Changes in jaw muscle activity and the physical properties of foods with different textures during chewing behaviors

Effect of carbonation and thickening on voluntary swallow in healthy humans

BACKGROUND

Liquid modification is a widely established strategy of treatment for patients with dysphagia. The modification of liquid particularly by thickening or carbonation is a common approach to promote safe swallowing.

OBJECTIVE

This study sought to investigate how carbonated and/or thickened water modulates swallowing behaviours during swallowing in healthy young individuals.

METHODS

Thirty-one healthy volunteers (9 men, 22 women; mean age ± standard deviation [SD], 25.7 ± 6.2 years) were instructed to swallow 20 mL of water, carbonated water and carbonated juice with and without added thickening agent. Electromyograms (EMGs) of the suprahyoid (S-hyo) muscles were recorded to evaluate swallowing behaviours. Obtained S-hyo EMG bursts was analysed using the following outcome parameters: onset latency, the time between swallowing que to onset of EMG burst; rising time and falling time, defined as the time between onset and peak, and between peak and offset, respectively; duration, defined as the time between onset and offset of EMG burst; and area integral value under the waveform.

RESULTS

Effects of thickening demonstrated the extended onset latency, EMG burst duration including falling time and the larger area of EMG in thickened liquid compared to thin liquid, but there was not much difference between thin and thickened carbonated liquids. Carbonation significantly decreased the duration including falling time for thickened but not for thin liquids.

CONCLUSION

Patients with dysphagia can benefit from use of carbonated or thickened water while the effects on swallowing physiology may differ between carbonation and thickening.

Association between Self-Perception of Chewing, Chewing Behavior, and the Presence of Gastrointestinal Symptoms in Candidates for Bariatric Surgery

Given the changes in the digestive tract post-bariatric surgery, adapting to a new pattern of eating behavior becomes crucial, with special attention to the specifics of chewing mechanics. This study aimed to investigate the association between self-perception of chewing, chewing behavior, and the presence of gastrointestinal symptoms in preoperative patients undergoing bariatric surgery. Sixty adult candidates for bariatric surgery at a public hospital in Belém (Brazil) were analyzed. Participants predominantly exhibited unilateral chewing patterns (91.6%), a fast chewing rhythm (73.3%), a large food bolus (80%), liquid intake during meals (36.7%), and 41.7% reported that chewing could cause some issue. Significant associations were found between the perception of causing problems and chewing scarcity (p = 0.006), diarrhea (p = 0.004), absence of slow chewing (p = 0.048), and frequent cutting of food with front teeth (p = 0.034). These findings reveal a relationship between the perception of chewing problems and chewing scarcity, presence of diarrhea, and fast chewing.

Effects of different food hardness on cognitive inhibitory control function

Mastication leads to an immediate enhancement in cognitive functions, including inhibitory control. Furthermore, the hardness of the food increases sympathetic nerve activity during and immediately after mastication. Hence, the cognitive function could be enhanced by increased sympathetic nerve activity. The present study aimed to investigate the effects of food hardness on cognitive inhibitory control function in humans. The participants were 23 healthy adults (19-22 years old). Experiments were conducted with two types of gummies (soft and hard). The participants ingested 13 g of gummies and performed a stop-signal task to measure cognitive inhibitory control function after they rested for 5 min. The reaction time for the stop-signal task after gummy consumption was significantly shorter in the hard gummy condition compared to the soft gummy condition (p < .05). Furthermore, the accuracy rate of the responses was also significantly higher in the hard gummy condition compared to the soft gummy condition (p < .05). The results of the present study suggest that food hardness enhances cognitive inhibitory control function in humans.

Resting Saliva Volume as a Risk Factor for Hypogeusia: A Retrospective Study

OBJECTIVES

The causes of hypogeusia include zinc deficiency, systemic illness, and consumption of drugs. Notably, patients with oral cavity diseases such as oral candidiasis and salivary gland hypofunction may present with risk factors that remain unreported. Hence, this study aimed to investigate the relationship between age, sex, smoking status, serum zinc concentration, oral candidiasis, saliva volume, and taste function in patients with hypogeusia.

SUBJECTS AND METHODS

Overall, 335 participants who complained of taste abnormalities underwent a taste test. Based on the recognition threshold value, the participants were classified as normal individuals (recognition threshold of 1 and 2) and patients with hypogeusia (recognition threshold of ≥3). The clinical characteristics, including resting saliva volume (RSV) and stimulated saliva volume (SSV), were compared, and a multivariate logistic regression analysis focusing on RSV was performed.

RESULTS

Patients with hypogeusia had a lower RSV than normal individuals for all tastes, but not for SSV. Based on the results of regression analysis, RSV was identified as an independent predictor of hypogeusia for salty and bitter tastes. Moreover, the proportion of patients with decreased RSV increased as the number of taste qualities exceeding the reference recognition threshold increased. Furthermore, a decrease in RSV was associated with an increase in the recognition threshold for salty and bitter tastes.

CONCLUSIONS

Based on the results of the present study, moisturizing the oral cavity may be useful against hypogeusia.

A dynamic in vitro oral mastication system to study the oral processing behavior of soft foods

A bolus-oriented artificial oral mastication system was developed to simulate the dynamics of food mastication in the human mouth. The system consists of a chewing unit, a bolus forming unit, and provisions for the dynamic incorporation of saliva during mastication. The system performance was validated with in vivo trials (n = 25) considering time-dependent changes in particle size, textural attributes and rheological behavior of the bolus. Idli, a fermented and steamed black gram-rice-based Indian food was considered the model soft food for all trials measured in triplicates. The mastication dynamics were evaluated by analyzing bolus properties during every 3 s of mastication. Large strain shear rheology tests revealed that the viscosity of the sample decreased over time. Results of in vivo trials follow close trends in particle size and rheological behavior and have no significant change in correlation with in vitro mastication results. Similar observations were made in the half softening time of idli during mastication as determined using the relative change in hardness (hardness ratio (H_t/H₀)) values fitted to the Weibull model. Also, a model to simulate the time-dependent changes in bolus adhesiveness was developed.

Functional Role of Suprahyoid Muscles in Bolus Formation During Mastication

It still remains unclear how the suprahyoid muscles function in bolus formation during mastication. This study aimed to investigate the contributory role of the suprahyoid muscles during mastication. A total of 20 healthy young volunteers were asked to perform tongue pressure generation tasks and unilateral mastication tasks using peanuts and two different types of rice crackers. Surface electromyographic (EMG) activity of the masseter and suprahyoid muscles and mandibular kinematics were recorded. Suprahyoid activity increased with increasing tongue pressure. Masticatory duration until the first deglutition differed significantly among the different foods; the harder the food, the longer the duration. This was also the case in masseter activity per masticatory cycle. Masticatory rate and suprahyoid activity per masticatory cycle were significantly higher during soft rice cracker mastication. Masseter activity was higher on the masticatory side than on the non-masticatory side, however, there was no difference in suprahyoid activity between the sides. Suprahyoid activity and jaw gape showed significant positive correlation in the early stage on both the masticatory and non-masticatory sides. The suprahyoid muscles functioned dominantly for jaw-opening during peanut mastication, and for bolus formation, especially in the late stage during soft rice cracker mastication. Bolus formation was performed dominantly on the masticatory side during rice cracker mastication. These findings clearly demonstrate a functional role of the suprahyoid muscles during mastication of solid foods from assessments using both EMG activity and mandibular kinematic recordings.

Effects of textured food masticatory performance in older people with different dental conditions

BACKGROUND

Physiological deterioration (aging, poor dental status, and reduced tongue pressure) makes chewing difficult. This study aimed to investigate the chewing patterns of older people with or without dentures, evaluate the textural and masticatory properties of texture-modified radish Kimchi, and investigate the correlation between dental status and tongue pressure. Additionally, differences in the subjective-objective concordance of texture-modified Kimchi were investigated using the preference test.

METHODS

This study included 32 Korean women aged between 65 and 85 years. Masticatory behavior was recorded by electromyography, and tongue pressure was measured using the Iowa Oral Performance Instrument. A preference test, with hardness as the relevant textural property, determined the participants' preferences among the test samples (food with a homogeneous structure-radish Kimchi). To assess preference differences, a questionnaire suitable for older people was designed. The preference for cooked radish Kimchi with various blanching times based on overall acceptability and self-reporting of preference was investigated to develop elderly-friendly food. The subjective scores indicated whether the sample (radish Kimchi) was hard or soft based on the chewing ability of the participants. Dental status, muscle activities, and tongue pressure were considered for the food design with optimized texture. The relationship between subject score and mastication properties were examined using multiple regression analysis.

RESULTS

The number of chews and chewing time increased with hardness, significantly activating the masseter and temporalis muscles. The evaluation of masseter muscle activity, particularly for level-6 radish Kimchi, showed that older people with complete dentures chewed less actively than those with natural teeth (p < 0.05). The older people with natural teeth (18.94 ± 10.27 kPa) exhibited higher tongue pressure than those with complete dentures (10.81 ± 62.93 kPa), and the difference was statistically significant (p < 0.01). Older people preferred food with familiar tastes and textures. An association was found between the subjective hardness score and the objective hardness level. The perceived hardness intensity was linked to the chewing ability of the participant. Denture wearers exhibited a lower chewing ability, and at level 6, they perceived greater hardness of food than those with natural teeth.

CONCLUSIONS

Developing food with a modified texture can bridge the gap between physiological and psychological aspects of food texture; texture-modified radish Kimchi, with limited blanching time, may be favorable for older people.

Improvement of chewing and swallowing risks in community-dwelling older adults using texture-modified food

BACKGROUND/OBJECTIVES

SUBJECTS/METHODS

RESULTS

CONCLUSIONS

Impact of food texture modifications on oral processing behaviour, bolus properties and postprandial glucose responses

Several studies have demonstrated food texture manipulation on oral processing behaviour (OPB). We explored the effect of texture-differences of equivalent carbohydrate load on OPB, bolus properties and postprandial glycaemic responses (PPG). In a randomised cross-over, within-subjects, non-blinded design, healthy male participants (N = 39) consumed fixed portions of white rice (WR) and rice cake (RC) while being video recorded to measure microstructural eating behaviours. PPG was compared between test foods over a period of 120-min, and the bolus properties and saliva uptake at swallow were measured for both test foods. RC displayed higher instrumental hardness, chewiness and Young's modulus than WR (p = 0.01), and participants perceived RC as more springy and sticky than WR (p < 0.001). The RC meal was chewed more per bite (p < 0.001) and consumed at a faster eating rate (p = 0.033) than WR. WR bolus particles were smaller at swallow (p < 0.001) with a larger total surface area (p < 0.001), compared to RC. The glucose response for RC was significantly higher during the first 30-min postprandial period (p = 0.010), and lower in the later (30-120 min) postprandial period (p = 0.031) compared to WR. Total blood glucose iAUC did not differ significantly between WR and RC meals despite their large differences in texture, OPB and bolus properties. Oro-sensory exposure time was a significant predictor of glucose iAUC30min for both test meals (RC, p = 0.003; WR, p = 0.029). Saliva uptake in the bolus was significantly positively associated with blood glucose during the first 30-min postprandial period for the RC meal (p = 0.008), but not for WR. We conclude that food texture modifications can influence OPB and bolus properties which are key contributors to the dynamic evolution of the glycaemic response. Total blood glucose responses were the same for both test foods, though differences in oral processing and bolus properties influenced temporal changes in PPG.

The particle size of rice flour greatly affects the structural, textural and masticatory properties of steamed rice cake (Baekseolgi)

In this study, steamed rice cakes prepared with different particle sized flour were used to investigate how the structures of rice cakes affected masticatory properties and bolus starch hydrolysis. Decreasing the particle size increased the surface areas requiring hydration, resulting in a loose structure and fluffy starch network during gelatinization. Increasing the particle size led to a tight and firm network, but was easily melted in the oral cavity. The chewing cycle and time differed among the samples. The conditions of inter-individual salivary flow rate and salivary α-amylase were diverse. The oral carbohydrate hydrolysis in the bolus before swallowing showed no significant differences in reducing sugar levels among particle sizes. However, salivary concentration was related to initial starch hydrolysis in the oral cavity, indicating the food structures affected mastication factors and physiological conditions. This study provides food structure and physiological factor information that could help design customized foods in industry.

Textural properties and muscle activities during mastication of normal and ultrasonically softened sticky rice aimed for consumers with swallowing disorder: A pilot study

Ultrasonication was used to develop softer sticky rice for elder adults. Textural properties of original sticky rice (oSR) and ultrasonically modified sticky rice (mSR) were determined. In addition, jaw muscle activities during mastication of both oSR and mSR were investigated. Twenty-seven healthy elderly subjects, age 68.9 ± 7.6 years, were asked to masticate both types of sticky rice in random sequence for three times with a 5-min rest between each test. Activities of bilateral masseter and suprahyoid muscles were recorded. Root mean square (RMS) and mastication duration were analyzed. After mastication trials, subjects were asked to rate preference and softness of the samples. mSR exhibited significantly lower hardness than oSR, while cohesiveness and adhesiveness values of the two samples were not significantly different. Interestingly, all the muscle activities were not significantly different between masticating oSR and mSR, whereas the number of chewing cycles while chewing the mSR was larger. However, 92% of the subjects preferred mSR and felt that it was softer. mSR may therefore be regarded as having potential for elder people who have difficulty masticating hard solid foods based on its lower hardness and higher level of preference compared to oSR.

Impact of Individual Differences in Eating Rate on Oral Processing, Bolus Properties and Post-Meal Glucose Responses

PURPOSE

Modifying food texture has been shown to influence oral processing behaviour. We explored the impact of food texture on oral processing, bolus formation and post-prandial glucose responses (PPG) among fast and slow eaters.

METHODS

Male participants (N=39) were split into fast or slow eaters based on natural differences in eating rate when consuming two carbohydrate-equivalent test-meals differing in texture (white rice and rice cake). PPG and satiety responses were compared for fast and slow eaters over 120-min for each test-meal. Each groups test-meal PPG was compared for bolus and saliva properties at the point of swallow.

RESULTS

White rice displayed lower instrumental hardness, chewiness and Young's modulus and was perceived less chewy, springy and sticky than rice cake. Slow eaters (n=24, white rice: 13.3 g/min; rice cake: 15.1 g/min) required an average 42% more chews per bite (p < 0.001), had 60% longer oral exposure time (OET), and consumed both test-meals (p < 0.001) at half the eating rate of fast eaters (n=15). Slow eaters had higher PPG following the rice cake meal at 15 (p = 0.046) and 45 min (p = 0.034) than fast eaters. A longer OET was a positive predictor of early PPG at 30-min after the white rice meal (β = 0.178, p = 0.041) and saliva uptake was a significant predictor (β = 0.458, p = 0.045) of PPG for slow eaters when consuming rice cake. Increasing food hardness and stiffness (Young's modulus) had a greater impact on eating rate for slow eaters than fast eaters.

CONCLUSIONS

Eating rate, oral exposure time and bolus saliva uptake were the predictors of an individual's post-prandial glycaemic response amongst slow eaters. Increasing the number of chews per bite with a longer oral exposure time increased saliva uptake in the bolus at the moment of swallowing and enhanced temporal changes in PPG, leading to greater glycaemic peaks in rice cake meal. Differences in eating rate between slow and fast eaters when consuming rice cake meal influenced temporal changes in PPG but not total PPG, and bolus properties did not differ between eating rate groups.

Understanding the oral processing of solid foods: Insights from food structure

Understanding the relationship between the structure of solid foods and their oral processing is paramount for enhancing features such as texture and taste and for improving health-related factors such as management of body weight or dysphagia. This paper discusses the main aspects of the oral processing of solid foods across different categories: (1) oral physiology related to chewing, (2) in-mouth food transformation, (3) texture perception, and (4) taste perception, and emphasis is placed on unveiling the underlying mechanisms of how food structure influences the oral processing of solid foods; this is exemplified by comparing the chewing behaviors for a number of representative solid foods. It highlights that modification of the texture/taste of food based on food structure design opens up the possibility for the development of food products that can be applied in the management of health.

Coordinated features in jaw and neck muscle activities induced by chewing of soft and hard gum in healthy subjects

Backgrounds

Jaw and neck muscles may be activated by chewing load using a hard food. However, it remains unclear how effects the gum hardness to the coordinated features in jaw and neck muscle activities during chewing performance.

Objectives

This study was conducted to quantitatively elucidate the effects of the hardness of the gum on coordinated features in jaw and neck muscle activities using intermuscular EMG–EMG transfer function and EMG–EMG coherence function analyses in 18 healthy subjects.

Methods

Jaw and neck muscle activities were aggregated into the first peak frequency of the power spectrum, and power, gain, phase, and coherence parameters between jaw and neck muscle activities were examined in the first peak frequencies during soft and hard gum chewing.

Results

The first peak frequency was not significantly different between soft and hard gum chewing. In contrast, power values of the jaw and neck muscles were significantly increased by chewing of hard gum as compared with soft gum, whereas gain, phase, and coherence were not significantly changed by gum hardness.

Conclusions

The chewing rhythm, the quantitative and temporal coordination, and the functional coordination in jaw and neck muscle activities were not changed during soft and hard gum chewing, as well as increased jaw and neck muscles activities. It is therefore concluded that the chewing rhythmicity and jaw and neck muscles coordination accompanied with the increased jaw and neck muscle activities are maintained under the condition of the chewing load using gum hardness in the healthy individuals.

Easy to Swallow Rice Cake as a Carbohydrate Source during Endurance Exercise Suppressed Feelings of Thirst and Hunger without Changing Exercise Performance

The present guidelines for sports nutrition recommend relatively higher doses of carbohydrates (CHO) for endurance exercise. There is a need for novel food products that are solid but easy to swallow and supply a large dose of CHO without gastrointestinal distress (ingesting a large amount of sugar solution may cause gastrointestinal distress because of its high osmolality). We prepared a modified rice cake (SPRC, sweet potato rice cake) and assessed its properties in swallowing and mastication; we also assessed the availability of this modified rice cake as a CHO source during endurance exercise. The number of chewing strokes with the SPRC tended to be lower compared to glutinous rice cakes. The exercise protocol consisted of 1 h at 80% VO_2max plus a continuous time trial. The subjects were administered a commercially available jelly drink (CHO gel) or SPRC at 0 and 30 min during exercise and immediately after completing the time trial. Heart rate, oxygen consumption, blood glucose elevation, and the rate of perceived exertion did not differ among the trials during exercise. However, the visual analog scale rating revealed that SPRC significantly suppressed hunger and sweetness ratings (p<0.05) and tended to suppress thirst ratings (p<0.10) during exercise. The palatability rating did not differ between the SPRC and CHO gel during exercise at 80% VO_2max and immediately after the time trial. In conclusion, pre- and during exercise ingestion of the SPRC suppressed sweetness, thirst, and hungry ratings without interfering with exercise performance.

Changes of bolus properties and the triggering of swallowing in healthy humans

There is wide variation in chewing behaviours, even among healthy humans. Further, the way in which humans determine swallowing initiation when chewing solid foods remains unclear. The current study sought to investigate how the bolus properties change over time during chewing, and to clarify which factors affect chewing and swallowing behaviours, including swallowing initiation, in healthy humans. Twenty-four healthy volunteers were instructed to chew 8 g of steamed rice and spit it out at 50%, 100% and 150% of their own chewing duration, defined as the time of chewing from onset of the first chewing cycle to onset of the first swallow. Chewing and swallowing behaviours were monitored and determined by visual inspection of video recordings. The physical properties such as hardness, cohesiveness and adhesiveness as well as water content of the bolus were measured. In each subject, maximum bite force, tongue pressure and stimulated salivary flow rate were also measured. Hardness gradually decreased, and the cohesiveness and water content of the bolus did not change up to 50% of chewing duration, followed by a slight but significant increase. The adhesiveness of the bolus rapidly decreased at the beginning of chewing. Chewing duration was significantly related to stimulated salivary flow rate; greater salivary flow rate was associated with shorter chewing duration. Variation of chewing duration and swallowing initiation was not dependent on bolus properties during the chewing of steamed rice, but mainly depended on the surface lubrication of the bolus.

Effects of rehabilitation with complete dentures on bite force and electromyography of jaw and neck muscles and the correlation with occlusal vertical dimension

OBJECTIVES

The purpose of this study was to assess the effects of oral rehabilitation with complete dentures on bite force and electromyography of the suprahyoid and sternocleidomastoid muscles, and their correlation with occlusal vertical dimension (OVD). The research questions were "What are the effects of rehabilitation with complete dentures on bite force and electromyography of suprahyoid and sternocleidomastoid muscles, and how are they correlated with OVD?"

MATERIALS AND METHODS

Patients who are wearers of unsatisfactory removable complete dentures were attended in three sessions (T0, T1, and T2). At T0, while the patients still wore the old dentures, they were submitted to bite force and surface electromyographic exams of the suprahyoid and sternocleidomastoid muscles. These exams were repeated, and the OVD was measured while the patients wore their old and new prostheses, 30 days after insertion of the new prosthesis (T1). The exams were repeated 100 days after the insertion of the new prosthesis (T2). The data were submitted to the Shapiro-Wilk normality test, analysis of variance (ANOVA), and Pearson correlation and linear regression, all with 5% significance.

RESULTS

Fifteen patients participated in the study. No statistically significant difference was observed for bite force or electromyography in T0, T1, or T2. However, the correlation and regression tests showed important interactions between the OVD and maximum voluntary occlusal bite force, as well as the OVD and electromyography during deglutition for the suprahyoid muscles.

CONCLUSION

Rehabilitation did not impact bite force nor the activity of the assessed muscles (electromyography). On the other hand, OVD was shown to be an important factor for bite force, and deglutition of water after rehabilitation.

CLINICAL RELEVANCE

This study shows what are the influences of rehabilitation on oral functions and reinforces the importance of corrected reestablishment of OVD because it has been found to be an important factor for bite force and electromyography during deglutition.

Effect of food hardness on chewing behavior in children

Objective

To investigate the effects of food hardness on chewing behavior in children compared with adults.

Materials and methods

Healthy children (3–17 years) were equally divided into five groups based on their dental eruption stages. Each participant ate soft and hard viscoelastic test food models (3 each), while the three-dimensional jaw movements and electromyographic (EMG) activity of the bilateral masseter muscles were recorded. The data from the children were compared with a control group of healthy adults (18–35 years). The data were analyzed with nonparametric tests.

Results

There was no significant difference in the number of chewing cycles and the duration of the chewing sequence between children groups and adults. Children with primary dentition (3–5 years) showed shorter lateral jaw movement and higher muscle activity at the end of the chewing sequence, compared with adults. Further, children’s age-groups (3–14 years) failed to adapt their jaw muscle activity to food hardness. However, at the late-permanent dentition stage (15–17 years), children were capable of performing adult-like chewing behavior.

Conclusions

Overall, it seems that children as young as 3-year-old are quite competent in performing basic chewing function similar to adults. Yet, there are differences in the anticipation or adaption of jaw muscle activity and jaw kinematics to food hardness.

Clinical relevance

The study may have clinical implication in the diagnosis and management of children with chewing impairment associated with dental malocclusions and other orofacial dysfunctions.

Effects of Carbonation and Temperature on Voluntary Swallowing in Healthy Humans

We investigated how swallowing behaviors are affected by the temperature and carbonation of water in healthy humans. Twenty-nine healthy volunteers were instructed to drink as much natural water, carbonated water, or cider as they wanted, and we recorded the volume of solution swallowed and electromyographic (EMG) activity of the masseter and suprahyoid muscles. Sensory tests regarding the ease of holding the solution in the mouth and ease of swallowing were also performed. The volume of carbonated water swallowed was significantly lower than that of natural water and cider. The ease of holding and swallowing the solution significantly differed between solution types such that natural water was the easiest solution to hold and swallow, followed by cider and then carbonated water in both tests. EMG activity was also affected by the solution type. Masseter EMG activity was significantly lower when swallowing natural water compared with carbonated water. Suprahyoid EMG activity was significantly lower when swallowing natural water compared with carbonated water and cider. The volume of solution swallowed was significantly correlated with the ease of holding and swallowing the solution, but not with masseter or suprahyoid EMG activities. The ease of holding and swallowing the solution significantly affected masseter and suprahyoid EMG activities. The results suggested that when participants experienced difficulty holding and swallowing the solution, masseter and suprahyoid EMG activity increased. Considering our findings that mechanical stimulation with bubbles decreased the volume of solution swallowed and increased EMG activities, carbonated water swallowing may be useful in treating deglutition disorders.

Differentiation of Feeding Behaviors Based on Masseter and Supra-Hyoid Muscle Activity

Older adults with disorders of mastication and swallowing are often fed soft foods such as jelly or puree. The texture of such semi-solid foods allows them to be squeezed between the tongue and palate rather than being chewed. However, it is difficult to visually identify such strategies for the oral processing of food. This study aimed to test the hypothesis that there is a difference in the sequential coordination between the masseter and supra-hyoid muscles, and to identify feeding behaviors such as chewing and squeezing using electromyography. Seventeen male subjects (mean age: 30.8 years) were recruited. Four kinds of gels were prepared (two kinds of fracture force and fracture strain) as test samples. Subjects were instructed to consume the gels in three ways: squeezing with the tongue, chewing with the teeth and eating freely until swallowing. The amount of squeezing/chewing and the consumption time was unlimited. The masseter and supra-hyoid muscle activity were recorded during the entire consumption time and videofluorography was simultaneously recorded during each ingestion. Lissajous figures were made from the electromyographic activity of the two groups of muscles during the first stroke, and a regression line was made to determine the gradient of each figure to compare squeezing and chewing using the Mann-Whitney U-test. The masseter and supra-hyoid muscles were active simultaneously during squeezing with the tongue. However, the masseter was active after the supra-hyoid during chewing. The gradient of the regression line from the Lissajous figures between the masseter and supra-hyoid muscle activity was positive during squeezing, but negative during chewing. Analysis of the ROC curve showed that the cutoff value of the gradient for differentiating feeding behaviors was 0.097, with a sensitivity of 95.3% and specificity of 98.4%. When we allocated 68 free intakes into squeezing and chewing according to this cutoff value, we could distinguish with good precision, and the accuracy, sensitivity, and specificity were 86.8, 91.1, and 66.7% respectively. These results suggest that certain aspects of muscle activity differed among oral processing methods. Lissajous analysis of muscle activity was useful for identifying ingestion behaviors.

A Systematic Review of the Influence of Bolus Characteristics on Respiratory Measures in Healthy Swallowing

There have been a number of studies on the effect of bolus volume, consistency, texture, temperature and taste on the oropharyngeal swallowing physiology. However, its influence on the respiratory function associated with swallow is not well understood. This study aimed at systematically analysing and documenting the prevailing research literature on respiratory functions before, during, and after healthy swallows of boluses with varied characteristics. The PRISMA guidelines were followed for retrieval of relevant research. From among the 48,329 reports screened for inclusion criteria, 25 articles were included for data extraction. Each of these reports was evaluated for its design, methodology and reporting quality and also the level of evidence provided by them. The results revealed that the scientific evidence in this regard was restricted to level II. Majority of the studies included considered bolus volume as the variable than bolus consistency, taste or temperature. Expiratory phase was preferred surrounding the apnea irrespective of volume, consistency or taste but changed with temperature variations across age groups. The reports are equivocal on the duration of respiratory apnea, and length of respiratory cycles before and after the apnea. The temporal coordination of pharyngeal swallow events was found to be independent of bolus volume. This review concluded that bolus characteristics have differential effects on the respiratory functions during swallow beyond a 'central sensory threshold' level. Objective standardization of bolus characteristics may be the immediate requirement for generalization of future research findings in this direction.

Effect of Sudden Deprivation of Sensory Inputs From Periodontium on Mastication

Objective

To investigate the effect of sudden deprivation of sensory inputs from the periodontium on jaw kinematics and time-varying activation profile of the masseter muscle.

Methods

Fourteen (age range: 22–26 years; four men) healthy and natural dentate volunteers participated in a single experimental session. During the experiment, the participants were asked to eat six hard visco-elastic test food models, three each before and after an anesthetic intervention. The movements of the jaw in three dimensions and electromyographic (EMG) activity of the masseter muscle on the chewing side were recorded.

Results

The results of the study showed no significant differences in the number of chewing cycles (P = 0.233) and the duration of chewing sequence (P = 0.198) due to sudden deprivation of sensory inputs from the periodontium. However, there was a significant increase in the jaw opening velocity (P = 0.030) and a significant increase in the duration of occlusal phase (P = 0.004) during the anesthetized condition. The EMG activity of the jaw closing phase was significantly higher during the control condition [116.5 arbitrary units (AU)] than anesthetized condition (93.9 AU). The temporal profile of the masseter muscle showed a biphasic increase in the excitatory muscle drive in the control condition but this increase was virtually absent during the anesthetized condition.

Conclusion

Sudden deprivation of sensory inputs from the periodontium affects the jaw kinematics and jaw muscle activity, with a clear difference in the time-varying activation profile of the masseter muscle. The activation profile of the masseter muscle shows that periodontal mechanoreceptors contribute to approximately 20% of the EMG activity during the jaw closing phase.

Masseter muscle thickness and elasticity in periodontitis

This study aimed to compare the thickness and elasticity of the masseter muscle between patients with gingivitis and patients with periodontitis. A total of 124 patients (63 gingivitis, 61 chronic periodontitis) were recruited at the start of the study, but only 84 patients were declared as final participants. Patients were divided into two groups: (1) patients suffering from gingivitis and (2) those with generalized chronic periodontitis. Clinical (PI, plaque index; GI, gingival index; PD, probing depth; CAL, clinical attachment loss; and BOP, bleeding on probing scores) and ultrasonographic (thickness and elasticity of the masseter muscle) measurements of periodontitis were performed. There were no significant differences in gender, age, body mass index, education status, income level, or marital status between the two groups (P > 0.05). The mean age ± SD for the gingivitis and periodontitis groups was 39.5 ± 10.8 years and 44.8 ± 8.8 years, respectively. There were significant differences between the two groups in the number of PI, GI, PD, CAL, and BOP scores. There were significant differences between the two groups when thickness of masseter during contraction and at rest was taken into account. The gingivitis group had significantly thicker masseter during both contraction and rest. On the other hand, when the elasticity of the masseter was evaluated, there were no significant differences found between the two groups and two sides for each group. Masseter muscle thickness in the periodontitis group was found to be decreased compared with that in the gingivitis group. Furthermore, loss of periodontal tissues due to periodontitis reduces the masticatory ability.

Effect of attention on chewing and swallowing behaviors in healthy humans

We examined how attention alters chewing and swallowing behaviors. Twenty-one healthy volunteers were asked to freely eat 8 g of steamed rice in three separate trials, and we obtained the average number of chewing cycles (N) and chewing duration (T) prior to the first swallow in each trial. We also conducted an N-limited test, in which participants chewed the food while independently counting the number of chewing cycles and swallowed the food when they reached N, and a T-limited test, in which they chewed the food for T sec and then swallowed. We recorded electromyograms (EMGs) from masseter and suprahyoid muscles and collected videoendoscopic images. In the N-limited test, chewing speed decreased, masseter muscle activity (area under the curve of the rectified EMG burst) per cycle increased, and suprahyoid muscle activity per cycle decreased. In the T-limited test, the chewing speed increased, muscle activities per cycle decreased, and the number of cycles increased. The occurrence frequency of bolus propulsion into the pharynx before swallowing was smaller in the N- and T-limited tests than in the free chewing test. Further, the whiteout time was longer in the T-limited test than in the free chewing test. Attentional chewing changes not only chewing but also swallowing behavior.

A New Tridimensional Insight into Geometric and Kinematic Characteristics of Masticatory Cycles in Participants with Normal Occlusion

The aim of this study was to analyze the general, geometric, and kinematic characteristics of the masticatory cycle's movements in a tridimensional way, using a method developed by our study group to provide a new insight into the analysis of mandibular movements due to advancement in the potential of computational analysis. Ten individuals (20.1 ± 2.69 years), molar class I, without mandibular movement problems participated in this study. The movements of the masticatory cycles, frontal and sagittal mandibular border movements, were recorded using 3D electromagnetic articulography and processed with computational scripts developed by our research group. The number of chewing cycles, frequency (cycles/s), chewing cycle areas/mandibular border movements areas ratios, and the mouth opening and closing speeds on the 3D trajectory of the chewing cycle were compared. The cycles were divided and analyzed in thirds. The masticatory cycles showed high variation among the individuals (21.6 ± 9.4 cycles); the frequency (1.46 ± 0.21 cycles/s) revealed a moderate positive correlation (R = 0.52) with the number of cycles. The frontal area ratios between the cycle area and the mandibular border movement presented higher values in the first third (6.65%) of the masticatory cycles, and the ratios of sagittal areas were higher and more variable (first, 7.67%; second, 8.06%; and third, 10.04%) than the frontal view. The opening and closing mouth speeds were greater in the second third of the masticatory cycles (OS, 57.82 mm/s; CS, 58.34 mm/s) without a significant difference between the opening and closing movements when the same thirds were evaluated. Further studies are necessary to improve the understanding of the masticatory cycles regarding the standardization of parameters and their values.

Association of mastication and factors affecting masticatory function with obesity in adults: a systematic review

Background

A substantial number of adults suffer from obesity, that is caused by the risk factor, masticatory dysfunction. The association between mastication and obesity, however, is inconclusive. This systematic review aims to provide literature regarding the association between mastication and factors affecting masticatory function, and obesity in adults.

Methods

Four electronic databases (PubMed, EMBASE, Cochrane Library, and Web of Science) were used to search for publications that met the following criteria: published between 2007 and 2016, written in English, and assessed the associations between mastication and obesity among the population aged ≥18 years. The included publications were analyzed based on the study design, main conclusions, and strength of evidence identified by the two authors who screened all the abstracts and full-text articles and, abstracted data, and performed quality assessments by using a critical appraisal tool, the Critical Appraisal Skills Programme Cohort Studies Checklists.

Results

A total of 18 articles (16 cross-sectional, 1 cohort studies, and 1 randomized controlled trial [RCT]) met our inclusion criteria and were evaluated. Poorer mastication was associated with obesity in 12 out of 16 cross-sectional studies. One cohort study showed that the obesity group displayed higher tooth loss than the normal weight group. One RCT demonstrated that gum-chewing intervention for 8 weeks significantly decreased waist circumference.

Conclusions

Most studies revealed a positive association between mastication and obesity among adults. Nonetheless, most of them are cross-sectional studies, which are insufficient to demonstrate a causal relation. Further advancement requires RCT, especially an intervention of improvement of mastication and obesity needed to confirm this association.

Electronic supplementary material

The online version of this article (10.1186/s12903-018-0525-3) contains supplementary material, which is available to authorized users.

A review of diet standardization and bolus rheology in the management of dysphagia

PURPOSE OF REVIEW

Texture modification is a widespread practice as a strategy for the management of dysphagia and can be very effective in individual cases. However, it is often performed in a qualitative, subjective manner and practices vary internationally according to multiple sets of national guidelines. This article aims to identify best practice by reviewing the theory and practice of texture modification, focussing on recent advances.

RECENT FINDINGS

Instrumental assessment of texture modification in vivo is challenging, and studies including rheology and perception have indicated that fluid viscosity is only one of many factors affecting texture modification in practice. Systematic reviews have identified a historical lack of high-quality clinical evidence, but recent controlled studies are beginning to identify positive and negative aspects of thickened fluids. Research and practice to date have been limited by the lack of control and standardization of foods and drinks. However in 2015 a not-for-profit organization, the International Dysphagia Diet Standardisation Initiative, has published a framework for texture modification from thin liquids to solid foods based on all the existing documentation and guidance, and the - limited - available clinical evidence.

SUMMARY

Rheology exists in the lab; however, normal practice is often subjective or lacking control and standardization. In the near future, cohesion of practice and the availability of practical standardization tools may increase awareness and use of rheology.

Differing structural properties of foods affect the development of mandibular control and muscle coordination in infants and young children

The development of chewing is an essential motor skill that is continually refined throughout early childhood. From a motor control perspective, the advancement of textures is dependent upon the fit between a child's oral anatomic and motor system and food properties. The purpose of this exploratory study is to identify age-related changes in chewing motor coordination and control and to determine if these changes are associated with the differing structural properties of solid foods, as well as to explore the role of explanatory variables such as the emergence of teeth and bite force. The masticatory muscle coordination (i.e., coupling of synergistic and antagonistic muscle pairs) and control (i.e., speed, displacement, chewing rate, duration, and number of chews) of fifty children were assessed cross-sectionally at five ages: 9-, 12-, 18-, 24-, and 36-months using electromyography (EMG) and 3D optical motion capture while children ate three foods that had differing structural properties. The results of this study found that children made gains in their chewing motor control (decreased duration of chewing sequences and lateral jaw displacement) and coordination (improved jaw muscle coupling) throughout this period. The structural differences in foods also affected chewing performance at all ages. These preliminary findings suggest that some solid textures are better adapted for immature mandibular control than others and that the development of chewing is a protracted process that may be impacted by the emergence of teeth and changes to bite force.

Systematic Standardized and Individualized Assessment of Masticatory Cycles Using Electromagnetic 3D Articulography and Computer Scripts

Masticatory movements are studied for decades in odontology; a better understanding of them could improve dental treatments. The aim of this study was to describe an innovative, accurate, and systematic method of analyzing masticatory cycles, generating comparable quantitative data. The masticatory cycles of 5 volunteers (Class I, 19 ± 1.7 years) without articular or dental occlusion problems were evaluated using 3D electromagnetic articulography supported by MATLAB software. The method allows the trajectory morphology of the set of chewing cycles to be analyzed from different views and angles. It was also possible to individualize the trajectory of each cycle providing accurate quantitative data, such as number of cycles, cycle areas in frontal view, and the ratio between each cycle area and the frontal mandibular border movement area. There was a moderate negative correlation (−0.61) between the area and the number of cycles: the greater the cycle area, the smaller the number of repetitions. Finally it was possible to evaluate the area of the cycles through time, which did not reveal a standardized behavior. The proposed method provided reproducible, intelligible, and accurate quantitative and graphical data, suggesting that it is promising and may be applied in different clinical situations and treatments.

Bolus matters: the influence of food oral breakdown on dynamic texture perception

This review article focuses on design of food structure, characterisation of oral processing by boli characterisation and dynamic texture perception. Knowledge of the food properties governing bolus formation and bolus properties determining temporal changes in texture perception is of major importance. Such knowledge allows academia to better understand the mechanisms underlying texture perception and food industry to improve product texture. For instance, such knowledge can be used for developing foods with desired texture perception that fit in a healthy diet or that are customized to specific consumer groups. The end point of oral processing is the formation of a safe-to-swallow bolus. The transitions of solid and soft solid foods into bolus are accompanied by tremendous modifications of food properties. The review discusses dynamic changes in bolus properties resulting in dynamic changes of texture perception during oral processing. Studies monitoring chewing behaviour are discussed to complement the relationships between bolus properties and dynamic texture perception. We conclude that texture perception evolves over mastication time and depends on food properties, such as mechanical properties, mainly in the beginning of oral processing. Towards the middle and end of oral processing, bolus properties depend on food properties and explain texture perception better than food properties.

Mandibular movements in older people with rheumatoid arthritis

OBJECTIVE

The aim of this study was to compare the mandibular movements in older people with and without temporomandibular disorder (TMD) associated with rheumatoid arthritis (RA).

STUDY DESIGN

Thirty partially or completely edentulous older adults (65.33 ± 4.7 years) were assigned to 2 groups: (1) with RA and TMD and (2) without RA and TMD. Chewing movements of the jaws during mastication of the test material (Optocal) and the range of mandibular movements were evaluated by using the JT-3-D kinesiographic device before and after new removable prosthesis insertion. Multiple comparisons were made with analysis of variance (ANOVA) and the Tukey-Kramer test.

RESULTS

Comparisons between the 2 groups before and after new prosthesis insertion revealed that the RA and TMD group had reduced opening angles (P < .05) during chewing. After insertion of new prostheses, both groups showed increased opening and closing angles during chewing (P < .05). The mandibular range of motion results showed that patients with RA and TMD exhibited lower aperture and laterality movements (P < .05) compared with controls before and after new prosthesis insertion. However, there was an increase in aperture, lefty laterality, and protrusion values after new prosthesis insertion in both groups.

CONCLUSIONS

TMD associated with RA may impair mandibular movements. Well-fitted prostheses may improve mandibular movements in older adults, especially those with RA.