Arturo Manns

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.

The changes in electrical activity of the postural muscles of the mandible upon varying the vertical dimension

The relation between BT-EMG activity and variations of VD (1 to 41 mm of interocclusal distance) was studied in the masseter, anterior temporal, and posterior temporal muscles of eight normal experimental subjects. EMG activity was recorded with surface electrodes, and the VD was measured with a specially designed device. Recordings were performed with dynamic variations (series A) and with static variations (series B) of VD. Series A shows a gradual decrease of EMG activity starting from the occlusal position, passing through a range of maximum reduction at a certain interocclusal distance, and gradually increasing to the highest values close to maximum jaw opening. Series B shows the same progression, although it points out the exact VD at which minimum basal EMG activity is observed in each muscle studied (10 mm for the masseter muscle, 13 mm for the anterior temporal muscle, and 16 mm for the posterior temporal muscle).

Forward head posture: its structural and functional influence on the stomatognathic system, a conceptual study.

An extensive conceptual analysis to establish the primary role a forward head posture plays in the appearance of some craniomandibular dysfunctions and internal derangements of the temporomandibular joints, associated to craniocervical postural disturbances. The analysis is based on findings contributed by scientific investigations in the field of dentofacial orthopedics and dysfunction. Special emphasis has been put on the influence of forward head posture on the craniofacial growth as it can determine a morphoskeletal and neuromuscular pattern leading to a dysfunctional condition. A correlation is established between Class II Occlusion, forward head posture, and craniomandibular dysfunction. The concept of craniocervical postural position is defined, as well as its close relation to the mandibular postural position.

Influence of group function and canine guidance on electromyographic activity of elevator muscles

A comparative EMG study was done between two types of occlusal guidances: group function and canine guidance. The purpose was to determine which of the two occlusal schemes causes a greater reduction in muscle activity and thereby a decrease in muscle tension in eccentric mandibular positions. Full-coverage occlusal splints were made for six test subjects with normal function of the stomatognathic system. Left- and right-side integrated EMG recordings were made of the masseter and temporal muscles during static (clenching) and dynamic (lateral excursion and clenching) maximal contractions. The results showed an EMG activity reduction of the elevator muscles with group function relative to their activity in centric occlusion. A more marked reduction was observed on the mediotrusive side, mainly in the temporal muscle. With canine guidance, the reduction in elevator muscle activity is much greater, more significant, and mainly in the temporal muscle of the mediotrusive side. The clinical implications of this study suggest the use of canine guidance in laterotrusion for therapy with full-coverage occlusal splints.

Influence of the vertical dimension in the treatment of myofascial pain-dysfunction syndrome

Occlusal splints constructed at three different vertical heights were used to study the influence of vertical dimension in the etiology of bruxism and MPD syndrome. The vertical dimension of least EMG activity was determined for each of 75 patients who were randomly divided into three groups according to the vertical dimension at which the occlusal splint was constructed. Group I occlusal splints were constructed at 1 mm from the occlusal vertical dimension, group II splints at 4.42 mm, and group III splints at 8.15 mm. Results showed a faster and more complete reduction in clinical symptoms for groups II and III than for group I. The temporary use of occlusal splints with a vertical height exceeding the physiologic rest position did not encourage a greater muscular tonus or hyperactivity of jaw muscles. It can be concluded that elongation of elevator muscles to or near the vertical dimension of least EMG activity by means of occlusal splints is more effective in producing neuromuscular relaxation.

Patterns of electromyographic activity in subjects with different skeletal facial types

Integrated electromyographic activity of masseter and anterior temporal muscles was recorded using bipolar surface electrodes in 33 young adults. Subjects were skeletally classified according to ANB angle reading corrected both for maxillary position and rotation of the jaw. Postural activity for both muscles was higher in Class III subjects than in Class I and Class II, whereas in Class I and II subjects activity was similar. During swallowing, masseter muscle activity in Class III subjects was higher than Classes I and II, whereas anterior temporal muscle activity was not different between Classes III and I. During maximal voluntary clenching, activity was not different among classes. High correlations between electromyographic activity and corrected ANB angle as well as with overjet were observed. Skeletal classification used in the present study may have clinical relevance regarding treatment and prognosis, as well as in the assessment of the relationship between muscular activity and craniofacial characteristics.

Influence of vertical dimension on masseter muscle electromyographic activity in patients with mandibular dysfunction

Occlusal splints were adjusted to different vertical heights and used to single out the influence of vertical dimension of occlusion in increments on BT-EMG activity of the masseter muscle in patients with mandibular dysfunction. The vertical dimension of least EMG activity was determined for each of 60 patients, who were randomly divided into three groups according to the vertical dimension at which the occlusal splint was adjusted: group No. 1, 1 mm from occlusal vertical dimension; group No. 2, mean vertical dimension, 4.25 mm; group No. 3, mean vertical dimension, 8.25 mm. Results showed a significant reduction of masseter BT-EMG activity (series A and B) at the end of the 3-week treatment period for patients in group Nos. 2 and 3 in comparison with group No. 1. Furthermore, the short-term use of occlusal splints with a vertical height that exceeded the so-called physiologic interocclusal distance did not result in an increase in masseter BT-EMG activity. This study suggests that an increase of vertical dimension of occlusion to or near the vertical dimension of least EMG activity by means of occlusal splints can be an effective way to obtain a reduction in masseteric muscle activity.

Influence of variation in anteroposterior occlusal contacts on electromyographic activity

A full upper stabilization splint divided into three pairs of occlusal bilateral blocks was made for eight healthy young adult subjects. The three pairs of blocks allowed the location of the centric occlusal contacts to vary and to be distributed over equivalent periodontal surfaces. The electromyographic activity of the masseter and temporal muscles was recorded with surface electrodes during maximum voluntary clenching over the centric occlusal blocks. The electromyographic activity from the elevator muscles with the anterior blocks was significantly less than with the intermediate and posterior occlusal blocks. With use of the intermediate blocks, the activity from the elevator muscles was significantly less than with the posterior blocks. The elevator activity with the posterior blocks was similar to that with the full coverage splint.

Influence of the activator on electromyographic activity of mandibular elevator muscles

Integrated electromyographic (IEMG) activity was recorded in 15 children with Class II, Division 1 malocclusion undergoing treatment with an activator. EMG activity was recorded with surface electrodes from anterior temporal and masseter muscles, with and without the activator in the postural mandibular position, during saliva swallowing and maximal voluntary clenching. Similar IEMG activity in the postural mandibular position and during maximal voluntary clenching, with and without activator, was observed. During saliva swallowing, the activity in both muscles was significantly higher with the activator. This supports the rationale for diurnal wear of the activator. Simple linear regression analysis showed a significant negative correlation between the change of masseter muscular activity during saliva swallowing and age of the children (r = -0.51), suggesting that treatment with the activator should be started at an early age.

Influence of balanced occlusion and canine guidance on electromyographic activity of elevator muscles in complete denture wearers

Electromyographic recordings were made from the anterior temporal and masseter muscles during maximal voluntary clenching with complete dentures in the intercuspal position and in the laterotrusive jaw position with balanced occlusion and canine guidance. The different pattern of activity of the two muscles in the laterotrusive occlusal schemes studied suggests that their motoneuron pools receive different inputs. The lower activity in both muscles with canine guidance suggests that canine guidance may be a significant factor for preventing parafunctional activity in edentulous patients.