Taste is essential in controlling food intake: taste palatability is one of the most important factors that facilitate food intake and modulate the homeostatic control of feeding. The present article describes the mechanism of this phenomenon in terms of interplay of brain substances such as endogenous opioids, cannabinoids, dopamine and orexin. Taste information is sent to the reward system and feeding center via the prefrontal cortex in rodents and the orbitofrontal cortex in primates. The amygdala, which receives taste inputs, also influences reward and feeding. In terms of neuroactive substances, palatability is closely related to benzodiazepine derivatives, β-endorphin and cannabinoids, which facilitate consumption of food and fluid. The reward system contains the ventral tegmental area, nucleus accumbens and ventral pallidum and finally sends information to the lateral hypothalamic area, the feeding center. The dopaminergic system originating from the ventral tegmental area mediates the motivation to consume palatable food. To elucidate the brain mechanisms of the palatability-induced ingestion, we focused on the role of orexin, a hypothalamic neuropeptide, on the basis of recent findings that rats after intracerebral injection of orexin enhanced food intake accompanying the “binge eating pattern” and orexin-knockout mice decreased intake of palatable sucrose solution. Thus, palatability is one of the factors that regulates food and fluid intake and contributes to overconsumption in turn contributing to obesity.

View full abstract

Purpose : The purpose of this study was to investigate how the head and trunk behave during basic mandibular movement, and to clarify whether there is relationship between the range of motion of mouth opening and the range of motion of head or trunk movement.
Methods : We used a six-degree-freedom system (TRIMET II) for recording mandibular and head movement, and a motion-capture system (ProReflex) for recording the body movement. The subjects were six men (age 24~29 years, mean age 25.8 years) without stomatognathic problems. The subjects were instructed to open their mouths as widely as they possible without discomfort and to repeat the open-close movements at rate of 3Hz for 20 seconds. The reference points were upper and lower incisor points and the sternal bone point. We analyzed the vertical components of the mandibular and head movements, and the forward-backward horizontal component of the trunk movements.
Results : Head moved backward during mouth-opening and moved forward during mouth-closing, as the subjects were standing. The body moved forward as mouth opened and backward while the mouth closed. The range of head movement was 0.6~10.7mm, and the ratio of head movement to width of mouth opening was 5.2~40.5%. The range of trunk movement was 0.2~1.8mm, and the ratio of trunk movement to width of mouth opening was the 1.3~6.8%. According to the Spearman's rank correlation coefficient, the width of mouth opening significantly correlated with the range of head and trunk movement.
Conclusion : During open-close mandibule movements, co-operative head and trunk movements were observed. Conclusion for instance, when the mouth opened, the head tilted backward, resulting in a shift of balance with the weight of the head over the cervical segments. To compensate for the backward head motion, the body tended to move forward, and vice versa. Also, a wider opening of the mouth correlated to a larger the range of head and trunk motion was observed. These findings suggest that head and trunk movements facilitate the smoothness of jaw movements.

View full abstract

As mastication is a multivalent function, many modalities have been used for the evaluation of its efficiency. Regarding the methods utilizing gummy jelly as a test food, evaluation method for the elution of ingredient or comminution scoring method have been reported so far. However, the relationship between the comminuted particle analysis and the dissolution analysis has not been clarified yet. This study aimed to reveal the relationship between three masticatory efficiency evaluating methods, which are the amount of eluted β-carotene, visual score and particle distribution analysis, using standardized test gummy jelly. Seventeen healthy full dentate subjects (9 males, 8 females, mean age 30.8 ± 6.9 years) participated in this study. Particle analysis was achieved using digital imaging method. The elution of β-carotene under standardized conditions to 35 degree temperature controlled water of was evaluated. Masticatory performance was also scored by visual inspection according to 10-stage rating scale. Significant correlation was observed between the score and the area of the largest particle in sample bolus (p<0.001). Significant correlation between the elution sensor output and the relative rate of the total area of the particles, whose size were in the range of 1mm2 to 50mm2, to the total area of the whole bolus particles could also be observed (p<0.001). From the results of this study, it was revealed that the dissolution of β-carotene from the test gummy jelly, visually scored masticatory performance and the particle distribution analysis provide satisfactory correlations.

View full abstract

The aim of this study was to know a difference of lip-closing force (LCF) between 2 measuring methods; 1) the measuring probe was gripped by subjects during measurement (gripped method) and 2) the measuring probe was fixed on the pole (fixed method). In 40 healthy young subjects (15 females, 25 males, mean age = 29.8 ± 5.0 years), LCFs in eight directions during maximum voluntary pursing-like lip closure tasks were recorded by 2 kinds of methods. In male, summed values of LCFs for all eight directions (total LCF) by the gripped method was smaller than that by the fixed method. In female, total LCF was not different between 2 methods. In male, in many directional LCFs (5/6) and total LCF, significant correlations between 2 methods were observed. However, in female there were significant correlations between 2 methods only in 3 directional LCFs. From the results of male, LCF measured by gripped method might become smaller than that by fixed method. Because the data from female were variety, it was suggested that the data by gripped method in female were influenced by something beside the LCF.

View full abstract

Purpose : Periodontal mechanoreceptors sense the temporal, spatial, and intensive characteristics of forces exerted on the teeth. These characteristics contribute to the efficient control of jaw movement during mastication. The purpose of this study was to investigate the relationships between the periodontal tactile sensations of the lower premolars and molars and the occlusal loading conditions of the teeth.
The mandibular premolars and molars of 16 healthy adult male volunteers (25.8 ± 1.4 years old) with complete dentition were examined. The tactile detective threshold (TDT) of each tooth was determined using calibrated monofilaments (von Frey hairs). The occlusal force (OF) on each tooth at maximal voluntary clenching was measured with a pressure sensitive film. The occlusal contact area (OCA) of each tooth at the intercuspal position was registered with a silicon check-bite. The OF and OCA distributions for each tooth were calculated as a ratio to the total value on the mandibular arch. Preferred chewing side and main occluding area were determined by using cotton rolls and temporary filling materials, respectively.
The mean TDTs increased from the most anterior to the most posterior tooth. TDTs of the premolars were significantly smaller than those of the molars, although there were no differences between the first and second premolar, or between the first and second molar. The mean TDTs of individual subjects showed no significant correlation with total OFs or total OCAs. In any type of tooth, there was no significant positive correlation between TDT ratios and OF or OCA, although the regression lines between TDT ratio and OF distribution, and between TDT ratio and OCA distribution were diagonally right up. TDTs of the teeth in all directions on the preferred chewing side were significantly higher than those on the contralateral side. TDT of the tooth (molar) included in the main occluding area was significantly lower than that of adjacent molar on the ipsilateral side.
These results indicate periodontal tactile sensation is more closely related to the preferred chewing side and the main occluding area than OF and OCA, which suggests that periodontal tactile sensation might be modified by the functional loading conditions relating with the frequency and magnitude of the occlusal loads during mastication.

View full abstract

Purpose: The purpose of this study was to elucidate the effect of the habitual chewing side on masticatory performance by examining the functional difference between chewing on the habitual and the non-habitual chewing sides. Methods: Ten asymptomatic subjects (ages 26-33 years, mean age 28.7 years) who participated in the 7^th seminar of the Japanese Society of Stomatognathic Function were included in this study. The stability of masticatory path and rhythm and the patterns of masticatory movement path were compared between the habitual chewing side and the non-habitual chewing side during gum chewing. The glucose extraction as the indicator for masticatory function was compared between the two sides. Results: The values of the three indicators representing the stability of masticatory path and rhythm on the habitual chewing side were smaller compared to those on the non-habitual chewing side in 6 of 10 subjects. The glucose extraction on the habitual chewing side was significantly larger than that on the non-habitual chewing side. The majority of subjects, 8 of 10 subjects, showed Pattern I and Pattern III during chewing on the habitual chewing side. When the frequent pattern on the two sides was scored in order to evaluate quantitatively the stability of masticatory movement, the score for the habitual chewing side was larger than it for the non-habitual chewing side in 5 of 10 subjects, and the scores on the two sides were equal in 3 of 10 subjects. Conclusion: The present results suggested the following possibility: 1. Functional differences were found between chewing on the habitual chewing side and chewing on the non-habitual chewing side. Moreover, it was concluded that masticatory performance for chewing on the habitual chewing side was superior to it for chewing on the non-habitual chewing side. 2. Measurement of the glucose extraction as the indicator for ability of mastication, the pattern of masticatory movement path and the stability of masticatory path and rhythm (the values of the indicators representing the stability of masticatory path and rhythm) were useful for the quantitative evaluation of masticatory performance.

View full abstract

Physiotherapeutic exercise is used much less often for the management of temporomandibular disorders than for other chronic musculoskeletal pain conditions. This reduced use may be partly related to the uncertain effects of such exercises on the activation pattern of the jaw muscles. The current study aimed to clarify the effects of physiotherapeutic resistance exercise of the jaw on the path of masticatory movements. Fourteen normal volunteers were randomly divided into 2 groups, i.e., the exercise and control groups. The participants of both the groups underwent 2 sessions during which their jaw movements were recorded; the sessions were separated by a 10-min rest interval. During each session, the participants ingested a mouthful of cooked rice 5 times. In the exercise group, isometric resistance training was performed during the rest period; the subjects were asked to perform lateral jaw excursion against the opposing force created by their own fingers. The maximum amount of lateral deviation during chewing significantly increased only in the second session in the exercise group (p=0.028); the opening direction of the jaw in the frontal plane also changed significantly (p=0.028). No significant changes were observed in the control group. These findings may indicate that short-term resistance exercise can cause instantaneous changes in the muscle activation pattern of the jaw muscles during chewing. Further studies will be required to clarify the longitudinal effects of exercise training.

View full abstract