Developmental aspects of digital jaw motion and patient-specific articulator

Abstract

The human masticatory system has complex anatomy to allow an intricate set of jaw motions for different oral functions. During oral rehabilitation, tooth position, tooth alignment and occlusal morphology of the dental prostheses should be customized and in harmony with the individual patient’s jaw movements. In the conventional workflow, it is accomplished by an articulator, a mechanical device to simulate jaw movements. However, it cannot precisely replicate patient-specific jaw motion trajectories and hence, the fabricated prostheses still require a lot of adjustment at the chairside. With the advent of computer-aided design (CAD) and computer-aided manufacturing (CAM) technology, digital workflow including virtual planning, design and fabrication of dental restorations and prostheses has become popular in dental practice. Jaw motion analyzer (JMA) systems are available, but they are rarely used due to the high cost of installation and complexity of use.

This work described new methods for evaluating JMA accuracy by comparing predetermined positional and dynamic trajectories. Jaw motion data were used to set up a virtual articulator followed by fabrication of a patient-specific 3D printed articulator. Testing of the lighting conditions and positions of the sensors was performed during photometric motion tracking with the Prosystom ProAxis axiography device. Fiducial markers with visible central and corner points were placed on the upper and lower jaws and detected by the camera. Prosystom P-art software with the perspective-n-point (PnP) method was used to record the trajectory and estimate the mandibular position relative to the maxilla. The positional accuracy test was performed with indirect and direct light sources facing fiducial markers positioned in 4 different angulations, attached to the models inside the articulator, and guided by the custom incisal table. The patient-specific virtual articulator was developed using 3D computer graphics software based on the jaw motion data from the camera-based JMA, scanned dental arches, and control models for alignment. The virtual articulator was recreated digitally by processing mixed polygonal and motion data in open-source software. The mechanism for a fully 3D printed mechanical articulator was designed by exporting model instances of each keyframe into non-uniform rational basis spline (NURBS) software. The model with patient-specific articulation was fabricated using a stereolithography (SLA) printer.

The experimental results showed that the performance of the camera-based JMA was affected by lighting conditions and performed significantly better with dental operatory lights. Marker rotation had significantly better results when the upper marker was positioned perpendicular to the camera system and the lower marker was fixed at a 30-degree angle. The photometric system showed a positional accuracy of < 0.6 mm and a dynamic accuracy of < 1mm. Customized virtual articulators and 3D printed articulator models were shown to be able to reproduce various jaw motions.