Effect of bite force on the masseteric electromyographic silent period in man

The duration of the masseteric EMG silent period as induced by tapping on the chin was measured at different levels of sustained bite force. Under both open bite and normal occlusion, the duration of the silent period was inversely related to the magnitude of the bite force. For bite force of the same magnitude, the value of the silent period remained relatively constant for the same subject in different trials (SEM ? 1 per cent), whereas the absolute values of the silent periods ranged far and wide for different individuals even under similar experimental conditions.     

The effect of acrylic bite plane splints and their vertical dimension on jaw muscle silent period in healthy young adults

A significant question relative to treatment and disappearance of symptoms is raising the bite in combination with a maxillary bite plane splint in patients with TMJ muscle dysfunction. The objective of this research was to investigate the effect, if any, occlusal bite plane splints have on the latency and duration of the mention tap silent period and particularly whether the degree to which the bite is raised is of significance. Recordings were made in healthy young adults from both anterior temporal and masseteric muscles while subjects were clenching at their 70% maximum clenching effort. Placement of a splint significantly (P less than 0.05) prolonged the silent period duration (SPD). However, mean SPD values taken at two different vertical raised bites did not differ significantly (P greater than 0.05). The anterior temporal muscle SPD was less sensitive to a smaller change of vertical dimension than the masseteric SPD. Silent period latencies remained unchanged in all experimental conditions.     

The effect of voluntary activity on the masseteric silent period duration

This study examined both TMJ and normal groups for any changes in the masseteric silent period with variation of the subjects' occlusal force. An analog meter was used to give each subject feedback on how hard the teeth were clenched together. Five silent periods were elicited at each of the four levels of occlusal force from 40% to 100% of maximum force.Results showed a small decrease in silent period duration for both groups when occlusal force was increased.     

Correlations of electromyographic silent period duration and the Helkimo dysfunction index.

Fifty-eight patients seen for consultation concerning mandibular dysfunction symptoms were examined utilizing the Helkimo index of dysfunction and electromyographic silent period recordings from masticatory muscles. The data collected were analyzed for correlations between the two parameters. Several significant correlations were noted between certain variables of the dysfunction index and the duration of the silent period. The mean duration of the silent period increased with increasing dysfunction index value. However, the clinical significance of this correlation is not established as long as we do not know the validity of neither the dysfunction index nor the the EMG silent period duration.     

The silent period in the masseter muscle of patients with TMJ dysfunction.

The silent period (SP) following a jaw jerk elicited during sustained contraction in the masseter muscles has been studied in two groups of subjects, one with and one without, acute and distinct symptoms of TMJ dysfunction. The subjects with acute TMJ dysfunction symptoms showed significantly shorter latency and longer duration of the silent period and the period of their depressed activity (DA) was also significantly longer than in the group without TMJ dysfunction. The duration of the SP of both muscles was symmetrical in about 60% of subjects in each group. This study validates that the duration of the silent period may be a useful diagnostic tool of clinical interest.     

The silent period in the masseter and the anterior temporalis muscles in adult patients with mild or moderate mandibular dysfunction symptoms

The electromyographical silent period in the masseter and the anterior temporalis muscles during tooth tapping and jaw jerk were studied in patients with fairly mild temporomandibular joint dysfunction symptoms. The length of the silent periods in the patient group did not differ generally from that in a control group. During tooth tapping, however, patients with distinct muscular disorders had shorter silent period duration (7.7 ms) than patients with other symptoms or when compared with control subjects (10.5 and 11.3 ms, respectively). The duration returned to normal after correction of the muscular disorders. This finding suggests that the duration of the silent period is affected by the muscle condition. Patients with obvious muscular disorders of mild to moderate magnitude, thus, may show a shorter silent period duration during tooth tapping.     

The silent period in the masseter and anterior temporalis muscles in young adult subjects unaware of mandibular dysfunction symptoms

In fourteen individuals unaware of mandibular dysfunction symptoms, latency and duration of the silent period in the masseter and anterior temporalis muscles at tooth tapping and jaw jerk were reasonably reproducible after 5 weeks and 5 months. Although the subjects felt no discomfort in the stomatognathic system, in some of them mild to moderate muscle tenderness, TMJ sound and occlusal disharmony were found at clinical examination. The relationship between these symptoms and the silent period was analysed. Muscle tenderness was the only factor to affect the silent period. The subjects with muscle soreness had a shorter duration of the silent period than the subjects without such symptoms.     

Variation in the masseteric silent period in older dentate humans and in denture wearers

The masseteric silent period was elicited by chin taps at 40% clenching in the masseter muscle of the preferred chewing side in 22 younger dentate individuals, in 22 older dentate individuals, in 22 older experienced denture wearers and in 7 older inexperienced denture wearers. One simple and three combined types of silent period (combination of early and late phases of depression) were recorded in all groups. An early silent period was always elicited, the only exception being in some inexperienced denture wearers. Both the age and the extent of rehabilitation with dentures in the trained denture wearers affected reflex latencies (p < 0.05), while the variation in duration was not significant (p>0.05). The duration of the silent period was, however, affected by the type of silent period, thus by the measuring technique (p < 0.05). Increased variation was observed in the inexperienced denture wearers, who were in a period of adaptation.     

A comparison of the masseteric silent period in temporomandibular joint dysfunction and normal human subjects by surface electromyography and single motor-unit recordings

Single electric stimuli were delivered to the lower lip and the reflex effects were monitored in the ipsilateral masseter. Two strengths of stimulus were delivered at two levels of background excitation (defined in terms of the firing frequency of a single motor unit). Although the threshold stimulus intensity required to produce a silent period in the single motor units was the same for the patients with temporomandibular joint dysfunction and normal subjects, there were qualitative differences in the pattern of reflex responses between the two groups. Of the two phases of inhibition elicited by the stimulus, the short-latency inhibitory period was the more prominent and more resistant to changes in the background excitation levels in the dysfunction group. In normal subjects, however this was true of the long-latency inhibition. This difference may be due to the changes in the inputs to one or more of the interneurones linking the afferent limb of the reflex to the masseteric motoneurones.     

Jaw muscle silent periods before and after rapid palatal expansion.

1. The electromyographic silent period was observed in jaw-closing muscles during a maximal clench following a tap to the mandibular symphysis in eight subjects before and after rapid palatal expansion. 2. No differences in mean silent period duration were observed among the three jaw-closing muscles examined. 3. A large (r = 0.96) and statistically significant (p less than 0.01) correlation coefficient between two sets of silent period durations at one session indicates that these measurements are repeatable and reliable. 4. The mean silent period duration for the eight patients with malocclusions was 33.5 msec. prior to rapid palatal expansion and 51.2 msec. after the completion of palatal expansion. The difference was statistically significant (p less than 0.01) and represents a 61 percent increase. 5. Patients with symptoms of TMJ dysfunction are not the only group showing a prolonged silent period duration.     

The influence of stimulus type and stimulus strength on the silent period in human masticatory muscles

The silent period in the jaw-closing muscles of nine healthy subjects was investigated. The stimulus types used were the open–close–clench movement (OCC), the mechanical chin tap and electrical skin stimulation. Irrespective of the jaw-closing speed for the OCC movements only the unmeasurable and single type silent periods were observed. Increasing the chin tap strength resulted in a decreasing percentage of single type silent periods and an increasing number of depressed, double and merged silent periods. The duration of the short and combined silent period was shorter for the OCC movements than for the chin taps. For the chin taps an increasing stimulus strength resulted in longer silent periods. Only the transition from hard to painful chin tap showed a slight, but significant decrease in short silent period duration. The beginning of the late inhibitory period, which could sometimes be evoked by electrical skin stimulation, coincided with the beginning of the second inhibitory phase of the chin-tap evoked double silent period. The long silent period as shown by one of the subjects cast doubt on the validity of the relationship between silent period duration and TMJ dysfunction.     

An exploratory study on increases in masseteric muscle activity induced by caffeine

In a crossover double blind experimental design, the nocturnal masseteric activity of 14 selected volunteers was evaluated by means of a portable electromyograph recording unit. The recordings lasted for a period of 16 days following ingestion of caffeine or placebo for five specific days each. There were no significant differences between caffeine or placebo on masseteric activity associated with bruxism. But when the two periods were compared, there was a tendency towards reduction of masseteric area activity and increase of stress levels in the second period of ingestion.     

The variability of EMG silent periods in TMJ patients

The variability of the EMG silent period in jaw closing muscles of TMJ dysfunction patients was examined. Considerable within-subject variability was found in the duration of the silent period. This variability increased with symptom severity. The authors recommend that multiple measurements be averaged to obtain a more accurate estimate of the silent period duration.     

Influence of auriculotemporal nerve anaesthesia on the masseteric silent period

Silent periods were evoked from the masseter muscles bilaterally in response to chin taps during a clench. Injection of 0.75 ml of 3% Mepivicaine posteromedial to each condyle led to a distribution of skin anaesthesia consistent with the distribution of the auriculotemporal nerve. Silent periods were evoked prior to and during anaesthesia in ten subjects. The silent period latencies (mean +/- standard deviation) prior to anaesthesia were 12.5 +/- 1.8 ms and 11.9 +/- 2.5 ms in the right and left masseters. During anaesthesia the latency decreased by 0.3 +/- 1.3 ms in the right masseter and by 0.3 +/- 2.1 ms on the left masseter. Neither change was statistically significant (P greater than 0.05). The silent period durations prior to anaesthesia were 20.3 +/- 4.0 ms and +/- 22.8 +/- 7.1 ms in the right and left masseters. During anaesthesia, these decreased by 2.74 +/- 5.8 ms on the right and 2.15 +/- 4.4 ms on the left. These decreases were not statistically significant (P greater than 0.05). These results failed to demonstrate an influence of the predominant nerve supply of the TMJ on either the latency or the duration of the masseteric silent period.     

Electromyographic silent periods and jaw motion parameters: quantitative measures of temporomandibular joint dysfunction.

The purpose of this research was to compare, in the subjects, the duration of the EMG silent period with jaw motion error. The results indicate that both jaw motion error and silent period duration are large in patients with TMJ-muscle-pain dysfunction, both are small in normal subjects, and both are small in successfully treated patients. There is a statistically significant correlation (r=0.91; P less than 0.01) between the two diagnostic parameters of TMJ-muscle-pain dysfunction.     

Electromyographic screening of myogenous and arthrogenous TMJ dysfunction patients

Sixty patients, clinically examined for TMJ dysfunction, were also electromyographically screened. The TMJ dysfunction pain in forty patients was evaluated to be mainly of a myogenous origin and in fourteen patients of a mainly arthrogenous origin. Due to lack of findings in the clinical examination six patients were not to be classified into either of the two groups. They were excluded from the EMG study. For the EMG examination the patients were asked to clench for 30 s in the intercuspal position at 50% of the maximum EMG activity of the masseter muscles. Surface electromyograms of the right and the left masseter and anterior part of the temporalis muscles were monitored. The amplitude of the EMG signal, the duration of the silent period and the changes in the frequency composition of the signal during the 30 s contraction were analysed. Statistically significant differences between the two patient groups were found in EMG amplitude and in silent period duration. However, the difference in silent period duration was due to the dependency of the silent period on the activation level of the muscle. No statistically significant difference in silent period was found when this dependency was corrected for in the data. The EMG parameters related to muscular fatigue phenomena did not show any difference between the two groups. The difference in EMG amplitude and consequently the difference in silent period duration support the clinically made distinction into mainly a myogenous or mainly an arthrogenous origin of TMJ dysfunction pain.     

The effect of bite force on the duration and latency of the menton tap silent period

The purpose of this research was to investigate the effect of bite force changes on the duration and latency of the menton tap silent period and particularly whether a decrease in bite force can increase the duration of the silent period to the extent which may be found in dysfunctional patients. The menton tap silent period was recorded from both anterior temporal and masseter muscles while the subject was clenching at different force levels. A bilaterally stable force transducer was used to monitor the clenching force. The results indicated no statistically significant differences in the mean durations and latencies of silent periods at different clenching forces. They suggest that duration and latency are not related to the degree of clenching force.     

The measurement of masseteric silent periods after experimental tooth grinding

Masseteric silent periods were recorded in normal subjects who performed experimental bruxism. All subjects showed a significant increase in silent period duration immediately following and 3 h after a session of experimental bruxism. The silent period had returned to presessional levels by 3 weeks.     

The effect of the bite plane splint on the electromyographic silent period duration

An electromyographic study of the masseter and anterior part of the temporalis muscles was performed on ten patients presenting temporomandibular joint dysfunction symptoms. The EMG silent periods (SP) produced in the open-close-clench cycle and jaw-jerk reflex were compared for duration before and after treatment with an occlusal bite splint. Following use of the splint, there was a shortening of SP indicating the possible use of the duration of SP as a diagnostic measurement, and also as an indication of treatment effectiveness.     

Three year follow-up TMJ patients: success rates and silent periods

A telephone survey to assess treatment success was conducted 2-3 years after treatment of patients suffering from TMJ syndrome. Pre-treatment silent period durations were compared among groups of patients determined by their response to the telephone survey. The short-term (immediately post-treatment) improvement rate was 81%. Some 35% of patients were completely cured. There was no statistically significant difference in mean silent period duration among the groups of patients that achieved complete, partial or no relief of symptoms. The long-term (2-3 years after treatment) persistence of improvement rate was 72%. There was also no statistical difference in the mean silent period duration between those patients who had experienced persistence of success and those who reported either no relief or relapse of symptoms.