Citation: Marinelli, F.; Lezcano, M.F.; Alarcón, J.; Navarro, P.; Fuentes, R. A Novel Technique to Accurately Measure Mouth Opening Using 3D Electromagnetic Articulography. Bioengineering 2022, 9, 577. https:// doi.org/10.3390/bioengineering9100577 Academic Editor: Xiaoxiao Cai Received: 1 September 2022 Accepted: 4 October 2022 Published: 19 October 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). bioengineering Article A Novel Technique to Accurately Measure Mouth Opening Using 3D Electromagnetic Articulography Franco Marinelli 1 , Maria Florencia Lezcano 2 , Josefa Alarcón 1,3 , Pablo Navarro 1,4 and Ramón Fuentes 1,5, * 1 Research Centre in Dental Sciences (CICO-UFRO), Dental School—Facultad de Odontología, Universidad de La Frontera, Temuco 4780000, Chile 2 Laboratorio de Cibernética, Departamento de Bioingeniería, Facultad de Ingeniería, Universidad Nacional de Entre Ríos, Oro Verde 3100, Argentina 3 Doctoral Program in Morphological Sciences, Faculty of Medicine, Universidad de La Frontera, Temuco 4780000, Chile 4 Universidad Autónoma de Chile, Santiago 4780000, Chile 5 Department of Integral Adults Dentistry, Dental School—Facultad de Odontología, Universidad de La Frontera, Temuco 4780000, Chile * Correspondence: ramon.fuentes@ufrontera.cl; Tel.: +56-(452)-325-775 Abstract: The mouth opening is an important indication of the functionality of the temporomandibu- lar joint (TMJ). Mouth opening is usually evaluated by asking the patient to open their mouth as wide as possible and measuring the distance between the edges of the frontal incisors with a ruler or caliper. With the advancement of technology, new techniques have been proposed to record mandibular movement. The aim of this work is to present a novel technique based on 3D electromag- netic articulography and data postprocessing to analyze the mouth opening considering distances, trajectories, and angles. A maxilla-mandible phantom was used to simulate the mouth opening movement and fixed position mouth opening. This was recorded using the AG501 3D EMA (Carstens Medizinelektronik GmbH, Bovenden, Germany). The collected data was processed using Matlab (Mathworks, Natick, MA, USA). Fix and mobile mouth opening of 1, 2, 3 and 4 cm were simulated. It was possible to evaluate the mandibular opening through the vertical distance, the Euclidean distance, the trajectory, and the opening angle. All these values were calculated and the results were consistent with expectations. The trajectory was the highest value obtained while the vertical distance was the lowest. The angle increased as the mouth opening increased. This new technique opens up new possibilities in future research since oral opening can be analyzed using multiple variables without the need to use different devices or depending on the researcher’s experience. This will make it possible to establish which parameter presents significant differences between groups of patients or between patients who have undergone some treatment. Keywords: mouth opening; electromagnetic articulography; vector calculus 1. Introduction The mouth opening is an important indication of the functionality of the temporo- mandibular joint (TMJ) [1]. A limitation in the degree of opening can be symptom of TMJ dysfunction [2]. It is usually defined as the distance between the incisor crests when the mouth is open to its maximum, or as the interincisal distance plus the overbite [3]. The mouth opening is usually measured simply by asking the patient to their mouth as wide as possible and measuring the distance between the edges of the frontal incisors with a ruler [4] or caliper [5], and in some cases, the overlapping of the incisors is added [6,7]. All these methods have in common that the measurements are usually taken manually and are dependent on the experience of the professional taking them. The mouth opening continues to be measured rudimentarily, and there is still no universal criterion to include the overbite or not. Bioengineering 2022, 9, 577. https://doi.org/10.3390/bioengineering9100577 https://www.mdpi.com/journal/bioengineering