# 3D-Printed Helmet for Electromagnetic Articulograph Applied in the Study of Oral Physiology
## 4 Discussion  
Electromagnetic articulography is a technique that allows the recording of mandibular movement while compensating for head motion. It differs from other technologies, such as video-based marker tracking [13], ultrasound systems [14], or kinesigraphy [15], by enabling the attachment of the motion sensor inside the oral cavity and by not requiring a facebow to eliminate head movement. However, since reference sensors must remain in a fixed position throughout the entire recording to perform head correction, multiple calibrations may be necessary during a single session. This can be a limitation for long recordings or for protocols requiring border movements. In addition, participants must be instructed to avoid excessive head movements to prevent the cables from pulling on the sensors. This may cause discomfort to the subject and restrict the types of studies that can be conducted using this technology. In the present study, a sensor fixation device was developed to address these limitations and expand the applicability of electromagnetic articulography in dental research. A reduction in the need to perform repeated head corrections during the session when using the helmet was observed; however, this difference was not statistically significant (Table 1). In addition, the total number of head correction procedures required per session tended to decrease. This is illustrated in Figures 7 and 8, where, in the case of participants with reference sensors attached to the skin, one subject required four head corrections to complete the recording session (Session 1), and four others required three head corrections (three in Session 1 and one in Session 2). In contrast, when using the helmet, only one subject required three head corrections to complete the recording session (Session 1). Table 2 shows an improvement when using the helmet in both sessions 1 and 2; however, no statistically significant differences were found. The need for multiple head corrections during a session may be influenced by the type of exercises performed in each session. As shown in Table 3, there was a significant reduction in the number of head corrections required between Session 1 and Session 2, regardless of helmet use. This difference may be explained by the fact that, in Session 1, the [PERSON]'s envelope exercises were performed, which involve instructing the participant to make extensive border mandibular movements. These movements can displace the skin where the reference sensors are attached, leading to potential misalignment of the reference system. Moreover, it was observed during the study that some participants tended to rotate their heads while performing lateral border movements, as well as during the frontal and horizontal envelope exercises, potentially pulling the cables and misaligning the reference system. This may explain why more head corrections were required in Session 1 compared to Session 2. In Table 4, participants who completed both sessions were  
\begin{table} \begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Session**} & **Reference Sensors** & **N** & **HC** & **Mean** & \(p\) \\  & **Placement** & & & & \\ \hline \multirow{2}{*}{1} & Skin & 17 & 29 & 1.71 & 0.02 * \\  & Helmet & 18 & 25 & 1.39 & 0.03 * \\ \hline \multirow{2}{*}{2} & Skin & 12 & 15 & 1.25 & \textgreater{}0.05 \\  & Helmet & 11 & 11 & 1.00 & \textgreater{}0.05 \\ \hline \hline \end{tabular}   
*compared. Again, Session 1 required more head corrections in both groups; however, no statistically significant differences were detected. Ideally, only one Head Correction would be required per recording session, but because of skin motion, the reference sensors can move and a new Head Correction is required to continue with the recordings. Table 5 presents a comparison of the number of head corrections performed in Sessions 1 and 2, with and without the helmet, against the ideal value of one head correction per session. In Session 2, neither the helmet nor the non-helmet group showed significant differences compared to the ideal value.