[Development of an analyzing system of multiple points for mandibular movements using Selspot and its application to...

An analyzing system of multiple points for mandibular movements using Selspot was developed in this study. This measuring system is able to analyze simultaneously the movements of multiple required points in three dimensions, and was proved to be sufficient for use with young children because of the small burden imposed on them while taking measurements. Regarding the accuracy of this system, a method to correct the three dimensional distortion of the output values was devised, and a computer program was developed for this method. Therefore, the three dimensional distance between input values and corrected values was squeezed to 60 microns on the average for 80 points which were arrayed in the three dimensional lattice within the range for measurement. By using this measuring system, lateral excursions from the centric occlusion were measured in 9 children (3 boys and 6 girls) with primary dentition. The distance and direction of movements were then calculated around 5 analyzed points on their lower dentition (incisal point, right and left primary canines, right and left primary second molars). For comparing each movement, lateral excursions were standardized at the distance of 2 mm and 4 mm for which the incisal point moved. As a result, the primary second molar point at the working side showed the smallest movement, and the primary canine point at the balancing side showed the largest one. According to the angle of frontal and sagittal projection, the larger the distance of the mandibular movements increased, the more horizontally the lower dentition shifted. The angle of horizontal projection scarcely varied during two standardized movements. Right and left lateral excursions of each subject were statistically very symmetrical. Comparing with formerly reported data for adults, it was thought that the lateral excursions of children with primary dentition shifted more forward and more horizontally.