An Optical Measurement System for Open-Source Tracking of Jaw Motions

TL;DR

This work addresses the need for accessible jaw-tracking tools for temporomandibular disorders (TMDs) and jaw rehabilitation devices. It presents an open-source, low-cost optical motion capture pipeline comprised of a mandibular tracking array, a cranial reference array, and a digitizing pointer, with a complete processing pipeline from calibration to data storage. In a four-participant study, the system demonstrated sub-millimeter positional and sub-degree angular precision, indicating feasibility comparable to commercial solutions for key metrics. The open-source, modular design aims to accelerate jaw exoskeleton development and clinical research, with future work focused on broader validation and real-time capabilities.

Abstract

Precise tracking of the jaw kinematics is crucial for diagnosing various musculoskeletal and neuromuscular diseases affecting the masticatory system and for advancing rehabilitative devices such as jaw exoskeletons, a hardly explored research field, to treat these disorders. We introduce an open-source, low-cost, precise, non-invasive, and biocompatible jaw tracking system based on optical motion capture technology to address the need for accessible and adaptable research tools. The system encompasses a complete pipeline from data acquisition, processing, and kinematic analysis to filtering, visualization, and data storage. We evaluated its performance and feasibility in experiments with four participants executing various jaw movements. The system demonstrated reliable kinematic tracking with an estimated precision of $(182 \pm 47) μm$ and $(0.126 \pm 0.034) °$. Therefore, the open-source nature of the system and its utility comparable to commercial systems make it suitable for many research and development contexts, especially for applications such as the integration and design of jaw exoskeletons and customized diagnostic protocols. The complete system is available at GitHub with the aim of promoting innovation in temporomandibular disorders research and jaw assistive technology.

Figures (3)

• Figure 1: The jaw tracking system consists of a mandibular tracking array attached to the lower teeth with dental glue, a cranial reference array on the forehead, and a pointer for anatomical landmark digitization. The optical motion capture system tracks the 3.0D positions of all markers. An exemplary trajectory of the lower incisal point is shown on the lower right. The image of the head was generated with OpenAI's DALL-E 3.0.
• Figure 2: Illustration of the jaw tracking system's data acquisition and processing pipeline. The setup begins with the attachment of the MTA to the lower teeth and the CRA to the forehead. The system utilizes an OMoCap system to record the $3$D positions of reflective markers attached to these arrays. The DP is used to register anatomical landmarks on the teeth, defining local coordinate systems for the mandible and maxilla. During operation, the patient performs various jaw movements, and the system records the marker trajectories. The raw data is processed to calculate relative mandibular motion, isolate jaw kinematics, and register the motion to a virtual jaw model. The final output includes filtered kinematic data, which can be visualized and stored for further analysis.
• Figure 3: The $3$D trajectories of all recorded jaw movements of the four participants, including opening and closing, protrusion and retrusion, lateral motions, and cyclic motions. The reference point on the jaw is the incisal point in the middle of the lower teeth.