The Development and Use of an Intraoral Force Transducer in the Diagnosis and Treatment of Myasthenia Gravis

Abstract

Myasthenia gravis is a neuromuscular disease characterized by variable weakness following voluntary muscle exertion. Because responses to the disease vary considerably between muscle groups, as well as between stages of the disease, diagnosis sometimes becomes a difficult and subjective evaluation. The purpose of this investigation was to fabricate an intraoral force transducer for measuring incisive biting force, and to test its usefulness in obtaining an objective and quantifiable evaluation of an "individual's myometric response during the standard diagnostic procedures. A cantilever beam force transducer was developed, along with a technique for using it diagnostically in conjunction with the intravenous injection of an anticholinesterase drug (Tensilon). Twenty-three known myasthenic patients were tested, as well as nine normal individuals. This examination consisted of a battery of tests to determine the subjects’ incisive biting force, vital capacity, grip strength, strength of neck flexion and extension, range of eye movements, speech, jaw opening power, palpebral distance, and visual acuity. The tests were conducted three times: First, to establish a basal level; Second, after a placebo injection; Third, after the injection of the anticholinesterase. The data were tabulated and evaluated using an analysis of variance with repeat measures design technique. The results of the statistical analysis of data verifies that the placebo effect was not significant, and that the biting force instrument recorded a significant variation in the response of a myasthenic individual as compared with a normal individual when subjected to the administration of a standard diagnostic drug. Consequently, it was concluded that an intraoral force transducer of this design is of significant value in the diagnosis and treatment of the disease, myasthenia gravis.