###### Abstract  
Clinical use of portable optical tracking system in dentistry could improve the analysis of mandibular movements for diagnostic and therapeutic purposes. A new workflow for the acquisition of mandibular kinematics was developed. Reproducibility of measurements was tested in vitro and intra- and inter-rater repeatability were assessed in vivo in healthy volunteers. Prescribed repeated movements (n = 10) in three perpendicular directions of the tracking-device coordinate system were performed. Measurement error and coefficient of variation (CV) among repetitions were determined. Mandibular kinematics of maximum opening, left and right laterality, protrusion and retrusion of five healthy subjects were recorded in separate sessions by three different operators. Obtained records were blindly examined by three observers. Interlades correlation coefficient (ICC) was calculated to estimate inter-rater and intra-rater reliability. Maximum in vitro measurement error was 0.54 mm and CV = 0.02. Overall, excellent intra-rater reliability (ICC > 0.90) for each variable, general excellent intra-rater reliability (ICC = 1.00) for all variables, and good reliability (ICC > 0.75) for inter-rater tests were obtained. A lower score was obtained for retrusion with \"moderate reliability\" (ICC = 0.557) in the inter-rater tests. Excellent repeatability and reliability in optical tracking of primary movements were observed using the tested portable tracking device and the developed workflow. kinematics; dentistry; mandible +
Footnote †: journal: Medical  
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University Canada) and has been successfully used in several medical fields [7; 8], showing promising results. This device has the advantage of small size and simple set-up requirements. Studies using this system were conducted in neurosurgery, spinal surgery, robotic surgery, and facial transplantation [7] with a distance error of 0.35 mm RMS (root mean square-85% of cases) [8]. This type of device may be also introduced in a clinical context in the field of dentistry to quantitatively analyze the range of motion of the mandible. In fact, non-invasive tracking systems can detect irregularities in the mandibular function that can otherwise appear clinically normal. For instance, in the case of mandibular movements with a normal mouth opening, a tracking system can identify a change of the mandibular movements during mouth opening into their rotatory (lower temporo-mandibular (TMJ) compartment) and translatory elements (upper TMJ compartment) [9; 10]. Furthermore, for a more sophisticated biomechanical analysis of the mandibular motion, a three-dimensional animating technique called dynamic stereometry, has been developed in the past based on active markers, optoelectronic motion-tracking and subject-specific anatomical information obtained utilizing standard tomographic methods (e.g., CBCT, MRI). This method allows the dynamic representation of the relative movement of the mandible with respect to the head and performs quantitative measurements within the joint of the analyzed subject. In particular, the intra-articular space can be quantified and any anatomical point on the articular surface of the joint during functional movements can be tracked [11]. The combination of motion and anatomy, until now confined mainly within the research field, could allow innovative dynamic diagnostic tests applicable for example in DC-TMD nosological classification when translated into the clinical settings [12]. For this reason, a precise and reliable determination of the mandibular motion relative to the head has to be provided by the selected tracking system. Effectively tracked motion of mandibular positioning and movements in 3D could allow precise recreation of its digital dynamic model. Therefore, its accuracy is crucial for the evaluation of the device's effectiveness.