title: Magnetic resonance spectroscopy of the masseter muscle in different facial morphological patterns.
abstract: The aims of this study were (1) to develop a reliable noninvasive method to evaluate the masseter muscle metabolism, by using (31)P-magnetic resonance spectroscopy, and (2) to evaluate the metabolic profile of the masseter muscle in subjects with various facial patterns. The maxillary-mandibular relationship, which varied from hypodivergent to hyperdivergent, was measured on lateral cephalograms of 20 adults, 22 to 35 years of age. (31)P-spectra were acquired from the masseter muscle at rest with a custom-made, single-turn, double-tuned, 3 x 5-cm oblong surface coil. The inorganic phosphate to phosphocreatine (Pi/PCr) ratios were measured and compared in relation to vertical and sagittal cephalometric measurements. A statistically significant (R(2) = 0.65, r = 0.81, P = .001) relationship was found between Pi/PCr ratio and the palatal-to-mandibular plane angle. As the maxillary-to-mandibular divergence increased, the Pi/PCr ratio decreased. This correlation suggests that muscles with a higher Pi/PCr ratio have a higher resting metabolic activity than those with a lower Pi/PCr ratio. Consequently, these muscles may keep bone under more tension and influence its growth in a more horizontal direction. Another possible explanation of the results is that the fiber type composition of the masseter muscle varies with facial morphology.
authors.affiliation: University of Pennsylvania, Philadelphia 19104, USA.
authors.forename: E T
authors.initials: ET
authors.lastname: Al-Farra
authors.forename: K
authors.initials: K
authors.lastname: Vandenborne
authors.forename: A
authors.initials: A
authors.lastname: Swift
authors.forename: J
authors.initials: J
authors.lastname: Ghafari
mesh_terms: D000328:Adult; D002508:Cephalometry; D005145:Face / Q000033:anatomy & histology*; D006801:Humans; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008406:Masseter Muscle / Q000378:metabolism*; D008445:Maxillofacial Development / Q000502:physiology*; D010710:Phosphates / Q000378:metabolism; D010725:Phosphocreatine / Q000378:metabolism; D010759:Phosphorus Isotopes / Q000378:metabolism; D012044:Regression Analysis
chemical_list: D010710:Phosphates; D010759:Phosphorus Isotopes; D010725:Phosphocreatine