Evidence of an influence of asymmetrical occlusal interferences on the activity of the sternocleidomastoid muscle

The Effect of Asymmetrical Occlusion on Surface Electromyographic Activity in Subjects with a Chewing Side Preference: A Preliminary Study

The relationship between asymmetrical occlusion and surface electromyographic activity (sEMG) in people with different chewing preferences is not clear. In this study, the 5 s sEMG changes in the masseter muscle (MM), sternocleidomastoid (SCM), lateral (LGA), and medial (MGA) gastrocnemius muscles were recorded in controls, and subjects with chewing side preference (CSP) during clench with bilateral (BCR), left (LCR), and right (RCR) posterior teeth placement of cotton rolls. The images of the middle 3 s were selected and expressed as the root mean square (unit: μV/s). The EMG waves of bilateral muscles were compared by computing the percentage overlapping coefficient (POC). Only the POCMM of the CSP showed gender differences at BCR and RCR. Between the control group and the CSP group, there were significant differences in the POCMM and the POCLGA at BCR. In addition, there was a significant difference in POCMM and POCSCM between the two populations in different occlusal positions. The change in the POCSCM correlated with the change in the POCMM (r = 0.415, p = 0.018). The experiment-induced asymmetrical occlusion showed that the altered symmetry of the MM correlated with the altered symmetry of the SCM. Long-term asymmetrical occlusion (i.e., CSP) not only affects MM but also has potential effects on other superficial muscles (e.g., LGA).

Relationship between cervical angle and temporomandibular disorders in young and middle-aged population

OBJECTIVE

To verify temporomandibular disorders (TMDs) and cervical angles in a young and middle-aged population.

METHODS

Ninety participants were included, 45 of whom had TMDs. The participants were diagnosed according to the Research Diagnostic Criteria for TMDs. Lateral cervical radiographs were taken, and relevant cervical angles were measured. The general characteristics of the TMD group and control group were analyzed using chi-square analysis, and the relationship between cervical angles and TMDs was evaluated using the unpaired t-test.

RESULTS

The decrease in C2-C7 Cobb and increase in the posterior occipitocervical angle (POCA) were associated with the incidence of TMDs (p < 0.0001).

CONCLUSION

This study revealed that the cervical angle was related to TMDs. People with a long-time habit of head bending posture had a decrease in C2-C7 Cobb and an increase in the POCA. This group of people was more likely to develop TMDs.

The effect of a controlled mandible position mouthguard on upper body strength and power in trained rugby athletes - A randomized within subject study

BACKGROUND

It is widely accepted that mouthguards are effective for injury protection in sports. However, findings on the effects of mouthguards in strength and power production remains controversial. Therefore, the aim of this study was to determine whether controlled-mandible position mouthguards influence strength and power production in well trained athletes.

METHODS

Twenty-two male amateur rugby players (25 ± 3.84 yrs; 1.92 ± 0.07 m; 93.91 ± 11.99 kg) volunteered for this study. Every participant performed an 1RM bench press test (113.20 ± 16.83 kg) to determine his maximal strength. In a randomized order, a ballistic bench press using 40% of the obtained 1RM (44.93 ± 6.76 Kg) was performed in a guided bar attached to a linear position transducer (LPT) for the following conditions: a) no mouthguard (CON); b) controlled mouthguard (MCM - jaw in centric relation); c) non-controlled mouthguard (NCM) and d) occlusal splint (OS). Vertical dimension of occlusion was also assessed for each of the testing conditions.

RESULTS

Athletes using a controlled mouthguard demonstrate a significant (p < 0.05) higher peak acceleration and peak force than those using no mouthguard. Additionally, when analysing the results of vertical dimension of occlusion, a significant difference (p < 0.05) was observed between controlled mouthguard and the other tested conditions.

CONCLUSION

Controlled mouthguards enhance peak force and peak acceleration in the ballistic bench press exercise without negatively affecting any other measure assessed in this study. We speculate that this is possibly due to an increased stability of temporomandibular joint.

Efficacy of different combinations of physiotherapy techniques compared to exercise and patient education in temporomandibular disorders: A randomized controlled study

OBJECTIVE

This study aims to investigate the efficacy of different types of physiotherapy approaches in individuals with cervical myofascial painful temporomandibular disorders (TMDs).

METHODS

Seventy-five participants with myofascial pain of jaw muscles and cervical myofascial pain were randomized into three groups: exercise group (E), low-level laser therapy group (LLLT), and manual pressure release group (MPR). All patients were assessed before treatment and after 12 sessions of treatment.

RESULTS

Significant improvement was seen in all groups' pressure pain threshold (PPT) values (p < 0.01). Some masticatory and neck muscles' PPT changes in MRP and LLLT groups were significantly higher than the exercise group (p < 0.05).

CONCLUSION

Exercise therapy is an effective approach for treatment of TMDs. Additionally, LLLT combined with exercise and MPR combined with exercise have better effects than only exercise therapy. Multimodal treatment approaches should include exercise to achieve better results in clinical practice.

Mediotrusive Occlusal Contacts: Best Evidence Consensus Statement

PURPOSE

The impact of mediotrusive (MT) occlusal contacts has been a topic of controversy and confusion in both clinical practice and in the dental literature. The purpose of this Best Evidence Consensus Statement was to explore whether MT interferences are harmful in the natural or therapeutic occlusion directed by 4 focus questions relating to prevalence, jaw function, jaw dysfunction and biomechanical models.

MATERIALS AND METHODS

An electronic search in October 2020 sought evidence in MEDLINE (Ovid) using (mediotrus* OR nonworking side OR nonworking contact OR balancing side OR interfer* side OR premature contact) in the multipurpose (.mp) search field; and in Google Scholar using permutations of the above. Supplementary articles were sourced from the associated reference lists. There was no language restriction. The search yield was reviewed in duplicate.

RESULTS

The electronic search identified 420 articles. Following screening, 164 were selected for eligibility assessments. Of these, 47 were included in the current paper.

CONCLUSIONS

Non-standardized nomenclature and methodology is used to identify MT interferences in patient populations, with resultant prevalence varying from 0% to 77%, (median = 16%). MT interferences may alter the biomechanics of mandibular function. Together with the presence of repeated high loads resultant strain can manifest as pathophysiology of the temporomandibular joint and associated muscle structures. MT interferences should be avoided in any therapeutic occlusal scheme to minimize pulpal, periodontal, structural and mechanical complications or exacerbation of temporomandibular disorders (TMDs). Naturally occurring molar MT interferences should be eliminated only if signs and symptoms of TMDs are present. Literature supports there being a biomechanical basis which can explain how MT interferences may affect temporomandibular joint morphology and jaw function.

Translational research on Myology and Mobility Medicine: 2021 semi-virtual PDM3 from Thermae of Euganean Hills, May 26 - 29, 2021

On 19-21 November 2020, the meeting of the 30 years of the Padova Muscle Days was virtually held while the SARS-CoV-2 epidemic was hitting the world after a seemingly quiet summer. During the 2020-2021 winter, the epidemic is still active, despite the start of vaccinations. The organizers hope to hold the 2021 Padua Days on Myology and Mobility Medicine in a semi-virtual form (2021 S-V PDM3) from May 26 to May 29 at the Thermae of Euganean Hills, Padova, Italy. Here the program and the Collection of Abstracts are presented. Despite numerous world problems, the number of submitted/selected presentations (lectures and oral presentations) has increased, prompting the organizers to extend the program to four dense days.

Effect of a sports mouthguard on the functional range of motion of the spine and the upper body posture in taekwondo

Background

The aim is to investigate to what extent the different oral protections compared to the habitual occlusion affect the upper body posture in statics and during taekwondo-specific movement.

Methods

12 Taekwondoka (5 f/7 m) of German national team were measured by using a 3d back scanner and an ultrasonic distance measuring (upright stand, taekwondo attack and defense movement, two taekwondo specific combinations) in habitual occlusion, with a custom-made and ready-made mouth protection

Results

There are no significant changes in the upper body posture (p ≥ 0.05). Depending on the dynamic measurements, different significant reactions of the spinal position were found while wearing the custom made mouthguard or the ready-made mouthguard according to the conducted movement.

Conclusion

The measured changes in dynamic movements are not clinical relevant. Based on the positive responses from the participants, the custom-made mouth protection can be recommended combined with an individual analysis.

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.

Dental occlusion as one cause of tinnitus

There is large support in literature linking tinnitus to dental occlusion and temporomandibular joint disorders (TMD). However, there is no model to explain such a link. This hypothesis explains how the fusimotor system of the muscles innervated by the trigeminal motor nucleus is affected by inadequacies in the occlusion of the teeth that cause changes in posture and movement of the mandible. Reptile to mammal evolution shows that stomatognathic structures underwent changes related to mastication. Among several changes, there was the appearance of a new articulation between the mandible and skull: the temporomandibular joint. The bones of the old reptile joint, quadrate-articular, have detached from the mandible and are part of the middle ear bone chain. The former becomes the incus and the latter the malleus. This bone change also carried the tensor tympani and its trigeminal motor innervation. Inadequate occlusal contacts give rise to an adapted function of the mandible and the most common compensatory muscular response is hypertonia involving all mandibular muscles, including the tensor tympani. A fundamental clinical feature that demonstrates the involvement of the trigeminal fusimotor system is the characteristic pain by palpation, but no pain on the mandibular movement. Muscle pain is always felt in the dermatome innervated by the mandibular branch of the trigeminal nerve, which carries the motor fibers, reported as tightening, similar to cramp, and has regular behavior in intensity, duration and frequency. In addition, the patient has increased musculature volume, detected by palpation of certain anatomical landmarks, but with loss of functional efficiency. The neuromotor control of the mandibular movements is poor and when asked to make lateral jaw movement touching the teeth, it is common to observe that the patient moves the lips, eyes, and even turns the head in the same direction as the movement. There is also difficulty eating hard foods and talking fast. Tongue biting while chewing is frequent, meaning that these non-physiological events surpass protective reflex circuits. The report of ear pain, tinnitus, blocked ear sensation and sudden hearing loss is common in such patients, compatible with the tonic contraction of the tensor tympani. The fusimotor system hypothesis is able to explain all events related to the symptoms and helps to establish a correct diagnosis for certain types of hearing disorders.

Effects of occlusal splints on shoulder strength and activation

Introduction: The use of oral appliances to enhance sports performance has been advocated by some authors, however, studies addressing the effectiveness of these strategies are inconclusive. Methods: Here we investigate the effects of dental occlusions on shoulder strength. Fourteen healthy male subjects (age = 21.67 ± 0.86 years) without temporomandibular joint (TMJ) disorder participated in this study. Isokinetic strength was evaluated in shoulder abduction/adduction and arm external/internal rotation tests. Three randomised conditions were assessed: (1) occlusal splint (OS), which repositioned the TMJ in centric relation; (2) placebo splint (PS); and (3) no-splint (N). The strength tests were performed at a speed of 60°/sec in concentric mode. Muscle activity was measured by surface electromyography (EMG) in the main muscles engaged in the movements. Results: Significant differences in peak torque between OS and both of the other experimental conditions were found in some of the analyzed variables. Moreover, there was significantly higher muscular EMG activation in the OS condition when compared to the other conditions for some of the tested muscles. These data suggest that splints may have a positive ergogenic effect on shoulder muscular strength in healthy male subjects. Conclusion: OS may provide an advantage for healthy subjects engaged in sports whereby shoulder and arm strength are important for performance. Key messages Occlusal splints in centric relation position have an ergogenic effect, by increasing strength and muscle activation on shoulder in healthy subjects. These results could have implications for sports or other physical activities were arm and shoulder strength are important.

Effects of Dental Occlusion on Body Sway, Upper Body Muscle Activity and Shooting Performance in Pistol Shooters

Occlusal splints, to some extent, have been related to reduced body sway in a static position and increased muscle activity in the upper limbs. However, how dental occlusion status affects sports performance remains unclear. Here, we investigated whether occlusal splints that reposition the temporomandibular joint (TMJ) influenced body posture, muscle activity, and performance in 10-meter pistol shooters. Thirteen national-level male shooters (age = 38.8 ± 10.9 yrs) were recruited for this study, and cleared of any cervical pathology. An occlusal splint (OS) and a placebo splint (PS) were fabricated for each of the subjects, with the mandibular and maxillary position verified by an expert dentist, with the aid of an adjustable articulator. Surface electromyography (EMG) was assessed in the upper limb that holds the pistol while the subjects were standing on a force platform. Subjects performed two series of 10 shots for each of the three experimental conditions (OS, PS, N (no splint)) in randomized order, with the mandible in a rest position. Results revealed similar centre of pressure (COP) parameters in all conditions, despite a reduction in the average oscillation area caused by the OS. There were also no significant differences in EMG activity between conditions in the five upper limb muscles monitored. Consistent with this, shooting performance was similar in all conditions, despite a reduction in shot dispersion in subjects using OS. Thus, changes in dental occlusion status induced by OS do not affect body posture, upper limb EMG muscle activity, or shot performance in healthy male pistol shooters.

Electromyographic activity of the jaw muscles and mandibular kinematics in young adults with theoretically ideal dental occlusion: Reference values

Background

A necessary step to use neuromuscular analysis as diagnostic tool is to establish normal reference values for the physiological range in a healthy population. Surface electromyographic (sEMG) activity of the jaw muscles and mandibular kinematics were measured in young adults with theoretically ideal dental occlusion to determine normal reference values during different tasks. Differences between the sexes were evaluated.

Material and Methods

Forty young adults (20 men, 20 women; mean age 22.8 ± 3.9 years) with theoretically ideal dental occlusion were selected using very restrictive criteria. sEMG activity of the anterior temporalis (AT), posterior temporalis, masseter (MA), and suprahyoid muscles were evaluated in the rest position and during swallowing, mastication, and clenching. Mandibular kinematics in the rest position and during maximum excursions were assessed. Asymmetry, activity, and torque indices and MA/AT ratios were calculated.

Results

For all muscles, sEMG values were 1.01-3.57 µV at rest, 3.50-10.85 µV during swallowing, and 41.04-86.59 µV during mastication. During clenching, values were 230.08-243.55 µV for the AT and MA muscles. Mean total asymmetry, activity, and torque indices at rest were 20.34 %, -15.04 %, and 19.02 %, respectively; during clenching, these values were 6.14 %, -2.62 %, and 4.46 %. MA/AT ratios were near 1. Kinematic measurements during lateral excursion, protrusive and maximum opening were 7.54, 8.44, and 37.38 mm respectively; lateral mandibular shift was 1.41 mm; free way and lateral displacement at rest were 1.40 and 0.26 mm. Right MA activity during mastication and clenching was higher in men than women.

Conclusions

Reference values for sEMG activity and mandibular kinematics were determined. Some muscular asymmetry and torque were observed.

Key words:Electromyography, masticatory muscles, kinesiography, jaw movements, normal dental occlusion, sexual dimorphism.

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.

Natural mediotrusive contact: does it affect the masticatory and neck EMG activity during tooth grinding?

OBJECTIVES

There is scarce knowledge regarding the influence of a natural mediotrusive contact on mandibular and cervical muscular activity. The purpose of this study was to analyze the EMG activity of the anterior temporalis (AT) and sternocleidomastoid (SCM) muscles during awake grinding in healthy subjects with or without a natural mediotrusive occlusal contact.

METHOD

Fifteen subjects with natural mediotrusive occlusal contact (Group 1) and 15 subjects without natural mediotrusive occlusal contact (Group 2) participated. Bilateral surface EMG activity of AT and SCM muscles was recorded during unilateral eccentric or concentric tooth grinding tasks. EMG activity was normalized against the activity recorded during maximal voluntary clenching in intercuspal position (IP) for AT muscles and during maximal intentional isometric head-neck rotation to each side, for SCM muscles.

RESULTS

EMG activity of AT and SCM muscles showed no statistical difference between groups. EMG activity of AT muscle was higher in the working side (WS) than in the non-WS (NWS) in Group 1 during concentric grinding (0.492 vs 0.331, p = 0.047), whereas no difference was observed in Group 2. EMG activity of SCM was similar between working and NWSs in both groups and tasks. Asymmetry indexes (AIs) were not significantly different between groups.

DISCUSSION

These findings in healthy subjects support the assumption that during awake tooth grinding, central nerve control predominates over peripheral inputs, and reinforce the idea of a functional link between the motor-neuron pools that control jaw and neck muscles.

The Immediate Effect of Changing Mandibular Position on the EMG Activity of the Masseter, Temporalis, Sternocleidomastoid, and Trapezius Muscles

This study investigated the immediate effect of changing mandibular position on the electromyographic (EMG) activity of the masseter (MS), temporalis (TM), sternocleidomastoid (SCM) and trapezius (TR) muscles. Thirty-three (33) asymptomatic subjects (16 males and 17 females), ages 23 to 52 were selected. Surface EMG recordings were obtained for all muscles bilaterally with the mandible in a relaxed open position (relaxed) and during maximal voluntary clenching (fullbite) for the following: a non-repositioning appliance (NONREPOS) and repositioning appliance (REPOS). REPOS significantly reduced EMG activity of all muscles bilaterally during fullbite. During relaxation, reduction in EMG activity was only found for TR bilaterally. NONREPOS decreased the EMG activity bilaterally for TM and TR and unilaterally (left) for MS and SCM during fullbite. During relaxation, NONREPOS decreased muscle activity bilaterally for TR and SCM. A unilateral reduction was found for TM (right). These findings suggest that immediate alterations in mandibular position affect the cranio-cervical system. Both mandibular positions tested lowered the EMG activity of masticatory and cervical muscles in the relaxed and fullbite positions. The trapezius muscle was the most responsive to alterations in mandibular position.

Effect of mandibular mobilization on electromyographic signals in muscles of mastication and static balance in individuals with temporomandibular disorder: study protocol for a randomized controlled trial

BACKGROUND

The stomatognathic system and dysfunction in this system may be related to postural control. The proposal of the present study is to assess the effect of mandibular mobilization in individuals with temporomandibular disorder using surface electromyography of the muscles of mastication and stabilometric variables.

METHODS/DESIGN

A randomized, controlled, blind, clinical trial will be carried out, with the participants divided into three groups: 1) facial massage therapy (control group), 2) nonspecific mandibular mobilization and 3) specific mandibular mobilization. All groups will be assessed before and after treatment using the Research Diagnostic Criteria for Temporomandibular Disorders, surface electromyography of the masseter and temporal muscles and stabilometry. This study is registered with the Brazilian Registry of Clinical Trials (RBR9x8ssz).

DISCUSSION

A large number of studies have employed surface electromyography to investigate the function/dysfunction of the muscles of mastication and associations with signs and symptoms of temporomandibular disorders. However, it has not yet been determined whether stabilometric variables offer adequate reliability in patients with this disorder. The results of the proposed study will help determine whether specific and/or nonspecific mandibular mobilization exerts an effect on the muscles of mastication and postural control. Moreover, if an effect is detected, the methodology defined in the proposed study will allow identifying whether the effect is local (found only in the muscles of mastication), global (found only in postural control) or generalized.

Assessment of thickness and function of masticatory and cervical muscles in adults with and without temporomandibular disorders

OBJECTIVE

The aim of this study was to evaluate the maximal bite force (MBF), electromyographic (EMG) activity and thickness of the masseter, anterior part of the temporalis and sternocleidomastoid (SCM) muscles in a group of young adults with and without temporomandibular disorders (TMDs).

DESIGN

Nineteen individuals comprised the TMD group (6 males/13 females, aged 25.4±3.8 years), classified based on the Research Diagnostic Criteria for TMD (RDC/TMD), and 19 comprised the control group (6 males/13 females, aged 24.1±3.6 years). The MBF was determined with a transducer placed between the dental arches at the first molars level (N). The muscles were evaluated bilaterally at rest and during maximal voluntary clenching (MVC) by assessing EMG activity and performing ultrasonography (USG). The mean values of these measures for both sides of the mouth were used. The normality of the distributions was assessed by the Shapiro-Wilks test. Variables between groups and genders were compared using two-way factorial ANOVA test and correlated using the Spearman coefficient (α=0.05). Unpaired t test was used to compare variables between TMD subgroups. Logistic regression analysis was used to identify the variables associated with the presence of TMD.

RESULTS

MBF, EMG and USG data were similar among clinical groups and among TMD subgroups. The thickness of masseter and SCM muscles in the relaxed and clenching states were significantly higher in males than females. On the other hand, the EMG of the temporalis muscle in the rest state was significantly higher in females than males. Additionally, the MBF was positively correlated with the USG characteristics of masseter and SCM muscles, as well as with the EMG activity of masseter and temporalis muscles in the TMD group. In this group, there was also a positive correlation between the thickness of the masseter muscle and its activity. On the other hand, the thickness of the SCM muscle was negatively correlated with its activity. A lower MBF was independently associated with the presence of TMD.

CONCLUSIONS

Subjects with TMD exhibited similar values of MBF, thickness and electrical activity of masticatory and cervical muscles when compared with controls; positive correlations observed between these variables may suggest a muscular alteration in TMD patients and a co-activation of masticatory and cervical muscles during mandibular movement. This fact may also be confirmed by the negative association between bite forces and presence of TMD.

EMG spectral characteristics of masticatory muscles and upper trapezius during maximum voluntary teeth clenching

To assess the surface electromyographic spectral characteristics of masticatory and neck muscles during the performance of maximum voluntary clench (MVC) tasks, 29 healthy young adults (15 men, 14 women, mean age 22years) were examined. Electromyography of masseter, temporalis and upper trapezius muscles was performed during 5-s MVCs either on cotton rolls or in intercuspal position. Using a fast Fourier transform, the median power frequency (MPF) was obtained for the first and last seconds of clench, and compared between sexes, muscles, sides, tests and time intervals using ANOVAs. On average, the MPFs did not differ between sexes or sides (p>0.05), but significant effects of muscle (MPF temporalis larger than masseter, larger than trapezius muscles), test (larger MPFs when clenching in intercuspal position than when clenching on cotton rolls) and time (larger MPFs in the first than in the fifth second of clench) were found. In conclusion, a set of data to characterize the sEMG spectral characteristics of jaw and neck muscles in young adult subjects performing MVC tasks currently in use within the dental field was obtained. Reference values may assist in the assessment of patients with alterations in the cranio-cervical-mandibular system.

Chin force in violin playing

Force generated between the left mandible of violinists and the chinrest of the violin was examined using a force-sensing chinrest developed in this study. A strain-gauge force sensor was built, and it was fixed between the violin's top plate and a chin cup. Fifteen professional/amateur violinists held the violin statically, played musical scales with different sound properties and sounding techniques, as well as an excerpt from a Max Bruch concerto. Peak and mean forces were evaluated for each task. In a separate experiment, lateral movement of the lower teeth due to different levels of voluntary chin force exertion was measured. Static holding forces observed were 15 and 22 N with and without the help of the left hand, respectively. Peak force increased from 16 N at soft dynamics to 20 N at strong dynamics during scales. The force further increased to 29 N with the use of vibrato technique and 35 N during shifts. Tempo and hand position did not affect the force. Playing a Bruch concerto induced a mean peak force of 52 N, ranging from 31 to 82 N among the violinists. The developed force-sensing chinrest could accurately record the generated chin force. Typical chin force to stabilize the violin during ordinary musical performance was less than 30 N, but it could momentarily exceed 50 N when technically demanding musical pieces were performed. The lateral shift of the mandible was fairly small (<0.4 mm) even with high chin-force exertion, possibly due to clenching of the molars.

Professional musicians with craniomandibular dysfunctions treated with oral splints

Craniomandibular dysfunction (CMD) symptoms occur frequently in violin/viola and wind players and can be associated with pain in the neck, shoulders and arm. In the current study, the effect of oral splint treatment of CMD on reducing pain and symptoms especially in these areas was investigated. Thirty (30) musicians undergoing CMD treatment with oral splints participated in this study. They completed a questionnaire that addressed CMD symptoms, localization of pain, and subjective changes in symptoms. Pain in the shoulder and/or upper extremity was the most frequent symptom reported by 83% of subjects, followed by neck pain (80%) and pain in the teeth/TMJ regions (63%). Treatment with oral splints contributed to a significant decrease in neck pain in 91%, teeth/TMJ pain in 83%, and shoulder and upper extremity pain in 76% of the musicians. Eighty percent (80%) of the patients reported improvement of their predominant symptoms. CMD can be a potential cause for pain in the neck, shoulders, and upper extremities of musicians. It is paramount that musicians with musculoskeletal problems be examined for CMD symptoms. Treatment with oral splints seems to be valuable. Further prospective, randomized controlled studies are necessary to confirm efficacy of oral splint treatment in CMD-associated pain and problems in the neck, shoulder, and the upper extremities in musicians.

Stomatognathic adaptive motor syndrome is the correct diagnosis for temporomandibular disorders

Temporomandibular disorder is a generic and inadequate conception to be used as a diagnosis. It fails to express the etiology or the pathophysiology and it is mainly associated with the anatomical site. Moreover, the clinical condition presents a mandibular motor problem and not a joint problem. The hypothesis presents the new diagnosis stomatognathic motor adaptive syndrome, which comprehend a motor response and the adaptive processes it induces. Inadequate occlusal contacts cause the mandible to shift in order to reach an ideal intercuspal position. The condylar displacements are proportional to such movements. Temporomandibular joint (TMJ) receptors respond to the capsular mechanical stress and the information reaches the trigeminal sensory nuclei. The mandibular modified position seems to be relevant information and may interfere with catecholaminergic neurotransmission in basal ganglia. The main motor responses comprise increased jaw muscle tone, decreased velocity of movements and incoordination. The overload of muscle function will produce adaptive responses on many stomatognathic structures. The muscle adaptive responses are hypertonia, pain, fatigue and weakness. Temporomandibular joint presents tissue modification, disc alteration and cracking noise. Periodontium show increased periodontal membrane, bone height loss and gingival recession. Teeth manifest increased wear facets, abfraction and non-accidental fractures. The periodontal and teeth adaptive processes are usually identified as occlusal trauma. The altered stomatognathic functions will show loss of velocity during mastication and speech. Fatigue, weakness in jaw muscle and difficulties to chew hard food are related to hypertonia. Incoordination between stomatognathic muscles groups is found, causing involuntary tongue/cheek biting and lateral jaw movements on speech. Otologic complaints, as aural fullness and tinnitus, are related to the tensor tympani muscle, innervated by the trigeminal nerve.

Cervical spine alignment and hyoid bone positioning with temporomandibular disorders

The relationships between temporomandibular joint (TMJ) disorders and cervical structure dysfunctions have already been demonstrated. The aim of the present study was to investigate functional and structural alterations of the head and neck of 17 individuals with TMJ disorders (TMD group), compared with a control group of 17 asymptomatic subjects in a cross-sectional design. The outcome variables included pain on palpation of the sternocleidomastoideus, superior trapezius and subocciptal muscles, as well as radiographic measures of alignment of the cervical spine and positioning of the hyoid bone. Cervical alignment, determined by measures of the cervical curvature angle, was investigated by the Cobb method. Independent Student t-tests were used to investigate differences between groups for all outcome variables (alpha < 0.05). The results demonstrated that individuals with TMJ disorders, when compared with asymptomatic subjects, presented higher levels of perception of pain in all cervical muscles (P < 0.0001). No significant differences were found between groups for the cervical alignment measures. In the TMD group, the position of the hyoid bone in relation to the cervical spine did not appear to be different from the control group.

Desempenho mastigatório em adultos relacionado com a desordem temporomandibular e com a oclusão

TEMA: desordem temporomandibular e mastigação. OBJETIVO: comparar sujeitos com desordem temporomandibular a um grupo controle quanto à mastigação e analisar as variáveis relacionadas. MÉTODO: 20 sujeitos com desordem temporomandibular (grupo com DTM) e 10 do grupo controle, ambos selecionados de acordo com o exame clínico e anamnese, responderam sobre a sua auto-percepção de severidade de dor e sons nas articulações temporomandibulares, dor nos músculos, sintomas otológicos, cefaléia e dificuldade para abrir a boca. Foram também submetidos ao exame clínico, considerando o número de elementos dentários presentes e a análise funcional da oclusão - medidas de abertura bucal, excursão lateral da mandíbula, interferências oclusais e contatos oclusais do lado de trabalho e balanceio. A mastigação foi avaliada quanto ao tempo para ingerir, ao número de golpes mastigatórios e ao tipo mastigatório (unilateral ou bilateral), usando um biscoito recheado, cuja força máxima para quebrá-lo no primeiro momento foi de 4341,8g, como verificado com o auxílio do Texture Analyser TA-XT2 (Stable Micro Systems). Os grupos foram comparados por análise de variância e as correlações entre as variáveis foram calculadas pelo teste produto-momento de Pearson. RESULTADOS: a maioria dos sujeitos do grupo controle apresentou tipo mastigatório bilateral, enquanto que no grupo com DTM houve tendência ao tipo mastigatório unilateral. No grupo controle foram estatisticamente maiores os escores do tipo mastigatório e as medidas de lateralidade. No grupo com DTM foram maiores as médias de idade, o tempo de mastigação, o número de golpes mastigatórios e a severidade da DTM. O tempo e o tipo mastigatório foram correlacionados, respectivamente de modo positivo e negativo, à severidade da DTM e ao número de interferências oclusais. CONCLUSÃO: no grupo com DTM a mastigação diferiu do padrão fisiológico normal. O número de interferências oclusais e a severidade da DTM foram as variáveis correlacionadas à mastigação.

Fatigue in the Sternocleidomastoid Muscle and Hip Dysplasia: A Surface Electromyographic Assessment in Adult Women

OBJECTIVE

The aim of this study is to assess a possible relationship between unilateral hip dysplasia and sternocleidomastoid muscle function during a fatiguing task.

METHODS

In this patient-control, cross-sectional study, 11 female patients (aged 37-63 years) with unilateral coxoarthrosis subsequent to hip dysplasia and 9 female control subjects matched for age were assessed. Surface electromyography of the right and left sternocleidomastoid muscles was measured in the women performing a standardized endurance test. The median power frequency was calculated at the beginning (T0) and at the end of the task (T1, endurance time). For each subject and muscle, percentage decrements in the median power frequency were computed at T1.

RESULTS

Endurance time ranged between 15 and 125 s (control group), and 10 and 200 s (patient group), without a significant difference between the 2 groups (Mann-Whitney test, P > .05). In the patient group, no significant differences in the median power frequency between the ispilateral to coxoarthrosis and contralateral sides were found (Wilcoxon test, P > .05). The percentage decrements of the median power frequency in the control (right and left side pooled) and patient group did not significantly differ either in the ispilateral to coxoarthrosis and contralateral sides (Mann-Whitney test, P > .05).

CONCLUSIONS

The lack of significant differences between the sternocleidomastoid muscles of healthy women and those of women with hip dysplasia does not support the presence of a common noxa causing both congenital muscular torticollis and hip joint alterations. Alternatively, the coexistence of the 2 alterations in infancy may disappear during adult life.

The influence of occlusion on jaw and neck muscle activity: a surface EMG study in healthy young adults

The electromyographic (EMG) characteristics of masseter, temporalis and sternocleidomastoid (SCM) muscles during maximum voluntary teeth clench were assessed in 27 male and 35 female healthy young adults. Subjects were divided into two groups: (i) 'complete' Angle Class I (bilateral, symmetric canine and molar Class I relationships), and (ii) 'partial' Angle Class I (one to three canine/molar Class I relationships, the remaining relationships were Class II or Class III). On average, standardized muscular symmetry ranged 80.7-87.9%. During maximum voluntary teeth clench, average co-contraction of SCM muscle was 13.7-23.5% of its maximum contraction. On average, all torque coefficients (potential lateral displacing component) were >90%, while all antero-posterior coefficients (relative activities of masseter and temporalis muscles) were >85%. The average integrated areas of the masseter and temporalis EMG potentials over time ranged 87.4-106.8 muV/muV s%. Standardized contractile muscular activities did not differ between 'complete' and 'partial' Angle Class I, and between sexes (two-way analysis of variance). A trend toward a larger intragroup variability in EMG indices was observed in the subjects with 'partial' Angle Class I than in those with 'complete' Angle Class I (significant difference for the temporalis muscle symmetry, P = 0.013, analysis of variance). In conclusion, the presence of a complete or partial Angle occlusal Class I did not seem to influence the standardized contractile activities of masseter, temporalis and SCM muscles during a maximum voluntary clench. Subjects with a 'complete' Angle Class I were somewhat a more homogenous group than subjects with 'partial' Angle Class I.

Occlusion, sternocleidomastoid muscle activity, and body sway: a pilot study in male astronauts

The modifications induced by microgravity on the coordinated patterns of movement of the head, trunk, and limbs are reported on extensively. However, apparently there is little data on the masticatory muscles. In normal gravitational conditions, information from the neck and stomatognathic apparatus play a role in maintaining the body's balance and equilibrium. The current pilot study used normal gravity conditions to investigate the hypothesis of a functional coupling between occlusion and neck muscles and body postural oscillations. The immediate effect of modified occlusal surfaces on the contraction pattern of the sternocleidomastoid muscles during maximum voluntary clenching and on the oscillation of the center of foot pressure was analyzed in 11 male astronauts (aged 31-54 yrs). All subjects were healthy and free from pathologies of the neck and stomatognathic apparatus. Occlusal splints were prepared using impressions of their dental arches. The splints were modeled on the mandibular arch, had only posterior contacts, and were modified to obtain a more symmetric, standardized contraction of the masseter and temporalis muscles during teeth clenching. Surface EMG activity of the sternocleidomastoid muscles was recorded during a maximal voluntary clench with and without the splint. Sternocleidomastoid potentials were standardized as percent of the mean potentials recorded during a maximum contralateral rotation of the head, and the symmetry of the EMG waves of left- and right-side muscles was measured. Body sway was assessed with and without the splint, either with eyes open or closed. The variations of the center of foot pressure were analyzed through bivariate analysis, and the area of the 90% standard ellipse was computed. Within each visual condition (eyes open or closed), the difference between the areas of oscillation measured with and without the splint was computed. Muscular activity was more symmetric with the splint. The area of oscillation of the center of foot pressure was larger without the splint than with the splint, both with eyes open and eyes closed. The modifications, induced by the occlusal splint in the sternocleidomastoid muscles' symmetry, and center of foot pressure differential area with closed eyes, were significantly related (p < 0.05): the larger the increment in muscular symmetry, the smaller the area of oscillation with the splint as compared to without the splint. A functionally more symmetric maxillo-mandibular position resulted in a more symmetric sternocleidomastoid muscle contraction pattern and less body sway. Modifications in the contraction of the masticatory muscles may therefore affect the whole body.