Relationship between chewing ability and high-level functional capacity in an 80-year-old population in Japan

The Single Midline Implant in the Edentulous Mandible-Current Status of Clinical Trials

The single midline implant in the edentulous mandible is a treatment concept that has often been controversially discussed. Nearly 30 years ago, the first available clinical results revealed high implant survival rates and remarkable improvements in oral comfort, function, patient satisfaction and oral health-related quality of life for edentulous patients compared to the situation with no implant. However, the clinical trials were predominantly conducted with a small number of patients over a short to medium follow-up period. Today, numerous clinical investigations on the single midline implant in the edentulous mandible, which increasingly include longer-term observation periods, are available. It is the aim of this overview to present the current literature and to highlight the clinical problems. This article is a 2023 update of a review published by the authors in the German language in 2021 in the German journal Implantologie. In total, 19 prospective clinical trials with a follow-up period of 0.5-10 years were analyzed. Over this observation period, single implants with modern rough implant surfaces in the edentulous mandible reveal high implant survival rates of between 90.9 and 100% when a conventional delayed loading protocol was applied.

Does the Loss of Teeth Have an Impact on Geriatric Patients’ Cognitive Status?

Significant changes in the microstructure of the brain cause dementia and other mental declines associated with aging and disease. Although research has established a connection between oral health and dementia, the underlying pathologic mechanisms are still unknown. Aim: Our aim was to evaluate dentures’ impact on the cognitive state of geriatric patients. Material and methods: A total of 108 individuals seeking treatment at the Faculty of Dental Medicine in Iasi, Romania, participated in the study, which ran from May 2022 to October 2022. Cognitive dysfunction was assessed using the Mini-Mental State Examination. The acquired data were analyzed with IBM SPSS 26.0, and the p-value was set at 0.05. Results: The average value of the MMSE score was 21.81 ± 3.872. Differences between groups of wearer/non-wearer subjects were statistically significant for most of the questions in the questionnaire. Linear regression analysis showed that individuals with a high MMSE score have prosthodontic treatment. A decrease in the MMSE score is associated with a decrease in masticatory efficiency (B = 1.513, p = 0.268). Conclusions: This study provides further evidence that tooth loss is associated with worse cognitive performance. It is thus conceivable that the necessary effects can be achieved by increasing the efforts dedicated to preventing tooth loss in the adult population.

Food Hardness Modulates Behavior, Cognition, and Brain Activation: A Systematic Review of Animal and Human Studies

Food hardness is one of the dietary features that may impact brain functions. We performed a systematic review to evaluate the effect of food hardness (hard food versus soft food diet) on behavior, cognition, and brain activation in animals and humans (PROSPERO ID: CRD42021254204). The search was conducted on 29 June 2022 using Medline (Ovid), Embase, and Web of Science databases. Data were extracted, tabulated by food hardness as an intervention, and summarized by qualitative synthesis. The SYRCLE and JBI tools were used to assess the risk of bias (RoB) of individual studies. Of the 5427 studies identified, 18 animal studies and 6 human studies met the inclusion criteria and were included. The RoB assessment indicated that 61% of animal studies had unclear risks, 11% had moderate risks, and 28% had low risks. All human studies were deemed to have a low risk of bias. The majority (48%) of the animal studies showed that a hard food diet improved behavioral task performance compared to soft food diets (8%). However, 44% of studies also showed no differential effects of food hardness on behavioral tests. It was also evident that certain regions of the brain were activated in response to changes in food hardness in humans, with a positive association between chewing hard food, cognition performance, and brain function. However, variations in the methodologies of the included studies hindered the meta-analysis execution. In conclusion, our findings highlight the beneficial effects of dietary food hardness on behavior, cognition, and brain function in both animals and humans, however, this effect may depend on several factors that require further understanding of the causality.

Dental Care for Older Adults

There is a global increase in the older population. Unfortunately, dental conditions in the older population can sometimes be poor as a result of worsened physical conditions and the cumulative damage caused by dental diseases in the past. Many suffer from oral diseases such as dental caries and periodontal disease but receive no regular dental care. Oral conditions and systemic problems are interrelated. Chronic medical problems and polypharmacy are common among them. These conditions may lead to xerostomia with or without a decrease in saliva output. Additionally, many older adults have deteriorated masticatory function associated with physical health issues such as frailty. Preventive measures are crucial to stop oral diseases from progressing and the replacement of missing teeth is needed when masticatory function is impaired. Older adults also suffer a higher risk of oral cancer because of their less resilient but more permeable oral mucosa. With the increasing need for elderly dental care, dentists should equip themselves with knowledge and skills in geriatric dentistry. They should help older adults to develop and maintain the functional ability that enables well-being in older age. This communication article aims to discuss the relevant medical conditions, common dental diseases, and dental care for older adults.

Relationship between chewing ability and malnutrition, sarcopenia, and frailty in older adults

BACKGROUND

Several studies reported that impaired nutrition is associated with reduced muscle mass, muscle strength, and physical performance. Chewing ability is essential to maintain balanced oral nutrient intake. The study was designed to define the possible relationship between chewing ability and nutrition-related problems (malnutrition, sarcopenia, and frailty) in a holistic perspective.

METHODS

This cross-sectional study recruited adults aged ≥65 years. All patients were evaluated with comprehensive geriatric assessment. Sarcopenia was diagnosed according to European Working Group on Sarcopenia in Older People criterion. Malnutrition was determined according to body mass index, calf circumference, and Mini Nutritional Assessment short form (MNA-SF). Frailty status was diagnosed with the Clinical Frailty Scale. Masseter and gastrocnemius muscle thicknesses (MTs) were measured via ultrasonography imaging. Oral examinations were carried out by a dentist, and chewing performance was examined with a color-changeable chewing gum.

RESULTS

Overall, 135 older adults (76 females) were analyzed. Mean ± SD age was 75.7 ± 7.2 years; 37.0% of the patients were frail, 3.7% were malnourished, 12.6% were sarcopenic, and 20.0% had poor chewing function. In the poor chewing function group, age and frailty scores were increased and the MNA-SF scores, handgrip strength, skeletal muscle index, and masseter MT were reduced (all P < 0.05). After adjusting for confounders, regression analysis showed that low grip strength and low gastrocnemius MT were independently associated with poor chewing ability.

CONCLUSIONS

Chewing ability was related to sarcopenia. Age and low grip strength in females and low cognitive scores and having low gastrocnemius MT in males were independent variables affecting chewing ability.

Single mandibular implant study - chewing efficiency - 5-year results from a randomized clinical trial using two different implant loading protocols

PURPOSE

To investigate the chewing efficiency of edentulous patients wearing complete dentures, treated with a single implant in the mandible, placed underneath the existing mandibular dentures, using two different loading protocols (immediate loading or conventional loading), over an observation period of 5 years.

METHODS

One-hundred and fifty-eight (158) edentulous seniors aged 60-89 years received an implant in the midline of the lower jaw and were randomized either to the immediate loaded group A (n=81) or the conventional loaded group B (n=77). Chewing efficiency was obtained before treatment, one month after implant placement during the submerged healing phase (only group B) and 1, 4, 12, 24 and 60 months after implant loading.

RESULTS

After 5 years, chewing tests from 89 patients (45 in the immediate loading group and 44 in the conventional loading group) were available for every recall visit and thus statistically analyzed. The chewing efficiency increased over time in both groups. A significant increase was observed up to 4 months after loading (p≤0.05). Later, chewing efficiency further increased, but not significantly. Between the two loading protocols, chewing efficiency did not differ significantly (p>0.05) at any follow-up investigation.

CONCLUSION

A single mandibular implant placed underneath existing mandibular dentures improves chewing efficiency of edentulous patients significantly over an observation period of 5 years, irrespective of the loading protocol.

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.

Factors related to removable denture use in independent older people: A cross-sectional study

BACKGROUND

Denture use for recovery of major tooth loss can reduce the need for care, and thus, it is important for dentists to identify the types of patients who use removable dentures.

OBJECTIVE

To identify factors associated with removable denture use in independent older Japanese people.

METHODS

This cross-sectional study investigated the oral condition; demographics; lifestyle; dental visit behaviour; and higher-level functional capacity, as assessed using the Tokyo Metropolitan Institute of Gerontology index of competence (TMIG index), of independent older people aged 65-74 years. Participants were divided into four groups based on sex and condition of the posterior occluding pairs (POPs). Multivariate-adjusted logistic regression analyses were performed for each group, with denture use or non-use as the dependent variable and the other items as independent variables.

RESULTS

Denture use or non-use was significantly associated with only dental consultation behaviour (regular dental visits and time since the last dental visit) in all groups. Subsequent analyses excluding dental consultation behaviour demonstrated that denture use or non-use was significantly associated with educational background in female participants with decreased POPs, with the type of household in male participants with lost POPs and with the TMIG index (social role) in female participants with lost POPs.

CONCLUSIONS

Denture use was associated with dental consultation behaviour. We revealed factors related to denture use or non-use in females with decreased POPs and both males and females with lost POPs.

Cross-sectional association between medical expenses and intellectual activity in community-dwelling older adults

Background

Little is known concerning the lifestyle habits and health conditions in community-dwelling elderly who do not get medical care. We investigated the cross-sectional association between medical expenses (ME) and intellectual activity (IA) in community-dwelling older Japanese.

Methods

Self-administered questionnaires were mailed to all residents born between 1945 and 1949 and covered by A City’s medical insurance system (n = 19,354). Independent variables including health behaviors, oral health, social capital, neighborhood environment, and physical and mental functioning were included in the questionnaires. Medical fee receipts were used to evaluate ME for fiscal 2014, and respondents were classified into no, low, medium, and high ME groups. Higher-level functional capacity was evaluated using the Tokyo Metropolitan Institute of Gerontology Index of Competence, which is comprised of three subscales: instrumental activities of daily living, IA, and social role. Poisson regression models were used to examine the association of ME with IA, with the low ME group as reference.

Results

Questionnaires were returned by 12,747 individuals (response rate 65.9%). The no ME group had the lowest response rate, the worst lifestyle behaviors, and the lowest social capital, but no problems with neighborhood environment. Higher-level functional capacity, especially IA, was reduced in both the high ME and no ME groups. After adjustments for age, gender, health insurance, accessibility to public facilities in their residential area, family size, body mass index, and physical and mental functioning, the prevalence ratio (PR) for impaired IA lost its significance in the high ME group (PR 0.97, 95% confidence interval 0.90–1.05), but remained significant in the no ME group (1.19, 1.08–1.31). After additional adjustments for health behaviors (i.e., health checks, smoking, fitness, and dietary variety), the PR of the no ME group was attenuated towards the null (1.08, 0.98–1.20).

Conclusions

Community-dwelling elderly who did not seek medical treatment were indifferent to health surveys and health-promoting behaviors, and undesirable health behaviors were a possible determinant of their impaired IA. Further longitudinal research is needed to confirm the causal associations.

Electronic supplementary material

The online version of this article (10.1186/s12199-017-0672-1) contains supplementary material, which is available to authorized users.

Predictors of chewing ability among community-residing older adults in Korea

AIMS

Decreased chewing ability in older adults can lead to poor nutritional and physical conditions, and eventually death. The present study examined the relationships between chewing ability and related characteristics (e.g. health promotion habits, health status and functional status), and identified predictors of chewing ability in community-residing older adults.

METHODS

Among the total of 11 542 participants in the 2011 National Survey on Older Adults in Korea, data from 10 543 participants were used for analysis. Chewing ability was evaluated using a self-report of chewing ability. Exercise ability was assessed by objective exercise ability and perceived exercise ability in both the upper and lower extremities. Depression and cognitive functions were measured using the Geriatric Depression Scale-Short Form and the Mini-Mental State Examination, respectively.

RESULTS

A total of 56.9% of participants had poor chewing abilities. After adjusting for age and sex, logistic regression analysis showed that depression (OR 1.76, 95% CI 1.60-1.92), cognitive impairment (OR 1.28, 95% CI 1.17-1.40), objective exercise ability (OR 1.24, 95% CI 1.11-1.41), regular exercise habits (OR 1.23, 95% CI 1.13-1.34), medical check-up history (OR 1.17, 95% CI 1.05-1.32), number of chronic diseases (OR 1.12, 95% CI 1.09-1.15) and perceived exercise ability in the lower extremities (OR 1.08, 95% CI 1.05-1.10) were significant predictors of chewing ability.

CONCLUSION

Chewing ability in older adults should be improved in consideration of mental and general health condition. Geriatr Gerontol Int 2017; 17: 78-84.

How functional disability relates to dentition in community-dwelling older adults in Brazil

OBJECTIVE

To assess the association between dentition status and functional disabilities among community-dwelling older individuals.

SUBJECTS AND METHODS

A total of 5012 individuals aged 65-74 were interviewed in 2013 during a nationwide community-based survey. This cross-sectional study used a questionnaire including information on dentition, locomotion impairment, difficulties in basic and instrumental activities of daily life, socio-demographic characteristics, behaviour and general health status. Poisson regression models assessed prevalence ratios (PR) and 95% confidence intervals (95% CI).

RESULTS

About 31.3% of older people in Brazil reported having ≥21 preserved teeth, the condition for a functional dentition without prosthetic appliances. This proportion was significantly lower among individuals with locomotion impairment and difficulties in basic and instrumental activities of daily life. After adjusting for relevant covariates, functional dentition remained statistically associated with severe (PR = 0.69, 95% CI = 0.15-0.63) and total (PR = 0.69, 95% CI = 0.26-0.44) locomotion impairments, and difficulties in basic activities of daily life (PR = 0.70, 95% CI = 0.53-0.93).

CONCLUSION

Having a functional dentition was significantly less prevalent among those affected by functional disabilities, and this association is unlikely to be due to insufficient control for relevant covariates. The association between dentition and functional disability is bidirectional and involves a complex interplay of one upon the other, and of factors that influence both outcomes.

Association of Psychosocial Conditions, Oral Health, and Dietary Variety with Intellectual Activity in Older Community-Dwelling Japanese Adults

Background

This study examined the factors related to intellectual activity in community-dwelling elderly persons.

Methods

Self-administered questionnaires mailed to all people aged ≥65 years in a dormitory suburb in Japan (n = 15,210). The response rate was 72.2%. Analytical subjects (n = 8,910) were those who lived independently and completely answered questions about independent and dependent variables and covariates. Independent variables included psychosocial conditions (i.e., social activities, hobbies, and a sense that life is worth living (ikigai)), oral health (i.e., dental health behaviors and oral function evaluated by chewing difficulties, swallowing difficulties, and oral dryness), and dietary variety measured using the dietary variety score (DVS). A dependent variable was intellectual activity measured using the Tokyo Metropolitan Institute of Gerontology Index of Competence. Covariates included age, gender, family structure, pensions, body mass index, alcohol, smoking, medical history, self-rated health, medications, cognitive function, depression, and falling. Logistic regression was used to estimate the odds ratio (OR) for poor intellectual activity.

Results

Poor intellectual activity was reported by 28.9% of the study population. After adjustment for covariates and independent variables, poor intellectual activity was significantly associated with nonparticipation in social activities (OR = 1.90, 95%CI = 1.61–2.24), having neither hobbies nor ikigai (3.13, 2.55–3.84), having neither regular dental visits nor daily brushing (1.70, 1.35–2.14), the poorest oral function (1.61, 1.31–1.98), and the lowest DVS quartile (1.96, 1.70–2.26).

Conclusion

These results indicate that psychosocial conditions, oral health, and dietary variety are independently associated with intellectual activity in elderly persons. The factors identified in this study may be used in community health programs for maintaining the intellectual activity ability of the elderly.

Factors associated with self-rated oral health among community-dwelling older Japanese: A cross-sectional study

OBJECTIVES

A cross-sectional study was carried out to investigate the determinants of self-rated oral health among community-dwelling older people in Japan.

METHODS

The participants were 897 (357 men and 540 women) aged 65 years and over who participated in a comprehensive geriatric health examination, which included an oral examination, a face-to-face interview assessing cognitive function, questionnaires regarding depressive symptoms and functional capacity, and a medical examination. The oral examination measured indices of oral health status: number of present teeth, number of functional teeth, occlusal force and amount of resting saliva. Multiple logistic regression analyses were carried out to determine the factors associated with poor self-rated oral health.

RESULTS

The mean age of the participants was 73.5 ± 5.0 years. The prevalence of poor and rather poor self-rated oral health was 11.5% and 29.5%, respectively. Multiple logistic regression analyses showed that the number of present teeth (odds ratio [OR] 0.97, 95% confidence intervals [CI] 0.95-0.99), difficulty in mastication (OR 3.20, CI 2.18-4.70), presence of xerostomia (OR 1.43, CI 1.02-2.01), total score on the MoCA-J (OR 1.06, CI 1.01-1.11), and reduction in frequency of leaving the house (OR 1.64, CI 1.12-2.41) were significantly associated with poor self-rated oral health.

CONCLUSIONS

The present results suggested that self-rated oral health was a significant factor in oral health status as well as overall well-being among community-dwelling older Japanese people.

Masseter muscle tension, chewing ability, and selected parameters of physical fitness in elderly care home residents in Lodz, Poland

BACKGROUND

Maintaining good physical fitness and oral function in old age is an important element of good quality of life. Disability-related impairment of oral function contributes to a deterioration of the diet of older people and to the reduction of their social activity.

OBJECTIVES

Investigate the association between masseter muscle tension, dental status, and physical fitness parameters.

MATERIALS AND METHODS

Two hundred fifty-nine elderly care home residents (97 men, 162 women; mean age, 75.3±8.9 years) were involved in this cross-sectional study. Their chewing ability was evaluated by masseter muscle tension palpation, differences of masseter muscle thickness, self-reported chewing ability, number of present and functional teeth, and number of posterior tooth pairs. Masseter muscle thickness was measured by ultrasonography. To assess physical fitness, hand grip strength and the timed up-and-go test were performed. Nutritional status was assessed using body mass index and body cell mass index (BCMI), calculated on the basis of electrical bioimpedance measurements. Medical records were used to collect information on systemic diseases and the number of prescribed medications. Subjects were also evaluated for their ability to perform ten activities of daily living.

RESULTS

Ninety-seven percent of the subjects suffered from systemic diseases. The three most prevalent illnesses were cardiac/circulatory 64.5%, musculoskeletal 37.3%, and endocrine/metabolic/nutritional 29.3%. Of the participants, 1.5% were underweight and more than one third (34.4%) were overweight. Malnutrition (BCMI below normal) was found in almost half (45.2%) of the subjects. Only 5.8% had a sufficient number of functional natural teeth. Statistically significant correlations were found between palpation of masseter muscle tension and perceived chewing ability, number of present teeth, number of functional teeth, number of posterior tooth pairs, timed up-and-go, hand grip strength, body mass index, BCMI, and activities of daily living. In a multivariate model, after adjusting for age, sex, and education, subjects with higher BCMI, higher hand grip strength, and more present teeth had a significantly higher chance of strong masseter muscle tension.

CONCLUSION

There is a relationship between chewing ability and physical fitness in elderly people. Efficiency of masseter muscles is related to physical fitness in the elderly. Masseter muscle tension examined by palpation can be used in public dentistry as one of the indicators of quality of life.

Associations between higher-level competence and general intelligence in community-dwelling older adults

OBJECTIVES

Higher-level competence is crucial for healthy and socially independent living, and general intelligence may underlie heath status. The aim of this study was to elucidate associations between general intelligence and higher-level competence in elderly individuals without dementia.

METHODS

A total of 207 community-dwelling elderly persons, aged 70-74 years, were enrolled. A personal interview was performed to obtain data on socio-demographic and medical factors; higher-level competence was evaluated using the Tokyo Metropolitan Institute of Gerontology index of competence (TMIG index). Raven's Coloured Progressive Matrices (RCPM) test was used to assess general intelligence. Correlations between the TMIG index, its subscale scores and the RCPM score were evaluated by Spearman's rank correlation coefficients. Ordinal regression models were conducted with the TMIG index and its subscales as the dependent variables, RCPM as the principal independent variable, and age, sex, type of household, employment status, educational background, chronic medical conditions and number of natural teeth as the potential independent variables.

RESULTS

There were significant but weak positive correlations between total score on the TMIG index, scores on the intellectual activity and social role subscales and RCPM score. In ordinal regression models, RCPM and educational background were significantly associated with total score on the TMIG index and the intellectual activity subscale, and only RCPM was associated with the social role subscale score, after adjusting for other potential variables.

CONCLUSION

General intelligence may be significantly associated with higher-level competence, especially with intellectual activity and social role subscales, in community-dwelling older adults.

Oral health-related quality-of-life in homebound elderly dependent on moderate and substantial supportive care for daily living

OBJECTIVES

To describe the oral health-related quality-of-life in homebound elderly dependent on moderate and substantial supportive care for daily living.

MATERIALS AND METHODS

A total of 302 selected persons in three counties in Sweden over 65 years of age and in need of daily support from society participated in the study. Half of the participants had moderate needs of support, defined as supportive care of 15-50 h per month and half had substantial needs of supportive care, i.e. 3-times a day with a night overview. An oral examination was performed and structured questions were asked about general health and living conditions, medication, oral care routines and quality-of-life, using the instrument GOHAI (Geriatric Oral Health Assessment Instrument).

RESULTS

Cardiovascular disease was common and an average of seven prescription drugs was used. More than half of the participants had dentures. The strongest correlation with GOHAI was the total number of teeth. There was a significant difference between individuals with moderate and substantial needs according to GOHAI, irrespective of gender. More elderly people with substantial needs of support had low GOHAI values. Decayed teeth, DT/T, root remnants and dry mouth were negatively correlated to GOHAI among individuals with substantial needs.

CONCLUSIONS

This study found that elderly homebound individuals with substantial needs of supportive care had a lower quality-of-life than elderly homebound individuals with moderate needs of supportive care, although both medical and odontological variables were similar in the groups.

Masseter muscle tension and chewing ability in older persons

AIM

Mastication is an important function to maintain, not only for oral health, but also for quality of life. An easy-to-use method to evaluate the chewing ability of elderly people in any environment is necessary. Few studies have discussed the effectiveness of the masseter muscle by palpation. The purpose of this study was to clarify the availability of masseter muscle tension assessment methods by investigating its relationship with oral health status, and comparing it with other methods of assessing chewing ability.

METHODS

This cross-sectional study was carried out with 547 community-dwelling elderly subjects (246 men and 301 women; mean age 73.8 ± 6.2 years) who participated in a comprehensive annual geriatric health examination in 2010 at Kusatsu, Gunma, Japan. Chewing ability was evaluated by masseter muscle tension palpation, differences of masseter muscle thickness, occlusal force, self-reported chewing ability, and the number of remaining and functional teeth. Masseter muscle thickness was measured by ultrasonography.

RESULTS

Masseter muscle thickness and occlusal force showed significant differences between males and females. The strength of masseter muscle tension palpation was significantly associated with men's occlusal force, masseter muscle thickness, the number of remaining and functional teeth, and self-reported chewing ability (P < 0.05). Female participants showed a significant association with occlusal force, masseter muscle thickness, the number of remaining teeth, and self-reported chewing ability and results of palpation (P < 0.05).

CONCLUSION

These results showed that the palpation of masseter muscle tension is a reliable and easy-to-use method to evaluate the chewing ability of elderly people.

Self-assessed masticatory ability and hospitalisation costs among the elderly living independently

The escalating medical costs are a social problem in many countries. Masticatory ability is thought to be related to the general health conditions. The purpose of this study was to show relationships between self-assessed masticatory ability and medical costs among the elderly living independently in community. Data on background factors and self-assessed masticatory ability were collected from 702 Japanese elderly persons by questionnaires. An intra-oral examination was performed to examine the number of remaining teeth. Self-assessed masticatory ability was classified into one of three categories: ability to chew all kinds of food (Good), ability to chew only slightly hard food (Fair) or ability to chew only soft or pureed food (Poor). Data on the annual medical excluding dental costs were obtained from the Japanese National Health Insurance system. The Kruskal-Wallis test was used to examine differences in outpatient costs and hospitalisation costs among the three groups of self-assessed masticatory ability. Univariate unconditional logistic regression models and multivariate logistic regression models were used with medical costs as the dependent variable and self-assessed masticatory ability as the principal independent variable. A significant difference (P=0·039) in hospitalisation costs but not outpatient costs was found among the three groups of self-assessed masticatory ability. The multivariate logistic regression analysis showed that severely impaired masticatory ability (Poor) was significantly related to higher costs of hospitalisation. Self-assessed impairment of masticatory ability may be a significant and independent indicator of higher costs of hospitalisation among community-dwelling elderly persons.

Influence of voluntary control of masticatory side and rhythm on cerebral hemodynamics

The aim of this study was to investigate the influence on cerebral hemodynamics of voluntary control of masticatory side and rhythm during gum chewing. Blood flow velocity in the middle cerebral artery was measured using transcranial Doppler ultrasonography to evaluate cerebral circulation in healthy volunteers. Heart rate and masseter muscle activity were recorded simultaneously. Volunteers performed three tasks: (1) free gum chewing, (2) gum chewing in which mastication was limited to the right side, and (3) gum chewing in which mastication was limited to the right side and rhythm was set at 1.0 Hz. Changes in cerebral circulation during pre-task, on-task, and post-task periods were analyzed using random effects model, and differences in cerebral circulation and muscle activity between tasks were analyzed using the Friedman test. In all tasks, on-task cerebral circulation was greater than pre-task. Muscle activity and masticatory rhythm varied between tasks, whereas the rate of increase in cerebral circulation did not differ significantly among tasks. These results suggest that cerebral circulation is activated during gum chewing, irrespective of voluntary control of masticatory side and rhythm.