# 3D-Printed Helmet for Electromagnetic Articulograph Applied in the Study of Oral Physiology
## 1 Introduction  
The analysis of mandibular movement is of great interest in the field of dentistry. It has implications for the development of new full digital workflows for temporomandibular disorders treatment [1; 2], the study of the temporomandibular joint (TMJ) condition [3], bruxism [4], relationship between cognitive decline and kinematic parameters of mastication [5] and relationship between dental status and food intake [6] among others. Certain studies require simple recording methods, which capture only aspects such as chewing time, the number of masticatory cycles, and frequency (derived from the previous variables). For this purpose, video recording alone is sufficient [6; 7]. More complex studies that involve mandibular position in space require not only the tracking of mandibular movement but also the isolation of this movement from head movement [8; 9; 10; 11; 12]. Various technologies have been developed for this purpose. [PERSON] et al. designed a system based on external markers and motion capture using six cameras. Three of these markers were placed on the head, while the other three were attached to a frame fixed to the mandible [13]. Other systems are based on the emission of ultrasound, with the transmitter attached to the mandible and the receiver fixed to the head. The system determines the mandibular position by measuring the time it takes for the sound waves to reach the receiver [14]. Kinesiography is based on recording the movement of a magnet attached to the mandible by means of a sensing system fixed to the head [15]. Electromagnetic articulography (EMA) was originally developed for use in the field of speech-language pathology, enabling the recording of tongue movement during speech [16]. It consists of a set of emitter coils that generate electromagnetic fields at different frequencies. These induce a current in small receiver coils, which is acquired by the equipment and used to determine the spatial position of the receiver coils that act as motion sensors [17]. While there are various methods for recording the movement of external structures, such as the lips and mouth, during speech [18], EMA allows for the recording of internal structures, such as the tongue [19; 20]. These techniques appear to be safer than alternatives that require radiation, such as cineradiography [21] and fluoroscopy [22]. Ultrasound [23; 24] and MRI [25] are alternative techniques that provide movement records without exposing subjects to radiation. While these systems offer a full view of mouth and tongue movements, it is more difficult to determine spatial coordinates from these recordings. EMA has been employed in various studies conducted at the Oral Physiology Laboratory of the Universidad de La Frontera, focusing on dental research. This technique has been applied to the analysis of tongue and mandibular movements during chewing [26], speech [27], and swallowing [28], as well as in the evaluation of denture micromovements [29]. All these studies utilized the AG501 electromagnetic articulograph (Carstens Medizinelektronik GmbH, Bovenden, Germany). Tests using the AG 501 were conducted on young adults [26; 27; 28] or involved only chewing movements [29]; consequently, skin movement may have been reduced, as increased age is associated with greater skin laxity [30; 31]. This equipment not only allows for recording movement but also isolates it from other movements that may interfere. In the case of mandibular and tongue movements, it is possible to eliminate head movement using the head correction procedure. This consists in the use of reference sensors that are attached to skin on glabella and left and right mastoid processes [28]. With these sensors adhered to the patient's head, a first record is made and used as reference to eliminate head movement in the next records. This procedure uses the algorithms based on analysis of Procrustes developed by [PERSON] [32] as well as [PERSON] and [PERSON] [33].