Masticatory Muscle Dysfunction Research Articles

Anatomical factors influencing temporomandibular joint clicking in young adults: temporomandibular joint structure disorder or lateral pterygoid muscle dysfunction?

Objective: This study aimed to investigate the selected anatomical factors that can potentially influence temporomandibular joint (TMJ) clicking in young adults by assessing TMJ structures and lateral pterygoid muscle (LPM) function using magnetic resonance imaging (MRI). Methods: The patients were divided into four groups: the healthy control group; the clicking on mouth opening group; the clicking on mouth closing group; and the clicking on mouth opening and closing group. Additionally, we used clinical palpation to evaluate the masticatory muscles' functional state and employed MRI using the OCOR-T1WI-FSE-CLOSED, OSAG-PDW-FSE-CLOSED, and OSAG-PDW-FSE-OPEN sequences to analyze the texture of the lateral pterygoid muscle (LPM). Results: The proportion of any articular disc or condylar morphology class did not differ significantly between the TMJ clicking and HC groups. The articular disc position did not differ significantly between the TMJ clicking and HC groups. In the TMJ clicking group, the presence of masticatory muscle dysfunction differed significantly between the clicking and non-clicking sides. Moreover, the LPM accounted for the highest proportion among masticatory muscles with tenderness in all TMJ clicking subgroups (77.78%-100%). Therefore, in the TMJ clicking group, the LPM texture was less defined, more uniform in gray scale, and more similar to local texture (p < 0.0001). Conclusion: The occurrence of TMJ clicking in young adults is unrelated to the TMJ structure but related to the function of masticatory muscles, particularly the LPM.

MR sialographic assessment of the masseter muscle and the ductal kinking in patients with recurrent parotitis

Dysfunction of the masseter muscle may cause pathological kinking of the parotid duct leading to parotitis; MR sialography is a non-invasive radiological examination that allows to evaluate dynamically the ductal system of the parotid glands. In the present study we aimed to assess the relationships between Stensen’s duct and masseter muscle and their implications in the aetiopathogenesis of recurrent parotitis secondary to masseter muscle dysfunction. Forty-one patients with recurrent unilateral parotitis and nine with bilateral recurrent parotitis, all with a clinical suspicious of masseter muscle hypertrophy due to bruxism were enrolled. They underwent ultrasonography as a first line examination and then MR sialography and sialendoscopy. Different anatomical features were studied. Involved parotid glands had a wider duct compared to contralateral unaffected parotid glands of patients with recurrent parotitis (p = 0.00134); male subjects with parotitis had a longer duct compared to the salivary glands of healthy patients (p = 0.00943 for affected glands and p = 0.00629 for the contralateral). A concordance between the evidence of an acute duct angle during sialendoscopy and a wider duct in patients with parotitis was observed although not statistically significant. These initial findings suggest that the masticatory muscle dysfunction related to bruxism seems to condition alteration of parotid duct course and anatomy thus favouring the occurrence of recurrent parotitis. A specific diagnostic iter based on clinical evaluation, dynamic ultrasonography and MR sialography, is therefore, mandatory to confirm the relationship between masseter muscle anatomy and parotid duct anomalies; this is the premise for an adequate therapeutic approach to underlying masticatory muscle disorder.

Masticatory efficiency in patients with acute and chronic forms of masticatory muscle disorders

Introduction. Masticatory muscle disorders are frequently encountered in clinical dental practice, with a varied impact on the functionality of the stomatognathic system. The rehabilitation of mastication is a central objective in the treatment of these pathologies, thus there are required to employ objective and qualitative indices for the assessment and treatment efficiency quantification for the masticatory function. Aim of the study: Evaluation of masticatory efficiency parameters through the mixing ability test in patients with acute and chronic phases of masticatory muscle disorders. Material and methods. There were investigated 55 patients with masticatory muscle disorders (females, average age — 28.1 ±5.02 years), divided into 2 groups according to the phase of the disease (acute/chronic). There were determined the values of the descriptive indices of the dysfunctional process (pain intensity, severity of dysfunction, mandibular mobility, functional limitation). Masticatory efficiency was assessed subjectively and objectively based on mixing ability test indices. Results. In the chronic phase of masticatory muscle dysfunction, there is a more pronounced expression of the parameters of the dysfunctional process, but masticatory efficiency is rarely severely affected, possibly due to the initiation and involvement of functional compensation and adaptation mechanisms.

Functional magnetic resonance imaging evaluation of masticatory muscle dysfunction in unilateral exodontia rabbits.

Occlusal alteration due to tooth loss may cause overload of masticatory muscle and promote muscle dysfunction. This study explored the feasibility of using functional magnetic resonance imaging (fMRI) to evaluate muscle dysfunction in an established unilateral exodontia animal model. 6 rabbits were extracted right maxillary molars. T2 mapping, T2* mapping and Iterative Decomposition of water and fat with Echo Asymmetry and Least Square Estimation (IDEAL-IQ) were performed one day before extraction and every 2 weeks (2th~12th week) after extraction. The T2 and T2* values and fat fraction (FF) of bilateral temporal muscle (TM), masseter muscle (MM) and medial pterygoid muscle (MPM) were measured and compared between the extraction side and the contralateral side. Parameters of three monitoring time points (0th, 6th, 12th week) were also analyzed. T2 values of MM on extraction side were significantly higher than those of contralateral side-from fourth week to 12th week after extraction (p < 0.05). T2 values of MM and MPM on extraction side and TM on contralateral side were significantly higher in 12th week than those in 0th week (p < 0.05). And FF of bilateral MM was significantly higher in 12th week than those in 0th week (p < 0.05). T2* value showed no significant difference between extraction side and contralateral side and also at above three time points. T2 and T2* value and FF can be used as indicators of masticatory muscle dysfunction. fMRI is expected to be a non-invasive method for in vivo and real-time evaluation of masticatory muscle functional abnormality.

On Muscular Factor Question in the Correction of Transversal Incisor Occlusion

The aim of our study was to evaluate the role of the muscle factor and the effectiveness of manual treatment of masticatory muscle dysfunction in patients with transversal incisor occlusion (TIO). Methods and Results: We examined and treated 35 patients aged 18-25 years with clinical signs of TIO in the clinic of orthopedic dentistry. Diagnostic methods for TIO included an interview, face and oral cavity examination, and clinical functional tests. Occlusion was assessed using anthropometric measurements and examination of plaster jaw models in an articulator for additional diagnostics of the dental factor; a radiological method (jaw orthopantomography with the inclusion of articular joints) was also used for the articular factor diagnostics and examination of masticatory muscles and neck muscles. The treatment methods included manual treatment of masticatory muscle dysfunction: "myofascial trigger point release technique," "stretching-push," and "post-isometric relaxation." All patients' complaints were mainly confined to improper occlusion of the front teeth, namely, a misalignment of the centerline between the upper and lower anterior teeth. Moreover, 71.4% of patients noted intermittent clicking in one or both articular joints of the temporomandibular joint, 42.8% of patients reported pain in the region of one temporomandibular joint, 28.6% of patients noted noise in the ear of the same joint, as well as discomfort while chewing. On external examination, all patients had a slight asymmetry of the lips and cheeks on the habitual chewing side. The apex of the chin was positioned slightly to the side relative to the facial midline. All patients had a disturbed movement trajectory of the lower jaw. During mouth opening, the lower jaw trajectory changed relative to the facial midline: at first, it was straight, for a very short period, and then it deviated sideways, after which it returned to the center. There was a misalignment of the central line of the lower dentition relative to the midline of the face in the anterior region. The radiological picture showed signs of articular joint dysfunction: difference in the size of the articular gaps on the right and left sides. After a single session of manual treatment of masticatory muscles, all patients noted that the improper occlusion of the front teeth was corrected, pain and clicking sensations in the TMJ disappeared in 42.8% of patients, and pain disappeared in the area of one joint, along with noise in the ears and chewing discomfort. Headache in the parietal and temporal areas disappeared. The trajectory of lower jaw movements during mouth opening normalized in all patients after the performed manual treatment. Conclusion: We can conclude that when diagnosing and treating occlusal disorders, it is necessary to pay attention not only to the position of the teeth and the TMJ elements, but also to the muscular factor – the condition of the masticatory muscles. Special attention should be paid to the condition of the lateral wing muscles.

Temporomandibular Disorders and Perceived Emotional Stress Among Medical and Dental Students Studying in a Private Medical Institution in Kathmandu, Nepal

Introduction: Temporomandibular disorder (TMD) is a collection of complex signs and symptoms that typically involves the temporomandibular joint (TMJ) and masticatory muscles. Multifactorial etiologies of TMD include occlusal disharmony, oral habits, dysfunction of masticatory muscles and adjacent structures, emotional stress, and extrinsic and intrinsic changes on TMJ structure. Stress has been inflicted as one of the major etiological factors for developing TMD.&#x0D; Materials and Methods: An observational cross-sectional study was conducted among the medical and dental undergraduate students and interns studying in Nepal Medical College and Teaching Hospital, Kathmandu, Nepal from January 2018 to February 2018. Fonseca Amnestic Index (FAI) was used to evaluate and characterize the TMD signs and symptoms. The stress factor was assessed by the Cohen Perceived Stress Scale (CPSS-10) which is a self-report measure of stress level which consists of 10 questionnaires in which the subjects respond on how much they suffer from the listed symptoms. Data were analyzed using the Statistical Package of Social Sciences (SPSS) Version 16.0. Association of different variables was tested, with Chi-square test, with a value less than 0.05 as statistically significant.&#x0D; Results: A total of 487 students had participated. Among them 32.4%were male and67.6%were female. Among the participants, 44.6%were from dental school (BDS), and 55.4%were from medical school (MBBS). The age group of the participants was 17 to 27 years. The prevalence of TMD was 50.3% in the study participants. Among the participants with TMD, 81.2% had mild TMD, 17.2% had moderate TMD and 1.6% had severe TMD. Out of the total participants, 16.4% had low stress, 76.6% had moderate stress and 7% had high stress. This study showed a statistically significant association between stress factor and temporomandibular disease (p &lt;0.001).&#x0D; Conclusion: Higher rate of TMD and level of stress has become common in medical and dental college students. Identifying the TMD at an early age can control or at least minimize its long-term effects. Moreover, identifying the stress factor highlights the importance of providing support programs and implementing preventive measures to help students.

Beneficial effects of benzodiazepine on masticatory muscle dysfunction induced by chronic stress and occlusal instability in an experimental animal study

Psychological stress and occlusal alteration are important etiologic factors for temporomandibular/masticatory muscular disorders. In particular, the exact physiologic mechanism underlying the relation by occlusal alteration and temporomandibular disorders remains unclear. Our purpose was to test the hypothesis that benzodiazepine therapy is able to prevent metabolic and vascular changes in the medial pterygoid muscle of rats under chronic stress after 14 days of unilateral exodontia. Adult Wistar rats were submitted to unpredictable chronic mild stress (10 days) and/or unilateral exodontia and their plasma and medial pterygoid muscles were removed for analysis. A pre-treatment with diazepam was used to verify its effect on stress. The parameters evaluated included anxiety behavior, plasma levels of corticosterone, metabolic activity by succinate dehydrogenase, capillary density by laminin staining and ultrastructural findings by transmission electron microscopy. Occlusal instability induced anxiety-like behavior on elevated plus-maze test and diazepam administration blocked the appearance of this behavior. Unilateral exodontia promoted in the contralateral muscle an increase of oxidative fibers and capillaries and modification of sarcoplasmic reticulum. Chronic stress caused increased glycolytic metabolism, reduced capillary density and morphological changes in mitochondria on both sides. Association of both factors induced a glycolytic pattern in muscle and hemodynamic changes. Pharmacological manipulation with diazepam inhibited the changes in the medial pterygoid muscle after stress. Our results reveal a preventive benzodiazepine treatment for stress and occlusal instability conditions affecting masticatory muscle disorders. In addition, provide insights into the mechanisms by which chronic stress and exodontia might be involved in the pathophysiology of masticatory muscular dysfunctions.

Prevalence and character of occlusional disorders among young people.

Dynamic occlusion is the main indicator of the harmonious functioning of the dental apparatus. At the same time, irrational reconstructive treatment can lead to its disorders and, as a result, increased tooth wear, periodontal diseases, dysfunction of masticatory muscles and temporomandibular joints. To date, the computer diagnostic methods allow studying occlusion in dynamics. The aim of the research was to study the prevalence and character of occlusal disorders in young people with intact dentitions, and those whose defects in teeth and dentitions were restored by direct and indirect restorations.300 persons aged 25-44 years were examined, equally men and women: the first group – 100 persons with intact dentitions; the second one - 100 persons with direct composite restorations located on the occlusal surfaces of the molars; the third one - 100 persons, who had indirect restorations of the crowns of teeth and dentitions of small sizes. Intercuspidation were analyzed using methods of occlusiography, the study of diagnostic models in the articulator, and computer analysis of occlusion.According to the peculiarities of centric and eccentric occlusions, the sequence of formation of the maximum occlusal load vector, the balance of occlusion and the time of closing and opening of dentitions, occlusal disorders were diagnosed in 14.0% of the first group, 35.0% of the second one and 44.0% of the third one. In 100% of patients these disorders were compensated, asymptomatic. The presence of supracontacts in centric occlusion leads to a displacement of the mandible in a forced position in 17.7% of cases. In 83.0% of the examined persons, the occlusion balance was at the level of 50% - 50% and in 13.7% – 60% - 40%. The remaining 3.3% of patients had an occlusive imbalance in the range of 70% -30%. In this case, significant deviations of the total trajectory vector of the occlusal load were not revealed.The most common occlusion disorders were centric contacts, which are formed as consecutive single, multiple, unilateral and bilateral overload areas, constantly being changed on sliding in dynamic occlusion. Occlusive disorders are characterized by an increase in the time of closure and opening of the dentitions, and the time to reach the maximum number of interdental contacts. The efficiency of occlusiography was only 29.7%, the efficiency of the study of diagnostic models in the articulator was 59.7%, compared to the computer method with 100% of the information value. The widespread use of direct and indirect restorations of teeth and dentitions leads to an increased prevalence of occlusal disorders in young people. Usually, small restorations are integrated into the dentition by grinding their occlusal surface, focusing on patient's comfort on closing the teeth and unhindered movements of the mandible to the sides and forwards. This simplified approach is conformative and incapable of providing optimal functional occlusion. The presence of occlusal imbalance requires appropriate measures for its diagnosis and correction.

A clinical case of restoration of the destroyed crown part of the tooth complicated by changes in the bifurcation area

The destruction of the tooth crown should be regarded as the cause leading over time to the disruption of the morphofunctional unity of the dentition and pathological condition of the entire dentoalveolar system. Untimely treatment of defects of hard tooth tissues leads to functional disorganization of the dentoalveolar system. The most eliminated defects are those of crowns of teeth determining the quality of aesthetics, phonetics, functions of biting and chewing. The destruction of the tooth crowns, which do not cause significant disruption of the above functions, are painless and almost asymptomatic. In such cases, deformation of the dentition and occlusion, dysfunction of masticatory muscles and temporomandibular joints as well as the development of pathological changes in periodontium occur slowly. Of great importance are the early diagnosis of pathological reconstruction of dentoalveolar system and the knowledge of pathogenesis of possible complications after the extraction of the teeth that determine the indications for prophylactic orthopedic dental treatment. The article presents a clinical case of restoration of destructed tooth crown 3.6 complicated by changes in bifurcation area. The patient underwent coronary-radicular separation with the use of cast metal cores, which allowed restoration of the sufficient size of the stump, function and anatomical shape of the tooth and hence the unity of dental arch.

Temporomandibular dysfunction

Orofacial pain is a common presentation in the primary healthcare setting and temporomandibular dysfunction represents one of the major causes. Its aetiology is multifactorial, caused by both masticatory muscle dysfunction and derangement within the temporomandibular joint. The aim of this article is to provide an overview of temporomandibular dysfunction, its management and referral considerations for general practioners. Temporomandibular joint dysfunction affects a large number of adults. Conservative management involving non-pharmacological and pharmacological therapies is effective in the majority of cases.

Assessment of the Short-Term Effectiveness of Kinesiotaping and Trigger Points Release Used in Functional Disorders of the Masticatory Muscles.

Chronic face pain syndrome is a diagnostic and therapeutic problem for many specialists, and this proves the interdisciplinary and complex nature of this ailment. Physiotherapy is of particular importance in the treatment of pain syndrome in the course of temporomandibular joint functional disorders. In patients with long-term dysfunction of masticatory muscles, the palpation examination can localize trigger points, that is, thickening in the form of nodules in the size of rice grains or peas. Latent trigger points located in the muscles can interfere with muscular movement patterns, cause cramps, and reduce muscle strength. Because hidden trigger points can spontaneously activate, they should be found and released to prevent further escalation of the discomfort. Kinesiotaping (KT) is considered as an intervention that can be used to release latent myofascial trigger points. It is a method that involves applying specific tapes to the patient's skin in order to take advantage of the natural self-healing processes of the body. The aim of the study was to evaluate the effect of the kinesiotaping method and trigger points inactivation on the nonpharmacological elimination of pain in patients with temporomandibular disorders. The study was conducted in 60 patients (18 to 35 years old). The subjects were randomly divided into two subgroups of 30 people each. Group KT (15 women and 15 men) were subjected to active kinesiotaping application. Group TrP, composed of 16 women and 14 men, was subjected to physiotherapy with the release of trigger points by the ischemic compression method. The results show that the KT method and TrP inactivation brought significant therapeutic analgesic effects in the course of pain-related functional disorders of the muscles of mastication. The more beneficial outcomes of the therapy were observed after using the KT method, which increased the analgesic effect in dysfunctional patients.

Migraine and temporomandibular joint dysfunction: mechanisms of comorbidity

to analyze the frequency of different forms of temporomandibular joint dysfunction (TMJD) in episodic and chronic migraine and to study mechanisms of their comorbidity. Sixty-three patients with chronic migraine (CM) and 40 patients with episodic migraine (EM) were examined. Anxiety and depression were assessed with the HADS, quality-of-life related to headache was measured with the HIT-6. To evaluate the antinociceptive system function, we studied blink reflex (BR) and nociceptive flexion reflex (NFR). The higher frequency of TMJD was identified in patients with CM compared to those with EM (47.5 and 28.5%, respectively), CM patients more frequently had disturbances related to the myofascial pain syndrome of masticatory muscles. R3 BR and NFR thresholds were significantly decreased in CM patients as well. TMJD is a component of the pathogenesis in many patients with CM. Masticatory muscles may generate nociceptive impulses in CNS, ie be a source of peripheral sensitization, that promote pain chronification, including migraine. Dysfunction of masticatory muscles may reflect the central sensitization and disturbance of efferent pain control.

Influence of Unilateral Masseter Muscle Atrophy on Craniofacial Morphology in Growing Rabbits

The purpose of the study was to evaluate whether the induction of unilateral masticatory muscle dysfunction can alter the skeletal growth patterns. Twenty-one white male New Zealand rabbits (4 weeks old) were divided into 3 groups of 7 subjects: group 1 served as the control to study normal craniofacial growth. In groups 2 and 3, rabbits were injected with 5 units and 15 units of Botulinum toxin A (BTXA) into the right masseter muscle, respectively. The effect of a neuromuscular blockade of masseteric activity on craniofacial growth was evaluated with 3 samples of serial computed tomography (CT) scans with a slice thickness of 0.625 mm, taken at 4 weeks (base line), 8 weeks (endpoint of prepubertal craniofacial growth), and 24 weeks (after pubertal growth). The ipsilateral mandibular ramus height, zygomatic arch length, and masseteric length did not develop as much as those of the contralateral side after pubertal growth. At age 24 weeks, the masseter muscle volume asymmetry index reached -13.8% (group 2), -18.4% (group 3), and -1.6% for the control group. The ipsilateral side of the hemimandible showed less bone volume after 8 weeks but it showed partially recovered symmetry at 24 weeks. The maxillomandibular incisor midline and transverse molar discrepancies were not evident in any of the groups. The BTXA injection can be an effective method in inducing site-specific muscular hypofunctions so that masticatory muscle-craniofacial bone interaction can be investigated efficiently. The result showed that the unilateral atrophy of the masseter muscle in the growing subjects influenced the morphology of the local skeletal sites. This did not, however, result ultimately in mandibular midline asymmetry or right-left asymmetry in hemimandibular volume after growth. The results imply that alterations in specific masticatory muscle function can be compensated by the growth of other structural components.

Histological study of rat masseter muscle following experimental occlusal alteration

It has been suggested that occlusal interference results in masticatory muscle dysfunction. In our previous study, occlusal interference reduced the rat masseter energy level during masticatory movements. The purpose of this study was to investigate the histological alterations of rat masseter muscles following experimental occlusal alteration with unilateral bite-raising. A total of eight male adult Wistar rats were equally divided into control and experimental groups. The experimental rats wore bite-raising splints on the unilateral upper molar. However, 4 weeks after the operation, the anterior deep masseter muscles were removed and then stained for succinic acid dehydrogenase (SDH), haematoxylin eosin (HE) and myofibrillar ATPase. Most of the muscle fibres in experimental rats remained intact, although partial histological changes were observed, such as extended connective tissue, appearance of inflammatory cells in the muscle fibres and existence of muscle fibres with central nuclei and central cores. Moreover, the fibre area-fibre frequency histograms of experimental muscle indicated a broad pattern than that of controls. These results indicated that occlusal interference caused histological changes in masseter muscles and that this may be related to the fact that the masseter energy level was reduced during masticatory movements in unilateral bite-raised rats.

Excitability of the central masticatory pathways in patients with painful temporomandibular disorders

Much is unclear about the pathophysiological mechanisms underlying painful temporomandibular disorders. In addition to various other theories, masticatory muscle dysfunction and pain have also been attributed to primary central nervous system hyperactivity. We assessed this possibility in a study using recent neurophysiological techniques. From among outpatients whose diagnosis of temporomandibular disorders had been obtained in stomatognathic facilities, we studied 10 patients with bilateral pain and 15 patients with unilateral pain, in whom electromyographic examination of the trigeminal reflexes disclosed normal findings except for absence or amplitude asymmetry of the jaw jerk. Transcranial magnetic stimulation yielded masseter motor evoked potentials of normal latency and amplitude, but five patients had to exert a near-maximum contraction to obtain their responses. The masseter silent periods elicited by the double-shock technique recovered normally. Because these tests measure the excitability of the masticatory system (including motor cortex, corticobulbar and corticoreticular connections, reticular interneurones and lower motoneurones), the lack of facilitation in these patients' responses excluded central hyperactivity as the primary cause of their masticatory dysfunction and pain.

The effects of electrogalvanic stimulation therapy on masticatory muscle dysfunction as determined by the pantronic reproducibility index.

Patients with temporomandibular joint dysfunctional activity (TM dysfunction) present with a diverse spectrum of clinical signs and symptoms. The multifactorial aetiology of such disorders has been noted. Diagnostic and therapeutic problems arise due to the inadequacy of quantifying the dysfunction. TM dysfunction can affect the muscles of mastication which are responsible for mandibular movement. A pantographic reproducibility index (PRI) is available to quantitatively and qualitatively measure a subjects ability to reproduce mandibular border movements. Physical therapy modalities are used in the management of TM dysfunction. Electrogalvanic stimulation (EGS) is such an example. The effect of electrogalvanic stimulation on subjects with and without TM dysfunction was assessed by Pantronic PRI appraisal in 20 subjects. No statistically significant differences were noted. At the individual level, some changes were observed in susceptible subjects.

Microtrauma to Rat Superficial Masseter Muscles Following Lengthening Contractions

Repetitive lengthening contractions have been predicted as a mechanism causing injury, pain, and delayed soreness in the hyperactive masticatory muscle. This mechanism was examined by the mechanical lengthening of the contracted superficial masseter (SM) muscle in anesthetized rats. Repetitive stimulation of the left SM to tetanic tension was followed by mechanical lengthening, which stressed contracted muscle. The contralateral muscle was passively lengthened repetitively. Contractile tension in response to a varying frequency of stimulation was measured in pre- and post-lengthened SM muscles. A selective loss of force at all frequencies up to 100 Hz occurred in the muscles subjected to lengthening contractions. Low-frequency fatigue did not occur in SM muscles passively lengthened. All animals recovered without loss of weight or dehydration. They were killed at 24 or 72 h post-lengthening. The SM muscles were collected, and no significant differences were found in mean weight, length, or cross-sectional area when the right and left SM muscles were compared at 24 or 72 h. Two observers independently examined histological secretions of SM muscles and graded the localized inflammatory sites on a scale of 1-4. A non-parametric statistical test was used so that the inflammatory scale for each muscle could be ranked. There were significantly more injured sites in SM muscles subjected to lengthening contractions, compared with the lengthened (but relaxed) SM muscles. The SM muscles of anesthetized rats were internally injured by repetitive lengthening contractions, and they exhibited low-frequency fatigue. These findings support the hypothesis that repetitive lengthening contractions in the masticatory muscle could be a mechanism for the pain and dysfunction of masticatory muscles in humans with certain parafunctional habits.

Temporomandibular joint injuries.

The clinical and radiologic findings in 30 patients who sustained injuries to the temporomandibular joint (TMJ) were retrospectively analyzed. Imaging consisted of variable combinations of radiography, tomography, two-compartment arthrography, computed tomography, and magnetic resonance imaging and was performed 2 days to 24 months after injury. Indications for imaging included acquired and/or unstable occlusal disturbances, cephalalgia, facial pain, otalgia, TMJ pain, tinnitus, dizziness, hearing disturbance, masticatory dysfunction, and muscle atrophy. Radiologic findings included internal derangement of the TMJ meniscus, swelling of retrodiskal tissues, joint effusion, mandibular condyle and condylar neck fractures, osteochondritis dissecans, avascular necrosis, degenerative condylar remodeling, osteoarthritis, musculotendinous injuries, and atrophy of masticatory muscles. After imaging studies, seven patients underwent surgery, at which time imaging findings were confirmed; one patient underwent successful aspiration of a painful hemarthrosis. TMJ injuries may result in joint derangement, radiologically demonstrable joint degeneration, masticatory muscle dysfunction, pain, and progressive clinical disability.