## 4 Discussion  
To authors' knowledge, this is the first study describing the reliability analysis of a mandibular kinematic tracking set-up developed using a simple, light, and portable hardware with infrared cameras and passive markers, and self-developed software to relate the mandibular motion to the craniofacial structures of the subject. The aim of the newly developed procedure was to obtain a method to calculate and mathematically exclude all supplementary movements of the head and neck from motion tracking. This was possible using a custom-designed algorithm that subtracted the movements from the superior anchored markers to the inferior markers in real-time. Similar transformation \begin{table}
\begin{tabular}{c c c} \hline \hline
**Movement** & **Excursion Error (mm) (Mean \(\pm\) SD)** & **Coefficient of Variation (Mean \(\pm\) SD)** \\ \hline left-right & 0.45 \(\pm\) 0.28 & 0.002 \(\pm\) 0.001 \\ back-forth & 0.54 \(\pm\) 0.26 & 0.005 \(\pm\) 0.002 \\ up-down & 0.42 \(\pm\) 0.29 & 0.020 \(\pm\) 0.008 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Results of the in vitro reproducibility tests. The excursion error [mm] was used as a measure of the accuracy for the set-up; the coefficient of variation as a measure of its precision. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Observer 1**} & \multicolumn{2}{c}{**Observer 2**} & \multicolumn{2}{c}{**Observer 3**} \\ \hline
**Movement** & **ICC** & **95\%CI** [Low-Up]** & **ICC** & **95\%CI** [Low-Up]** & **ICC** & **95\%CI** [Low-Up]** \\ \hline Maximal Opening & 0.999 & 0.998–1.000 & 1.000 & 0.999–1.000 & 0.994 & 0.985–0.998 \\ Laterotrusion Right & 0.994 & 0.986–0.998 & 0.994 & 0.985–0.998 & 0.994 & 0.985–0.998 \\ Laterotrusion Left & 0.996 & 0.991–0.999 & 0.994 & 0.985–0.998 & 0.994 & 0.985–0.998 \\ Retrusion & 0.951 & 0.887–0.982 & 0.994 & 0.985–0.998 & 0.789 & 0.600–0.919 \\ Protrusion & 0.994 & 0.986–0.998 & 0.994 & 0.985–0.998 & 0.984 & 0.963–0.994 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: ICC estimates for intra-rater reliability and their 95% confidence intervals. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Movement** & **ICC** & **95\%CI** \\ \hline Maximal Opening & 0.764 & 0.649–0.852 \\ Laterotrusion Right & 0.779 & 0.666–0.863 \\ Laterotrusion Right & 0.782 & 0.679–0.864 \\ Retrusion & 0.557 & 0.390–0.705 \\ Protrusion & 0.702 & 0.561–0.813 \\ Maximal Opening & 0.764 & 0.649–0.852 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: ICC estimates for inter-rater reliability of each variable and their 95% confidence intervals. algorithms for the detection of relative mandibular motion were applied in the past by other authors by using a sophisticated custom-built tracking system based on active-markers and custom-made software [11]. The proposed workflow included 3D printing of custom-made adapters for the participants and 3D-scanning of the parts to obtain the geometrical relationship between the markers and the anatomy, allowing in short-time, implementation of an anatomically related tracking system. Previous studies showed that the precision and reliability of 3D scans and CAD techniques for digitalization of prosthodonic procedures was very high, although slightly dependent on the selected acquisition system [26; 27]. Furthermore, the anchorage method played an important role in the registration of the movements. For the experiments, the shape of the arches was obtained from 3D digital scans of the dental cast models [21] and a resin model with a metal connection to the 3D printed connector was used in order to align with the anatomy of the inferior teeth of each volunteer. The use of a resin splint was also proposed with good results by [PERSON] et al. [14] with a full arch inferior resin splint including the lingual and vestibular surfaces, but this methodology might not apply to all patients. In contrast, [PERSON] et al.