Influence of restricted mastication on swallowing function.

BACKGROUND: Oral food processing is an important part of daily food intake. A major part of this process is mastication, which prepares a bolus of food for swallowing by mechanically crushing and grinding ingested food between the teeth using rhythmic movements. Masticatory dysfunction is common in the elderly and in some neurological disorders and can have serious negative health consequences. OBJECTIVE: This study investigated the effect of restricted mastication, achieved by experimentally reducing the duration of mastication, on masticatory patterns and subsequent swallowing function. METHODS: Thirty healthy men (25 ± 3 years old) were instructed to chew gum jelly with a free mastication duration (G100), a half and a quarter duration of G100. Masseter and digastric electromyographic (EMG) activity was recorded to assess mastication and swallowing activity, respectively. In addition, the acceleration of the thyroid cartilage ridge was measured with an accelerometer. The root mean square (RMS) of muscle EMG activity in the masseter and digastric muscles, the number of masseter EMG bursts, time to peak and total duration of each masseter EMG burst, swallowing duration and laryngeal elevation latency were analysed. RESULTS: Restricting masticatory duration reduced the number of mastication cycles (p < .001), prolonged the time to peak (p < .001) and total duration of masseter EMG bursts (p < .001) and resulted in an overall increased RMS score of masseter muscle activity (p = .017). Furthermore, restricted masticatory duration led to a decrease in both swallowing duration (p = .001) and laryngeal elevation latency (p = .012), with a significant increase in the RMS score of digastric muscle activity (p < .001). CONCLUSIONS: Under the experimental conditions of restricted mastication, several adaptation features were observed, including changes in masticatory cycle characteristics and swallowing duration. Thus, although the overall masticatory efficiency was reduced, these adaptations allowed healthy individuals to still swallow safely.

The mechanism for regulating the isometric contraction of masseter muscles is involved in determining the vertical dimension of occlusion.

We previously demonstrated that accurate regulation of isometric contraction (IC) of jaw-closing muscles to counteract the ramp load applied to the jaw in the jaw-opening direction is achieved through the calibration between the two sensations arising from muscle spindles (MSs) and periodontal mechanoreceptors (PMRs). However, it remains unclear whether this calibration mechanism accurately works at any jaw positions, i.e., any vertical dimensions of occlusion (VDO). In the present study, we examined the effects of altering VDO on the IC of the masseter muscles in complete dentulous and edentulous subjects. At a VDO higher than the original VDO (O-VDO), the root mean square (RMS) of masseter EMG activity increased more steeply with a load increase, resulting in an over-counteraction. The regression coefficient of the load-RMS relationship significantly increased as the VDO was increased, suggesting that the overestimation became more pronounced with the VDO increases. Consistently also in the edentulous subjects, at a higher VDO than the O-VDO, a steeper increase in the RMS emerged with a delay in response to the same ramp load whereas a similar steeper increase was seen surprisingly even at a lower VDO. Thus, the edentulous subjects displayed a delayed overestimation of the ramp load presumably due to less and slowly sensitive mucous membrane mechanoreceptor (MMR) in alveolar ridge compared with the PMR. Taken together, the accurate calibration between the two sensations arising from MSs and PMRs/MMRs can be done only at the O-VDO, suggesting that the O-VDO is the best calibration point for performing accurate IC.NEW & NOTEWORTHY Since 1934, the vertical dimension of occlusion (VDO) in edentulous individuals has been anatomically determined mostly by referring to the resting jaw position. However, such a static method is not always accurate. Considering the dynamic nature of clenching/mastication, it is desirable to determine VDO dynamically. We demonstrate that VDO can be accurately determined by measuring masseter EMG during the voluntary isometric contraction of jaw-closing muscles exerted against the ramp load in the jaw-opening direction.

Effect of jaw clenching on head acceleration during a predictable load impact.

BACKGROUND: Jaw clenching is considered to reduce head acceleration while receiving a strong impact on the body during sport activities. OBJECTIVE: The present study aimed to clarify the effect of jaw clenching on reduction of head acceleration during a predictable load impact to the body. METHODS: Seven healthy participants were exposed to a predictable load impact with and without jaw clenching. We recorded the electromyographic activity of the masseter (MA) and digastricus (DIG) muscles, occlusal pressure and head acceleration throughout the experiment. RESULTS: When participants were not instructed to clench their jaws, they naturally positioned their jaws without occlusal contact at the time of pendulum impact by co-contracting the jaw opener and closer muscles. When participants were instructed to clench their jaws, neither the activity of the jaw opener muscle nor the head acceleration differed at the time of pendulum impact when compared with when participants were not instructed to clench their jaws. CONCLUSIONS: A slightly distanced jaw position (co-contracting the jaw opener and closer muscles without occlusal contact) might serve inherently safety for reduction of head acceleration during predictable body impact, while jaw clenching does not contribute to reduction of head acceleration in response to pendulum impact more than the distanced jaw position does. Notably, DIG activation to minimise the head acceleration in response to pendulum impact was similar in clenching and no clenching positions. This suggests that DIG may play a crucial role in the reduction of head acceleration, regardless of MA muscle activity.

[Ultrasound structural assessment of masseter muscles in subjects with different types of craniofacial growth]. / Ul'trazvukovaya otsenka zhevatel'nykh myshts pri razlichnykh tipakh rosta litsevogo cherepa.

THE AIM OF THE STUDY: Was to assess the correlation of various maxillofacial structures in subjects with different types of craniofacial growth. MATERIALS AND METHODS: The results of comparing the morphology of the masseter muscles (thickness, area, echostructure) in 30 volunteers aged from 18 to 25 years without malocclusions and different type of craniofacial growth were presented. RESULTS: A significant correlation between the thickness of the masseter muscles and morphology of the facial skull was observed: the smallest thickness of masseter muscles was in subjects with vertical type of craniofacial growth, the largest - in patients with horizontal type of craniofacial growth. The study results improved ultrasound technique of masseter muscles assessment including methods for measuring the thickness, area and echostructure on ultrasound images. CONCLUSION: The obtained results may be seen as reference points for assessment of the same structures in patients with malocclusions.

Thickness change of masseter muscles and the surrounding soft tissues in female patients during orthodontic treatment: a retrospective study.

BACKGROUND: Facial esthetics is a major concern of orthodontic patients. This study aims to evaluate orthodontic treatment-related thickness changes of the masseter muscles and surrounding soft tissues and the potential factors that would influence these changes during orthodontic treatment in female adults. METHODS: Forty-two female adult patients were included in this retrospective study and were divided into extraction (n = 22) and nonextraction (n = 20) groups. Pretreatment and posttreatment cone-beam computed tomography (CBCT) images were superimposed and reconstructed. The thickness changes of the masseter area of facial soft tissue (MAS), masseter muscles (MM) and surrounding fat tissue (FT) were measured. Pretreatment age, treatment duration, sagittal relationship (ANB), and vertical relationship (Frankfort-mandibular plane angle, FMA)-related MAS, MM and FT changes were compared between extraction and nonextraction groups. Spearman's correlation coefficient was calculated between the above variables. Regression analysis was conducted to confirm the causal relations of the variables. RESULTS: The thickness of MAS and MM significantly decreased in both groups, with larger decreases (> 1 mm) in the extraction group. There were strong correlations (r > 0.7) between the thickness decrease in MAS and MM in both groups and moderate correlations (r > 0.4) between MAS and FT in the nonextraction group. A significantly greater decrease of MAS and MM were found to be moderately correlated with a smaller FMA (r > 0.4) in the extraction group. Scatter plots and regression analysis confirmed these correlations. CONCLUSIONS: Masseter muscles and the surrounding soft tissue exhibited a significant decrease in thickness during orthodontic treatment in female adults. Low-angle patients experienced a greater decrease in soft tissue thickness in the masseter area in the extraction case. But the thickness changes were clinically very small in most patients.

Novel Strategies for Orofacial Soft Tissue Regeneration.

Significance: Orofacial structures are indispensable for speech and eating, and impairment disrupts whole-body health through malnutrition and poor quality of life. However, due to the unique and highly specialized cell populations, tissue architecture, and healing microenvironments, regeneration in this region is challenging and inadequately addressed to date. Recent Advances: With increasing understanding of the nuanced physiology and cellular responses of orofacial soft tissue, novel scaffolds, seeded cells, and bioactive molecules were developed in the past 5 years to specifically target orofacial soft tissue regeneration, particularly for tissues primarily found within the orofacial region such as oral mucosa, taste buds, salivary glands, and masseter muscles. Critical Issues: Due to the tightly packed and complex anatomy, orofacial soft tissue injury commonly implicates multiple tissue types, and thus functional unit reconstruction in the orofacial region is more important than single tissue regeneration. Future Directions: This article reviews the up-to-date knowledge in this highly translational topic, which provides insights into novel biologically inspired and engineered strategies for regenerating orofacial component tissues and functional units.

Is scoliosis related to mastication muscle asymmetry and temporomandibular disorders? A cross-sectional study.

OBJECTIVE: Patients with adolescent idiopathic scoliosis (AIS) may face motor control problems and health disability barriers during mandibular movements and chewing. However, studies investigating the extent of these disadvantages, and possible associated factors are quite limited in patients with AIS. This study was conducted to gain a deeper perspective on the effect of AIS on temporomandibular disorders (TMD) and to contribute to the small amount of data on this subject. METHODS: Twenty-nine patients with AIS and 29 age- and sex-matched asymptomatic controls participated in this cross-sectional study. Cobb's method was used to measure scoliosis curves. In both groups, the volume of the masseter muscle was determined on magnetic resonance imaging, and Helkimo and Fonseca anamnestic indexes were used to evaluate temporomandibular joint (TMJ). RESULTS: It was observed that the TMD symptoms were higher in the AIS group (22.6- Helkimo and 1.2 - Fonseca) than the asymptomatic group (13.6 - Helkimo and 0.7 - Fonseca). There was no significant asymmetry in masseter volume in patients with AIS, however the volume of the masseter muscles was smaller in the AIS group (R = 14.6/L = 13.6) compared to the control group (R = 16.1/L = 16.2). CONCLUSIONS: The study results indicate that spinal curvatures affect the anatomical, biomechanical, and kinesiological features of the masticatory system, and individuals with AIS may experience more chewing problems than asymptomatic individuals. Examining musculoskeletal properties of masticatory system can provide information about the limitation of the TMJ in patients with AIS.

Gestational Intermittent Hypoxia Induces Mitochondrial Impairment in the Geniohyoid Muscle of Offspring Rats.

Introduction Gestational intermittent hypoxia (IH), a hallmark of obstructive sleep apnea during gestation, alters respiratory neural control and diaphragm muscle contractile function in the offspring. The geniohyoid (GH) muscle is innervated by the respiratory-related hypoglossal nerve and plays a role in tongue traction and suckling, motor behaviors that then give way to chewing. Here, we aimed to investigate the effects of gestational exposure to IH on the muscle development and metabolism of GH and masseter muscles in male offspring rats. Materials and methods Pregnant Sprague-Dawley rats were exposed to IH (3-min periods of 4-21% O2) for eight hours/day during gestational days 7-20. The GH and masseter muscles from 35-day-old male offspring (n = 6 in each group) were analyzed.  Results Gestational IH induction reduced type IIA fiber size in the GH muscle of the offspring but not in the masseter muscle. Western blot analysis showed that gestational IH-induced significant downregulation of peroxisome proliferator-activated receptor (PPAR)-gamma coactivator 1-alpha (PGC1α) protein in the GH muscle but not in the masseter muscle. Moreover, optic atrophy 1 and mitofusin-2 proteins were decreased and mitochondrial fission 1 protein levels were increased in the GH muscle of the offspring exposed to gestational IH. Mitochondrial adenosine triphosphate (ATP) synthase subunit alpha and transcriptional factor A (TFAM) were decreased in the GH muscle post-gestational IH. Conclusion These findings suggest that gestational IH-induced impaired mitochondrial metabolism and alteration of oxidative myofibers of the GH muscle in the pre-adolescent offspring, but not the masseter muscle, owing to the susceptibility of GH muscular mitochondria to gestational IH.

Masticatory Functional Load Increases the mRNA Expression Levels of ACTN2 and ACTN3 and the Protein Expression of α-Actinin-2 in Rat Masseter Muscle.

OBJECTIVES: α-actinins play structural and regulatory roles in cytoskeletal organization. They form a lattice structure that secures actin in thin filaments, which generate and transmit muscle contractile forces. The morphological and biochemical characteristics of rat masseter muscles are known to change reactions to masticatory functional loads, but their effect on α-actinins remains unknown. This study aimed to determine the response of α-actinins to masticatory functional loads. MATERIALS AND METHODS: Twenty-four male Wistar rats aged 3 weeks were divided randomly into 3 groups of liquid diet (LD), soft diet, and hard diet (HD). The rats were then sacrificed at the end of 8 weeks. The middle part of superficial masseter muscles was examined to investigate the masticatory effect of functional load on the mRNA expression levels of ACTN2 and ACTN3 and the protein expression levels of α-actinin-2 and α-actinin-3. RESULTS: The mRNA expression levels of ACTN2 and ACTN3 and the protein expression levels of α-actinin-2 of the HD group were significantly higher than those of the LD group, which served as the control group. CONCLUSION: Masticatory functional load organizes the mRNA expression levels of ACTN2 and ACTN3 and the protein expression levels of α-actinin-2 in rat masseter muscles through stimuli during muscle physiological adaptation.

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.

Ultra-low-frequency transcutaneous electric nerve stimulation (ULF-TENS) in subjects with craniofacial pain: A retrospective study.

Objective: The aim of the present study was to evaluate the effects of ultra-low-frequency transcutaneous electrical nerve stimulation (ULF-TENS) on pain and electromyographic values in subjects affected by temporomandibular disorders. Methods: A retrospective evaluation of 80 non-consecutive patients (58 women, 22 men, mean age 35.3 ± 9.9 years) suffering from pain associated with temporomandibular disorders was performed. The sample was treated with ULF-TENS, and outcomes were evaluated by anamnestic index, dysfunction index, visual analog scale, and surface electromyography of the masticatory muscles. Results: An improvement was seen in pain and electromyographic values. The visual analog scale showed a mean decrease from 8 to 2; surface electromyographic values in the masseter area decreased from 2.7 ± 0.1 to 1.5 ± 0.1. Conclusion: ULF-TENS seems to be effective in reducing pain symptomatology of subjects affected by temporomandibular disorders, with a reduction in the surface electromyographic activity in the masseter area.

Electromyography analysis of natural mastication behavior using varying mouthful quantities of two types of gels.

The objectives of this study were to examine the effects of mouthful quantities and mechanical properties of gels on natural mastication behaviors using electromyography (EMG). Two types of hydrocolloid gels (A and K) with similar fracture loads but different moduli and fracture strains were served to eleven normal women in 3-, 6-, 12-, and 24-g masses in a randomized order. EMG activities from both masseter muscles were recorded during natural mastication. Because of the similar fracture loads, the numbers of chews, total muscle activities, and entire oral processing times were similar for similar masses of both gel types. Prior to the first swallow, the more elastic K gel with a higher fracture strain required higher muscle activities than the brittle A gel, which had higher modulus. Majority of subjects had preferred sides of chewing, but all subjects with or without preferred sides used both masseters during the consumption of gels. Similar effects of masses and types of gels were observed in EMG activities of both sides of masseters. Contributions of the dominant side of chewing were diminished with increasing masses of gels, and the mass dependency on ratio of the dominant side was more pronounced with K gel. More repetitions of smaller masses required greater muscle activities and longer periods for the consumption of 24-g gel portions. Reduction in the masses with an increased number of repetitions necessitated slower eating and more mastication to consume the gel portions. These observations suggest that chewing using both sides is more effective and unconsciously reduces mastication times during the consumption of gels.

Eating tools in hand activate the brain systems for eating action: a transcranial magnetic stimulation study.

There is increasing neuroimaging evidence suggesting that visually presented tools automatically activate the human sensorimotor system coding learned motor actions relevant to the visual stimuli. Such crossmodal activation may reflect a general functional property of the human motor memory and thus can be operating in other, non-limb effector organs, such as the orofacial system involved in eating. In the present study, we predicted that somatosensory signals produced by eating tools in hand covertly activate the neuromuscular systems involved in eating action. In Experiments 1 and 2, we measured motor evoked response (MEP) of the masseter muscle in normal humans to examine the possible impact of tools in hand (chopsticks and scissors) on the neuromuscular systems during the observation of food stimuli. We found that eating tools (chopsticks) enhanced the masseter MEPs more greatly than other tools (scissors) during the visual recognition of food, although this covert change in motor excitability was not detectable at the behavioral level. In Experiment 3, we further observed that chopsticks overall increased MEPs more greatly than scissors and this tool-driven increase of MEPs was greater when participants viewed food stimuli than when they viewed non-food stimuli. A joint analysis of the three experiments confirmed a significant impact of eating tools on the masseter MEPs during food recognition. Taken together, these results suggest that eating tools in hand exert a category-specific impact on the neuromuscular system for eating.

Hipertermia severa post cirugía cardiaca: presentación de un caso / Severe hyperthermia present after a heart surgery

Introducción: La hipertermia maligna es una miopatía hereditaria causada por un trastorno del receptor rianodine del retículo sarcoplásmico rugoso del músculo estriado; se manifiesta en pacientes susceptibles por la exposición a agentes halogenados o succinilcolina. Objetivo: Presentar la evolución de una paciente con hiperpirexia severa post cirugía cardiaca. Caso clínico: Paciente de 56 años, anunciada para reemplazo valvular aórtico, ASA III, clase funcional NYHA II-III, sin otros antecedentes. A su llegada a la Unidad de Cuidados Intensivos Postoperatorios se constató gran contractura muscular, generalizada y en particular de los músculos maseteros, incremento progresivo del CO2 arterial (105 mmHg), acidosis metabólica, bajas relaciones paO2/FiO2, orinas de color rojo vino, hiperpotasemia, taquicardia sinusal con contracciones ventriculares prematuras frecuentes, salvas autolimitadas de taquicardia ventricular, bajo gasto cardiaco severo e hiperpirexia mantenida de 41ºC para lo cual se tomaron medidas sintomáticas. Después de 8 horas, disminuyó la fiebre, se restableció el medio interno, el aclaró el color de la orina, la hemodinámica se estabilizó y se constató elevación de la creatinina sérica, que disminuyó progresivamente en los días siguientes. A las 48 horas se destetó de la ventilación mecánica. Se dio el alta de la UCIP al quinto día. Conclusiones: Independientemente, que no se realizaron pruebas específicas para hipertermia maligna, se trata de un caso complejo con una hiperpirexia severa y evolución satisfactoria.

Introduction: Malignant hyperthermia is a hereditary myopathy caused by a rianodine receptor disorder of rugous sarcoplasmic reticulum of the skeletal muscle becomes clear in patients oversensitive to exposition to halogen agents or to succinylcholine. Objective: To present the course of patient presenting with a severe hyperpyrexia after a heart surgery. Clinical case: Patient aged 56 programmed for an aortic valvular replacement, ASA III, functional class NYHA-II-III without other backgrounds. At her arrival to Postperative Intensive Care Unit (POICU) it was noted a significant widespread muscular contracture mainly in masseter muscles, a progressive increase of the arterial CO2 (105 mm Hg), metabolic acidosis, low paO2/FiO2 relations, urine of red wine color, hyperpotassemia, sinus tachycardia with frequent early ventricular contractions, self-limited of ventricular tachycardia, a sever and low cardiac output and sustained hyperpyrexia if 41°C taking measures related to symptoms. At 8 hours fever decreased with restoration of internal environment, urine color cleared, hemodynamics was stable verifying a rise of serum creatinine which decreased progressively after few days. At 48 hours patient was weaned of the mechanical ventilation. At 5 days she was discharged from the POICU. Conclusions: Apart from there were not specific tests to malignant hyperthermia, it is a complex case presenting with a severe hyperpyrexia and a satisfactory course.