Breathing type and body position effects on sternocleidomastoid and suprahyoid EMG activity.

The objective of this study was to determine the effects of breathing type and body position on sternocleidomastoid and suprahyoid electromyographic (EMG) activity. The sample included 18 subjects with upper costal breathing type (study group) and 15 subjects with costo-diaphragmatic breathing type (control group). All individuals had natural dentition and bilateral molar support. EMG recordings at rest and while swallowing saliva were carried out by placing surface electrodes on the left sternocleidomastoid and left suprahyoid muscles. EMG activity was recorded while standing, seated upright, and in the lateral decubitus position. Upper costal breathing type subjects showed a significantly higher suprahyoid EMG activity at rest than costo-diaphragmatic subjects in all body positions studied (mixed model with unstructured covariance matrix). In the lateral decubitus position, both breathing types showed a significantly higher sternocleidomastoid EMG activity at rest and while swallowing saliva. The suprahyoid muscles demonstrated a significantly higher EMG activity at rest as well as in the lateral decubitus position (mixed model with unstructured covariance matrix). These results are relevant because sternocleidomastoid and suprahyoid muscles play an important role in controlling the head posture and mandible dynamics. The neurophysiological mechanisms involved are discussed.

Vertical dimension. Part 1: comparison of clinical freeway space.

This study was conducted in order to compare the clinical freeway space measurements using three simple methods commonly used by dentists in their practices. The study was performed in 15 young healthy subjects with natural dentition and bilateral molar support. Artificial landmarks (adhesive tape) were placed on the more prominent parts of the nose and chin of each subject. Vertical dimension of occlusion (VDO) was measured in the intercuspal position. Postural vertical dimension (PVD) was measured in the following functional conditions: after swallowing saliva, after pronouncing the word "Mississippi", and in a relaxed postural mandibular position (RPMP). Then, the clinical freeway space value in each functional condition was obtained by subtracting VDO from PVD value. Significant differences among clinical freeway space values using three different methods were observed (ANOVA). A significantly higher clinical freeway space value was found using phonetics method than after swallowing and with the mandible in a relaxed postural position (Bonferroni multiple comparison test). No significant differences between swallowing and relaxed methods were found. These results seem to suggest that the measures of clinical freeway space depend upon the method used.

Effects of head and neck inclination on bilateral sternocleidomastoid EMG activity in healthy subjects and in patients with myogenic cranio-cervical-mandibular dysfunction.

This study was conducted in order to determine the effect of head and neck position on bilateral electromyographic (EMG) activity of the sternocleidomastoid muscles. The study was performed on 16 patients with myogenic cranio-cervical-mandibular dysfunction (CMD) and 16 healthy subjects. EMG recordings at rest and during swallowing of saliva and maximal voluntary clenching were performed by placing surface electrodes on the right and left sternocleidomastoid muscles. EMG activity was recorded in the left lateral decubitus position, in a darkened room and with the individual's eyes closed, under the following experimental conditions: 1. Head, neck, and body horizontally aligned; 2. Head and neck upwardly inclined with respect to the body, simulating the effect of a thick pillow, 3. Head and neck downwardly inclined with respect to the body, simulating the effect of a thin pillow. Variation of head and neck positions was determined by measuring the distance from the angle of neck and shoulder and the apex of the shoulder (SND = shoulder-neck distance) of each individual. Then, head and neck were forward or downwardly inclined with respect to the body at one-third of SND. A significantly higher contralateral EMG activity and a more asymmetric EMG activity were observed in the CMD group than in the healthy subjects (Kruskal-Wallis Test). These results suggest a different behavior of bilateral sternocleidomastoid EMG activity in CMD patients than in healthy subjects depending on the positioning of the head and neck.

Body position effects on EMG activity of the temporal and suprahyoid muscles in healthy subjects and in patients with myogenic cranio-cervical-mandibular dysfunction.

This study was conducted in order to determine the effects of body position on integrated electromyographic (IEMG) activity of anterior temporal and suprahyoid muscles. The study was performed on 15 patients with myogenic cranio-cervical-mandibular dysfunction (CMD) and 15 healthy subjects. IEMG recordings at rest and during swallowing of saliva and maximal voluntary clenching were performed by placing surface electrodes on the anterior temporal and suprahyoid muscles in the following body positions: standing, seated, supine, and lateral decubitus position. Insignificant changes in IEMG activity of both muscles were observed upon variations in the body position. Insignificant differences in IEMG activity were observed between patients with myogenic CMD and healthy subjects. A pattern of higher IEMG at rest and during swallowing of saliva was observed in the suprahyoid muscles than in the anterior temporal muscles, whereas during maximal clenching activity, an opposite pattern was observed. Results of the present study seem to suggest that for the anterior temporal and suprahyoid muscles there is no specific body position that could be relevant to initiate and/or to perpetuate a craniomandibular dysfunction.

Effects of two types of pillows on bilateral sternocleidomastoid EMG activity in healthy subjects and in patients with myogenic cranio-cervical-mandibular dysfunction.

This study was conducted in order to determine the effects of two types of pillows on bilateral electromyographic (EMG) activity of the sternocleidomastoid muscles. The study was performed on 15 patients with myogenic cranio-cervical mandibular dysfunction (CMD) and 15 healthy subjects. EMG recordings at rest and during swallowing of saliva and maximal voluntary clenching were performed by placing surface electrodes on the right and left sternocleidomastoid muscles. EMG activity was recorded in the supine position and in the lateral decubitus position (according to each individual's normal resting habit), with their eyes closed and with the head supported by means of: 1. a Sleep Easy Pillow (Interwood Marketing Groups, Concord, Ontario, Canada) and 2. a Standard Pillow (INDUVET). In the lateral decubitus position a significantly higher contralateral than ipsilateral EMG activity at rest in the sternocleidomastoid muscles was observed with both types of pillows in all the sample studied (ANOVA and Duncan's Multiple-Range Test). Asymmetrical bilateral EMG activity in the lateral decubitus position with both types of pillows in healthy subjects and in patients with myogenic CMD, suggests that if this body posture is prolonged, it could be important in the genesis of sternocleidomastoid hyperactivity.

Visual input effect on EMG activity of sternocleidomastoid and masseter muscles in healthy subjects and in patients with myogenic cranio-cervical-mandibular dysfunction.

This study was conducted in order to determine the input visual effect on electromyographic (EMG) activity of the sternocleidomastoid and masseter muscles in the supine and lateral decubitus positions. The study was performed on 22 patients with myogenic cranio-cervical-mandibular dysfunction (CMD) and 18 healthy subjects. EMG activity at rest and during swallowing of saliva and maximal voluntary clenching was recorded in the supine and lateral decubitus positions in the following conditions: 1. with eyes open; and 2. with eyes closed after 5 minutes in a dark room. A significant decrease of EMG activity at rest with closed eyes in both groups was observed in the sternocleidomastoid (lateral decubitus position) and in the masseter muscle (supine position). During swallowing of saliva a significant decrease of EMG activity with closed eyes was observed only in the sternocleidomastoid muscle (lateral decubitus position) in healthy subjects. During maximal voluntary clenching any significant differences were observed upon variation in the visual input. The significant change in EMG activity, mainly observed at rest, suggests that the visual input effect is weak. The absence of a significant change in EMG activity during maximal voluntary clenching upon variation in the visual input could be clinically relevant in patients with myogenic CMD who habitually brux.

Body position effects on EMG activity of sternocleidomastoid and masseter muscles in healthy subjects.

This study was conducted in order to determine the effects of body position on integrated electromyographic (IEMG) activity of sternocleidomastoid and masseter muscles in 20 healthy subjects. EMG recordings at rest and during swallowing of saliva and maximal voluntary clenching were performed by placing surface electrodes on the sternocleidomastoid and masseter muscles (contralateral to the habitual side of sleeping of each subject), in the following body positions: standing, seated, supine, and lateral decubitus position. Significant higher EMG activities were recorded in the sternocleidomastoid muscle in the lateral decubitus position, whereas significant lower EMG activities were recorded in the masseter muscle in the supine position. This finding supports the idea that there may exist a differential modulation of the motor neuron pools of the sternocleidomastoid and masseter muscles of peripheral and/or central origin. Significant differences in the EMG pattern as well as in the levels of EMG activities upon variations in body positions were observed between healthy subjects and patients with myogenic craniomandibular dysfunction reported by Palazzi, et al.

Body position effects on sternocleidomastoid and masseter EMG pattern activity in patients undergoing occlusal splint therapy.

This study was conducted in order to determine the effects of body position on electromyographic (EMG) activity of sternocleidomastoid and masseter muscles, in 15 patients with myogenic cranio-cervical-mandibular dysfunction undergoing occlusal splint therapy. EMG activity was recorded by placing surface electrodes on the sternocleidomastoid and masseter muscles (contralateral to the habitual sleeping side of each patient). EMG activity at rest and during swallowing of saliva and maximal voluntary clenching was recorded in the following body positions: standing, supine and lateral decubitus. In the sternocleidomastoid muscle significant higher EMG activities at rest and during swallowing were recorded in the lateral decubitus position, whereas during maximal voluntary clenching EMG activity did not change. In the masseter muscle significant higher EMG activity during maximal voluntary clenching in a standing position was observed, whereas EMG activity at rest and during swallowing did not change. The opposite pattern of EMG activity supports the idea that there may exist a differential modulation of the motor neuron pools of the sternocleidomastoid and masseter muscles, of peripheral and/or central origin. This suggests that the presence of parafunctional habits and body position could be closely correlated with the clinical symptomatology in these muscles in patients with myogenic craniomandibular dysfunction.