The present study proposed and established a Proof-of-concept for the synchronization of two electromedical sytems, 3D electromagnetic articulography and surface electromyography, explaining it in detail so that it can be replicated by other research groups. The implementation of the synchronization and further analysis aims to improve understanding of the complexity of mandibular functional movements which may be applied to study different clinical situations.
The study of functional movements through analysis of kinematics and muscle activity is widely approached in various disciplines , including dentistry [1–3,5,7–9,11,13–14,16,28], which reveals the importance of analyzing these complex movements by various methods that complement each other.
Simultaneous measurements of different biomechanical variables of mandibular movements have been carried out for many years. Bigland measured the speed of contraction, the EMG activity, and the tension applied controlled by putting different weights . More recent studies have also analyzed mandibular movements with simultaneous recordings of electromyographic activity and jaw movements in dentate individuals  and patients with maxillary and mandibular complete dentures  without synchronizing both recordings. These studies, even with clinical value, have its limitations due to the lack of synchronization of their recordings or lack of more detailed explanation of the methodology employed. Thus, limiting the extrapolation of their results in the clinical understanding of mandibular movements that reveal the need for a more complete analysis.
Other authors have developed studies demonstrating the concern to synchronize the signals recorded by different electromedical equipment related to mandibular movements with the electromyographic activity of the muscles of the stomatognathic system [6–7,9–11,14], however, these studies did not provide enough information regarding the methods to be replicated.
Some studies have shown the synchronization between electromedical equipment applied to different analyses of the stomatognathic system, using arrangements or equipment specially developed for this purpose. Widmalm et al. designed and built a special device to combine recordings of vibration and EMG activity . Nakazawa et al. performed a master-slave arrangement for palatal pressure, mandibular movement, and EMG recordings with 1 ms delay in the synchronization . Kerstein used a specific synchronization module for EMG signal analysis and occlusal force distribution analyzed using the T-SCAN system [32–33]. And Grigoriadis et al. synchronized EMG records of masseter muscle and mandibular movements using 2D magnetic sensors using a commercial system .
Other studies performed the synchronization of the recordings by generating an independent and identifiable event in the signals acquired by different systems. Ahlgren used a light signal to synchronize EMG and cinematography recordings . A pulse generator was used to synchronize EMG activity and mandibular movements by videofluorography and cineradiography [3–5]. Freitas et al. synchronized the recordings of mandibular movements obtained by a Kinect sensor and EMG activity through a computational custom made system .
Synchronization through the generation of a specific event was the method chosen by our research group to synchronize the EMG recordings of masticatory muscles and mandibular movements. In our case, we used a “switch” device that comes with EMG equipment and a sound recorder that comes with AG501 3D-EMA equipment. Activation of this switch generated an independent and distinguishable event in both registers, which in the case of EMG was recorded as a square electrical signal and in the EMA a peek in the acoustic signal, which was used to synchronize both recordings.
Our recording method is a novelty in the scientific literature, and has the advantage of the high accuracy of the movement-recording method demonstrated in previous articles from our research group [22–24]. In addition, this synchronization was performed using only the components that already accompany both equipment selected, a fact that besides facilitating its realization and replication, does not add costs to its realization.
In general, our results obtained during synchronized recordings showed no distortion/alteration outside the limit values informed by the manufacturers. Even though both instruments are very sensitive to electromagnetism, the EMA AG501 and the EMGs proposed in this methodology do not generate interferences between them during the simultaneous recording. Probably because the bandwidths with which each system works do not overlap.