A multifactorial model of masticatory performance: the Suita study.

Previous studies have identified various factors related to masticatory performance. This study was aimed to investigate variations and impacts of factors related to masticatory performance among different occlusal support areas in general urban population in Japan. A total of 1875 Japanese subjects (mean age: 66·7 years) were included in the Suita study. Periodontal status was evaluated using the Community Periodontal Index (CPI). The number of functional teeth and occlusal support areas (OSA) were recorded, and the latter divided into three categories of perfect, decreased and lost OSA based on the Eichner Index. Masticatory performance was determined by means of test gummy jelly. For denture wearers, masticatory performance was measured with the dentures in place. The multiple linear regression analysis showed that, when controlling for other variables, masticatory performance was significantly associated with sex, number of functional teeth, maximum bite force and periodontal status in perfect OSA. Masticatory performance was significantly associated with number of functional teeth, maximum bite force and periodontal status in decreased OSA. In lost OSA, masticatory performance was significantly associated with maximum bite force. Maximum bite force was a factor significantly influencing masticatory performance that was common to all OSA groups. After controlling for possible confounding factors, the number of functional teeth and periodontal status were common factors in the perfect and decreased OSA groups, and only sex was significant in the perfect OSA group. These findings may help in providing dietary guidance to elderly people with tooth loss or periodontal disease.

Fully automatic measuring system for assessing masticatory performance using ß-carotene-containing gummy jelly.

Despite the importance of masticatory performance in health promotion, assessment of masticatory performance has not been widely conducted to date because the methods are labour intensive. The purpose of this study is to investigate the accuracy of a novel system for automatically measuring masticatory performance that uses ß-carotene-containing gummy jelly. To investigate the influence of rinsing time on comminuted jelly pieces expectorated from the oral cavity, divided jelly pieces were treated with two types of dye solution and then rinsed for various durations. Changes in photodiode (light receiver) voltages from light emitted through a solution of dissolved ß-carotene from jelly pieces under each condition were compared with those of unstained jelly. To investigate the influence of dissolving time, changes in light receiver voltage resulting from an increase in division number were compared between three dissolving times. For all forms of divided test jelly and rinsing times, no significant differences in light receiver voltage were observed between any of the stain groups and the control group. Voltages decreased in a similar manner for all forms of divided jelly as dissolving time increased. The highest coefficient of determination (R(2)  = 0·979) between the obtained voltage and the increased surface area of each divided jelly was seen at the 10 s dissolving time. These results suggested that our fully automatic system can estimate the increased surface area of comminuted gummy jelly as a parameter of masticatory performance with high accuracy after rinsing and dissolving operations of 10 s each.

Measuring masticatory performance using a new device and ß-carotene in test gummy jelly.

Objective methods for evaluating masticatory performance are invaluable for quantitative comparisons between various dental treatments as well as diagnosing masticatory disorder. The purpose of this study was to develop an accurate method for automatically measuring masticatory performance using a new measuring device consisting of light-emitting diodes and a photodiode and test gummy jelly. First, the relationship between six known ß-carotene concentrations in aqueous solution and the voltage values exhibited on a photodiode was investigated. Mean voltage obtained by red light incident on the photodiode indicated a significantly high correlation (r=0·999 in a cubic function, P<0·01) with ß-carotene concentration in the aqueous solution. Second, to establish the optimal measuring conditions for evaluating masticatory performance, factors influencing mean voltage were investigated, such as water temperature and times for rinsing the gummy jelly and dissolving ß-carotene from the jelly. A stable mean voltage was obtained by measuring under the following conditions: rinsing water temperature, 35°C; rinsing time, 30s; water dissolving temperature, 35°C; dissolving time, 10s. Finally, the relationship between seven surface area values of divided gummy jelly and ß-carotene concentrations dissolved from the divided jellies was investigated. The increase in surface area of divided test gummy jelly particles was accurately calculated (r=0·992, P<0·001) from mean voltage on the photodiode to change with ß-carotene concentration dissolved from the jelly surface. This new method using test gummy jelly and an automatic measuring device appears useful for precisely evaluating masticatory performance.

Association of symptomless TMJ sounds with occlusal force and masticatory performance in older adults.

This study investigated associations between temporomandibular joint (TMJ) sounds and occlusal force or masticatory performance stratified by posterior occlusal supports in older Japanese adults. The subjects consisted of 1646 independently living people over 60 years. Masticatory performance, occlusal force, TMJ sounds and maximal mouth opening were examined. Posterior occlusal supports were classified by the Eichner Index. The prevalence of TMJ sounds was 27.7%, limitation of mouth opening (< 40 mm) was 7.9% and TMJ pain was only 1.5%. In the Eichner C group, TMJ sounds were significantly associated with lower occlusal force (OR = 3.20, P = 0.046) and lower masticatory performance (OR = 3.18, P = 0.041) after controlling for gender and age. These associations were not found in the Eichner A and B groups. Within the limitations of this study, the presence of TMJ sounds, even if they were symptomless, was associated with impairment of masticatory function in older adults with reduced occlusal support.

Factors Influencing the Changes in Masticatory Performance: The Suita Study.

INTRODUCTION: Although previous studies have identified various factors related to masticatory performance, which factors affect longitudinal changes in masticatory performance have not been clarified. OBJECTIVES: We aimed to clarify factors involved in changes to masticatory performance and construct models from factors related to masticatory performance in a longitudinal study of a general urban population in Japan. METHODS: A total of 1,005 Japanese subjects (411 men, 594 women; mean age at baseline, 65.7 ± 7.7 years; mean follow-up period, 5.0 ± 0.9 years) were included in the Suita study. These subjects participated in dental checkups both at baseline (June 2008-December 2011) and at follow-up (June 2013-January 2017). The number of functional teeth and occlusal support areas was recorded and the latter assessed using the Eichner index. Subjects' periodontal status was evaluated based on the Community Periodontal Index. Masticatory performance was determined using test gummy jelly. Factors affecting masticatory performance at follow-up and the degree of their effect were investigated by multiple linear regression analysis. RESULTS: In multiple linear regression analysis with masticatory performance at follow-up as the dependent variable, baseline age, masticatory performance, number of functional teeth, and maximum bite force were significant independent variables. The results of multiple linear regression analyses by occlusal support at baseline identified only maximum bite force at baseline in subjects who were Eichner A and baseline age, masticatory performance, and number of functional teeth in subjects who were Eichner B as significant independent variables concerning masticatory performance at follow-up. CONCLUSION: Our study showed a relationship between longitudinal changes in masticatory performance and age, number of functional teeth, and maximum bite force and furthermore showed that the effects of these factors vary according to the residual number of occlusal support areas. KNOWLEDGE TRANSFER STATEMENT: Patients and clinicians should recognize the importance of objective and quantitative assessment for chewing efficiency and understand that various factors are related to longitudinal changes in masticatory performance. The results of this study can provide basic data for preventing or improving the decline in masticatory performance for elderly people with varying numbers of occlusal support areas.

Task-induced activation and hemispheric dominance in cerebral circulation during gum chewing.

In elderly persons, it is thought that maintenance of masticatory function may have a beneficial effect on maintenance of cerebral function. However, few studies on cerebral circulation during mastication exist. This study aimed to verify a possible increase in cerebral circulation and the presence of cerebral hemispheric dominance during gum chewing. Twelve healthy, young right-handed subjects with normal dentition were enrolled. Bilateral middle cerebral arterial blood flow velocities (MCAV), heart rate, and arterial carbon dioxide levels were measured during a handgrip exercise and gum chewing. During gum chewing, electromyography of the bilateral masseter muscle was recorded.MCAV and heart rate significantly increased during exercise compared to values at rest. During gum chewing, there were no differences in the rate of increase in MCAV between the working and non-working sides, but during the handgrip exercise, the rate of increase in MCAV was significantly greater for the non-working side than for the working side. During gum chewing,muscle activity on the working side was significantly greater than that on the non-working side. These results suggest that during gum chewing, cerebral circulation increases bilaterally and does not show contralateral dominance, as it does during the handgrip exercise.

Effect of reinforcement on overdenture strain.

Because the abutment becomes the fulcrum, and the denture base over the coping is usually thin, the overdenture is susceptible to fracture. We hypothesized that rational reinforcement can reduce strain and prevent deformation and fracture of the overdenture. We investigated the effect of reinforcement on overdenture strain around the copings and at a midline. A mandibular edentulous model with a 2-mm-thick artificial mucosa and abutment teeth installed bilaterally in the canine position was produced. The coping had a dome-shaped upper surface with a height of 6 mm. On the lingual polished surface, strain gauges were attached at the canine position and at the midline. A vertical load of 49 N was applied on the occlusal surface. Among several kinds of reinforcements, the cast metal reinforcement that covers both the midline and the coping top significantly reduced the strain on the overdenture. It is suggested that this simple reinforcement is effective in preventing deformation and fracture of the overdenture.

Influence of human jaw movement on cerebral blood flow.

Temporal changes in cerebral blood flow induced by jaw movement have yet to be investigated. To assess the influence of pattern and intensity of muscle contraction during jaw movement on task-induced change in cerebral blood flow, we performed bilateral transcranial Doppler ultrasound examination during clenching, gum chewing, and tooth tapping in healthy volunteers. A random-effects model analysis revealed a significant increase in middle cerebral artery blood flow velocity during clenching (high muscle activity) and gum chewing (moderate muscle activity), compared with the preceding rest period; however, such an increase was not detected during tooth tapping (low muscle activity). Cerebral blood flow was greater on the working side during the intensive isometric contraction of the masseter muscle in clenching. These results suggest that task-induced change in cerebral blood flow during jaw movement is influenced by the change in peripheral circulation evoked by muscle contraction.

Coordination of tongue pressure and jaw movement in mastication.

The tongue plays an important role in mastication and swallowing by its contact with the hard palate. Using an experimental palatal plate with 7 pressure sensors, and recording jaw movement using mandibular kinesiography, we assessed, in healthy subjects, the coordination of tongue and jaw movements during the entire masticatory sequence of solids, by measuring tongue pressure against the hard palate. Tongue pressure appeared during the occlusal phase, reached a peak near the start of opening, and disappeared during opening. Specific patterns in order, duration, and magnitude of tongue pressure were seen at the 7 pressure sensors in each chewing stroke. Magnitude and duration were significantly larger in the late stage of chewing (8 strokes before initial swallowing) than in the early stage (until 8 strokes after starting mastication). The normal pattern of tongue contact against the hard palate, control of tongue activity, and coordination with jaw movement during mastication is described.

Ontogeny of NADPH-diaphorase in rat forebrain and midbrain.

This study characterizes the developmental expression of NADPH-diaphorase from embryo to adulthood in the forebrain, midbrain and cerebellum of rat brain via histochemical staining. On embryonic day 12 no neurons stained. Labeling was observed in certain nuclei from E15 through the postnatal period to adulthood. Labeling in neurons increased or maintained a constant level with increased age. The embryo demonstrated substantial labeling in neurons of the caudate putamen, bed nucleus of the stria terminalis, preoptic area, lateral hypothalamic area, paraventricular thalamic nucleus, ventromedial hypothalamic nucleus, magnocellular nucleus posterior commissure, and periaqueductal central gray. Additional neuronal labeling was observed postnatally in the olfactory bulb, cerebral cortex, amygdala, various nuclei of the thalamus, interpeduncular nucleus, linear nucleus of the raphe, pretectal area and superior colliculus. In the cerebellum, labeling appeared only after P14 in cells of the molecular cell layer and granular cell layer. The sizes of labeled neurons developed significantly from P4 to P14 in several nuclei. The distinctive temporal and spatial expression pattern of NADPH-diaphorase implies that the NO/cGMP system may play an important role in physiological and developmental functions.

Perception of dry mouth in a sample of community-dwelling older adults in Japan.

The purpose of this study was to examine the prevalence of perceived dry mouth among a group of independently-living elderly persons in Japan, and to determine its association with general disease, medication, and dental status, as well as its effect on oral function. The study population consisted of participants of the Senior Citizens' College. The subjective sensations of oral dryness on waking and while eating a meal were measured by a questionnaire. The number of usable questionnaires was 1003 or 77.9%. The mean age of the subjects was 66.3 +/- 4.2 years, and 53.0% were male. More than one-third (37.8%) of the subjects reported oral dryness on waking. Only 9.1% of them noticed a subjective feeling of dry mouth during eating. Persons who had at least one of these symptoms made up 41.0%. A multiple stepwise logistic regression analysis indicated the following results: Perception of dry mouth on waking was more frequent among males (p < 0.001), persons who had a low BMI (p < 0.05), and those taking two or more prescribed drugs (p < 0.01). Sensation of dry mouth when eating was more frequent among subjects with a low BMI (p < 0.001) and those who wore a denture in the maxillary arch (p < 0.05). Perception of dry mouth when eating was associated with self-assessed chewing ability (p < 0.01) and dissatisfaction with speaking clearly (p < 0.05), as well as dental status. However, dissatisfaction with tasting a meal had a significant relationship with the reports of mouth dryness on waking (p < 0.01). Our findings suggest that a substantially higher percentage of persons have the perception of dry mouth on waking than when eating, which was associated with medications, being male, and having a low BMI. This perception may influence oral function, especially the reported dissatisfaction with tasting foods.

[Clinical studies on crevicular fluid of abutment tooth. 3. Effect of tannin-fluoride preparation on gingival health].

It was examined, in this study, whether the tannin-fluoride preparation (HY preparation), which might have a caries reductive, plaque inhibiting and astringent action, could reduce the incidence of gingival inflammation around abutment teeth for removable partial dentures. Zinc oxide eugenol cement mixed with HY preparation filled in the cavity prepared in the resin base facing the abutment tooth. Crevicular fluid (Periotron unit: GCF), gingival index (GI), plaque index (PII), probing depth and caries activity around the abutment tooth were measured during 12 months. The following results were obtained: 1. GCF decreased at 1 month later and showed low values at 2, 3, 6 and 12 months. 2. The percentage of low GI value showed an increasing tendency during the experimental period. 3. There was slight variation in PII and probing depth during the experimental period. 4. Caries activity showed a decreasing tendency. These results indicate that the tannin-fluoride preparation reduces not only caries activity but also gingival inflammation around abutment tooth.

[Effect of bite plane on electromyographic activity of masticatory muscles. 1. Muscle activity during tapping movement].

The purpose of this study is to examine the influence of the insertion of bite plane on masticatory muscle activity during tapping movement, and find out useful parameters for examination and diagnosis of stomatognathic dysfunction. The subjects in this study were twenty normal subjects with intact dentition and no signs of mandibular dysfunction as the control group, and twelve subjects with unilateral temporomandibular joint pain during jaw opening or closing movement as the patient group. Electromyographic activity in the bilateral anterior temporal and masseter muscles and mandibular movement using the Mandibular Kinesiograph were recorded simultaneously during tapping movement. The usefulness of the 61 items used in this study was evaluated. The results were summarized as follows: 1. In the patient group, a significant correlation between the jaw opening degree during tapping movement and the maximal jaw opening one without pain was recognized. 2. The total muscle activity in the patient group decreased significantly by the insertion of the bite plane. 3. Many subjects of the patient group showed a significant difference between the right and left activity of each muscle. 4. A significant difference between the two groups was found in the duration of muscle activity before and after Silent period, those coefficients of variation and the difference between those durations of the right and left muscle activity. This study suggests that the above factors are very useful parameters for examination and diagnosis of temporomandibular joint dysfunction.

[Simulation of bone resorption in denture patients using finite element analysis. 1. Application of optimization method].

The purpose of this study was to simulate the process of bone resorption under removable denture bases. Two dimensional finite element models were prepared for the frontal section of a maxillary complete denture with its supporting mucosa and bone in the first molar region. Simulations were performed with the optimization program which could proportionally move the nodal points according to the stress level difference between the actual and the reference stress level. By exerting loads on occlusal table of the model, the bone resorption progressed in the similar manner to reported clinical observations. The location and magnitude of the resorption were highly related to the location and direction of the loads.

[Teeth arrangement of anterior artificial teeth. 1. Age and teeth exposure].

In selecting and arranging anterior artificial teeth for edentulous patients, it is necessary to consider their sex, personality, age and other factors. The relation of upper and lower lip lines to incisal edge has been one of the standards for the selection and the arrangement of anterior artificial teeth. The purpose of this report was to establish and to evaluate decision bases for the selection and arrangement. We recorded and measured the exposure rate of anterior natural teeth (48 men, 46 women) during function, such as smile, pronunciation, by means of the image analysis. Following results were obtained. 1. As the age of patients increased, upper anterior teeth appeared less than lower's. 2. Differences in exposure ratio between upper and lower teeth were found more remarkable in smiling rather than in pronunciation.