## 4 Discussion
[28] in their dynamic stereometry studies used metal clutches rigidly connected with dental polymers to the dental arches and an additional external face-bow carrying a reference for the anatomy registration. [PERSON] et al. [29] described inter-rater reliability of a six-camera motion system with fifteen individual markers capturing at 120 Hz. The use of a 3D-printed custom-fitting design, allowed the operator to avoid the use of dental polymers for the retention in most of the cases. The precision of the NDI Polaris Spectra was tested in previous works [30], showing a maximal length error as 0.514 mm and a maximum clinical error, dependent on the markers configuration, of 1.3 mm during static recordings. In our in vitro tests, the mean error was calculated based on dynamic data, and gave comparable results as the maximal length error. As expected, the direction perpendicular to the cameras (z or back-forth) gave the highest errors. Furthermore, the variability measured with the coefficient of variation was very low, in the order of \(10^{-3}\). The reproducibility of the method by different operators showed the highest precision (0.7-0.9) during simple movements as mouth opening and laterality, while the lowest values (0.5-0.7) were observed for retrusion. This was probably related to the difficulty of the movements and efforts of volunteers even after the training session. In comparison, [PERSON] et al. [10] published ICC values between 0.57 and 0.76 using more complicated and non-portable instrumentation. The overall simplicity of the proposed system was reported by all operators, also the volunteers did not report any discomfort or pain during the measurement sessions. The advantage of the system is that it could be rapidly applied to patients in different settings and conditions and in a near future used as a diagnostic tool in the TMD scenario, and also be used in dental offices in combination with 3D data to the CBCT and the patients (Figure 4). The superimposition of CBCT and digital motion scans can be achieved by the use of the mucogingival junction as a reference as described by [PERSON] et al. (2018). The visualization of the movement of the craniofacial structures avoids the necessity of performing more complicate and expensive exams as dynamic RMI and could offer a new method for gathering dynamic records from the patient in an era where full digitalization of the patient's records still represents a challenge ([PERSON] et al., 2018). Figure 4: (**a**) The superimposition of the CBCT craniofacial structures with a photograph of the volunteer during the experimental session. (**b**) Combination of CBCT data with the mandibular kinematics recorded during the experiments. The figure shows the position of the condylar head of the mandible in closed (left), light open (middle) and maximal opening position (right). The study was conducted in a small sample of healthy subjects under controlled conditions. Further data should be collected under different experimental conditions and involving dysfunctional patients in a wider population with better distribution considering the specific variables of the sample. Furthermore, gender- and age-related variables should be considered to avoid bias as described by other authors [33]. A technical limitation of the proposed system could be the difficulty to attach the connectors in patients with the absence or altered anatomy of the inferior teeth. Possible improvements of the system might include as well the development of an automatic detector for the maximal excursion position in order to exclude the intra-operator variability and increase the precision of the method. Based on these results further research is need to describe the variability range into different stomatognathic pathological conditions or mastication were the mandibular range of motion could be used as valuer or risk predictor of disease.