Electric activity of stomatognatic muscles and opening of the lower jaw

OBJECTIVES The aim of this work was to com-pare electromyographically and ki-nesiographically a group of dysfunctional subjects with a group of non-dysfunctional subjects evaluating the existence of significant correlations between the results of the electromyographic values and the kinesiographic data concerning the maximum voluntary mandibular opening of these subjects. MATERIALS AND METHODS 20 dysfunctional and 15 non-dysfunctional patients were enrolled and all underwent electromyographic and kinesiographic examinations assisted with TENS. The instrument used was the K7 (Myo-tronics Inc., Seattle, USA). Electromyograph. Seattle, whilst the J5 Myomonitor device (Myotronics Inc., Seattle, USA) was used for TENS. After positioning the three electrodes of TENS (right sigmoid incision, left sigmoid incisor and nape), the bipolar electromyograms were positioned on the stomatognathic muscles listed below. Subse-quently, we moved on to positioning the kinesiograph. It is an electronic system, currently totally computer-ized, consisting of a small intraoral magnet that is placed in the arch at the level of the lower incisors and by a frame with sensors made soli-dal with the patient’s head through a sot of eyeglasses frame. The sensors read and measure changes in the position of the magnetic field during mandibular movements; a special software processes the signals transforming them into graphical plots. The activity of 4 bilaterally studied muscles was recorded: masseter, anterior temporal, digas-tric, as chewing muscles; sterno-cleidomastoid, as a neck muscle. The following recordings were made: SCAN 9 (electric activity at rest), SCAN 11 (muscle activity during the frame), SCAN 1 (kine-siography, maximum opening of the mouth), SCAN 2 (kinesiography, opening speed), SCAN 3 (free space at rest). After applying the TENS (0.66 hertz, 45 impulses per minute) for a few minutes, the following recordings were made: SCAN 10 (electrical activity after TENS), SCAN 4 (free space after TENS), SCAN 5 (SCAN 4 in sagit-tal-frontal mode). The operator was blind about the actual diagnosis of TMD; for this purpose numerical codes have been used. RESULTS AND CONCLUSIONS The electromyography of dysfunctional patients and functional controls showed a significant difference between the values expressed in millivolts (mV) obtained by summing all the muscles of the stomatognathic system. Dysfunctional patients were characterized by greater muscle contraction activity compared to controls. The mean mV of dysfunctional patients was found to be 17.34±8.25, while that of functional controls was 10.71±3.15. Dysfunctional patients had a lower voluntary maximum opening compared to functional controls. In fact, the maximum voluntary openness of dysfunctional patients was found to be 37.13 mm±5.78 while that of functional controls was 41.81 mm±4.34. The results obtained would seem to show that in the dysfunctional patients the examined muscles show more widespread hyper-tones than the functional subjects; the maximum voluntary opening of the mandible was statistically reduced in dysfunctional patients compared to functional subjects. CLINICAL SIGNIFICANCE Electromyography, a low cost, non-invasive and painless procedure, could be an additional aid in subjects suffering from TMD as an adjuvant and integrative analysis. The electromyographic and kinesiographic traces, before and after TENS, can be a useful method for diagnosing and verifying possible therapies, both prosthetic and orthodontic. Moreover, these data indicate that a treatment aimed at reducing the electromyographic activity of the chewing muscles could bring benefits in terms of masticatory functions.