title: Analyses of muscular activity, energy metabolism, and muscle fiber type composition in a patient with bilateral masseteric hypertrophy.
abstract: Hyperwork of the masseter muscles due to habitual parafunction is thought to induce masseteric hypertrophy (so called work hypertrophy). However, the causes underlying this disease are not yet fully understood. Recently, we had a patient with bilateral masseteric hypertrophy, and we performed a partial excision of the masseter muscles. In this patient's case, we examined muscular activity, energy metabolism, and fiber type composition of the masseter muscles using electromyograms (EMG), 31P-magnetic resonance spectroscopy (MRS), and enzyme-histochemistry. The EMG showed no hyperactivity, and the 31P-MRS showed normal energy spectral patterns and PCr contents of the masseter muscles. The fiber type composition, however, in the muscles in this case was very different from that in muscles with "work hypertrophy" and also that in normal masseter muscles: 1. Loss of type IIB fibers; 2. Increases in type IIA and in type IM & IIC fibers; and 3. Decrease in type I fibers. The findings suggest that this is not a case of work hypertrophy but a case of compensatory hypertrophy possibly due to a lack of high-tetanus-tension type IIB fibers.
authors.affiliation: Crown & Bridge Prosthodontics, Dept. of Oral Functional Science, Graduate School of Dental Medicine, Hokkaido University, Sapporo, Japan. satoh.k@den.hokudai.ac.jp
authors.forename: K
authors.initials: K
authors.lastname: Satoh
authors.forename: T
authors.initials: T
authors.lastname: Yamaguchi
authors.forename: K
authors.initials: K
authors.lastname: Komatsu
authors.forename: N
authors.initials: N
authors.lastname: Inoue
authors.forename: K
authors.initials: K
authors.lastname: Minowa
authors.forename: T
authors.initials: T
authors.lastname: Kanayama
authors.forename: S
authors.initials: S
authors.lastname: Yoshida
authors.forename: N
authors.initials: N
authors.lastname: Ohata
mesh_terms: D000255:Adenosine Triphosphate / Q000032:analysis; D000328:Adult; D004576:Electromyography; D004734:Energy Metabolism / Q000502:physiology*; D006651:Histocytochemistry; D006801:Humans; D006984:Hypertrophy; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008406:Masseter Muscle / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D009119:Muscle Contraction / Q000502:physiology*; D018656:Muscle Fibers, Fast-Twitch / Q000145:classification / Q000473:pathology; D018485:Muscle Fibers, Skeletal / Q000145:classification* / Q000648:ultrastructure; D018657:Muscle Fibers, Slow-Twitch / Q000145:classification / Q000473:pathology; D009218:Myosins / Q000032:analysis; D010710:Phosphates / Q000032:analysis; D010725:Phosphocreatine / Q000032:analysis; D010759:Phosphorus Isotopes
chemical_list: D010710:Phosphates; D010759:Phosphorus Isotopes; D010725:Phosphocreatine; D000255:Adenosine Triphosphate; D009218:Myosins