A RANGE-FINDER-BASED DISPLACEMENT METER FOR MEASURING TOOTH MOBILITY IN 6 DEGREES OF FREEDOM - MEASUREMENT PRINCIPLE AND ERROR PROPAGATION ANALYSIS

Efforts have been cumulated to measure tooth mobility, in order to acc urately characterize the mechanical Features of periodontal tissues. T his paper provides a totally neu; technique for accomplishing the task of measuring tooth displacement in 6 degrees of freedom, using a rang e finder. Its intraoral equipment comprises two elements, a moving pol yhedron and a referential device, both of which are secured to a subje ct tooth and several other teeth splinted together. The polyhedron has 6 planar surfaces, each oriented in a distinctly different direction, with each plane facing an opposing range Ender mounted on the referen tial part. If the sensor geometry is provided. the position and orient ation of the movable part. vis-a-vis the reference, can be determined theoretically from the distances between all the range finders and the ir opposing surfaces. This computation was mathematically formulated a s a non-linear optimization problem, the numerical solution of which c an be obtained iteratively. Its error-propagation formula was also pro vided asa linear approximation.