A Range-Finder-Based Displacement Meter for Measuring Tooth Mobility in 6 Degrees of Freedom: Measurement Principle and Error Propagation Analysis

Toyohiko HAYASHI  Kazuyuki KAZAMA  Takahiro ABE  Michio MIYAKAWA  

IEICE TRANSACTIONS on Information and Systems   Vol.E80-D   No.8   pp.808-816
Publication Date: 1997/08/25
Online ISSN: 
Print ISSN: 0916-8532
Type of Manuscript: PAPER
Category: Medical Electronics and Medical Information
tooth mobility,  6-degree-of-freedom measurement,  range finder,  nonlinear optimization,  error propagation,  

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Efforts have been cumulated to measure tooth mobility, in order to accurately characterize the mechanical features of periodontal tissues. This paper provides a totally new technique for accomplishing the task of measuring tooth displacement in 6 degrees of freedom, using a range finder. Its intraoral equipment comprises two elements, a moving polyhedron and a referential device, both of which are secured to a subject 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 finder mounted on the referential part. If the sensor geometry is provided, the position and orientation of the movable part, vis-a-vis the reference, can be determined theoretically from the distances between all the range finders and their opposing surfaces. This computation was mathematically formulated as a non-linear optimization problem, the numerical solution of which can be obtained iteratively. Its error-propagation formula was also provided as a linear approximation.