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.
The current scientific knowledge of TMJ pathologies points to the importance of etiological research and the need for differential diagnosis using the most modem technological resources. Those include MRI, computed tomography, serologic studies, genetic mapping, and bioelectronic instruments which allow clinicians to study, understand, and measure respectively, the structural changes of soft and hard tissues, infections, genetic susceptibility for autoimmune diseases, and stomatognathic function. The purpose of this article is an overview of the current knowledge and related tools for the diagnosis of TMJ pathologies.
In a prior study, the spatial relationship of the mandibular condyle was studied through a cephalogram based on laminographies of the temporomandibular joint (TMJ). The present method was developed with the aim of analyzing TMJ morphology and the spatial relationship of the mandibular head within the mandibular fossa, considering references far from these structures, as they may suffer shape alterations. This study was conducted in view of the importance of the study of morphology and the hard structures relationship, which constitutes the temporomandibular joint. Its purpose is to validate a new TMJ cephalogram method by analyzing joints with and without alterations in the orientation of the condylar axis growth. Sixty joints were studied through laminographies in maximal occlusion, examining those joints with and without alterations in the orientation of the axis during condylar growth for subsequent analysis. Results showed that those joints were in a posterior position and rotation of the mandibular head, and that they presented a greater inclination in the articular eminence compared to joints without alterations in the axis orientation. Moreover, a new cephalometric method could be validated, demonstrating that changes in the condylar axis orientation imply pathology; they could also be correlated with changes in the condylar position and in the glenoid fossa morphology.
The clinical observation of the incisors overbite is the most common form used to evaluate the occlusal vertical dimension (OVD); however, this technique offers poor information about the compression state of the TMJ. In order to obtain such information, it is necessary to evaluate the electrical activity of the elevator muscles using surface electromyography (EMG). In case of a compressive irritation of the joint receptors, the trigeminal nucleus returns an inhibitory motor response of the elevator muscles that can be measured. The Learreta's EMG decompression test is done by measuring the EMG response of the masticatory muscles at maximal occlusion in four different OVD positions in such a way that the reduction of the TMJ pressure, and subsequently, relief of the inhibitory motor response can be studied. The aim of this study is to illustrate this technique, its clinical use and its limitations.
The early evaluation of this joint and the collaborative work of odontologists and rheumatologists are both necessary for a better management of TMJ pathologies.
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