Revisiting the link between cognitive decline and masticatory dysfunction

Evaluation of the extent of plaque removal and users' experience of alternative toothbrushes: A randomized single-blind crossover study

INTRODUCTION

In residential care, tooth brushing with a manual toothbrush can be challenging because of technical difficulties, time consumption and poor patient cooperation, resulting in a sub-optimal cleaning. The study aimed at comparing the efficiency in plaque removal, brushing time and users' experience between three toothbrushes: a single-headed conventional manual toothbrush, a triple-headed manual toothbrush and a U-shaped electric toothbrush.

METHODS

This was a single-blind crossover study with three pre-post-test conditions. Participants were 26 dental students divided into fixed pairs to play the role of caregivers and care receivers. Pre/post plaque scores were determined by two independent investigators according to the Quigley-Hein Plaque Index (QHI). Questionnaires evaluated participants' experiences. Statistical tests of significances of differences and ANOVA were performed.

RESULTS

Results showed that plaque removal was more effective for the manual toothbrush and the triple-headed toothbrush compared to the U-shaped electric toothbrush (p < 0.001). Brushing time was the longest for the single manual toothbrush (149 s). The U-shaped electric toothbrush showed significantly better results for aspects related to comfort and salivation. The manual and triple-headed toothbrush showed better results for aspects related to cleanliness and motivation to use.

CONCLUSION

Notwithstanding its favourable comfort, tooth plaque removal is not enhanced by a U-shaped electric toothbrush. The triple-headed and single-headed toothbrushes reduced plaque more substantially than the U-shaped toothbrush. In addition, the triple-headed manual toothbrush was not only effective in plaque removal, but also had a shorter brushing time and was easy to use, being an adequate alternative for care-dependent patient groups.

Structural brain feature is associated with changes of masticatory performance in healthy elderly people: Evidence from longitudinal neuroimaging research over two years

BACKGROUND

Human neuroimaging studies have revealed the association between brain structure and masticatory function. However, the majority of the studies adopted a cross-sectional design, which hardly reveals the change in masticatory function and brain structure between different timepoints, and the dynamical association between changes in masticatory function and changes in brain structure has not been elucidated.

OBJECTIVE

With a longitudinal design, we assessed the association between changes in masticatory performance (MP) and regional brain volume.

METHODS

Twenty-two elderly participants received assessments of the number of missing teeth and MP (via colour-changeable chewing gum) when they entered the study (i.e. the initial stage, T0 ), approximately 6 months later (T0.5 ), and approximately 1-2 years later (T1 ). Difficulty of food intake was assessed using a questionnaire. The participants received magnetic resonance imaging (MRI) at T0 and T1 . The brain volume of the motor-related area was estimated using FreeSurfer for MRI data. The associations between different stages were analysed using Spearman's rho correlation coefficients.

RESULTS

(1) Individually, a smaller volume of right primary motor cortex at T0 was associated with increased MP from T0 to T1 , suggesting the brain's role in changing oral functions; (2) higher MP at T0 was associated with an increased volume of the left superior frontal cortex from T0 to T1 p, suggesting a potential effect on brain plasticity, and (3) increased difficulty to eat was associated with decrease MP but not brain volume of motor-related area.

CONCLUSIONS

The preliminary findings revealed a complicated pattern of structural brain features and masticatory function in elderly people, and either the hypothesis that the brain predisposes masticatory function or the hypothesis that mastication reshapes the brain is oversimplified.

Molecular mechanisms underlying the effect of tooth shortening on memory dysfunction in Wistar male rat

OBJECTIVE

We investigated the effects of molar tooth shortening on the mRNA expression of the AβPP/BACE1, BDNF/TrkB, and Bax/Bcl-2 signaling pathways in the Wistar male rat hippocampal regions.

DESIGN

Four groups (n = 5 per group) of male Wistar rats (control, SRM (shortened right molar), SLM (shortened left molar), and SBM (shortened bilateral molar)) were used. RNA was isolated from the hippocampus and transformed into cDNA. Real-time quantitative PCR was used to evaluate the mRNA expression levels of AβPP, BACE1, Bax, Bcl-2, BDNF, and TrkB.

RESULTS

Differential mRNA expression was observed in rat groups. SBM significantly upregulated the AβPP, BACE1, and Bax mRNA expressions, whereas the expression levels of Bcl-2, BDNF, and TrkB were decreased. SRM and SLM approximately had the same effect on the expression enhancement of AβPP, BACE1, and Bax; however, SRM was more effective than SLM in increasing the expression of these genes.

CONCLUSIONS

Symmetrical molar teeth shortening affected the mRNA expression of AβPP and BACE1, which is related to learning and memory dysfunction.

An umbrella review on the association between factors of oral health and cognitive dysfunction

An increasing number of systematic reviews and meta-analyses have been published on the association between oral health and cognitive dysfunction, also known as oral-cognitive links. However, there is great diversity in the oral and cognitive factors included in these studies, with different opinions for clinical practice drawn from the evidence. To understand which oral and cognitive factors are involved in those associations, we conducted an umbrella review of 28 systematic reviews, including 12 meta-analyses, on oral-cognitive links. We found that (a) periodontal diseases, oral microbiome, and dementia were frequently studied, while other factors, such as mastication and mild cognitive impairment, were less commonly investigated, and (b) severe deterioration of oral health, such as severe periodontitis or extensive tooth loss, rather than the presence of oral diseases alone, was strongly associated with cognitive dysfunction. In conclusion, the diversity of oral and cognitive factors included in the review studies reflects the complexity of oral-cognitive links. Clarifying the factors helps to form evidence-based clinical advice for healthcare.

An assessment of masticatory efficiency and occlusal load distribution in adolescent patients undergoing orthodontic treatment with functional jaw orthopedics: A prospective cohort study

INTRODUCTION

Functional jaw orthopaedics, produces a radical change in the occlusal scheme and the masticatory apparatus, particularly in patients with Class II malocclusion. It remains to be seen how the changes brought about by a functional appliance alter the masticatory ability of a growing child, who needs the necessary nutrition to properly grow the craniofacial region.

MATERIALS AND METHODS

Pretreatment and Post-treatment values of masticatory efficiency and the distribution of the occlusal load at centric occlusion were evaluated and compared for 20 patients with Class II division 1 malocclusion undergoing functional jaw orthopaedics.

RESULTS

Significant increase in the masticatory efficiency was seen during and after treatment (p < 0.5) There was an increase in the anterior distribution of occlusal load associated with a concomitant decrease in the posterior region at centric occlusion.

CONCLUSION

Improvement in the masticatory efficiency was observed after treatment of a retrognathic mandible with functional jaw orthopaedics in the adolescent participants with Class II malocclusion. This highlights the importance of treatment with functional jaw orthopaedics, which apart from providing esthetic and functional improvement also improves the ability of a growing child to extract proper nutrition from his/her diet.

Tooth loss and dementia amongst older adults residing in long-term care facilities in Vancouver: A case-control study

OBJECTIVE

The purpose of this case-control study was to determine the association between dementia and the number of missing teeth, functional occlusal units and denture use in older adults residing in Long-Term Care (LTC) facilities.

BACKGROUND

Many studies have shown an association between dementia and tooth loss. However, few studies with a large sample size have been reported describing the relationship between dementia and the number of missing teeth, remaining teeth and functional occlusal units.

METHODS

An oral health assessment database of 2160 older adults admitted to LTC facilities in Vancouver, Canada, between 2015-2019 was utilised. Participants with a diagnosis of dementia in their medical records (N = 1174) were compared to those without dementia (N = 986). Multiple logistic regression analysis was used to explore a potential association between the number of missing teeth, functional occlusal units and the use of dentures and dementia.

RESULTS

The number of remaining teeth (OR = 1.0, 95% Confidence Interval = 1.0-1.0; P = .054) and number of functional occlusal units (OR = 1.0, 95% CI = 1.0-1.0; P = .059) were not associated with dementia after adjusting for age, sex, oral self-care and systemic conditions. Denture use (OR = 1.1, 95% CI = 0.5-2.4; P = .790) was not associated with dementia in edentulous patients.

CONCLUSION

There was no association between dementia and the number of remaining teeth, functional occlusal units or wearing dentures.

White matter abnormalities mediate the association between masticatory dysfunction and cognition among older adults

BACKGROUND

Masticatory parameters, such as reduced number of teeth and posterior contacts, have been shown to be associated with reduced cognitive status. The underlying mechanisms that affect these associations, are however, not well understood.

OBJECTIVES

The study aims to investigate the association between masticatory dysfunction and cognition and explore the mediating effect of brain structure.

METHODS

In this cross-sectional study, 45 older adults with subjective masticatory dysfunction (mean age 72.3 ± 4.0 years) were included. Mini-Mental State Examination score <25, brain trauma, neurological disease, neurodegenerative disorders, depression or poor Swedish language skills were criteria for exclusion. Cognitive functions (executive function and episodic memory) and masticatory dysfunction defined by functional occluding status (FOS; the number of occluding units and number of remaining teeth) were analysed with partial correlation models. Structural magnetic resonance imaging was performed on 28 feasible participants. Multiple regression analyses were performed to evaluate the predictive value of brain structure and white matter hypointensities (WM-hypo) on cognitive functions. A mediation analysis was applied to assess significant predictor/s of the association between FOS and cognition.

RESULTS

Both episodic memory and executive functions were positively correlated with FOS. WM-hypo predicted cognitive status (executive function, p ≤ .01). WM-hypo mediated 66.6% (p = 0.06) of the association between FOS and executive functions.

CONCLUSION

Associations between FOS and cognitive functions are reported, where FOS, a potential modifiable risk factor, was related to both episodic memory and executive functions. The mediating effect of WM-hypo on the association between FOS and executive functions highlights the impact of the vascularisation of the brain on the link between mastication and cognition. The present study provides increased knowledge that bridges the gap between masticatory dysfunction and cognition.

Cerebellar Prediction and Feeding Behaviour

Given the importance of the cerebellum in controlling movements, it might be expected that its main role in eating would be the control of motor elements such as chewing and swallowing. Whilst such functions are clearly important, there is more to eating than these actions, and more to the cerebellum than motor control. This review will present evidence that the cerebellum contributes to homeostatic, motor, rewarding and affective aspects of food consumption.Prediction and feedback underlie many elements of eating, as food consumption is influenced by expectation. For example, circadian clocks cause hunger in anticipation of a meal, and food consumption causes feedback signals which induce satiety. Similarly, the sight and smell of food generate an expectation of what that food will taste like, and its actual taste will generate an internal reward value which will be compared to that expectation. Cerebellar learning is widely thought to involve feed-forward predictions to compare expected outcomes to sensory feedback. We therefore propose that the overarching role of the cerebellum in eating is to respond to prediction errors arising across the homeostatic, motor, cognitive, and affective domains.

Importance of oral health in mental health disorders: An updated review

Background

Mental disorders are indeed an expanding threat, which requires raised awareness, education, prevention, and treatment initiatives nationally and globally. This review presents an updated review on the relationships between oral health and mental health disorders and the importance of oral health in mental health disorders.

Method

A literature search was done regarding mental disorders and oral health approaches in Google Scholar and PubMed from the year 1995 until 2023. All the English-language papers were evaluated based on the inclusion criteria. Publications included original research papers, review articles and book chapters.

Results

Common mental disorders include depression, anxiety, bipolar disorder, Schizophrenia, dementia, and alcohol and drug use disorders. The interplay of oral health and mental disorders involves dysregulated microbiome, translocated bacteria, and systemic inflammation, among others.

Conclusion

There is a complex relationship between mental disorders and oral diseases. Various oral health problems are associated with mental health problems. The interplay of oral health and mental disorders involves dysregulated microbiome, translocated bacteria, and systemic inflammation, among others. Mental health nurses including physicians and dental professionals should be involved in the oral health care of mental health disorder patients. Therefore, multidisciplinary should be involved in the care of mental health disorders, and they should consider oral health care as an essential part of their care for patients with mental health disorders. Future investigations should strive to elucidate the exact biological relationships, to develop new directions for treatment.

Dementia and the history of disease in older adults in community

INTRODUCTION

Many studies have revealed the effect of medical history on dementia. The aim of this study was to explore the relationship between the history of disease and onset of dementia.

METHODS

This was a multi-center, cross-sectional study, with 2595 older adults enrolled. The onset of dementia was evaluated with Revised Hasegawa Dementia Scale (HDS-R). The diagnosed diseases after the age of 40 of the participants were investigated, including respiratory system diseases, digestive system diseases, cardiovascular diseases, endocrine disorders, genitourinary system diseases, nervous system disease, sensory system diseases, dental/oral diseases, bone/joint diseases and mental illnesses.

RESULTS

Data of 2458 older adults were analyzed. Univariate analysis showed that diabetes, thyroid disease, mental illness, hearing loss, stroke, dental/oral disease, Denture use, fracture/osteoporosis, kidney disease and number of diseases were risk factors for dementia. After controlling for demographic sociological variables, diabetes, dental/oral disease, and denture use were independent risk factors for dementia. Thyroid disease (P = 0.313), mental illnesses (P = 0.067), hearing loss (P = 0.595), stroke (P = 0.538), fractures/osteoporosis (P = 0.069), kidney disease (P = 0.168) were no longer significant to dementia.

CONCLUSION

Diabetes, dental/oral disease and denture use were main risk factors for dementia.

Pre-Adolescent Diet Normalization Restores Cognitive Function in Young Mice

Mastication is a fundamental function critical for human health. Controlled by the central nervous system (CNS), it influences CNS development and function. A poor masticatory performance causes cognitive dysfunction in both older adults and children. Improving mastication may prevent cognitive decline. However, no study has determined the period of masticatory dysfunction that impairs children's later acquisition of cognitive function. Herein, we developed an animal model wherein a soft diet was switched to a normal diet at early and late time points in young mice. We aimed to investigate the impact of restored mastication on learning and memory function. Behavioral studies were conducted to evaluate learning and memory. Micro-CT was used to evaluate orofacial structural differences, while histological and biochemical approaches were employed to assess differences in the hippocampal morphology and function. Correction to a hard-textured diet before adolescence restored mastication and cognitive function through the stimulation of neurogenesis, extracellular signal-regulated kinases, the cyclic adenosine monophosphate-response element-binding protein pathway, and the brain-derived neurotrophic factor, tyrosine receptor B. In contrast, post-adolescent diet normalization failed to rescue full mastication and led to impaired cognitive function, neuronal loss, and decreased hippocampal neurogenesis. These findings revealed a functional linkage between the masticatory and cognitive function in mice during the juvenile to adolescent period, highlighting the need for adequate food texture and early intervention for mastication-related cognitive impairment in children.

Molar tooth shortening induces learning and memory impairment in Wistar rat

OBJECTIVE

This study aimed to investigate the relationship between different patterns of molar crown loss and the association between symmetrical and asymmetrical shortening molar teeth with memory impairment.

MATERIALS AND METHODS

Male Wistar rats were divided into four groups (n = 10) including control, SLM (shortened left molar), SRM (shortened right molar), and SBM (shortened bilateral molar) groups. Morris water maze (MWM) and passive avoidance test (PAT) were performed to assess spatial and fear memory, respectively. Besides, histological assessment of hippocampus and gingival tissues was done.

RESULTS

In the MWM test, SBM and SLM groups had higher escape latency over training trials and spent less time in the target quadrant in the probe trial (p < 0.01). In the PAT, step-through latency was significantly reduced in three groups, and time spent in the dark compartment increased in SBM (p < 0.01) and SLM (p < 0.05) groups. In addition, each teeth shortening group indicated a reduction in density (p < 0.01) and thickness layer (p < 0.05) of pyramidal cells. Gingival was normal after shortening of the molar crown.

CONCLUSIONS

Different patterns of molar teeth shortening induced learning and memory impairment; however, symmetrical molar teeth shortening has more effects on memory impairment.

Time-varying exposure analysis of the relationship between sustained natural dentition and cognitive decline

AIM

Tooth loss and cognitive decline progress over time and influence each other. This study estimated the impact of sustaining natural dentition on cognitive function in U.S. adults, accounting for the fact that dental and cognitive statuses change over time.

MATERIALS AND METHODS

Data from adults aged ≥51 years who participated in five waves of the Health and Retirement Study from 2004 to 2016 (n = 10,953) were analysed. The impact of retaining some natural teeth from 2006 to 2012 on cognitive function score (0-27) and cognitive impairment (defined as having a cognitive function score of <12) in 2016 was evaluated using the doubly robust targeted maximum likelihood estimation method by considering both time-invariant and time-varying confounders, including cognitive function at baseline and during follow-up.

RESULTS

Respondents with some natural teeth between 2006 and 2012 had a 0.40 point (95% confidence interval [CI]: 0.10-0.71) higher cognitive function score and 3.27 percentage point (95% CI: 0.11-6.66) lower cognitive impairment prevalence in 2016 than those with complete tooth loss.

CONCLUSIONS

Considering past cognitive function assessed at multiple time points, sustained natural dentition was associated with better cognitive function.

Tooth loss and regional grey matter volume

OBJECTIVES

To investigate whether tooth loss was associated with regional grey matter volume (GMV) in a group of community dwelling older men and women from Ireland.

METHODS

A group of 380 dementia-free men and women underwent a dental examination and had a Magnetic Resonance Imaging (MRI) scan as part of The Irish Longitudinal Study of Aging (TILDA). Cortical parcellation was conducted using Freesurfer utilities to produce volumetric measures of gyral based regions of interest. Analysis included multiple linear regression to investigate the association between tooth loss and regional GMVs with adjustment for various confounders.

RESULTS

The mean age of participants was 68.1 years (SD 7.3) and 51.6% of the group were female. 50 (13.2%) of the participants were edentulous, 148 (38.9%) had 1-19 teeth, and 182 (47.9%) had ≥20 teeth. Multiple liner regression analysis with adjustment for a range of potential confounders showed associations between the number of teeth and GMVs in the paracentral lobule and the cuneus cortex. In the paracentral lobule, comparing participants with 1-19 teeth versus edentates there was an increase in GMV of β=323.0mm³ (95% Confidence Interval [CI] 84.5, 561.6) and when comparing participants with ≥20 teeth to edentates there was an increase of β=382.3mm³ (95% CI 126.9, 637.7). In the cuneus cortex, comparing participants with ≥20 teeth to edentates there was an increase in GMV of β=380.5mm³ (95% CI 69.4, 691.5).

CONCLUSIONS

In this group of older men and women from Ireland, the number of teeth was associated with GMVs in the paracentral lobule and the cuneus cortex independent of various known confounders.

CLINICAL SIGNIFICANCE

Although not proof of causation, the finding that tooth loss was associated with regional reduced GMV in the brain may represent a potential explanatory link to the observed association between tooth loss and cognitive decline.

The Test of Mastication and Swallowing Solids and the Timed Water Swallow Test: Reliability, associations, age and gender effects, and normative data

BACKGROUND

Quantitative measures can increase precision in describing swallowing function, improve interrater and test-retest reliability, and advance clinical decision-making. The Test of Mastication and Swallowing Solids (TOMASS) and the Timed Water Swallow Test (TWST) are functional tests for swallowing that provide quantitative results.

AIMS

To explore the relationship between TOMASS and TWST; evaluate test-retest and interrater reliability; explore age and gender effects; and gather normative data.

METHODS & PROCEDURES

Healthy community dwelling participants (n = 298, ≥ 20 years old) were recruited. Of those, 126 were included in the reliability study. Participants completed the TWST and TOMASS.

OUTCOMES & RESULTS

Associations between TWST and TOMASS measures were found using Pearson's correlation coefficient. Age was positively associated with an increase in the number of bites (n = 292, r = 0.15, p = 0.009), masticatory cycles (n = 291, r = 0.33, p < 0.0001) and duration (n = 292, r = 0.32, p < 0.0001) for the TOMASS. For the TWST, age was positively associated with an increase in duration (n = 296, r = 0.23, p < 0.0001), and negatively associated with volume (n = 296, r = -0.205, p < 0.0001), and swallowing capacity (n = 296, r = -0.24, p < 0.0001). Females required more bites, masticatory cycles, swallows and longer time than males in TOMASS. In TWST, females required more swallows, longer time, and had lower volume per swallow and reduced swallowing capacity than males. Intraclass correlation coefficient (ICC) revealed good test-retest reliability and moderate to excellent interrater reliability.

CONCLUSIONS & IMPLICATIONS

This study provides support for the validity of the TOMASS and TWST. Reduced efficiency in one of the tests might indicate a need to evaluate performance in the other. Extended chewing time and increased number of masticatory cycles might be compensatory behaviours for reduced oral processing abilities that are motor, sensory and/or mechanical.

WHAT THIS PAPER ADDS

The TOMASS and TWST are functional tests of swallowing that provide quantitative results. They are easy to incorporate as part of the clinical evaluation of swallowing due to low cost and quick administration. Age and gender effects were found for the TWST and TOMASS, but they were only tested on relative measures rather than absolute measures. Different types of crackers used for TOMASS led to differences in performance and in normative values. What is already known on the subject Associations between performance during TWST and TOMASS were found: time, number of swallows and time per swallow were correlated, meaning that need for more time and more swallows is reflected in both drinking and chewing. The study provides further support for age and gender effects in TWST and TOMASS, on both relative and also on absolute measures, which were not investigated previously. Longer durations in TOMASS and TWST with an increase in age, are likely to be the result of compensatory behaviours to allow safe swallowing. Normative data for a country-specific cracker are presented (Israel). What are the potential or actual clinical implications of this work? Reduced efficiency in one of the tests might indicate a need to evaluate performance in the other. Establishing country specific norms for commonly available crackers is necessary, since crackers size and ingredients, such as fat content and moisture, influence chewing and swallowing. There is a balancing act between safety and efficiency in older adults' swallowing behaviour. Reducing pace in eating and drinking probably supports safer swallowing.

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.

Association of Tooth Loss with Alzheimer's Disease Tau Pathologies Assessed by Positron Emission Tomography

BACKGROUND

Deterioration of the oral environment is one of the risk factors for dementia. A previous study of an Alzheimer's disease (AD) model mouse suggests that tooth loss induces denervation of the mesencephalic trigeminal nucleus and neuroinflammation, possibly leading to accelerated tau dissemination from the nearby locus coeruleus (LC).

OBJECTIVE

To elucidate the relevance of oral conditions and amyloid-β (Aβ) and tau pathologies in human participants.

METHODS

We examined the number of remaining teeth and the biofilm-gingival interface index in 24 AD-spectrum patients and 19 age-matched healthy controls (HCs). They also underwent positron emission tomography (PET) imaging of Aβ and tau with specific radiotracers, 11C-PiB and 18F-PM-PBB3, respectively. All AD-spectrum patients were Aβ-positive, and all HCs were Aβ-negative. We analyzed the correlation between the oral parameters and radiotracer retention.

RESULTS

No differences were found in oral conditions between the AD and HC groups. 11C-PiB retentions did not correlate with the oral indices in either group. In AD-spectrum patients, brain-wide, voxel-based image analysis highlighted several regions, including the LC and associated brainstem substructures, as areas where 18F-PM-PBB3 retentions negatively correlated with the remaining teeth and revealed the correlation of tau deposits in the LC (r = -0.479, p = 0.018) primarily with the hippocampal and neighboring areas. The tau deposition in none of the brain regions was associated with the periodontal status.

CONCLUSIONS

Our findings with previous preclinical evidence imply that tooth loss may enhance AD tau pathogenesis, promoting tau spreading from LC to the hippocampal formation.

Differences in Brain Volume by Tooth Loss and Cognitive Function in Older Japanese Adults

BACKGROUND

We investigated the association between tooth loss and structural brain volume and its mediating effect on the association between tooth loss and cognitive function in older Japanese.

METHODS

A cross-sectional study was conducted by using the data of 494 randomly sampled community-dwelling individuals aged 65-84 years living in Tokamachi City, Japan. Total brain volume (TBV), gray matter volume (GMV), white matter volume (WMV), and hippocampal volume (HV) were measured with magnetic resonance imaging. The association of self-reported number of teeth (≥20, 1-19, and 0) with cognitive function assessed with the Japanese version of the Quick Mild Cognitive Impairment screen and structural brain volume was examined. Causal mediation analysis was performed to evaluate the mediating effect of structural brain volume. Age, sex, socioeconomic status, health behavior, comorbid conditions, and total intracranial volume were adjusted.

RESULTS

Respondents with no teeth showed lower cognitive function (coefficient = -4.01; 95% confidence interval [CI]: -7.19, -0.82), lower TBV (coefficient = -10.34; 95% CI: -22.84, 2.17), and lower GMV (coefficient = -6.92; 95% CI: -14.84, 0.99) than those with ≥20 teeth (P for trends were 0.003, 0.035, and 0.047, respectively). The number of teeth was not significantly associated with WMV or HV. GMV showed a significant mediating effect on the association between the number of teeth and cognitive function (coefficient = -0.38; 95% CI: -1.14, -0.002, corresponding to 9.0% of the total effect), whereas TBV did not.

CONCLUSIONS

GMV was suggested to mediate the relationship between tooth loss and lower cognitive function.

Tooth Loss Induces Memory Impairment and Glial Activation in Young Wild-Type Mice

Background

Tooth loss is closely associated with Alzheimer's disease (AD). Previously, we reported that tooth loss induced memory impairment in amyloid precursor protein knock-in mice by decreasing neuronal activity and synaptic protein levels and increasing glial activation, neuroinflammation, and pyramidal neuronal cell loss without altering amyloid-β levels in the hippocampus. However, the effects of tooth loss in young wild-type mice have not been explored yet.

Objective

We investigated the effects of tooth loss on memory impairment, neuronal activity, synaptic protein levels, glial activation, and pyramidal neuronal cell loss in young wild-type mice.

Methods

Two-month-old wild-type mice were randomly divided into control and tooth loss groups. In the tooth loss group, maxillary molar teeth on both sides were extracted, whereas no teeth were extracted in the control group. Two months after tooth extraction, we performed a novel object recognition test to evaluate memory function. Glial activation, neuronal activity, synaptic protein levels, and the number of pyramidal neurons were evaluated using immunofluorescence staining, immunohistochemistry, and western blotting.

Results

The tooth loss group exhibited memory impairment and decreased neuronal activity and the levels of synaptic proteins in both the hippocampus and cortex. Moreover, tooth loss increased the activation of phosphorylated c-Jun N-terminal kinase (JNK), heat shock protein 90 (HSP90), and glial activation and reduced the number of pyramidal neurons in the hippocampus.

Conclusion

Tooth loss in the young wild-type mice will attenuate neuronal activity, decrease synaptic protein levels, and induce pyramidal neuronal loss, and eventually lead to memory impairment.

Musculoskeletal Deficits and Cognitive Impairment: Epidemiological Evidence and Biological Mechanisms

PURPOSE OF REVIEW

Cognitive impairment is associated with obesity, sarcopenia, and osteoporosis. However, no critical appraisal of the literature on the relationship between musculoskeletal deficits and cognitive impairment, focusing on the epidemiological evidence and biological mechanisms, has been published to date. Herein, we critically evaluate the literature published over the past 3 years, emphasizing interesting and important new findings, and provide an outline of future directions that will improve our understanding of the connections between the brain and the musculoskeletal system.

RECENT FINDINGS

Recent literature suggests that musculoskeletal deficits and cognitive impairment share pathophysiological pathways and risk factors. Cytokines and hormones affect both the brain and the musculoskeletal system; yet, lack of unified definitions and standards makes it difficult to compare studies. Interventions designed to improve musculoskeletal health are plausible means of preventing or slowing cognitive impairment. We highlight several musculoskeletal health interventions that show potential in this regard.

Associations between self-reported masticatory dysfunction and frailty: A systematic review and meta-analysis

Background

Oral health is a key factor of overall health and closely associated with well-being and quality of life. Mastication is one the most important oral functions and may deteriorate with aging. Evidence on association between masticatory dysfunction and frailty in the literature is scarce and not coherent.

Methods

A search strategy was developed to conduct a systematic review of the literature in PubMed, CINAHL, and AMED in accordance with the PRISMA 2020 guidelines. We searched for studies published in 2000 or later that examined associations between self-reported masticatory dysfunction and frailty risk. The reference lists of the relevant articles were reviewed for additional studies. We calculated pooled odds ratios (OR) of association between self-reported masticatory dysfunction and the risk of frailty by fixed-effects meta-analysis. The Joanna Briggs Institute Critical Appraisal Checklist was used to assess risk of bias. Publication bias was assessed by visually inspecting a funnel plot.

Results

A total of 285 studies were identified by the literature search. Among 5 studies selected for this review, 4 cross-sectional studies including a total of 7425 individuals were used for meta-analysis. The pooled results by a fixed-effects model showed that there was a significant association between self-reported masticatory dysfunction and frailty risk (pooled OR = 1.83, 95%CI = 1.55–2.18, p<0.00001). There was no evidence of publication bias observed.

Conclusions

This systematic review and meta-analysis highlighted pooled cross-sectional evidence that community-dwelling older people who report masticatory dysfunction are significantly more likely to be frail than those who do not. The limitations of this study are: inclusion of only cross-sectional studies, no gold standard to measure masticatory functions, self-reported information on masticatory function, and the limited number of included studies. More longitudinal studies are warranted for further understanding of the causal pathways and elucidate underlying mechanisms.

Registration: PROSPERO CRD42021277173

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.

The Relation between Masticatory Function and Nutrition in Older Individuals, Dependent on Supportive Care for Daily Living

Introduction: Associations between masticatory function and nutritional status have been suggested. Masticatory function can be divided into two subdomains, the objective capacity of an individual to mix solid food and the individual’s subjectively assessed ability to masticate solid food. Aim: The aims of this study were to assess the relationship between these subdomains and nutritional variables in older, care-dependent individuals. Materials and methods: From a group of 355 individuals with care dependency and functional limitations, individuals aged 60 and older were selected. By home visits, the subjects underwent an oral examination and answered chewing related questions. Nutritional status was assessed using the Mini Nutritional Assessment. A total of 196 individuals met the age requirement of 60 years or older. Of these, 86 subjects were able to answer the questions. Results: We could not find any concluding significant associations between the subdomains of masticatory function or the nutritional variables. Conclusions: The absence of associations could be explained by the lack of standardized and validated methods to assess masticatory function and they possibly reflect varying underlying constructs. Self-reported questionnaires seem less useful among older and care-dependent individuals, while an objective clinical measurement will be needed when evaluating masticatory function.

The effects of continuous oromotor activity on speech motor learning: speech biomechanics and neurophysiologic correlates

Sustained limb motor activity has been used as a therapeutic tool for improving rehabilitation outcomes and is thought to be mediated by neuroplastic changes associated with activity-induced cortical excitability. Although prior research has reported enhancing effects of continuous chewing and swallowing activity on learning, the potential beneficial effects of sustained oromotor activity on speech improvements is not well-documented. This exploratory study was designed to examine the effects of continuous oromotor activity on subsequent speech learning. Twenty neurologically healthy young adults engaged in periods of continuous chewing and speech after which they completed a novel speech motor learning task. The motor learning task was designed to elicit improvements in accuracy and efficiency of speech performance across repetitions of eight-syllable nonwords. In addition, transcranial magnetic stimulation was used to measure the cortical silent period (cSP) of the lip motor cortex before and after the periods of continuous oromotor behaviors. All repetitions of the nonword task were recorded acoustically and kinematically using a three-dimensional motion capture system. Productions were analyzed for accuracy and duration, as well as lip movement distance and speed. A control condition estimated baseline improvement rates in speech performance. Results revealed improved speech performance following 10 min of chewing. In contrast, speech performance following 10 min of continuous speech was degraded. There was no change in the cSP as a result of either oromotor activity. The clinical implications of these findings are discussed in the context of speech rehabilitation and neuromodulation.

Determination of Chewing Count from Video Recordings Using Discrete Wavelet Decomposition and Low Pass Filtration

Several studies have shown the importance of proper chewing and the effect of chewing speed on the human health in terms of caloric intake and even cognitive functions. This study aims at designing algorithms for determining the chew count from video recordings of subjects consuming food items. A novel algorithm based on image and signal processing techniques has been developed to continuously capture the area of interest from the video clips, determine facial landmarks, generate the chewing signal, and process the signal with two methods: low pass filter, and discrete wavelet decomposition. Peak detection was used to determine the chew count from the output of the processed chewing signal. The system was tested using recordings from 100 subjects at three different chewing speeds (i.e., slow, normal, and fast) without any constraints on gender, skin color, facial hair, or ambience. The low pass filter algorithm achieved the best mean absolute percentage error of 6.48%, 7.76%, and 8.38% for the slow, normal, and fast chewing speeds, respectively. The performance was also evaluated using the Bland-Altman plot, which showed that most of the points lie within the lines of agreement. However, the algorithm needs improvement for faster chewing, but it surpasses the performance of the relevant literature. This research provides a reliable and accurate method for determining the chew count. The proposed methods facilitate the study of the chewing behavior in natural settings without any cumbersome hardware that may affect the results. This work can facilitate research into chewing behavior while using smart devices.

Tooth loss, dental prostheses use and cognitive performance in older Brazilian adults: The SABE cohort study

AIM

To investigate the within- and between-person longitudinal effects of tooth loss and the use of dentures, clinically assessed by dentists, on cognitive decline in a representative sample of community-dwelling older Brazilian adults.

METHODS

Data came from 1265, 1112 and 1021 individuals aged ≥60 years who participated in the second (2006), third (2010) and fourth (2015) waves, respectively, of the Health, Well-being and Aging study (SABE). Cognitive performance was evaluated with the abbreviated version of the Mini-Mental State Examination (MMSE). The number of natural teeth was classified according to three categories: none, 1-19 and ≥20 teeth. The presence of removable full or partial dentures in each dental arch (yes/no) was recorded. Hybrid regression models, adjusted for sociodemographic, behavior and health-related covariates, were used to estimate the between- and within-person effects of the longitudinal association between cognitive performance and oral health.

RESULTS

Participants with 1-19 and no teeth had, respectively, 1.15 (95% CI 0.65-1.66) and 1.54 (95% CI 0.99-2.09) units lower MMSE score than those with ≥20 teeth. Denture wearers had 1.54 (95% CI 1.13-1.95) units greater MMSE score than non-denture wearers, and those who started wearing dentures during the follow up had 0.83 (95% CI 0.21-1.45) units greater MMSE score after the transition.

CONCLUSION

Our main findings showed that the use of dental prostheses might be a protective factor for cognitive decline. Geriatr Gerontol Int 2021; 21: 1093-1098.

Chewing function and related parameters as a function of the degree of dementia: Is there a link between the brain and the mouth?

Background

To date, no study has investigated the association between chewing function and related parameters as a function of the degree of dementia using a finer subdivision of the values of the Mini‐Mental State Examination (MMSE).

Objective

This study aimed to investigate the differences in chewing function and related parameters as a function of the degree of dementia.

Methods

An analysis of cross‐sectional data obtained from the OrBiD (Oral Health, Bite Force, and Dementia) pilot study was performed. The participants were stratified into five groups based on the outcomes of the MMSE (no dementia, MMSE 28–30; mild cognitive impairment, MMSE 25–27; mild dementia, MMSE 18–24; moderate dementia, MMSE 10–17; severe dementia, MMSE <10). The chewing efficiency, maximum occlusal force and related parameters (number of supporting zones, number of teeth, Eichner index, tooth/denture status, denture quality, and dental treatment needs) were recorded.

Results

The MMSE groups showed significantly different chewing efficiencies (p = .003, Jonckheere‐Terpstra test) and maximum occlusal forces (p = .003, Jonckheere‐Terpstra test), but the number of supporting zones (p = .055, chi‐square test) and the number of natural teeth (p = .126, chi‐square test) were not different. The Eichner index, tooth/denture status, denture quality and dental treatment need showed no significant associations with the degree of dementia.

Conclusion

An improvement in the usability of the measurement methods for assessing chewing function in people with dementia is needed. Research involving people with dementia is necessary because the nutritional situation often deteriorates rapidly within a multifactorial system, which includes chewing ability and oral health.

Comparative Evaluation of Occlusion before and after Soft Tissue Mobilization in Patients with Temporomandibular Disorder-Myofascial Pain with Referral

The aim of the study was to evaluate occlusal parameters in patients with myofascial pain with referral before and after soft tissue mobilization. The study group consisted of 50 people (37 females and 13 males, average age 23.36 ± 2.14 years) diagnosed with myofascial pain with referral. All patients underwent triplicate soft tissue mobilization. Occlusal parameters were evaluated six times, before and after each treatment, using T-scan III. A decreasing tendency of the occlusion time was observed after the first, second, and third therapy. After the third treatment, the mean occlusion time in the entire study group was 0.119 s. The 1st soft tissue mobilization shortened both right and left disclusion times to 0.181 s and 0.185 s, respectively. After the third treatment, these parameters amounted to 0.159 s and 0.165 s, respectively. The Friedman test for the entire study group indicated that soft tissue mobilization altered the occlusion time and both disclusion times (p < 0.05). In conclusion, soft tissue mobilization affects biotensegrity of the masticatory system, thus modifying occlusal parameters. The occlusion time and both disclusion times cannot be considered as cofactors of the existing temporomandibular disorders-myofascial pain with referral.

Cognitive changes and neural correlates after oral rehabilitation procedures in older adults: a protocol for an interventional study

BACKGROUND

Epidemiological studies show an association between masticatory function and cognitive impairment. This has further strengthened the notion that tooth loss and impaired masticatory function may be risk factors for dementia and cognitive decline. Animal experiments have indicated a causal relationship and several possible mechanisms have been discussed. This evidence is, however, lacking in humans. Therefore, in the current interventional study, we aim to investigate the effect of rehabilitation of masticatory function on cognition in older adults.

METHODS

Eighty patients indicated for prosthodontic rehabilitation will be randomly assigned to an experimental or a control group. Participants will conduct neuropsychological assessments, masticatory performance tests, saliva tests, optional magnetic resonance imaging, and answer questionnaires on oral health impact profiles and hospital anxiety and depression scale before, 3 months, and 1 year after oral rehabilitation. The difference between the two groups is that the control group will be tested an additional time, (at an interval of about 3 months) before the onset of the oral rehabilitation procedure. The primary outcome is a change in measures of episodic memory performance.

DISCUSSION

Although tooth loss and masticatory function are widespread in older people, it is still an underexplored modifiable risk factor potentially contributing to the development of cognitive impairment. If rehabilitation of masticatory function shows positive effects on the neurocognitive function, this will have great implications on future health care for patients with impaired masticatory status. The present project may provide a new avenue for the prevention of cognitive decline in older individuals.

TRIAL REGISTRATION

The protocol for the study was retrospectively registered in ClinicalTrials.gov Identifier: NCT04458207, dated 02-07-2020.

Risk Factors of Composite Attachment Loss in Orthodontic Patients during Orthodontic Clear Aligner Therapy: A Prospective Study

BACKGROUND

The composite attachment loss during orthodontic clear aligner therapy is an adverse event that commonly happens in our daily practice. However, there is a lack of related statistical analysis and studies analyzing the related risk factors. Therefore, the aim of this study is to assess the incidence of attachment loss during orthodontic clear aligner therapy and to identify rick factors that may predict such event.

MATERIALS AND METHODS

The demographics and clinical variables of 94 patients undergoing clear aligner therapy (27 males and 67 females; average age: 27.60 ± 0.86 years) were recorded. Both patient-related and tooth-related attachment loss was recorded. The chi-squared test and logistic regressive analysis were applied to identify the potential risk factors. SPSS for Mac (version 23.0, IBM, USA) was used for statistical analyses. P < 0.05 was considered statistically significant.

RESULTS

Our study suggested that the risk factors for attachment loss include frequent aligner removal (≥ 5 times a day) (losing rate = 60.0%, P = 0.005), aligner wear time less than 18 hours a day (losing rate = 50.8%, P = 0.014), eating without aligners inserted (losing rate = 47.9%, P = 0.034), utilizing aligner tray seaters (losing rate = 48.2%, P = 0.006), and unilateral mastication (losing rate = 52.1%, P = 0.002). The multivariable logistic regression analysis indicates that aligner wear time less than 18 hours a day (P = 0.020, B = 0.925), using aligner tray seaters (P = 0.007, B = 1.168), and unilateral mastication (P = 0.034, B = -0.458) were considered independent factors that can predict the composite attachment loss in orthodontic clear aligner therapy.

CONCLUSION

Wearing aligner less than 18 hours a day, using aligner tray seaters, and unilateral mastication may contribute to increased incidence of composite attachment loss during orthodontic clear aligner therapy.

Association between tooth loss and gray matter volume in cognitive impairment

Previous studies have reported an association between tooth loss and gray matter volume (GMV) in healthy adults. The study aims to elucidate the link between tooth loss, brain volume differences, and cognitive impairment by investigating the total and regional differences in GMV associated with tooth loss in older people with and without cognitive impairment. Forty older participants with mild cognitive impairment or Alzheimer's disease [the cognitive impairment (CI) group] and 30 age- and sex-matched healthy participants [the control (CON) group] received T1-weighted magnetic resonance imaging scans and assessments of oral functions, including masticatory performance (MP) and the number of missing teeth (NMT). Voxel-based morphometry was used to assess the total and regional GMV, including that of the medial temporal lobe and motor-related areas. (A) When the total intracranial volume and age were controlled for, an increased MP was associated with a larger GMV in the premotor cortex in the CON group. (B) In the CI group, an increased NMT was significantly correlated with smaller regional GMV of the bilateral primary motor cortex and the premotor cortex. (C) In the CI group, but not the CON group, an increased NMT was associated with both smaller total GMV and regional GMV of the left medial temporal lobe, including the left hippocampus and parahippocampus. Tooth loss may be preferentially related to the structural differences in the medial temporal lobe in cognitively impaired older people. Further research is required to understand the mechanisms of the relationships.

Associations between Chewing Difficulty, Subjective Cognitive Decline, and Related Functional Difficulties among Older People without Dementia: Focus on Body Mass Index

OBJECTIVE

This study aimed to determine whether chewing difficulty is associated with subjective cognitive decline (SCD) and related functional difficulties by body mass index.

DESIGN

A population-based cross-sectional study.

SETTING AND PARTICIPANTS

A nationwide sample of 54,004 individuals aged ≥65 years from the 2018 Korea Community Health Survey.

MEASUREMENTS

SCD and SCD-related functional difficulties were measured using the cognitive decline module of the Behavioral Risk Factor Surveillance System. Chewing difficulty was assessed based on a self-report questionnaire from an oral health-related behaviors interview survey. BMI was calculated from objective values by measuring height and weight through a physical meter.

RESULTS

Among the 54,004 individuals, the prevalence of SCD in underweight, overweight, and obesity group was 33.6% (n = 806), 30.3% (n = 9,691), and 28.7% (n=5,632) respectively. Chewing difficulty was associated with SCD and SCD-related functional difficulties. This association was more pronounced in underweight (BMI: <18.5 kg/m2) people [underweight: (odds ratio [OR] = 1.68, 95% confidence interval [CI] 1.48-1.92); normal weight: OR = 1.13, 95% CI 1.04-1.22; obese: OR = 1.15, 95% CI 1.05-1.27]. Similar trends were demonstrated for SCD-related functional difficulties (underweight: OR = 1.53, 95% CI 1.17-2.01; normal weight: OR = 1.36, 95% CI 1.15-1.63; obese: OR = 1.50, 95% CI 1.22-1.86).

CONCLUSIONS

Chewing difficulty was associated with SCD and SCD-related functional difficulties in older people. Our results suggest that underweight status may play roles in the associations between chewing difficulty and SCD and SCD-related functional difficulties.

Involvement of the basal nucleus of Meynert on regional cerebral cortical vasodilation associated with masticatory muscle activity in rats

We examined the neural mechanisms for increases in regional cerebral blood flow (rCBF) in the neocortex associated with mastication, focusing on the cortical vasodilative system derived from the nucleus basalis of Meynert (NBM). In pentobarbital-anesthetized rats, parietal cortical rCBF was recorded simultaneously with electromyogram (EMG) of jaw muscles, local field potentials of frontal cortex, multi-unit activity of NBM neurons, and systemic mean arterial pressure (MAP). When spontaneous rhythmic EMG activity was observed with cortical desynchronization, an increase in NBM activity and a marked rCBF increase independent of MAP changes were observed. A similar rCBF increase was elicited by repetitive electrical stimulation of unilateral cortical masticatory areas. The magnitude of rCBF increase was partially attenuated by administration of the GABAergic agonist muscimol into the NBM. The rCBF increase persisted after immobilization with systemic muscle relaxant (vecuronium). rCBF did not change when jaw muscle activity was induced by electrical stimulation of the pyramidal tract. The results suggest that activation of NBM vasodilator neurons contributes at least in part to the rCBF increase associated with masticatory muscle activity, and that the NBM activation is induced by central commands from the motor cortex, independently of feedback from brainstem central pattern generator or contracting muscles.

Masticatory ability in older individuals: A qualitative interview study

Aim

To explore older individuals’ experienced masticatory ability and the impact of masticatory ability in daily life.

Material and methods

This study applied an open‐ended exploratory approach using inductive reasoning. The design was inspired by the qualitative method grounded theory. The final sample consisted of twelve older participants. Seven were men, and five were women. The interviews were audio‐recorded and transcribed verbatim. The interviewer successively read the transcribed data and analysed the material in cooperation with the authors.

Results

Three categories developed from the data; Deteriorating oral health and functional loss, Eating habits, Prosthetic rehabilitation and function. A core category named Adaptation emerged. Adaptation describes how individuals successfully could adapt to a decreased function and in spite of this develop a positive view of their masticatory ability.

Discussion

The participants described an experience of gradually deteriorating oral function that had affected their masticatory ability. By adapting to this functional degradation, some of the participants overcame the functional deficiencies. Most participants perceived their masticatory ability to be good, even though their ability to process some food types was described as inadequate.

Conclusion

The participants had experienced deteriorating oral health and function throughout life, and they overcame this through adaptation by adjusting their eating habits. Even though prosthetic treatment might be considered successful by the participant, this does not necessarily improve dietary habits. Future research should therefore focus on how dental treatment can be combined with other interventions, such as dietary counselling and physiotherapy to recover physiological function.

The relationship between DMFT index and cognitive impairment: A descriptive cross-sectional study

Background and Aims

Cognitive disorders are characterized by major impairments in functions such as memory, judgment, language and attention. One of the tests used to assess these disorders is called the Montreal Cognitive Assessment Test, which is one of the most recent tests known in this field. DMFT index is the most important dental index for evaluation of decayed, missing and filled teeth. Since alteration or damage to the sensory function of teeth can cause changes in chewing function and different levels of cognitive disorders. The objective of this study was to determine the relationship of DMFT index with cognitive disorders in people aged 25-55 in Rafsanjan in 2019.

Materials and Methods

This cross-sectional study was performed on 350 patients chosen by simple random sampling within age range of 25-55 years, referred to Rafsanjan Dental School in 2019. Patients' demographic information was recorded and each was given a consent form and also Montreal Cognitive Assessment Test. Dental examination regarding decayed, missing and filled teeth was then carried out by a dentist and The DMFT index was recorded. Data were then analyzed by SPSS version 21; P value less than 0.05 was considered as significant level.

Results

Data showed that the MOCA index had a negative significant relationship with DMFT (P = 0.001) and age (P = 0.001) and had a significant positive relationship with education (P = 0.001), but it had no significant relationship with gender (P = 0.853), time of last dental appointment (P = 0.231) and place of residence (P = 0.428). The effect of age (P = 0.67) and gender (P = 0.525) on the relationship of DMFT and MOCA was not significant. But the effect of education (P = 0.001), place of residence (P = 0.0003) and time of last dental appointment (P = 0.002) on it was significant.

Conclusion

The results of this study showed that the relationship between DMFT index and cognitive disorders was significant and the higher the score of this index, the more severe cognitive disorders.

Update and review of the gerodontology prospective for 2020's: Linking the interactions of oral (hypo)-functions to health vs. systemic diseases

New lines of evidence suggest that the oral-systemic medical links and oral hypo-function are progressively transcending beyond the traditional clinical signs and symptoms of oral diseases. Research into the dysbiotic microbiome, host immune/inflammatory regulations and patho-physiologic changes and subsequent adaptations through the oral-systemic measures under ageism points to pathways leading to mastication deficiency, dysphagia, signature brain activities for (neuro)-cognition circuitries, dementia and certain cancers of the digestive system as well. Therefore, the coming era of oral health-linked systemic disorders will likely reshape the future of diagnostics in oral geriatrics, treatment modalities and professional therapies in clinical disciplines. In parallel to these highlights, a recent international symposium was jointly held by the International Association of Gerontology and Geriatrics (IAGG), Japanese Society of Gerodontology (JSG), the representative of USA and Taiwan Academy of Geriatric Dentistry (TAGD) on Oct 25th, 2019. Herein, specific notes are briefly addressed and updated for a summative prospective from this symposium and the recent literature.

Tooth Loss and Dementia: A Critical Examination

Dementia is a major contributor to dependence and disability in older people, with aging societies characterized by growing numbers of people living with the condition. Dementia rates are highest in those with low education early in life, midlife hypertension, midlife hearing loss, depression, obesity, loneliness, a sedentary lifestyle, or sustained exposure to smoking or diabetes. Tooth loss is a putative risk factor for dementia which has received increasing research attention, but systematic review findings are mixed. Three main mechanisms have been proposed, involving 1) tooth loss leading to compromised nutrition and then leading to poorer central nervous system (CNS) function; 2) tooth loss resulting in fewer interocclusal contacts and so less somatosensory feedback to the CNS, leading to impaired cognition; and (3) chronic periodontitis resulting in tooth loss, but not before the inflammation has affected the CNS, impairing cognition. None of these is supported by compelling empirical evidence. Here, we use the life course approach to propose a plausible, empirically supported explanation for the associations between missing teeth and poorer cognitive function in older people. Evidence from longstanding cohort studies demonstrates that the putative association arises from cognitive function much earlier in life, in childhood. People with better childhood cognitive function have better oral health and access to routine dental care as they go through life, losing fewer teeth along the life course. They are also much more likely to have better cognitive function in old age. Their less cognitively able childhood counterparts will experience higher disease rates and poorer access to care, resulting in greater incremental tooth loss. Comparison of the 2 groups at any age from the mid-20s on will show greater numbers of missing teeth in the group who were less cognitively able in childhood. Those differences will be most pronounced in old age.

Altered mastication adversely impacts morpho-functional features of the hippocampus: A systematic review on animal studies in three different experimental conditions involving the masticatory function

Recent results have established that masticatory function plays a role not only in the balance of the stomatognathic system and in the central motor control, but also in the trophism of the hippocampus and in the cognitive activity. These implications have been shown in clinical studies and in animal researches as well, by means of histological, biochemical and behavioural techniques. This systematic review describes the effects of three forms of experimentally altered mastication, namely soft-diet feeding, molar extraction and bite-raising, on the trophism and function of the hippocampus in animal models. Through a systematic search of PubMed, Embase, Web of Science, Scopus, OpenGray and GrayMatters, 645 articles were identified, 33 full text articles were assessed for eligibility and 28 articles were included in the review process. The comprehensiveness of reporting was evaluated with the ARRIVE guidelines and the risk of bias with the SYRCLE RoB tool. The literature reviewed agrees that a disturbed mastication is significantly associated with a reduced number of hippocampal pyramidal neurons in Cornu Ammonis (CA)1 and CA3, downregulation of Brain Derived Neurotrophic Factor (BDNF), reduced synaptic activity, reduced neurogenesis in the Dentate Gyrus (DG), glial proliferation, and reduced performances in behavioural tests, indicating memory impairment and reduced spatial orientation. Moreover, while the bite-raised condition, characterized by occlusal instability, is known to be a source of stress, soft-diet feeding and molar extractions were not consistently associated with a stress response. More research is needed to clarify this topic. The emerging role of chewing in the preservation of hippocampal trophism, neurogenesis and synaptic activity is worthy of interest and may contribute to the study of neurodegenerative diseases in new and potentially relevant ways.

Functional Connectivity Between the Trigeminal Main Sensory Nucleus and the Trigeminal Motor Nucleus

The present study shows new evidence of functional connectivity between the trigeminal main sensory (NVsnpr) and motor (NVmt) nuclei in rats and mice. NVsnpr neurons projecting to NVmt are most highly concentrated in its dorsal half. Their electrical stimulation induced multiphasic excitatory synaptic responses in trigeminal MNs and evoked calcium responses mainly in the jaw-closing region of NVmt. Induction of rhythmic bursting in NVsnpr neurons by local applications of BAPTA also elicited rhythmic firing or clustering of postsynaptic potentials in trigeminal motoneurons, further emphasizing the functional relationship between these two nuclei in terms of rhythm transmission. Biocytin injections in both nuclei and calcium-imaging in one of the two nuclei during electrical stimulation of the other revealed a specific pattern of connectivity between the two nuclei, which organization seemed to critically depend on the dorsoventral location of the stimulation site within NVsnpr with the most dorsal areas of NVsnpr projecting to the dorsolateral region of NVmt and intermediate areas projecting to ventromedial NVmt. This study confirms and develops earlier experiments by exploring the physiological nature and functional topography of the connectivity between NVsnpr and NVmt that was demonstrated in the past with neuroanatomical techniques.

The effect of masticatory behaviour on generalized attention in heathy volunteers

AIM

As our society ages, the number of people living with dementia also steadily increases. Some work has focused on masticatory behaviour as a form of daily health care that could help prevent cognitive impairment and dementia. However, it is not yet clear how masticatory behaviour influences various cognitive functions. Therefore, the purpose of this study was to examine the effect of masticatory behaviour on the decline of generalized attention, an important cognitive function.

METHODS

Participants were 35 healthy, dentulous individuals without stomatognathic abnormalities (24 men, 11 women; mean age: 56.8 ± 4.8 years). All participants completed three interventions: mastication, foot-stepping, and none (control). Pre- and post-intervention measures of generalized attention were measured by using neuropsychological tests to examine general attention; the results were then compared. Simultaneously, during the generalized attention task, the functional activity of the prefrontal cortex was observed on functional near-infrared spectroscopy.

RESULTS

Response time of generalized attention improved in both the masticatory and foot-stepping interventions. There was a transient increase in oxyhaemoglobin activity in the right and left prefrontal cortices in the masticatory intervention.

CONCLUSIONS

Masticatory behaviour may be involved in a partial improvement of generalized attention and may induce prefrontal cortex activity in middle-aged and older adults.

Prediction of Frailty and Dementia Using Oral Health Impact Profile from a Population-Based Survey

Oral health and dentition have been associated with cognitive ability and frailty, but an applicable screening tool has not yet been developed. This study aimed to establish risk prediction models for dementia and frailty. A sample of 2905 community-dwelling older adults aged ≥58 years using the Taiwan Longitudinal Study on Aging (TLSA) survey was adapted and analyzed for this study. Risk scores were estimated by stepwise logistic regression. In models adjusted for covariates, increased age, female sex, no dental prosthesis (adjusted Odds ratio [adjOR], 1.61; 95% confidence interval [CI], 1.11–2.35), diabetes mellitus, chronic kidney disease, and an increased Oral Health Impact Profile (OHIP)-7T Q3 score (adjOR, 1.33; 95% CI, 1.19–1.49) were all significantly associated with frailty. In addition to these factors, an inability to self-report height or weight (adjOR, 4.52; 95% CI, 3.52–5.81) and an increased OHIP-7T Q7 score (adjOR, 1.21; 95% CI, 1.06–1.37) were significantly associated with dementia. The cut-off points of the risk scores for frailty and dementia were 80 (sensitivity, 80.0%; specificity, 81.2%) and 77 (sensitivity, 83.4%; specificity, 71.5%), respectively. The findings highlighted a number of composite risk factors of frailty and dementia. Importantly, the developed prediction models were easily applicable to screen for frailty and dementia in communities or dental clinics.

Jidong cognitive impairment cohort study: objectives, design, and baseline screening

The risk of dementia increases in patients with cognitive impairment. However, it is not clear what factors contribute to the onset of dementia in those with cognitive impairment. In this prospective cohort study, we will investigate the every-five-year incidence of cognitive impairment and prognostic factors for cognitive impairment. The Jidong cognitive impairment cohort was established from April 2012 to August 2015, during which we recruited 5854 healthy participants (55.1% male) older than 45 years (mean, 57 years). Participants received a health examination in the Staff Hospital, Jidong Oilfield Branch, China National Petroleum Corporation. Baseline data and blood samples were collected. Cognitive impairment was evaluated using the Mini-Mental State Examination, and was defined as a Mini-Mental State Examination score of less than 24. Dementia was assessed using the criteria of Diagnostic and Statistical Manual of Mental Disorders (Fourth edition), the International Working Group criteria, and the Mini-Mental State Examination score. The follow-up will continue until December 2024, during which a prognostic model will be constructed. The primary outcome is the presence/absence of dementia and the secondary outcome is quality of life. Baseline screening results showed the following: (1) Cognitive impairment was apparent in 320 participants (5.5%). These participants will be excluded from the Jidong cohort study, and the remaining participants will be followed up. (2) Of the 320 participants with cognitive impairment, there was a significantly higher prevalence of illiteracy than other education levels (35.9%, P < 0.05). Age, arterial hypertension, alcohol consumption, and passive smoking differed significantly between the cognitive impairment and healthy groups (P < 0.05). Multivariate logistic regression models showed that age (odds ratio [OR] = 1.059, 95% confidence interval [CI]: 1.044–1.074) and arterial hypertension (OR = 1.665, 95% CI: 1.143–2.427) were risk factors for mild cognitive impairment. With the increase of educational level (illiteracy, primary school, junior high school, high school, university, and above), cognitive impairment gradually decreased (OR < 1, P < 0.05). (3) This cohort study has initially screened for several risk factors for cognitive impairment at baseline, and subsequent prospective data will further describe, validate, and evaluate the effects of these risk factors on cognitive impairment and dementia. These results can provide clinical evidence for the early prevention of cognitive impairment and dementia. The study was approved by the Ethics Committee of Kailuan General Hospital of Tangshan City and the Medical Ethics Committee, Staff Hospital, Jidong Oilfield Branch, China National Petroleum Corporation on July 12, 2013 (approval No. 2013 YILUNZI 1).

Masticatory Dysfunction by Extensive Tooth Loss as a Risk Factor for Cognitive Deficit: A Systematic Review and Meta-Analysis

Background: An amount of cognition decline is normal with aging; however, intrinsic and extrinsic risk factors may exacerbate it, affecting social and occupational tasks. Masticatory dysfunction (MD), as a general term, refers to an impairment in the masticatory function triggered by a structural factor, such as tooth loss; functional factors, such as weaker bite force or a poorer masticatory performance; or both factors. MD acting as a source of chronic stress, promotes functional and morphological changes on the hippocampus, a brain area crucial for learning and memory abilities. This study aimed to synthesize evidence on the association between MD and cognitive deficit (CD), and demonstrate whether might be adequately considered as a risk factor.

Methods: Observational studies were screened in seven online databases; the search strategy (PECO) was focused in observational studies with humans as a population (P), presenting groups exposed (E), and non-exposed (C) to tooth loss, in which cognition parameters were measured and compared between groups (O). The final selection included only those studies comparing the effect in cognition between subjects having ≥20 remaining teeth and <20 remaining teeth, considering the latter as a structural factor triggering MD by the literature. Searching and data extraction were conducted following PRISMA guidelines. Qualitative and risk of bias evaluations were performed. The meta-analysis (MA) was constructed including the odds ratio (OR) and its 95% confidence interval (CI) comparing two groups—with/without MD. The level of evidence was rated by Grading Recommendations Assessment, Development and Evaluation (GRADE) approach.

Results: In total, 5,666 citations were identified, 14 accomplished our eligibility criteria, and nine were include in the MA. The MA demonstrates that individuals with MD had 46% higher chance to presented CD (OR 2.24 [1.73, 2.90], p < 0.00001, I² = 46%). The level of evidence was rated as low by GRADE.

Conclusion: Despite the low certainty in evidence, according to our MA, MD is positively associated with increased risk of CD. However, more studies including other factors underlying MD and similar measurements should be conducted to obtain a strong estimate of the risk.

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.