Masseter muscle

About: Masseter muscle is a research topic. Over the lifetime, 3225 publications have been published within this topic receiving 63083 citations.

Pathophysiology of blepharospasm and oromandibular dystonia

Abstract: The pathophysiology of reflexes mediated by the fifth and seventh cranial nerves has been studied in 16 patients with blepharospasm and oromandibular dystonia compared with normal age-matched subjects. The EMG activity of the dystonic spasms in the periocular and jaw muscles was similar to that described in other muscles in patients with generalized torsion dystonia. The latency of the R1 and R2 components of the blink reflex and of the corneal reflex was normal. However, the amplitude and the duration of the R1 and R2 and the duration of the corneal reflex were increased. In some patients the R1 component was also present on the side contralateral to the stimulus, while in normal subjects it was present only on the ipsilateral side. The excitability cycle of recovery of the R2 component of the blink reflex after a prior conditioning shock was enhanced in the patients. There were no EEG potentials preceding blepharospasms in the patients, although a Bereitschaftspotential was seen beginning some 500 ms prior to voluntary blinks in the same individuals. Exteroceptive suppression in the contracting masseter and orbicularis oculi muscles was absent in 40 to 50 per cent of the patients. The jaw jerk was present in all the patients with normal latency. These results indicate that the neuronal arcs of the facial reflexes in blepharospasm and oromandibular dystonia are normal. However, there is an abnormal excitatory drive, perhaps from the basal ganglia, to the facial motoneurons and the interneurons which mediate the facial reflexes in the brainstem.

Contribution of Jaw Muscle Size and Craniofacial Morphology to Human Bite Force Magnitude

Abstract: The existence of an interaction among bite force magnitude, jaw muscle size (e.g., cross-sectional area, thickness), and craniofacial morphology is widely accepted. Bite force magnitude depends on the size of the jaw muscles and the lever arm lengths of bite force and muscle forces, which in turn are dictated by craniofacial morphology. In this study, the relative contributions of craniofacial morphology and jaw muscle thickness to the bite force magnitude were studied. In 121 adult individuals, both magnitude and direction of the maximal voluntary bite force were registered. Craniofacial dimensions were measured by anthropometrics and from lateral radiographs. The thicknesses of the masseter, temporal, and digastric muscles were registered by ultrasonography. After a factor analysis was applied to the anthropometric and cephalometric dimensions, the correlation between bite force magnitude, on the one hand, and the "craniofacial factors" and jaw muscle thicknesses, on the other, was assessed by stepwise multiple regression. Fifty-eight percent of the bite force variance could be explained. From the jaw muscles, only the thickness of the masseter muscle correlated significantly with bite force magnitude. Bite force magnitude also correlated significantly positively with vertical and transverse facial dimensions and the inclination of the midface, and significantly negatively with mandibular inclination and occlusal plane inclination. The contribution of the masseter muscle to the variation in bite force magnitude was higher than that of the craniofacial factors.

Effects of increased hardness on jaw movement and muscle activity during chewing of visco-elastic model foods

Abstract: When food is chewed, sensory feedback adapts the motor program to the characteristics of the food. However, the relationship between the physical properties of different foods and the motor response is poorly understood. In this study, we developed edible and well-controlled model foods in order to describe some of the stimulus-response functions of the food-mastication loop. Four gelatine-based visco-elastic model foods identical in shape and size but differing in hardness were prepared. They displayed reproducible sensory and physical characteristics and were distributed on a wide hardness scale. Electromyographic activity of masseter and temporalis muscles and jaw movements in the frontal plane were simultaneously recorded during mastication in 15 young men with intact dentition and good oral status. Almost all EMG and jaw movement parameters were clearly affected by increasing hardness of model foods. However, it is possible to summarise the results by reducing the number of parameters to three: the number of chewing cycles, EMG activity of any one of the two temporal or the two masseter muscles and the amplitude of the opening mandibular movements. Indeed, these were the best transcriptors of the hardness range of the model foods used in this study. As inferred from these parameter recordings, the food hardness modifications were strongest during the first five strokes, began as early as the first stroke and lasted for the whole sequence.

Rhythmic Masticatory Muscle Activity during Sleep in Humans

Abstract: Rhythmic Masticatory Muscle Activity (RMMA) is frequently observed during sleep in normal subjects and sleep bruxers. We hypothesized that some normal subjects exhibit RMMA at a lower frequency than sleep bruxers. Polysomnographic data from 82 normal subjects were compared with data from 33 sleep bruxers. RMMA episodes were defined as three or more consecutive bursts of masseter EMG activity, with or without tooth-grinding. Such episodes were observed in nearly 60% of normal subjects. A lower frequency of episodes was noted in normal subjects than in bruxers. Sleep organization was similar between groups. Bruxers had twice as many masseter muscle bursts per episode and episodes of higher amplitude compared with controls with RMMA. The high prevalence of RMMA observed in normal subjects suggests that this activity is related to certain sleep-related physiological functions, including autonomic activation.

Relation between facial morphology and activity of the masticatory muscles

Abstract: Summary The relation between muscle activity and facial morphology was studied in twenty-five boys and twenty-seven girls, aged 9–11 years. The activity in the anterior and posterior parts of the temporal muscle, the masseter muscle and the upper lip was recorded bilaterally with the mandible in postural position and during chewing, swallowing and maximal bite. The electromyograms were analysed in respect of maximal mean voltage amplitude and the duration of muscle activity. Facial morphology was studied with the aid of profile roentgenograms and model analysis. The activity in postural position was found to be greater in the posterior than in the anterior part of the temporal muscle. The average mean voltage amplitude in the temporal and masseter muscles was greatest during maximal bite, smaller during chewing and smallest during swallowing. In the orbicularis oris muscle the activity was greater during the opening phase of the chewing cycle than during the closing phase. In postural position the activity in the anterior and posterior parts of the temporal muscle were positively correlated. The amplitudes in the anterior and posterior parts of the temporal muscle and in the masseter muscle were positively correlated during chewing, swallowing and maximal bite. The amplitudes in these muscles during chewing were positively correlated with those in the same muscles during maximal bite. During swallowing the amplitude in the upper lip was negatively correlated with that in the anterior part of the temporal muscle. The clearest correlations between muscle activity and facial morphology were found during chewing and maximal bite. During these functions the amplitudes in the temporal and masseter muscles were large in cases with a tendency to parallelism between the jaws bases and between the mandibular occlusal line and the mandibular line. These cases with considerable muscle activity are characterized by rectangular shape of the face in profile and small lower face height.