Development of a novel system to measure and calculate tooth movements for studying the properties of the periodontal ligament

Motion analysis techniques have been widely used in biomechanics for measuring large-scale motions such as gait, posture etc, but have not yet been significantly explored for measuring smaller movements such as tooth movement under load. In principle, very accurate measurements could be possible and this could provide a valuable tool in many engineering applications. The aim of this study was to develop a novel system to measure and calculate tooth movements with 6DOF in 3D space for studying the properties of the periodontal ligament. The Qualisys ProReflex-MCU120 motion capture system has been developed to measure micro-movements. The calibration frame was designed and made for the system calibration. The system accuracy was 1.17%, 1.67% and 1.31% for diamond markers 1.81%, 2.37% and 1.39% for spherical markers in x, y and z directions in the range of 20 - 200pm. These results demonstrated that the system is accurate enough to measure small-scale movements. To measure tooth movement, two retroreflective marker clusters, two pointers and one plane for the pointer calibration were created. The two marker clusters were fixed on the measured tooth and the reference tooth for measurements. The pointer was used to identify the three landmarks for identifying anatomical coordinate system of tooth. Data analysis software was developed and evaluated for calculating tooth movement in 6DOF. In the data analysis software, the three coordinate systems method was used with transformation matrices to give 6DOF results. The evaluation results of a complete system were 3.2%, 2.8% and 2.4% for rotations 5.3%, 7.7% and 4.7% for translations in x, y and z directions in the term of accuracy. For producing tooth measurements, loading devices and loading control system were designed and tested. The experiments were carried out on human volunteers in clinical setting. Loads of 0.196N, 0.294N and 0.49N were separately applied to the measured tooth in the buccal direction and the intrusive direction for 10s and 30s, respectively. The experimental results demonstrated that, with the buccal loading, the tooth translations were 32pm for load of 0.294N, and 41pm for load of 0.49N in the y direction of the anatomical coordinate system, tooth rotations were 0.09 and 0.07 for load of 0.294N, and 0.1 and 0.06 for load of 0.49N in the x and z directions with the intrusive loading, tooth movements were 37pm, 15pm and 54pm for load of 0.196N, and 140pm, 51pm and 25pm for load of 0.49N in the x, y and z directions, tooth rotations were 0.04 , 0.07 and 0.2 for load of 0.196N, and 0.26 , 0.195 and 0.35 for load of 0.49N about the x, y and z directions. Overall, a novel system of measuring and calculating tooth movement has been developed. It could be useful in applications in many other engineering fields