Digital Facebow System for Mandibular Movement Tracking Using Near-Infrared Optical Measurement

Accurate recording of mandibular movements is essential in stomatology for the diagnosis of functional disorders and the planning of restorative treatments. Although commercially available electronic facebows, developed through diverse technical approaches, offer greater accuracy than mechanical facebows, their high costs and operational complexity have limited their widespread use in clinical practice. This paper presents a digital facebow system that modifies a conventional Girrbach mechanical facebow with reflective marker balls and integrates it with a dual-camera near-infrared (850 nm) optical measurement system. A novel two-stage calibration procedure ensures high measurement accuracy, and a spatial-constraint-based decoding algorithm enables robust identification of non-encoded marker balls in three-dimensional (3D) space. Subsequently, the system registers mandibular movement by calculating the relative pose between the upper and lower facebows in real-time. Experimental validation, including trajectory tracking on precision slides and a simulated scenario using a head model, demonstrates the system's accuracy and clinical feasibility. The proposed solution provides a cost-effective and low-complexity pathway for digital mandibular movement registration, facilitating the integration of mechanical facebows into digital dental workflows.