The Developmental Mechanism and the Treatment of Malocclusion Accompanied with Progressive Muscular Dystrophy

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The purpose of the present research was to examine the developmental mechanism of malocclusion accompanied with Progressive Muscular Dystrophy (PMD).In 30 patients with PMD in the Nishibeppu national hospital, the relation between the changes of masticatory muscle activities and occlusal morphology was investigated. Muscle activities were measured by surface electromyography, microvibration of muscles, tongue and lip pressure and occlusal force. Mrophological examination were made by intraoral and facial photographs, cephalometric radiographs and plaster models.Results. 1. It seems that the open bite observed in PMD patients was due to the combination of clockwise mandibular rotation, lateral expansion in the lower molar region and lingual tipping of the anterior teeth. 2. The muscular strength of the masticatory muscles was decreased as well as the other masculature of the body. 3. Regarding the change of the overbite, two groups, bite opening and overbite stable group, were observed. Lissajous' figures were drawn from EMG power spectra of the masseter and the anterior belly of the digastric muscle to analyze the change of the jaw opening and closing muscle balance. In the bite opening group, the time to change the slope of the figure obviously existed, when was coincided with rapid decrease of the activities of serum creatine kinase. 4. The longitudinal materials of a monozygotic twin were analyzed on the influence of heredity and environmentupon the growth and development. The timing and degree of the decrease and imbalance of muscle function and the increase of negative overbite were different between them. Differences in form and function of orofacial complex between them might be cause by their polygene heredity and the large size of DMD gene (XP21). Therefore, for the analysis of the difference of gene, the ranks of the amino acid of DNA extracted from the monocyte are examined at present.