Electromyographic activity of the jaw-closing muscles during jaw opening--comparison of cases of masseter muscle contracture and TMJ closed lock

Effects of a botulinum toxin type A injection on the masseter muscle: An animal model study

BACKGROUND

The aim of this study was to investigate the effect of a botulinum toxin type A (BTX-A) injection in the masseter muscle using electromyography (EMG) in an animal model.

METHODS

Ten male adult (>3 months of age) New Zealand white rabbits were used. Muscle activity was continuously recorded from 8 hours before to 8 hours after BTX-A injection. The rabbits received unilateral BTX-A injections of either 5 units (group 1, n = 5) or 20 units (group 2, n = 5).

RESULTS

The masseter muscle activity of the rabbits was significantly reduced immediately after BTX-A injection (P < 0.05 for both groups). When the results from group 1 were compared with those from group 2, only the peak voltage was significantly decreased in group 2 (P = 0.013).

CONCLUSION

Masseter muscle activity measured by EMG was immediately decreased after a BTX-A injection.

Examination of a Large Patient Population for the Presence of Symptoms and Signs of Temporomandibular Disorders

Temporomandibular Disorder (TMD) is a term generally applied to a condition or conditions characterized by pain and/or dysfunction of the masticatory apparatus. Its characterization has been difficult because of the large number of symptoms and signs attributed to this disorder and to variation in the number and types manifested in any particular patient. For this study, data on 4,528 patients, presenting over a period of 25 years to a single examiner for TMD treatment, was made available for retrospective analysis and determination of whether the TMD care-seeking patient can be profiled, particularly pain difficulties. All patients in this database filled out a questionnaire and were examined for the prevalence of a range of symptoms and clinical examination findings (signs) commonly attributed to TMD. There was no attempt in this study to assign patients to TMD diagnostic subcategories. The data collected were analyzed to determine which of these symptoms and signs were sufficiently "characteristic of the TMD condition" that they might be used in diagnosis, research and treatment, especially in patients needing relief from pain and discomfort. All 4,528 patients reported symptoms and all but 190 of them also showed signs upon examination. Symptoms most commonly reported on the questionnaire included (i) pain (96.1%), (ii) headache (79.3%), (iii) temporomandibular joint discomfort or dysfunction (75.0%) and (iv) ear discomfort or dysfunction (82.4%). In the 4,338 patients who showed signs, the most prevalent was tenderness to palpation of the pterygoid muscles (85.1%), followed by tenderness to palpation of the temporomandibular joints (62.4%). Pain symptoms and signs were often accompanied by compromised mandibular movements, TMJ sounds and dental changes, such as incisal edge wear and excessive overbite. Clearly prevalence of pain disclosed by the symptoms and signs examinations was high. Patients showed variable prevalence and nonprevalence of eight categories of painful symptoms and seven categories of painful signs. Despite the variability, these might be developed in the future into TMD scores or indices for studying and unraveling the TMD conundrum.

Parameters of an Optimal Physiological State of the Masticatory System: The Results of a Survey of Practitioners Using Computerized Measurement Devices

While bioelectronic instruments have been available for nearly 30 years to assist dentists in day-to-day evaluations of patients' masticatory systems, little guidance has been published to support physiological norms or ideals. An electronic questionnaire was developed and administered to an international group of dentists familiar with the use of bioelectronic instrumentation. Respondents were asked to provide feedback on the norms or ideal parameters of jaw movement, masticatory muscle function with electromyography, and joint sounds through electrosonography that they use in guiding evaluation and treatment of patients with temporomandibular disorders, neuromuscular occlusion, and orthodontics. Surveys were collated to determine areas of consensus. Out of 150 surveys, 55 responses were received from dentists representing nine different countries. Sixty percent of the respondents reported treating more than 150 cases in the past five years using bioelectronic testing. While experience ranged from 2-30 years with different types of devices, average experience was longer with mandibular/jaw tracking (mean 15.3 years) and electromyography (mean 14.1 years) than with electrosonography (mean 7.0 years). Parameters proposed as norms or ideals for electromyographic rest and clench values, and mandibular tracking (velocity, freeway space, and trajectory to closure) were very consistent. Although a smaller number of respondents reported utilization of electrosonography, their criteria for data significance and tissue-type genesis of joint sounds were consistent. While the intra-patient variability may limit the diagnostic use of bioelectronic instruments, the current study demonstrates that through decades of experience, dentists have independently arrived at very consistent definitions of an ideal physiology that can be used to guide treatment.

Classification, causation and treatment of masticatory myogenous pain and dysfunction

This article focuses on chronic myogenous pains affecting the masticatory muscles, including focal myalgia, regional myalgia, myofascial pain, and fibromyalgia. The probable mechanisms are discussed and treatment options, including self-directed treatment, physical medicine modalities, and several types of pharmacologic agents, are presented.

Establishment of a temporomandibular physiological state with neuromuscular orthosis treatment affects reduction of TMD symptoms in 313 patients

The objective of this investigation was to test the hypothesis that alteration of the occlusions of patients suffering from temporomandibular disorders (TMD) to one that is neuromuscularly, rather than anatomically based, would result in reduction or resolution of symptoms that characterize the TMD condition. This hypothesis was proven correct in the present study, where 313 patients with TMD symptoms were examined for neuromuscular dysfunction, using several electronic instruments before and after treatment intervention. Such instrumentation enabled electromyographic (EMG) measurement of the activities of the masticatory muscles during rest and in function, tracking and assessment of various movements of the mandible, and listening for noises made by the TMJ during movement of the mandible. Ultra low frequency and low amplitude, transcutaneous electrical neural stimulation (TENS) of the mandibular division of the trigeminal nerve (V) was used to relax the masticatory muscles and to facilitate location of a physiological rest position for the mandible. TENS also made it possible to select positions of the mandible that were most relaxed above and anterior to the rest position when the mandible was moved in an arc that began at rest position. Once identified, the neuromuscular occlusal position was recorded in the form of a bite registration, which was subsequently used to fabricate a removable mandibular orthotic appliance that could be worn continuously by the patient. Such a device facilitated retention and stabilization of the mandible in its new-found physiological position, which was confirmed by follow up testing. Three months of full-time appliance usage showed that the new therapeutic positions achieved remained intact and were associated with improved resting and functioning activities of the masticatory muscles. Patients reported overwhelming symptom relief, including reduction of headaches and other pain symptoms. Experts consider relief of symptoms as the gold standard for assessment of effectiveness of TMD treatment. It is evident that this outcome has been achieved in this study and that taking patients from a less to a more physiological state is an effective means for reducing or eliminating TMD symptoms, especially those related to pain, most notably, headaches.

Changes in jaw muscle EMG activity and pain after third molar surgery

Limited jaw-opening capacity is frequently encountered following third molar surgery and may impair function. The aim of this study was to investigate the electromyographic (EMG) activity in jaw muscles after third molar surgery to obtain more insight into the mechanisms of restrictions in jaw opening. Twenty subjects were examined before, 24 h and 1 week after surgery. Ten healthy controls were subjected to the same examination at two different occasions for intersession variability. The EMG activity of the masseter and anterior digastricus muscles was recorded at different jaw positions and during maximum voluntary clenching. Pain intensity was assessed at rest and during movements. The EMG activity in the jaw muscles increased with opening level (P < 0.01), but did not change after surgery. In contrast, the EMG activity during clenching was decreased in all muscles after surgery (P < 0.05). The pain intensity after surgery increased with jaw opening level (P < 0.001), but was in general not correlated to EMG level. Pain intensity during clenching was increased after surgery (P < 0.001), but not correlated to EMG level. The EMG activity did not change between visits in the control group. In conclusion, the results indicate that third molar surgery does not influence the EMG activity in the masseter and anterior digastricus muscles during various levels of static jaw opening, but decreases the EMG activity during clenching. However, these changes are not influenced by pain intensity. The results have implications for the understanding of the phenomenon of trismus.