Influence of experimental occlusal discrepancy on masticatory muscle activity during clenching

Electromyographic changes in masseter and sternocleidomastoid muscles can be applied to diagnose of temporomandibular disorders: An observational study

Background

The diagnosis of temporomandibular disorders (TMDs) is an important part of the functional cerebrospinal technique (FCST). In addition, surface electromyography (sEMG) is an important candidate for diagnosing TMD. In FCST, despite the importance of the cranio-cervical-mandibular system, few sEMG parameters consider TMDs. Thus, this study evaluated the possibility of TMD diagnosis by sEMG.

Methods

The study was conducted as an assessor-blinded cross-sectional study. Each of 35 participants were recruited for patient group and normal group separately based on the Diagnostic Criteria for TMD Symptoms Questionnaire (DC/TMD SQ). The sEMG was measured by attaching electrodes to sternocleidomastoid muscles (SCMM) and masseter muscles (MM) before and after wearing the temporomandibular joint balance appliance (TBA).

Results

The percentage overlapping coefficient (POC) value of the healthy control group was increased compared with the TMD group. Receiver operating characteristic (ROC) analysis revealed that the area under the curve (AUC) value of the SCMM was greater than that of the MM. POC values before and after the SCMM also revealed significant changes compared to the MM.

Conclusion

This study showed that the sEMG measurement of the SCMM is useful for TMD diagnosis in traditional Korean medicine.

The Influence of Dental Occlusion on Dynamic Balance and Muscular Tone

Excellent postural control is essential to improve the physical performance of athletes. Stability of the body during motor tasks depends on different physiological systems. The influence of dental occlusion on body balance has been widely investigated in the past few years. It has been suggested that this relationship is strengthened by disturbing environments for balance control (i.e., unstable platform, fatigue, development tasks.). Moreover, dental occlusion may influence the muscle tone of both masticatory and postural muscles, which are involved in the preservation of balance. Therefore, we attempted to determine whether (i) there are differences in dynamic balance assessed by the modified star excursion balance test between opposed dental occlusion conditions (dental contact: intercuspal position/no dental contact: cotton rolls mandibular position) and (ii) dental occlusion influences the biomechanical and viscoelastic properties of the masticatory and postural muscles assessed with MyotonPRO^®. Thirty physically active subjects were recruited for the study. The main findings were the following: (i) the Star Excursion Balance Test composite score was significantly higher for measurements made in cotton rolls mandibular position (p < 0.001) and also in subjects showing a correct occlusion (p = 0.04), and (ii) the biomechanic and viscolelastic properties of selected muscles showed different trend according to the presence of malocclusal traits. It is concluded that dental occlusion conditioned both dynamic stability and the biomechanic and viscoelastic properties of the analyzed muscles.

The electrical activity of the masticatory muscles in children with cleft lip and palate

BACKGROUND

Information regarding masticatory muscle function in children with cleft lip and palate (CLP) is limited. As a consequence, research on masticatory muscle activity in cleft subjects is needed.

AIM

To assess masticatory muscle activity in children surgically treated for CLP as well as identify the possible factors associated with this activity.

DESIGN

The sample comprised 82 children with mixed dentition and Class I occlusions (25 children with unilateral CLP and 57 subjects with no cleft abnormalities). A DAB-Bluetooth Instrument (Zebris Medical GmbH, Germany) was used to take electromyographical (EMG) recordings of the temporal and masseter muscles both in the mandibular rest position and during maximum voluntary contraction (MVC).

RESULTS

Patients with clefts showed a significant increase in temporal muscle activity at rest compared with the controls. The presence of clefts and unilateral posterior crossbites are factors strongly associated with increased temporal muscle EMG potentials during rest position.

CONCLUSIONS

Children with clefts have altered temporal muscle function. The presence of posterior crossbites affects the temporal muscle activity in cleft subjects. Early diagnosis and orthodontic treatment of malocclusions are necessary to achieve functional improvement in these patients.

Development of electromyographic indicators for the diagnosis of temporomandibular disorders: a protocol for an assessor-blinded cross-sectional study

Background

Noninvasive and easy-to-use surface electromyography (EMG) is frequently utilized for the diagnosis of temporomandibular disorders (TMDs). However, few EMG parameters that consider TMDs in addition to the cranio-cervical-mandibular system have been regarded as important in traditional Korean medicine.

Methods

This clinical trial will be conducted as an assessor-blinded cross-sectional study. The participants will be classified based on the Diagnostic Criteria for TMDs Symptom Questionnaire (DC/TMD SQ) and 30 TMD patients and 30 healthy controls will be enrolled. The primary outcome will be the percentage overlapping coefficient (POC; %) in the masseter and sternocleidomastoid muscles between the patient group and healthy control group in clenching and cervical side flexion. The secondary outcomes include the score from temporomandibular joint-related questionnaires, the difference in the absolute values of EMG for the healthy group and TMD group before/after wearing intraoral appliances, and the change in the location of the temporomandibular joint as determined by X-ray imaging and 3D face photography.

Discussion

This study will provide information about the objective diagnostic method for TMD using surface EMG and will verify the effectiveness of surface EMG in diagnosing TMD. Furthermore, the method or device for diagnosis TMD will improve the expansion of treatment area to TMD by accumulating evidence for the efficacy of TKM treatment.

Muscular Activity Disorders in Relation to Intentional Occlusal Interferences

The electromyographic activity (EMG) of the anterior temporal (AT), masseter (M), trapezius (T) muscles and anterior aspect of the digastric (D) was measured in 50 subjects, during six seconds of maximum contraction, bilaterally with and without unilateral premature contacts and individually for each tooth. Special occlusal interferences were designed to assess muscular activity. Muscular activity was measured simultaneously by placing premature contacts on each tooth, under T-Scan monitoring. Premature contacts reduced EMG activity during maximum contraction of the AT, D and M muscles, the highest disruption is in the AT muscle, at the level of upper right 2nd molar, with a 56% reduction in activity. Conversely, there was an increase of activity of the T muscle in all teeth when placing artificial occlusal premature contacts, with the highest difference in the upper right 1st bicuspid. Therefore, occlusal interferences can cause neuromuscular disruptions, thus inducing important muscular discrepancy. Both the EMG and T-Scan monitoring can be considered suitable methods to use in daily dental practice to identify premature contacts and to measure EMG activity.

Stable tooth contacts in intercuspal occlusion makes for utilities of the jaw elevators during maximal voluntary clenching

Data are inconsistent concerning whether the level of the surface electromyographic (SEMG) activity of jaw-closing muscles increases when biting forces elevated during maximal voluntary clenching (MVC). In this study, T-Scan III system and BioEMG III system were used to record bite force, occlusal contacts and SEMG activity of the anterior temporalis (TA) and of the masseter muscles (MM) simultaneously. Recordings were obtained from 16 healthy young adult males during different conditions: (i) a fast MVC from resting position to intercuspal position (ICP); (ii) mandibular movements from ICP to protrusive or lateral edge-to-edge positions with teeth in contact with biting; (iii) a fast MVC in protrusive and lateral edge-to-edge positions. A higher level of SEMG activity was associated with a higher bite force during occluding movements (P < 0.05). However, during fast MVC from rest to ICP, the largest number of occlusal contacts was achieved and distributed more symmetrically, the highest level of biting force was obtained, but the SEMG activity of the jaw elevator muscles was reduced compared with its maximum level (P < 0.05). This phenomenon was not observed during the fast MVC in protrusive or lateral edge-to-edge positions. The present results that a lower SEMG activity was associated with the largest number of occlusal contacts and the highest level of bite force during centric MVC demonstrated a complex integration of jaw-closing muscles when a stable occlusion is present.

Longitudinal evaluation of sEMG of masticatory muscles and kinematics of mandible changes in children treated for unilateral cross-bite

The aim of this study was to evaluate masticatory muscle activity and kinematics of mandible changes in children with unilateral posterior cross-bite (UPXB) after orthodontic treatment, and one year after retention. Twenty-five children with UPXB and functional mandibular shift were evaluated before treatment (mean age 12.5years), after treatment (mean age 14.9years), and one year after retention (mean age 16.8years). The same data were collected in a control group of thirty age-matched normocclusive children. Simultaneous bilateral surface electromyographic (sEMG) activity from anterior temporalis (AT), posterior temporalis (PT), masseter (MA), and supra-hyoid (SH) muscle areas were evaluated at rest, during swallowing, mastication and clenching. Kinematic records of rest position, mandibular lateral shift, swallowing and mastication were analyzed. Results showed a lateral shift of the mandible present at rest. During swallowing, sEMG activity of SH predominated before and post-treatment and retention. High frequency of immature swallowing was maintained post-treatment and retention. During mastication, MA activity increased significantly and its asymmetry was corrected post-treatment. During clenching, cross-bite side AT and MA activity increased significantly posttreatment and remained stable after retention, and MA/AT ratio reversed. These findings reinforce the advantages of treating children with UPXB and functional shift as early as possible.

Behavior analysis of electromyographic activity of the masseter muscle in sleep bruxers

The effects of occlusal splint on the electric activity of masseter were studied in 15 women who presented sleep bruxism using surface electromyography. Sleep bruxism was defined by its clinical characteristics. The signal acquisition was done during mandible occlusion without clenching and maximum voluntary contraction in two situations. The first was after a workday without using the occlusal splint; and the second, after a sleeping night using occlusal splints. Evaluating masseter muscles during mandible occlusion without clenching, it could be observed that lower values were noticed after splint wearing in both sides. The same results were verified in maximum voluntary contraction (MVC). These results confirmed that the use of occlusal splints reduced the electromyographic activity of the right and left masseters, showing its myorelaxing effect.

An electromyographic evaluation of bilateral symmetry of masticatory, neck and trunk muscles activity in patients wearing a positioner

This study was designed to investigate the attitude of a positioner (Finition) or an Hawley's retention appliance to create a symmetric function of the masticatory, neck and trunk muscles during the orthodontic retention phase. Sixteen patients (18.5 +/- 2.2 years) were included in the sample. All the patients received an orthodontic therapy for the treatment of an Angle's class I malocclusion and skeletal class I, for a period of 2 years. After removal of orthodontic brackets, eight patients wore a teeth positioner (group I) as retention appliance and eight subjects wore an Hawley's appliance as upper retention (group II). Surface electromyographic (sEMG) activity was recorded from the bilateral anterior temporal, posterior temporal, masseter, sternocleidomastoid (SCM), upper and lower trapezius and cervical muscles at mandibular rest position and during maximal voluntary clenching (MVC) at T0, i.e. soon after the removal of orthodontic brackets and at T1, i.e. after 3 months of retention treatment. No significant difference was observed between the two groups at T0. At T1, at mandibular rest position, the group I showed a significantly lower sEMG activity of anterior temporal and SCM muscles compared with the group II. During MVC, at T1, the group I showed a significantly lower sEMG activity of the SCM and posterior cervicals, compared with the group II. The positioner seems to show a relevant effect on the sEMG activity of masticatory, neck and trunk muscles.

Influence of altered occlusal guidance on masticatory muscle activity during clenching

This study investigated the influence of experimentally altered occlusal guidance on masticatory muscle activity. Twenty healthy human subjects (15 males and five females with an average age of 26.5 years) volunteered to participate in this study. Metallic occlusal overlays were fabricated for the lower working side canine and overlaid on the second molar and the non-working side second molar to simulate a canine-protected occlusion, group function occlusion and bilateral balanced occlusion. Electromyography (EMG) activities in the bilateral masseter, anterior and posterior temporalis were recorded during maximal clenching. The experimental occlusal pattern revealed to have statistically significant effects on EMG activity. As the most characteristic change, EMG activity in the anterior temporalis significantly increased in the simulated group function occlusion and the simulated bilateral balanced occlusion compared with the simulated cuspid protected occlusion. The increased teeth contacts to the posterior region altered the unilateral pattern of the anterior temporalis activity to the bilateral pattern, while that of masseter activity remained unchanged.

A working-side change to lateral tooth guidance increases lateral pterygoid muscle activity

The inferior head of lateral pterygoid (IHLP) is thought to play a critical role in the generation and control of lateral jaw movements.

AIM

The aim was to test the hypothesis that a change to the lateral tooth guidance (working-side occlusal alteration, OA) results in a significant change in the electromyographic (EMG) activity of the IHLP during standardised lateral jaw movements (laterotrusion) tracked by a jaw-tracking system.

METHODS

Ten trials of right laterotrusion were repeated under: control 1 (before occlusal alteration), OA (after occlusal alteration placement), and control 2 (after occlusal alteration removal) conditions in 14 subjects while recording left IHLP, bilateral anterior and posterior temporalis, masseter and submandibular muscles.

RESULTS

IHLP activity was significantly (p<0.05) increased with the occlusal alteration during the outgoing (movement from intercuspal position to approximately 5mm right) and return phases of laterotrusion. The other muscles demonstrated no change or a significant decrease in activity.

CONCLUSIONS

These findings suggest that a change to the occlusion on the working-side in the form of a steeper guidance necessitates an increase in IHLP activity to move the mandible down the steeper guidance. It must be emphasised that these data cannot be used as justification for occlusal therapy.

Subjective reactions to intervention with artificial interferences in subjects with and without a history of temporomandibular disorders

In a previous double-blind randomized controlled study, subjects with a history of temporomandibular disorder (TMD) reacted to artificial interference with more signs of TMD than did subjects with no TMD history. In the present study, we analysed the subjective reactions of these individuals on several symptom scales. Every day during the 2-week follow-up period, the subjects rated the intensity of their symptoms on 9 VAS scales (occlusal discomfort, chewing difficulties, tender teeth, fatigue in the jaws, headache, facial pain, opening difficulty, bruxism, ear symptoms). Subjects with a history of TMD and true interferences reported stronger symptoms than subjects with no TMD history and placebo interferences. The most prominent symptoms were occlusal discomfort and chewing difficulties. The difference in outcome between the groups with and without a TMD history suggests that there are individual differences in vulnerability to occlusal interferences. It is likely that the etiological role of occlusal interferences in TMD has not been correctly addressed in previous studies on artificial interferences.

The influence of altered occlusal guidance on condylar displacement during submaximal clenching

As cited in literatures, canine protected occlusion has a potential to reduce clenching induced temporomandibular joint loadings. However, these previous studies did not perform a control of the clenching level which differed with the depending occlusal conditions. This result may be due largely to an associated reduced jaw closing muscle activity. The present study has investigated clenching induced condylar displacements with controlled clenching level. Twenty healthy human subjects (15 males and five females with an average age of 26.5 years) volunteered to participate in this study. Metallic occlusal overlays were fabricated for the lower working side canine and overlaid to the second molar and the non-working side second molar in order to simulate a canine protected occlusion, group function occlusion and bilateral balanced occlusion. Electromyographic (EMG) activity from the bilateral masseter, anterior temporalis, and posterior temporalis was recorded. These signals were rectified, summarized, and presented to each subject using an oscilloscope screen. Using this visual feedback, subjects were asked to perform clenching tasks at a 50% level of maximal voluntary contraction exerted with simulated group function occlusion and three-dimensional condylar displacements were recorded. An experimental occlusal pattern that shows statistically significant affects on condylar displacements (anova: P<0.001) was found. When compared with the simulated canine protected occlusion, the simulated group function occlusion caused smaller working side condylar displacement and the simulated bilateral balanced occlusion caused significantly smaller non-working side and working side condylar displacements. These results suggest that the increased working side tooth contacts have a potential to reduce working side joint loadings, and a balancing side contact has a potential to reduce non-working side joint loadings, under the laboratory condition where the clenching level is controlled.

Activity of masticatory muscles in subjects with different orofacial pain conditions

The existence of a pathophysiological link between tonic muscle activity and chronic muscle pain is still being debated. The purpose of this retrospective, controlled study was to evaluate the electromyographic (EMG) activity of masticatory muscles in subjects with different orofacial pain conditions. The temporal and masseter EMG activity at rest and the masseteric reflex were recorded in two groups of patients with either myofascial pain (n=33) or neuropathic pain (n=20), one group of non-pain patients with disc derangement disorders (n=27) and one control group of healthy, asymptomatic subjects (n=32). The EMG activities of both muscles at rest were significantly higher in the pain patient groups compared to the asymptomatic control group. There was no significant difference between the disc derangement disorder group and the control group. The masseteric reflex amplitude was reduced in all patient groups when compared with the control group. In pain patient groups, the increased EMG activity at rest and the reduction of the masseteric reflex amplitude were equally distributed in the pain and non-pain sides. In addition, subjects presenting with bilateral pain showed higher EMG activity at rest than those with unilateral pain. These results suggested that the modulation of muscle activity was not the direct consequence of a peripheral nociceptive mechanism and seemed to indicate that a central mechanism was at work. The contrast between the increased EMG activity at rest and the reduction of the masseteric reflex amplitude may reflect modulations of motoneurones that differed in tonic versus phasic conditions in chronic pain patients.

Effect of artificial occlusal interferences depends on previous experience of temporomandibular disorders

Studies on artificial interferences in subjects with no temporomandibular (TMD) history have shown adaptation to the interference within a fairly short period of time. The role of occlusal factors in the etiology of TMD has therefore been questioned. The results might have been different, however, if subjects with a prior TMD history had been included in the study groups. To test this assumption in a randomized double-blind clinical set-up, we included healthy women without (n = 26) as well as with (n = 21) an earlier TMD history. Both groups were randomly divided into true and placebo interference groups. Artificial interferences were introduced in the true interference groups and simulated in the placebo groups. The subjects were followed for 2 weeks, after which the interferences were removed. The subjects without a TMD history showed fairly good adaptation to the interferences, but the subjects with a TMD history and true interferences showed a significant increase in clinical signs compared to the other groups. We suggest that the etiological role of occlusal interferences in TMD may not have been correctly addressed in previous studies with artificial interferences and allow no conclusions as regards TMD etiology.

Sixty-eight years of experimental occlusal interference studies: what have we learned?

STATEMENT OF PROBLEM

Understanding is needed regarding the effect that occlusal interferences have on the teeth, periodontium, and especially on jaw function.

PURPOSE

This article summarizes research in which experimental occlusal interferences have been placed on the teeth of animals and human volunteers.

MATERIAL AND METHODS

Data from 18 human and 10 animals studies were reviewed. Experimental occlusal interferences were grouped into those that alter intercuspal position and those contacting on lateral jaw movement only. The outcome of these interferences were analyzed according to their local pulpal-periodontal, jaw function, or bruxism effects.

RESULTS

Experimental occlusal interferences in maximum intercuspation had a deleterious effect on periodontal and pulpal tissues of the affected tooth; sometimes this produces a disruption of smooth jaw function and occasionally jaw muscle pain and clicking. Experimental occlusal interferences that contact only in a lateral jaw movement are infrequently harmful to jaw function. Furthermore, no reliable evidence demonstrates that occlusal interferences can cause nocturnal bruxism, or stop it.

CONCLUSION

Transient local tooth pain, loosening of the tooth, a slight change in postural muscle tension levels, chewing stroke patterns, and sometimes a clicking joint can be induced by an experimental occlusal interference. Because such findings are present in relatively asymptomatic patients, these data do not prove that occlusal interferences are causally related to a chronic jaw muscle pain or temporomandibular joint dysfunction problems.

The effects of a single intercuspal interference on electromyographic characteristics of human masticatory muscles during maximal voluntary teeth clenching

In 13 healthy subjects (eight men and five women, mean age, 22 years), an aluminum intercuspal interference (height, 0.25 mm) was placed on the maxillary right first premolar to study its effect on the contractile symmetry of the right and left masseter and anterior temporalis muscles when measured through a Percentage Overlapping Coefficient (POC), derived from surface electromyographic recordings of maximum voluntary teeth clenching. Additionally, and to estimate the potential of the experimental intercuspal interference to induce lateral displacement of the mandible, a Torque Coefficient (TC) was derived from surface electromyographic recordings. The conclusion was that the experimental occlusal interference gave rise to asymmetric contractile activity in the studied mandibular elevator muscles as well as a potential to displace the mandible in a lateral direction.

The validity and utility of disease detection methods and of occlusal therapy for temporomandibular disorders

Our evaluation of the clinical usefulness or devices for the diagnosis or treatment of temporomandibular disorders (TMD) led to the conclusion that the only current gold standard for TMD is a global clinical examination, because none of the instruments can be said to provide more than ancillary documentation and none have proven diagnostic validity or utility. Regarding the therapeutic efficacy of occlusal adjustment, we could find no comparative studies that test the efficacy of occlusal adjustment in preventing TMD. The studies we reviewed on the relationship of occlusion to TMD are not convincing, powerful, or practical enough to make any recommendations about a causal association.