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PubMed1989

Comparison of 133Xe clearance and laser Doppler flowmetry in assessment of blood flow changes in human masseter muscle induced by isometric contraction.

Changes induced by 30 s of isometric contraction at 10% and 50% of the maximum voluntary contraction were assessed in 10 healthy subjects; there was a median increase of 1.8 and 0.3 times in 133Xe clearance and 5.3 and 2.7 times in laser Doppler flowmetry. In the first minute after 10% maximum voluntary contraction, 133Xe clearance increased 12.1 times in relation to the initial resting level, and flowmetry values decreased to become 3.5 times higher than the basal flow; corresponding values after 50% maximum voluntary contraction were 24.3 times and 3.7 times. From the second minute after contraction, there was a rapid decrease in 133Xe clearance and a slow decrease in flowmetry values. Five minutes after biting at 10% maximum voluntary contraction, both methods showed a total net increase of about 15 times; after biting at 50% maximum voluntary contraction the corresponding values were 38 and 23 times. Thus laser Doppler flowmetry can be used to assess changes in blood flow in the masseter; it registers a greater increase in flow during isometric contraction than does 133Xe clearance. The significant difference between methods immediately after either chosen level of contraction disappears when the total net post-contraction hyperaemia is assessed over a period of 2 and 5 min, respectively.

Adult↗
PubMedDate not supplied

[Effects of orthodontic treatment on the masseter muscle inhibitory reflex].

OBJECTIVE: The aim of this study was to identify the effect of the orthodontic treatment on inhibitory masseteric reflex. METHODS: Twenty-three patients with any type of malocclusion and without any temporomandibular joint dysfunction were studied and treated under arch wire technique with Roth's brackets prescription (0.22" x 0.28"). Electromyographic record of the inhibitory masseteric reflex was obtained before and after orthodontic treatment. RESULTS: ANOVA test identified not reflex differences between molar relation types; using Student t test for paired data it was identified that with orthodontic treatment (14.65 +/- 2.40 months), the left reflex latency was increased from 6.17 +/- 9.29 ms to 37.00 +/- 66.33 ms (p < 0.05). However the left inhibition duration was decreased from 57.78 +/- 30.70 ms to 35.31 +/- 25.72 ms (p < 0.05), the right inhibition amplitude was decreased from 48.40 +/- 34.44 mV to 28.59 +/- 17.26 mV (p < 0.05) and the left inhibition amplitude was decreased from 40.72 +/- 29.75 mV to 18.73 +/- 17.68 mV (p < 0.05). CONCLUSIONS: Orthodontic treatment produced constraint of the masseter inhibitory capacity, which could be a transitory neuromuscular adaptation signal in the presence of sensorial scheme modifications. It is necessary to wait for a longer period of time before a new register to clarify the reflex morphology tendency.

Adolescent↗
PubMed1986

Post-stimulus EMG complexes in the masseter muscle following gingival electrical stimulation in man.

Post-stimulus EMG complexes (PSECs) were elicited by means of electrical stimulation of the gingiva in six subjects during clenching in three biting positions, namely the maximal occlusion, the incisor edge-to-edge and the hyperpropulsive biting position. No interrelationship was found between the mechanically and electrically elicited PSECs. With electrical stimulation the PSEC morphology was not related to the biting position in contrast with the PSECs elicited with mechanical stimulation. Following gingival electrical stimulation, a P wave was not present in the PSEC.

Adolescent↗
PubMed1998

Projections from dorsomedial part of the subnucleus oralis to the mesencephalic trigeminal neurons innervating the masseter muscle--a PHA-L and HRP double labeling study in the rat.

When PHA-L was injected to dorsomedial part of the subnucleus oralis of the spinal trigeminal nucleus (Vodm), anterogradely labeled varicosities and boutons were observed in the mesencephalic trigeminal nucleus (Vme). The PHA-L labeling was seen mainly in the Vine ipsilateral to the injection side. If the injection sites were placed more medially containing both Vodm and parvocellular reticular nucleus (PCRt), more PHA-L labeling in contralateral Vme was observed. It appeared that the Vodm neurons projected predominantly to the ipsilateral Vme, while neurons in the PCRt adjacent to the Vodm projected bilaterally to the Vme. It was also seen that many PHA-L labeled varicosities and boutons surrounded or contacted on the Vme neurons counterstained with cresyl violet. These contacts were seen frequently in the ipsilateral Vme, occasionally in the contralateral nucleus. Some Vme neurons ipsilateral to the injection side were retrogradely labeled in a solidly-filled appearance following injection of PHA-L into the Vodm. When PHA-L was applied to the Vodm and HRP was injected to the masseter nerve on the same side, the relationship between PHA-L labeled terminals and HRP labeled Vme neurons was studied. The contacts between PHA-L labeled boutons and HRP labeled somata or processes of the Vme neurons were observed occasionally. PHA-L labeled terminals sometimes contacted on none-HRP-labeled somata counterstained with neutral red. Besides the PHA-L labeling in the Vme, the labeling was also seen in the medial parabrachial nucleus ipsilaterally, in the motor trigeminal nucleus bilaterally with ipsilateral predominance. In addition, an outstanding labeling band along the medial border of the principal sensory trigeminal nucleus (Vp) was observed following injection of PHA-L into the Vodm. The labeled terminals were concentrated in dorsomedial part of the Vp (Vpdm) and in juxtatrigeminal nucleus (JX), meanwhile many labeled fibres were distributed between the Vpdm and JX in the intertrigeminal region.

Animals↗
PubMed1994

Electromyographic assessment of non-functional masseter muscle in an awake animal model.

Non-functional activities, such as bruxism, have been implicated in the development of temporomandibular disorders (TMD). It would be of value to have an animal model in which to investigate the processes underlying such disorders. The aim of this study was to determine the electromyographic (EMG) characteristics of experimentally induced, non-functional activity in the jaw-closing muscles of awake, behaving rats and how the EMG characteristics differed from those found under normal conditions. In the same animals, chronic EMG recordings were made prior to and following the insertion of an occlusal cap, which induced non-functional activity. A characteristic EMG pattern was found only during non-functional activity. The durations and amplitudes of the EMG bursts during this activity were significantly different statistically from those found in the same animals under normal conditions.

Animals↗
PubMed1994

Evaluation of the reproducibility of rest activity of the anterior temporal and masseter muscles in asymptomatic and symptomatic temporomandibular subjects.

There is a general assumption that temporomandibular disorders and the pain and tenderness of mastication muscles may be caused by hyperactivity. Five asymptomatic men, five asymptomatic women, and five women with temporomandibular disorders participated in this study. Multiple examinations were performed to provide information concerning the reproducibility of the rest electromyographic signals. No significant differences between groups were noted. This study supports the contention that the mean rest activity in women with pain and dysfunction is less than or equal to that of sex-matched controls.

Adult↗
PubMed1996

Ultrasonographic assessment of the swelling of the human masseter muscle after static and dynamic activity.

Work-related fatigue, pain and disorders in skeletal muscles have been related to prolonged static and dynamic activity. Such contractions have been shown to impair blood flow and increase muscle thickness and fluid. In the present study the effect of static and dynamic activity was evaluated from changes in masseter thickness as a measure of oedema, simultaneously with assessment of perceived pain/discomfort and cardiovascular responses. As static activity, fourteen young healthy women bit at 15% maximal voluntary contraction on bite-force transducers in the molar regions until exhaustion or 20 min at maximum (median endurance time 7.1 min). For dynamic activity, the same individuals chewed gum unilaterally until exhaustion or 40 min at maximum (all endured 40 min) with a cycle time of 725 ms, an average load of 9.3% of maximal electromyographic activity (maxEMG) and a peak mean voltage of 54.3% of maxEMG. Muscle thickness was measured by ultrasonography at the mid-portion of the ipsilateral masseter. Immediately after exercise, muscle thickness was significantly increased, more after static (14.0%) than dynamic (8.6%), and returned to pre-exercise values after 20-min recovery. Visual analogue scales (VAS) revealed the concomitant occurrence of pain (static 11.9 VAS%; dynamic 5.9 VAS%), and discomfort (static 8.1 VAS%; dynamic 5.9 VAS%), and both sensations decreased to pre-exercise values after 20-min recovery. Systolic blood pressure increased significantly, more during static (12.5%) than dynamic activity (4.3%), whereas heart rate rose significantly only during dynamic exercise (13.3%). Hence, activity was associated with muscular swelling and pain, and, despite the relatively small size of the masticatory muscles, also with general cardiovascular responses.

Adult↗
PubMed1993

Simple reaction-time responses to mechanical and electrical stimuli in human masseter muscle.

The latencies of the simple reaction-time responses for opening and closing of the jaws in response to taps and pushes on teeth and lip shocks were measured in human adults. The reaction times were scored from both the integrated electromyographic (EMG) signal in individual trials, and from the cumulative sum (CUSUM) of the averaged EMG response to 50 stimuli. The mean reaction times for both closing and opening were about 80-90 ms for taps and electrical lip shocks, and about 140 ms for push, measured from the CUSUMs. The reaction times in individual trials were difficult to measure from the EMG signal because of the unsteady baseline. In contrast, the reaction times measured from the CUSUMs were clearly defined by the point at which the record began to move sharply above or below the baseline. However, because of the delays inherent in the CUSUM procedure, they were systematically longer than the means of the trial-by-trial measurements.

Adult↗
PubMed1984

The influence of clenching level on the post-stimulus EMG complex, including silent periods, of the masseter muscles in man.

Standardized mechanical taps were delivered on an upper central incisor, while the nine subjects investigated maintained constant clenching levels of 5, 10, 20, 40 and 60 per cent of their maximal EMG outputs. Using statistical criteria, a computer program enabled an objective determination of the interaction between the clenching level and the sequence of upward and downward going waves following the stimulus in full-wave rectified and superimposed EMG, called a post-stimulus EMG complex (PSEC). The morphology of the PSEC, including one or two silent periods, was subject-specific and reproducible over one year. The surfaces of the waves were greatly influenced by the clenching level. In general, their total surface decreased as a function of the clenching level. However, the individual waves decreased selectively. The results suggest that the sequence of waves results from overlapping of inhibitory and excitatory inputs. The inhibitory waves, constituting the silent periods, are largely cancelled by the excitatory reflexes of the PSEC.

Adult↗
PubMed1993

Masseter muscle fatigue during sustained clenching in subjects with complete dentures, implant-supported prostheses, and natural teeth.

A sustained submaximal (50%) clenching effort was performed in four patient groups to establish whether implant-supported prosthetic reconstructions influence myoelectrical signal parameters. The first group consisted of patients with natural teeth in both jaws. The other three groups consisted of patients who were edentulous in both jaws: one group had complete dentures; one had an overdenture in the mandible on two implants connected by a bar; and the third had an implant-supported fixed prosthesis in either the maxilla or the mandible. Surface electromyography indicated an increased myoelectrical output level that paralleled a higher bite force level for implant-supported reconstructions compared with complete dentures. Power spectrum analysis revealed a downward shift of the mean power frequency during sustained clenching in all groups except the implant-supported fixed prosthesis. The absence of a spectral shift in the latter group probably reflected a fear of biting too hard and fracturing the prosthesis.

Adult↗
PubMed1988

Bilateral post-stimulus electromyographic complexes in human masseter muscles after stimulation of periodontal mechanoreceptors of bi- and unilaterally-innervated teeth.

These complexes (PSECs) were studied in full-wave rectified and averaged EMG in 13 subjects, who jaw-clenched at a controlled level. The PSECs were elicited by mechanical and electrical stimulation of receptors or their afferents in the unilaterally- and bilaterally-innervated periodontium of the upper first premolars and an upper central incisor. To exclude any contribution from acoustic receptors, subjects were exposed to high-intensity noise during mechanical stimulation. Comparison of peak amplitude and area from PSEC waves in normalized EMG amplitude-time plots suggests extensive crossing of the midline by periodontal afferent information. The small variation in latency of the first inhibitory wave on the two sides suggests that there are no additional synapses in the crossed pathway. Latency differences and wave incidence on the two sides of the later inhibitory and excitatory periods varied markedly between subjects suggesting that influences from higher centres affect masseteric motoneurones. In five subjects stimulation of periodontal receptors around different teeth resulted in different PSEC wave sequences.

Adult↗
PubMed1988

Morphology of single mesencephalic trigeminal neurons innervating masseter muscle of the cat.

The morphology of functionally identified single axons of mesencephalic trigeminal neurons was studied in the cat by the method of intra-axonal injection of horseradish peroxidase (HRP). Each axon can be divided into united (U), peripheral (P) and central branches (C). The united axon (U) descends from its soma within the tract of the trigeminal mesencephalic nucleus to the dorsal aspect of the trigeminal motor nucleus (Vmo), where it splits into peripheral and descending central branches with a Y-shaped bifurcation. The peripheral axon (P) joins the motor root of the trigeminal nerve to exit the brainstem. The central axon (C) travels caudally within the juxtatrigeminal regions (or lateral reticular formation). All 3 branches issue axon collaterals that distribute terminal boutons within the dorsolateral subdivision of Vmo, supra- and intertrigeminal regions. Collaterals emanating from the central axon (C) except for its proximal segment travel ventrolaterally within the juxtatrigeminal regions, and send their terminal branches into the lateral boundaries adjacent to the spinal trigeminal nucleus. The trajectory of terminal branches distinguishes group Ia afferents from the possible group II afferents. The majority of terminal boutons are found to distribute in the supra- and intertrigeminal regions for group II afferent fibers and in the dorsolateral subdivision of Vmo for group Ia afferents.

Afferent Pathways↗
PubMed1995

Masseter muscle fatigue before and after rehabilitation with implant-supported prostheses.

To establish whether different implant-supported prosthetic reconstructions influence jaw muscle resistance to clenching efforts, sustained submaximal (50%) clenching was performed in two groups of patients who were edentulous in one or both jaws. One group consisted of patients who were rehabilitated by means of an overdenture on two to four implants connected by a bar; the other group consisted of patients who were rehabilitated with an implant-supported fixed prosthesis on four to seven implants in either the maxilla or the mandible. Results indicated that after rehabilitation with implant-supported fixed reconstructions, the myoelectric output level increased over time, which was parallel to a higher bite force level. For the other group, such a time-dependent change in electromyographic amplitude did not occur. On the other hand, power spectrum analysis revealed a significant downward shift of the mean power frequency during sustained clenching after rehabilitation with implant-supported overdentures but not with implant-supported fixed prostheses. The absence of a spectral shift in the latter group probably expressed a fear of biting too hard and fracturing the prosthesis.

Adult↗
PubMed1988

A method for standardization of silent period measurements in human masseter muscle.

The effect of bite force and stimulus intensity on the electrically induced SP has been studied. The results from the present study and earlier investigations suggest that the following guidelines should be used in future SP studies. (i) The electrical rather than mechanical way of stimulation should be preferred since the stimulus parameters and the receptors stimulated can easily be determined. (ii) The sensory perception threshold (T) of subjects should be used when studying and comparing the SP between individuals rather than the actual values of the electrical stimulation since the value of the sensory perception threshold varies from subject to subject. (iii) Rectified and averaged EMG records should be used rather than single raw traces since it is not possible to measure the duration of SPs from single traces. (iv) The subject should be asked to perform 25% of his/her MBF and the BF should be given as a feedback. (v) A stimulus intensity of about 6T should be used so that small changes in the BF would not affect the SPD. (vi) A jaw separation of about 10 mm should be selected in the subjects with normal overjet (2-3 mm), this being slightly thicker than the average isometric force transducer. The transducer can be brought to this thickness using acrylic resin. (vii) A head rest should be used to keep the head position constant (and hence constant jaw position with respect to the transducer) since the head position alone may change the reflexes elicited in the jaws region.

Adolescent↗
PubMed1994

The effect of pain from orthodontic arch wire adjustment on masseter muscle electromyographic activity.

Pain has been shown to have an effect on muscle activity even when it does not originate in the muscle itself or in the related joint. The effect of pain from arch wire adjustment on jaw muscle activity is unclear. This study systematically evaluated the effects of orthodontic arch wire adjustment pain on masseter electromyographic (EMG) activity and on the swallowing threshold. The EMG recordings were made on 22 subjects (ages 11 to 15) under three conditions: chewing five peanuts (10 seconds), watching TV chewing gum (15 minutes), and watching TV with no gum (15 minutes). An arch wire adjustment or placebo adjustment was then made. Subjects returned after 48 hours, and the EMG measurements were made under the same conditions. After 3 weeks, subjects received arch wire or placebo treatment in a crossover design with identical recording procedures. The EMG levels while chewing peanuts decreased in 18 of 22 subjects after treatment, compared with 9 of 22 subjects after the placebo. While watching TV with gum, the EMG levels of 20 of 22 subjects decreased after treatment, compared with 9 of 22 subjects after the placebo. The number of chewing strokes before swallowing increased significantly after treatment compared with after placebo. The results suggest that orthodontic pain on teeth tend to reduce muscle activity during function.

Adolescent↗
PubMed1998

[Experimental microsurgery of the facial nerve: end-to-end suture versus approximated ends wrapped with masseter muscle aponeurosis].

As an alternative to end-to-end facial nerve microsurgery, we propose anastomosis of the sectioned nerve ends and wrapping with ipsilateral masseter fascia. This intervention was performed on the right facial nerve of 20 Wistar rats and compared with classical end-to-end anatomosis performed on the left nerve of the same rats. At the end of the experiment, histological studies were made of each nerve removed "en bloc" with the ipsilateral lip orbicular muscle. Five micra-thick sections were stained using conventional and immunohistochemical methods. We analyzed truncal integrity, fibroblast proliferation, demyelination, lymphocyte proliferation, granulomatous reaction, and muscle degeneration in both types of anastomosis. The differences between the two types of anastomosis were statistically non-significant, and both interventions produced similar functional results. Small differences between the techniques might condition the use of one or the other in selected cases.

Anastomosis, Surgical↗
PubMed1989

The sufficiency of blood flow in human masseter muscle during endurance of biting in the intercuspal position and on a force transducer.

Blood flow changes caused by endurance of voluntary isometric muscle contraction and the sufficiency of flow during contraction were assessed by measuring 133Xe clearance. Aiming at 50% maximum voluntary contraction (MVC), 9 healthy persons sustained biting in the intercuspal position (ICP group) at an actual medium EMG activity level of 55% MVC, while receiving a visual feedback of the average-integrated EMG activity. Eleven persons sustained unilateral biting (UBF group) on a force transducer at 40% MVC, receiving feedback of the force output. The significantly lower % MVC for the UBF group was due in part to a decrease in the EMG activity during endurance, while force was constant. Blood flow changes over time were significant; however, the changes differed significantly between groups during endurance: the ICP group had a median reduction in blood flow to 0.4 of the initial resting value, and the UBF group had a 0.2-fold median increase. Following endurance, flow changes integrated over 3 minutes were about 43-fold the initial resting values of both groups. This similarity was probably a result of their equivalent effort. The endurance flow accounted for 1% of the total change for the ICP group and 5% for the UBF group. Overall, the proportion of the total flow that took place during endurance decreased logarithmically with greater level of contraction and masseter effort. Therefore, sufficiency of blood flow to maintain muscle fibre homeostasis is less when the rate of metabolic turnover is greater, thus contributing to an earlier onset of masseter fatigue, pain and exhaustion at high contraction levels.

Adult↗
PubMed1976

Reflex activity in the masseter muscle of young individuals. I. Experimental procedure - results.

The monosynaptic myotatic (jaw jerk) potential (MSP) evoked in the relaxed masseter by a tap on the chin and recorded electromyographically in this muscle (latency 6-3 ms, duration 5-9 ms) was similar in subjects with, or without TMJ clicking. The latency of the myotatic potential was significantly shorter (5.8 ms) when evoked during isometric contraction. The duration was 5-2 ms. A potential with similar characteristics as the MSP was evoked by TMJ clicking, as we believe by excitation of muscle spindles from tissue transmitted vibrations (latency 5-5 ms, duration 5-6 ms). The TMJ click evoked MSP could in the contracting massester be followed by silent periods (SPs) both of the early (latency about 10 ms) and the late type (latency about 50 ms). A tap on the chin during isometric contraction of the jaw elevators, was followed by an SP of the early type (latency 12-2 ms, duration 17-5 ms) and sometimes by an SP of the late type (latency 58 ms, duration 18 ms). The late SP occurred significantly more often in patients with TMJ-dysfunction. The period of lower activity following an MSP can be divided into two phases: a first phase with a complete electrical silence, denoted SP, and a second phase during which the activity is slowly increasing to reach the control level. This latter phase will be called "depressed activity" (DA) and is introduced as a new parameter. The SP with tooth tapping (latency 10-5 ms, duration 9-4 ms) was similar in groups with or without TMJ clicking. The superimposed MSP (SMSP) preceding the SP at tooth tapping is supposed to be a manifestation of the "load-compensation reflex".

Adult↗