Measuring tooth movement in 3D Resolution, accuracy and reliability of the optical motion capture system

This paper presents the development of a novel application using motion analysis techniques to measure tooth movement in 3D. Measuring the relative displacements of teeth under load allows a greater understanding of the mechanical properties of the periodontal ligament (PDL). Two marker clusters were fixed onto the measured tooth and the reference tooth via orthodontic brackets and movements were captured using two 60 Hz infrared cameras. Software was modified to calculate 3D tooth displacements and rotations. The development of this system will provide reliable data for modelling the periodontal ligament (PDL). It is therefore important to evaluate the measurement system characteristics. • System accuracy, defined as % max. absolute error / measurement range, was 2.13 % using spherical markers and 1.5 % using diamond markers for a measurment range of 20-200μm. • System resolution, defined as minimum step size that the system could accurately detect, was 10μm. • System noise band was 5.76μm • System repeatability, defined as max. st. dev. in the measurement range, was measured in the x, y and z directions on different days (light intensity and temperature), five times, using step up and then step down measurements for the same step size and was range from ± 1.7μm to ± 3.9μm. These results demonstrate that the system is sufficiently accurate to measure tooth displacements (120160 μm) and could potentially be useful in many other applications. Keywords-component; tooth movement, system accuracy