/or dementia as outcomes were considered. Random effects pooled estimates and 95% confidence intervals were generated (pooled odds ratio for cognitive decline and hazards ratio for dementia) to assess whether poor periodontal health increases the risk of cognitive decline and dementia. Heterogeneity between studies was estimated by I2 and the quality of available evidence was assessed through quality assessment criteria.

RESULTS

Adopted search strategy produced 2132 studies for cognitive decline and 2023 for dementia, from which 47 studies (24 for cognitive decline and 23 for dementia) were included in this review. Poor periodontal health (reflected by having periodontitis, tooth loss, deep periodontal pockets, or alveolar bone loss) was associated with both cognitive decline (OR = 1.23; 1.05-1.44) and dementia (HR = 1.21; 1.07-1.38). Further analysis, based on measures of periodontal assessment, found tooth loss to independently increase the risk of both cognitive decline (OR = 1.23; 1.09-1.39) and dementia (HR = 1.13; 1.04-1.23). Stratified analysis based on the extent of tooth loss indicated partial tooth loss to be important for cognitive decline (OR = 1.50; 1.02-2.23) and complete tooth loss for dementia (HR = 1.23; 1.05-1.45). However, the overall quality of evidence was low, and associations were at least partly due to reverse causality.

CONCLUSIONS

Poor periodontal health and tooth loss appear to increase the risk of both cognitive decline and dementia. However, the available evidence is limited (e.g., highly heterogenous, lacking robust methodology) to draw firm conclusions. Further well-designed studies involving standardized periodontal and cognitive health assessment and addressing reverse causality are highly warranted.

Association between dentition and frailty and cognitive function in community-dwelling older adults

Objectives

To evaluate dentition status amongst community-dwelling older adults and its association with frailty and cognitive impairment.

Methodology

One thousand forty-seven community-dwelling older adults aged ≥65 years were surveyed in an epidemiologic population-based cohort study in Singapore between April 2015 and August 2016. Data on demographics, dentition status, chronic diseases, activities and instrumental activities on daily-living, cognition (age- and education-specific MMSE cut-offs), frailty (FRAIL scale), perceived health and functional status were collected. Multiple logistic regression was performed to examine the association between dentition, frailty and cognition.

Results

Mean age of participants was 71.2 ± 5.5 years. The prevalence of denture use was 70.7% and edentulism 7.9%. Compared to edentulousness, having teeth was associated with lower odds of cognitive impairment and higher odds of being robust or pre-frail. Denture-wearers compared with edentulous persons were less likely to be male, had higher education level and more likely be robust or pre-frail.

Conclusion and implications

There were significant associations between dentition status, frailty and cognition in our study where those with remining teeth and / or dentures had better overall outcomes. As oral health, frailty and cognitive impairments are all modifiable risk factors for healthy ageing, countries should consider population level screening for oral health, frailty and cognitive impairment.

Is the Number of Missing Teeth Associated With Mortality? A Longitudinal Study Using a National Health Screening Cohort

This study aimed to estimate the risk of mortality related to the number of missing teeth in a South Korean population. The ≥ 40-year-old population of the Korean National Health Insurance Service-Health Screening Cohort 2002–2003 was analyzed. Participants were selected from a total of 220,189 participants and included in groups of 0 teeth lost, 1–2 teeth lost, and ≥ 3 teeth lost. Among the total population, 17,211 participants were included in no missing teeth, 1–2 missing teeth, and ≥ 3 missing teeth and were randomly matched 1:1:1 for age and sex. Mortality from specific causes and all-cause mortality were compared among the groups. The hazard ratio (HR) of the number of missing teeth for all-cause mortality or each cause of mortality was analyzed using Cox proportional hazard models. According to the cause of death, the HRs for metabolic disease, digestive disease, and trauma were greater in the group with ≥ 3 missing teeth than in the no missing teeth group. The group with ≥ 3 missing teeth indicated a 1.19-fold higher HR for all-cause mortality than the no missing teeth group [95% confidence intervals (95% CIs) = 1.12–1.27, P &lt; 0.001]. The group with 1- 2 missing teeth did not show a higher HR for all-cause mortality. In the group with 1–2 missing teeth, the HRs for mortality from mental disease and digestive disease were higher than those in the no missing teeth group. The group with 1–2 missing teeth did not show a higher HR for all-cause mortality. The number of missing teeth was linked with a higher risk of mortality. For specific causes of mortality, mortality from metabolic disease, digestive disease, and trauma was higher in the participants with the number of missing teeth.

The Sedentary Lifestyle and Masticatory Dysfunction: Time to Review the Contribution to Age-Associated Cognitive Decline and Astrocyte Morphotypes in the Dentate Gyrus

As aging and cognitive decline progresses, the impact of a sedentary lifestyle on the appearance of environment-dependent cellular morphologies in the brain becomes more apparent. Sedentary living is also associated with poor oral health, which is known to correlate with the rate of cognitive decline. Here, we will review the evidence for the interplay between mastication and environmental enrichment and assess the impact of each on the structure of the brain. In previous studies, we explored the relationship between behavior and the morphological features of dentate gyrus glial fibrillary acidic protein (GFAP)-positive astrocytes during aging in contrasting environments and in the context of induced masticatory dysfunction. Hierarchical cluster and discriminant analysis of GFAP-positive astrocytes from the dentate gyrus molecular layer revealed that the proportion of AST1 (astrocyte arbors with greater complexity phenotype) and AST2 (lower complexity) are differentially affected by environment, aging and masticatory dysfunction, but the relationship is not straightforward. Here we re-evaluated our previous reconstructions by comparing dorsal and ventral astrocyte morphologies in the dentate gyrus, and we found that morphological complexity was the variable that contributed most to cluster formation across the experimental groups. In general, reducing masticatory activity increases astrocyte morphological complexity, and the effect is most marked in the ventral dentate gyrus, whereas the effect of environment was more marked in the dorsal dentate gyrus. All morphotypes retained their basic structural organization in intact tissue, suggesting that they are subtypes with a non-proliferative astrocyte profile. In summary, the increased complexity of astrocytes in situations where neuronal loss and behavioral deficits are present is counterintuitive, but highlights the need to better understand the role of the astrocyte in these conditions.