Applications of Motion Analysis System Measuring Micro-Movements in Three-Dimensional Space

This paper presents the development of a novel application using motion analysis techniques to measure tooth movement in 3D space. 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 motion camera units. Software was developed to calculate 3D tooth displacements and rotations. The system accuracy (i.e. percentage of maximum absolute error in range/measurement range), in the 20-200 mum ranges, was plusmn1.17%, plusmn1.67% and plusmn1.31% for the diamond markers in x, y and z directions, while the system accuracy for the spherical markers was plusmn1.81%, plusmn2.37% and plusmn1.39%. The system repeatability (i.e. maximum standard deviation in the measurement range) measured under the different days, light intensity and temperatures for five times, carried out step up and then step down measurements for the same step size, was plusmn1.7 mum, plusmn2.3 mum and plusmn1.9 mum for the diamond markers, and plusmn2.6 mum, plusmn3.9 mum and plusmn1.9 mum for the spherical markers in x, y and z directions, respectively. The system resolution was 10 mum. These results demonstrate that the motion analysis system can measure micro-displacement accurately such as tooth displacement and could potentially be useful in many other applications.