Electronic measurement ofmandibular positionthorough magnetic sensors.

Hidetoshi Hirano,ShojiKohno,Yoshiaki Yamada＊,Hiroshi Sugimoto
Department of RemovableProsthodontics,NiigataUniversity,School of Dentistry
(Chief:Prof.Shoji Kohno)
＊Department of Oral Physiology,Niigata University,School ofDentistry
(Chief:Prof.Yoshiaki Yamada)

Abstract:
Vertical dimension must be examined todetermine centric occlusionwhen treating patientswhose occlusion has collapsed. Up to now,we have
been using calipers to measure mandibular position,but thismethod does not assure accurate measure-ments of mandibularposition. We have developed asmall and light electronic measuringdevice whichcan measure mandibular position throughmagneticsensors.
This device consists of a magnet attached on thelower jaw, a pairof sensor units set on the sidesof the nose tip which are kept40mm apart from themagnet, and a sensor set on the forehead toavoidgeomagnetism.Calibration for the output from thesensor unitwas made, and the resulting outputcurve was approximated to astraight line. We alsotested several factors that could causemeasure-ment error such as temperature senshitivity of thesensor,temperature sebsitivity and drift of thecircuit, improvement oflinearity of the sensoroutput, and the influence of head unrestand geo-magnetism. When these factors were cleared, weproceededto try it clinically.
As a result, it was possible to measure mandibu-lar positionwithin a range of 30mm - 50mm with anerror margin of 3-5%. Forcentric occlusion andrest position, it became clear that wecouldmeasure mandibular position precisely by fixingthe magnetonto the gingiva of the lower anteriorincisor teeth.

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