Carmen Palazzi

EMG, bite force, and elongation of the masseter muscle under isometric voluntary contractions and variations of vertical dimension

The relation EMG activity, bite force, and muscular elongation was studied in eight subjects with complete natural dentition during isometric contractions of the masseter muscle, measured from 7 mm to almost maximum jaw opening. EMG was registered with superficial electrodes and bite force with a gnathodynamometer. In series 1, recordings of EMG activity maintaining bite force constant (10 and 20 kg) show that EMG is high when the bite opening is 7 mm, decreases from 15 to 20 mm, and then increases again as jaw opening approaches maximum opening. In series 2, recordings of bite force maintaining EMG constant show that bite force increases up to a certain range of jaw opening (around 15 to 20 mm) and then decreases as we approach maximum jaw opening. Results show that there is for each experimental subject a physiologically optimum muscular elongation of major efficiency where the masseter develops highest muscular force with least EMG activity.

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.

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 and Jaw Posture Effects on Supra- and Infrahyoid Electromyographic Activity in Humans

Abstract The purpose of this study was to record the pattern of electromyographic (EMG) activity of supra- and infrahyoid muscles at different body positions and jaw posture tasks. The sample included 22 healthy subjects with natural dentition, bilateral molar support, and absence of posterior occlusal contacts during mandibular protrusion. Bipolar surface electrodes were located on the left supra- and infrahyoid muscles for EMG recordings. In each subject EMG activity was recorded while standing and in the lateral decubitus position, during the following jaw posture tasks: swallowing of saliva, maximal clenching in the intercuspal position, grinding from intercuspal position to protrusive edge-to-edge contact position, and grinding from retruded contact position to intercuspal position. Suprahyoid EMG activity was significantly higher in the intercuspal position than in all the other jaw positions studied (mixed model with unstructured covariance matrix). Suprahyoid EMG activity was similar in both body positions studied. Infrahyoid EMG activity in the intercuspal position was significantly higher than grinding from intercuspal position to protrusive edge-to-edge contact position, similar to swallowing of saliva, and significantly lower than grinding from the retruded contact position to intercuspal position. Infrahyoid EMG activity in the lateral decubitus position was significantly higher than in the standing position. The EMG pattern observed could be of clinical importance in the presence of parafunctional habits, i.e., clenching and/or grinding. The neurophysiological mechanisms involved are discussed.

Vertical dimension. Part 2: the changes in electrical activity of the cervical muscles upon varying the vertical dimension.

ABSTRACT This study was conducted in order to determine the effect of vertical dimension variation on the electromyographic (EMG) activity of the sternocleidomastoid and trapezius muscles. The study was performed on 15 healthy subjects. Basal tonic electromyographic (BT-EMG) recordings were performed by placing surface electrodes on the left sternocleidomastoid and trapezius muscles. BT EMG activity was recorded upon varying the vertical dimension every five millimeters from vertical dimension of occlusion to 45 millimeters of jaw opening (series 1), following the habitual opening path. Afterward, BT-EMG activity was recorded every millimeter from vertical dimension of occlusion to 4 mm, and then every two millimeters from four to ten millimeters (series 2). In series 1, a significant increase of BT-EMG activity was observed in both muscles (simple logarithmic regression analysis). In series 2, a significant increase was observed in the sternocleidomastoid muscle whereas trapezius muscle did not present a significant change. BT-EMG behavior of the sternocleidomastoid muscle in series 2 could be relevant when dentists increase vertical dimension by means of intermaxillary appliances during a short-term period. Moreover, these results add further information to the concept of the interrelatedness between the different components of the cranio cervical-mandibular system.

Body Position Effects on EMG Activity of Sternocleidomastoid and Masseter Muscles 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 sternocleidomastoid and masseter muscles in 17 patients with myogenic cranio-cervical-mandibular dysfunction. 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 patient), 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 and in the supine position (except during swallowing), whereas a significant higher EMG activity was recorded in the masseter muscle during maximal voluntary clenching in standing and seated positions. The EMG pattern observed suggests that the presence of parafunctional habits and body position could be closely correlated with the clinical symptomatology in the sternocleidomastoid and masseter muscles at wakening and during waking hours, respectively, in patients with myogenic cranio-cervical-mandibular dysfunction.

Binaural interaction in the inferior colliculus of the frog

Abstract Neural activity in the torus semicircularis (colliculus) of the frog was studied. Tones of different frequency, intensity, and duration were used for stimulation of each ear or both ears simultaneously. Unit responses were classified as contralateral units, ipsilateral units, and bilateral units. This last category was subdivided into pure bilateral units, units with contralateral inhibition, and units with ipsilateral inhibition. Percentage of occurrence of these units are similar to these found in the cat and rabbit. This may imply that a general pattern of auditory functional projection is common to vertebrates.

Effects of laterotrusive occlusal scheme and body position on bilateral sternocleidomastoid EMG activity.

ABSTRACT This study was conducted to determine the effects of laterotrusive occlusal scheme and body position on bilateral sternocleidomastoid electromyographic (EMG) activity. The study was performed on 20 healthy subjects with natural dentition and bilateral molar support. During laterotrusive occlusal excursion (working side), each individual had to present canine guidance on one side and group function on the opposite side, without balancing-side contacts. Integrated EMG (IEMG) recordings were performed by placing bipolar surface electrodes on the right and left sternocleidomastoid muscles. IEMG activity was recorded seated upright with the head unsupported and in the right and the left lateral decubitus body positions (head, neck and body horizontally aligned), under the following experimental conditions: 1. Maximal voluntary clenching in the intercuspal position; 2. Laterotrusive occlusal excursion with canine guidance; 3. Laterotrusive occlusal excursion with group function. Bilateral sternocleidomastoid IEMG activity with canine guidance or group function was significantly lower than the intercuspal position in both body positions. In the seated upright position, significantly lower activity was observed with canine guidance than in group function. In the lateral decubitus position activity was similar with both laterotrusive occlusal schemes and significantly higher than seated upright. Results suggest that both laterotrusive occlusal scheme and body position have significant influence on sternocleidomastoid IEMG activity. The clinical relevance of both factors is discussed.

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

ABSTRACT 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.

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.