Age-related difference in oral adaptation to masticatory perturbation.

OBJECTIVES: Mastication can be influenced by intraoral perturbation (e.g., hard food). We developed the masticatory perturbation task (MPT) to assess the perturbation effect during mastication and quantify the degree of adaptation to masticatory perturbation in younger and older adults. DESIGN: Thirty-eight younger and 38 older participants completed the MPT, which consisted of three trials assessing masticatory performance (MP) without perturbation (i.e., the baseline condition) and three trials assessing MP with perturbation (i.e., the perturbation condition). Perturbation was implemented by concurrently chewing test food on the preferred side and a drinking straw on the nonpreferred side. We estimated the perturbation effect as the ΔMP between the baseline and perturbation conditions and the adaptation effect as the ΔMP between the third and the first trials for both age groups. RESULTS: We found a significant perturbation effect, i.e., a lower MP in the perturbation condition than in the baseline condition, and an adaptation effect, i.e., a higher MP in the third trial than the first trial, in both groups. Moreover, the older group showed a lower degree of adaptation than the younger group. CONCLUSION: The masticatory perturbation task revealed the perturbation effect during mastication and the adaptation to masticatory perturbation. The results revealed an association between age and masticatory adaptation.

Are demographic factors, masticatory performance and structural brain signatures associated with cognitive impairment in older people? A pilot study of cross-sectional neuroimaging data.

BACKGROUND: The occurrence of cognitive impairment (CI) is expected to increase within an ageing population. CI is associated with tooth loss, which influences masticatory performance. A decrease in masticatory performance may cause functional and morphological changes in the brain. However, whether CI is associated with masticatory performance, demographics, and structural brain signatures has not been studied yet. OBJECTIVES: To assess the associations between CI on the one hand, and masticatory performance, demographic factors, and structural brain signatures (i.e. cortical volume and thickness) on the other hand. METHODS: In total, 18 older adults with CI (mean ± SD age = 72.2 ± 9.5 years) and 68 older adults without CI (65.7 ± 7.5 years) were included in this study. Masticatory performance was quantified using a colour-changeable chewing gum. A Magnetic Resonance Imaging (MRI) scan was used to map structural brain signatures. To study our aim, a multivariate binary logistic regression analysis with backward selection was performed. RESULTS: The cortical volume of the right entorhinal cortex was negatively associated with CI (p < .01). However, demographic factors, masticatory performance, and the other structural brain signatures under investigation were not associated with CI. CONCLUSION: A decrease in the volume of the right entorhinal cortex is associated with CI in older people.

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.

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.

Towards an operational definition of oral frailty: A e-Delphi study.

OBJECTIVES: Building upon our recently developed conceptual definition of oral frailty (the age-related functional decline of orofacial structures), this e-Delphi study aims to develop an operational definition of oral frailty by identifying its components. METHODS: We used a modified e-Delphi study to reach a consensus among international experts on the components of oral frailty. Twelve out of fifteen invited experts in the field of gerodontology participated. Experts responded to three rounds of an online 5-point scale questionnaire of components to be included or excluded from the operational definition of oral frailty. After each round, scores and rationales were shared with all experts, after which they could revise their position. A consensus was reached when at least 70% of the experts agreed on whether or not a component should be included in the operational definition of oral frailty. RESULTS: The experts achieved a high level of agreement (80 - 100%) on including eight components of oral frailty and excluding nineteen. The operational definition of oral frailty should include the following components: 1) difficulty eating hard or tough foods, 2) inability to chew all types of foods, 3) decreased ability to swallow solid foods, 4) decreased ability to swallow liquids, 5) overall poor swallowing function, 6) impaired tongue movement, 7) speech or phonatory disorders, and 8) hyposalivation or xerostomia. CONCLUSION: This e-Delphi study provided eight components that make up the operational definition of oral frailty. These components are the foundation for the next stage, which involves developing an oral frailty assessment tool.

Neuroimaging meta-analysis of brain mechanisms of the association between orofacial pain and mastication.

BACKGROUND: Temporomandibular disorders (TMD) are characterized by pain and impaired masticatory functions. The Integrated Pain Adaptation Model (IPAM) predicts that alterations in motor activity may be associated with increased pain in some individuals. The IPAM highlights the diversity of patients' responses to orofacial pain and suggests that such diversity is related to the sensorimotor network of the brain. It remains unclear whether the pattern of brain activation reflects the diversity of patients' responses underlying the association between mastication and orofacial pain. OBJECTIVE: This meta-analysis aims to compare the spatial pattern of brain activation, as the primary outcome of neuroimaging studies, between studies of mastication (i.e. Study 1: mastication of healthy adults) and studies of orofacial pain (i.e. Study 2: muscle pain in healthy adults and Study 3: noxious stimulation of the masticatory system in TMD patients). METHODS: Neuroimaging meta-analyses were conducted for two groups of studies: (a) mastication of healthy adults (Study 1, 10 studies) and (b) orofacial pain (7 studies), including muscle pain in healthy adults (Study 2) and noxious stimulation of the masticatory system in TMD patients (Study 3). Consistent loci of brain activation were synthesized using Activation Likelihood Estimation (ALE) with an initial cluster-forming threshold (p < .05) and a threshold of cluster size (p < .05, familywise error-corrected). RESULTS: The orofacial pain studies have shown consistent activation in pain-related regions, including the anterior cingulate cortex and the anterior insula (AIns). A conjunctional analysis of mastication and orofacial pain studies showed joint activation at the left AIns, the left primary motor cortex and the right primary somatosensory cortex. CONCLUSION: The meta-analytical evidence suggests that the AIns, as a key region in pain, interoception and salience processing, contributes to the pain-mastication association. These findings reveal an additional neural mechanism of the diversity of patients' responses underlying the association between mastication and orofacial pain.

Association between masseter muscle volume, nutritional status, and cognitive status in older people.

OBJECTIVES: Clinical evidence has suggested that oral function is associated with cognitive, physical, and nutritional status of older people. A smaller volume of masseter, a crucial muscle for mastication, was associated with frailty. It has remained unknown if smaller masseter is associated with cognitive impairment. The current study investigated the association between masseter muscle volume, nutritional status, and cognitive status in older people. MATERIALS AND METHODS: We recruited 19 patients with mild cognitive impairment (MCI), 15 patients with Alzheimer's disease (AD), and 28 sex and age-matched non-cognitive impairment (non-CI) older subjects. The number of missing teeth (NMT), masticatory performance (MP), maximal hand-grip force (MGF), and calf circumference (CC) were assessed. The masseter volume index (MVI) was calculated based on the masseter volume measured using magnetic resonance imaging. RESULTS: The MVI was significantly lower in the AD group, compared to the MCI as well as the non-CI group. Multiple regression analyses revealed that the MVI was significantly associated with nutritional status (as indexed by CC) in the analysis of combination of NMT, MP, and the MVI. Moreover, the MVI was a significant predictor of CC only in patients with cognitive impairment (i.e., MCI+AD) but not in the non-CI group. CONCLUSIONS: Our findings suggested that in addition to the NMT and MP, masseter volume is a critical oral factor associated with cognitive impairment. CLINICAL RELEVANCE: Reduction of MVI should be carefully monitored for patients with dementia and frailty, to whom a lower MVI may indicate worse nutrient intake.

Evaluation of a digital game for teaching behavioral aspects of clinical communication in dentistry.

INTRODUCTION: Traditionally, dental students learn the skills for dentist-patient interaction and communication via on-site contact with patients, when they start clinical training. However, preclinical students (who have not started clinical practice) have fewer chances to realize the context of dentist-patient interaction. It has remained unclear if a gamification approach via digital media, i.e., a computer role-playing game, can help to learn clinical communication skills. The intervention-based study investigates the effectiveness of the clinical dentist-patient communication (CDPC) game on students' motivation, beliefs, and self-efficacy to learn behavioral issues of clinical communication. METHODS: Fifty-two dental students (Preclinical group) and 18 dental interns and dentists (Clinical group) played the CDPC game, which consists of 16 scenes of clinical context about dentist-patient communication (less than 40 min for playing), via web browsers. Pre-test and post-test questionnaires were used to assess their motivation, beliefs, and self-efficacy to learn behavioral issues of clinical communication. The effectiveness was examined by comparing pre-test and post-test scores within-subject and between-group difference was compared between Preclinical and Clinical groups, via non-parametric statistical tests. RESULTS: (A) In the Preclinical group, participants showed a significant increase in motivation and self-efficacy in learning after playing the CDPC game (p < 0.05, adjusted of multiple comparison). (B) In contrast, the Clinical group did not show a significant difference before vs. after playing the game. (C) After playing the game, the Preclinical group showed a significant association between motivation and beliefs (p = 0.024) and between motivation and self-efficacy (p = 0.001); the Clinical group showed a significant association between motivation and beliefs (p = 0.033). CONCLUSIONS: The current evidence suggests that gamification of learning helps preclinical students to understand the context of clinical dentist-patient interaction and increase their motivation and self-efficacy to learn behavioral issues of clinical communication.

Lower masticatory function relates to cognitive health and intrinsic brain network in older adults.

OBJECTIVES: Mastication is associated with brain activation at the primary somatosensory cortex (S1) and the primary motor cortex (M1). Masticatory functions differ between patients with cognitive impairment (CI) and cognitively healthy older adults (non-CI). The association between cognitive health, brain network of functional connectivity, and mastication has remained unknown. The study investigated the association between masticatory performance (MP) and the topological feature of the functional network at the M1 and S1 in the CI and non-CI groups. SUBJECTS AND METHODS: Forty-nine non-CI and 15 CI subjects received resting-state (rs) fMRI and assessment of MP. The topological feature of the M1 and S1 was quantified by eigenvector centrality (EC), an index that reflects a brain region as a functional "hub" of brain network. RESULTS: In the non-CI group, MP was significantly correlated with EC of the left M1 and the right M1. The correlation was not statistically significant in the CI group. Cognitive status (CI or non-CI) and EC of the left M1 and the right M1, respectively, were statistically significant predictors to individual MP. CONCLUSION: Cognitive status and the topological feature of the M1 in the intrinsic functional network may contribute to the individual difference in masticatory function.

Low masseter muscle mass is associated with frailty in community-dwelling older adults: I-Lan Longitudinal Aging Study.

BACKGROUND: Sarcopenia, defined as age-related diminution of muscle mass and strength, is a key determinant of frailty status and progression. We investigated the hypothesis that changing masseter muscle structure with advancing age may contribute to the development of frailty. METHODS: Study data were excerpted from the I-Lan Longitudinal Aging Study, a research cohort of community-dwelling residents aged ≥53 years from Yilan (I-Lan) County, Taiwan. The study sample comprised 56 subjects classified as frail, 41 pre-frail, and 41 robust, according to Cardiovascular Health Study criteria; all groups were matched by age and sex. Masseter muscle volume was quantified based on T1-weighted magnetic resonance imaging, and adjusted for height to derive the masseter volume index (MVI). Appendicular skeletal muscle mass index (SMI) was determined by dual-energy X-ray absorptiometry, and used to derive the height-adjusted skeletal mass index (SMI). Nutrition status was assessed with the Mini-Nutritional Assessment (MNA) form. RESULTS: The MVI was significantly smaller in frail versus pre-frail subjects. Among frail individuals, only the MVI was significantly correlated with MNA scores. MVI, but not SMI, was associated with increased risk of being frail versus pre-frail. An MVI cut-off score of 9.5 cm3/m2 in males discriminated frail from pre-frail status with acceptable sensitivity and specificity. Low MVI was associated with the frailty criteria of slowness. CONCLUSIONS: MVI is a potential clinical index for evaluating phenotypic frailty. Diminished masseter muscle volume may predispose pre-frail/frail elders to depletion of physical reserves, consequent to its detrimental effect on oral functioning and nutrient intake.

Association between pain, anxiety, and pain relief in patients receiving emergent endodontic treatment.

OBJECTIVES: The experience of pain relief is closely associated with the affective-cognitive processing of hedonic value. Higher pain relief plays a key role in patients' satisfaction with treatment and higher motivation to receive treatment. Previous studies focused on pain and anxiety of endodontic treatment. However, the association between pain relief, pain, and anxiety has not been investigated. MATERIALS AND METHODS: We investigated 35 patients (20 females and 15 males, with mean age 46.3 years old) with symptomatic irreversible pulpitis receiving emergent endodontic treatment. Pain-related experience, including pain relief, pain, and anxiety, was assessed before and after treatment, based on an 11-point numerical scale. RESULTS: We found that before treatment, the expected pain relief (median score = 8) that one anticipated was positively correlated with the degree of pain reduction perceived after treatment (two-tailed rho = 0.51, p = 0.002). Expected pain relief was also positively correlated with the post-treatment relief (two-tailed rho = 0.76, p < 0.001) and the relief recalled after 6 weeks (two-tailed rho = 0.69, p < 0.001). Moreover, logistic regression models revealed that expected pain relief was a significant predictor of the subgroups of low vs. moderate scores of post-treatment pain (B = - 1.06, p = 0.017) and anxiety (B = - 1.60, p = 0.009), controlled for the condition of pre-treatment medication. CONCLUSIONS: The current findings highlight that for patients with symptomatic irreversible pulpitis who received emergent endodontic treatment, their expected pain relief before treatment is a critical factor associated with pain reduction and post-treatment pain/anxiety. CLINICAL RELEVANCE: Assessment of expected pain relief may be integrated into pre-treatment assessment for painful dental patients.

Translation and validation of modified dental anxiety scale based on adult Taiwan population.

BACKGROUND: Dental anxiety is associated with negative experiences of dental treatment and dental-visiting behavior. The Modified Dental Anxiety Scale (MDAS) is widely used for assessing dental anxiety. The study aims to establish the psychometric properties of a Chinese version of the MDAS based on the Taiwan sample (i.e., T-MDAS). METHODS: The T-MDAS and dental-visiting behavior and experience were assessed for 402 adult subjects recruited from community and clinical sites. The following psychometric properties were assessed: (a) internal consistency, (b) temporal stability, (c) criterion-related validity (i.e., the association with the score of Index of Dental Anxiety and Fear, IDAF-4C), (d) discrimination validity (i.e., the difference in scores between the subjects with and without a habit of a regular dental visit, and (e) the construct validity from a confirmatory factor analysis (CFA). RESULTS: The T-MDAS showed good internal consistency (Cronbach's α = 0.88) and temporal stability (ρ = 0.69, p < 0.001). The score was significantly correlated with the score of the IDAF-4C (ρ = 0.76, p < 0.001) and differed between subjects who regularly visited a dentist or not, supporting good criterion-related validity and discrimination validity. Results from CFA supports good construct validity. Furthermore, higher dental anxiety was related to the lack of a regular dental visit, feeling pain during treatment, and feeling insufficient skills and empathy of dentists. A higher proportion of high-dental anxiety subjects in female subjects (8.5%), compared to male subjects (5.0%), was noted. CONCLUSIONS: The T-MDAS is a valid tool for assessing adult dental anxiety. The score is highly associated with dental-visiting behavior and experience of dental patients.

Magnification of fear and intention of avoidance in non-experienced versus experienced dental treatment in adults.

BACKGROUND: Dental fear is associated with the experience of prior dental treatment and avoidance of dental visits. It remains unclear if individuals show an intention of avoidance (IA) towards treatments that they have not received (i.e., non-experienced dental treatment). The study aims to investigated (a) if individuals showed an increased fear and IA to non-experienced, compared to experienced dental treatment, and (b) if fear and IA to non-experienced treatment is associated with dental anxiety. METHODS: Fear/IA of 12 common conditions of dental treatment of 402 adults were investigated. If subjects have experienced the condition, fear and IA were assessed based on subjects' prior experience (i.e., ExpFear/ExpIA). If they have not experienced the condition, fear and IA were assessed based on their anticipation (i.e., NExpFear/NExpIA). Trait dental anxiety was assessed using the Index of Dental Anxiety and Fear (IDAF-4C+). RESULTS: (A) NExpFear and NExpIA were significantly higher than ExpFear and ExpIA, respectively. (B) The IDAF-4C+ scores are positively correlated with NExpFear/NExpIA and negatively correlated with the magnification of fear (i.e., the discrepancy in the fear/IA of non-experienced vs. experienced conditions). (C) The condition 'extraction of a wisdom tooth' and 'root canal treatment' showed the highest ratings on NExpFear. CONCLUSIONS: Individuals may develop a high degree of fear and IA of the treatment they have not received. Trait dental anxiety plays a key role in the fear of non-experienced treatment.

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.

Six Months Guided Exercise Therapy Improves Motor Abilities and White Matter Connectivity in Children with Cerebral Palsy.

BACKGROUND: Diffusion magnetic resonance imaging (dMRI) provides the state of putative connectivity from lesioned areas to other brain areas and is potentially beneficial to monitor intervention outcomes. This study assessed the effect of a 6 months guided exercise therapy on motor abilities and white matter diffusivity in the brains of cerebral palsy (CP) children. METHODS: This is a single arm pre-and post-test research design involving 10 spastic CP children, aged 8-18 years and whose Gross Motor Function Classification System Expanded and Revised (GMFCS-E & R) at least Level 21 with the ability to ambulate independently. They were recruited from Paediatric Neurology Clinic, Hospital Universiti Sains Malaysia (HUSM) from December 2015-December 2016. All participants underwent 6 months of therapist-guided exercise session comprising progressive strength training at a frequency of twice a week, 1 h duration per session. The effect of exercise on motor abilities was assessed using the Gross Motor Function Measures (GMFM)-88. Six out of the 10 children consented for dMRI. Probabilistic tractography of the corticospinal tract (CST) was performed to determine the connectivity index of the tracts pre-and post-intervention. RESULTS: All the participants displayed statistically significant increment in GMFM-88 scores pre-to post-exercise intervention. This improvement was concurrent with increased connectivity index in the CST of upper limbs and lower limbs in the brain of these children. CONCLUSION: Our findings demonstrated that 6 months guided exercise therapy improves motor abilities of CP children concurrent with strengthening the connectivities of the motor pathways in the brain.

A novel method for assessing oral mixing ability based on the spatial clusters quantified by variogram.

BACKGROUND: The two-colour chewing test (TCCT) has been widely used for assessing oral mixing ability, a critical component of masticatory performance. Most studies focused on quantifying the evenness of colour distribution. It remained unknown if the variation of colour clustering was a valid index of oral mixing ability. OBJECTIVE: The study aims to investigate the oral mixing ability based on the spatial clusters quantified by variogram. METHODS: Fifty older people (15 male/35 female, age: 66.0 ± 7.8 years) were assessed for the TCCT and the colour-changeable chewing gum test (CCGT). For the CCGT, we quantified the degree of colour change (ΔE). For the TCCT, the highest peak in colour histogram (HP), the standard deviation of colour values (SDC) and the range of variogram from colour spatial distribution (VARG) were quantified. The participants were grouped according to the contacts of posterior teeth, as assessed by Eichner Index (EI). RESULTS: Highest peak, SDC and VARG showed statistically significant differences between the EI groups (two-tailed independent t test P < .05). Higher VARG (ie a lower degree of clustering) was significantly negatively correlated with ΔE (r = -.36, one-tailed P < .01). The binary logistic regression revealed that among the spatial indices (HP, SDC and VARG), only VARG achieved statistical significance in prediction to the EI group. Eliminating other indices was insignificant to the model performance. CONCLUSIONS: Our results show that the averaged cluster sizes, quantified by variogram, are a valid index for quantifying the TCCT. Compared with other spatial indices, it had the best predictability to the condition of posterior contact.

Association between regional brain volume and masticatory performance differed in cognitively impaired and non-impaired older people.

Older patients with cognitive impairment exhibit worse masticatory performance (MP), which may be attributed to poorer abilities of control, learning, and adaptation of oral sensorimotor functions. This study tested the hypothesis that the association between the structural signature of the right premotor cortex (which relates to sensorimotor integration) and masticatory performance would differ between cognitively impaired (CI) and healthy older people. Thirty-one CI and 31 non-CI older participants (aged 60-84 years; male: female = 28: 34) were recruited and between-group matched for the average age and sex ratio. All the participants received T1-weighted magnetic resonance imaging (MRI) and assessments of MP and the number of missing teeth (NMT). Voxel-based morphometry (VBM) was performed to quantify the gray matter volume (GMV). VBM analyses revealed that in the non-CI but not the CI group, MP was positively correlated with regional GMV at the right premotor cortex (PMC) (p = 0.036, corrected for familywise error under small volume correction), controlling for the participants' sex, age, NMT, and total intracranial volume. Multiple linear regression models revealed that in the non-CI group, the right PMC (beta = 0.3, p = 0.049) was a significant predictor of individual MP. In the CI group, only NMT (beta = -0.7, p = 0.001) was a significant predictor of MP. In non-CI older people, both the NMT and the regional GMV of the right PMC contributed to individual MP. In contrast, in CI patients, tooth loss was the dominant factor in MP. An altered association of the brain-stomatognathic system could be linked to cognitive impairment.

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.

What do we learn from brain imaging?-A primer for the dentists who want to know more about the association between the brain and human stomatognathic functions.

The number of neuroimaging studies on the brain and oral sensorimotor functions has increased recently. Behind the dazzling "brain maps," what does the neuroimaging evidence truly tell us? What can dentists learn from it to improve clinical practice? We summarise the pros and cons of applying magnetic resonance imaging (MRI)-based neuroimaging to study oral behaviours of the dental patients. This is a narrative review of previous neuroimaging research of oral functions, focusing on MRI-related studies of human subjects. MRI has gained popularity in dental research due to its non-invasive nature, its approachability and its versatility in quantifying a variety of brain signatures. We argue that MRI-based neuroimaging is suitable for investigating the association between the between-individual variations in brain structure (eg grey matter volume)/brain functions (eg brain activation) and oral behaviours of the patients. Two specific topics of the daily dental practice, mastication and dental fear and anxiety, are discussed to exemplify the potential of neuroimaging methods. The methodological and interpretive limitations of MRI techniques are highlighted, and most importantly, we emphasise that the neuroimaging findings should be carefully interpreted given these limitations. MRI-based neuroimaging techniques can provide a better evaluation of the association between the brain and stomatognathic functions, which could be pivotal to the evidence-based clinical management of dental patients.

Functional Adaptation of Oromotor Functions and Aging: A Focused Review of the Evidence From Brain Neuroimaging Research.

"Practice makes perfect" is a principle widely applied when one is acquiring a new sensorimotor skill to cope with challenges from a new environment. In terms of oral healthcare, the traditional view holds that restoring decayed structures is one of the primary aims of treatment. This assumes that the patient's oromotor functions would be recovered back to normal levels after the restoration. However, in older patients, such a structural-functional coupling after dental treatment shows a great degree of individual variations. For example, after prosthodontic treatment, some patients would adapt themselves quickly to the new dentures, while others would not. In this Focused Review, I argue that the functional aspects of adaptation-which would be predominantly associated with the brain mechanisms of cognitive processing and motor learning-play a critical role in the individual differences in the adaptive behaviors of oromotor functions. This thesis is critical to geriatric oral healthcare since the variation in the capacity of cognitive processing and motor learning is critically associated with aging. In this review, (a) the association between aging and the brain-stomatognathic axis will be introduced; (b) the brain mechanisms underlying the association between aging, compensatory behavior, and motor learning will be briefly summarized; (c) the neuroimaging evidence that suggests the role of cognitive processing and motor learning in oromotor functions will be summarized, and critically, the brain mechanisms underlying mastication and swallowing in older people will be discussed; and (d) based on the current knowledge, an experimental framework for investigating the association between aging and the functional adaptation of oromotor functions will be proposed. Finally, I will comment on the practical implications of this framework and postulate questions open for future research.