title: Masseter myosin heavy chain composition varies with mandibular asymmetry.
abstract: Human jaw dysmorphologies are frequent and often affect young patients, resulting in malocclusion of teeth and inappropriate jaw relationships. Treatment is performed by means of orthodontics with orthognathic surgery as required. Mandibular asymmetry is one of the most frequent dysmorphologies, but in many cases, the specific cause is unknown.In healthy patients who were undergoing orthognathic surgery for correction of malocclusion, we tested the hypothesis that masseter muscle phenotype composition, which determines contractile properties, was different between sides in patients with mandibular asymmetry but not in those without mandibular asymmetry. After cephalometric analysis, 50 patients from whom we obtained samples of both right and left masseter muscles were separated into 2 groups: with or without mandibular lateral deviation. Samples were immunostained with myosin-isoform-specific antibodies to identify 4 skeletal muscle fiber types, and their fiber areas and proportions were measured. Two-tailed Wilcoxon test for paired samples was used to compare the 4 fiber-type compositions by means of percent occupancy and mean fiber area on both sides. Patients with mandibular asymmetry were associated with a significant increase of type II fiber occupancy (P = 0.0035) on the same side as the deviation. This finding that masseter muscle phenotype is significantly linked to mandibular asymmetry is of relevance to physiotherapeutic and surgical managements of jaw discrepancies and merits further investigation in the light of its possible role in the etiology of this condition.
authors.affiliation: Université Lille Nord de France, UDSL, Lille, France. gwenael.raoul@gmail.com
authors.forename: Gwénaël
authors.initials: G
authors.lastname: Raoul
authors.forename: Anthea
authors.initials: A
authors.lastname: Rowlerson
authors.forename: James
authors.initials: J
authors.lastname: Sciote
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Codaccioni
authors.forename: Laurence
authors.initials: L
authors.lastname: Stevens
authors.forename: Claude-Alain
authors.initials: CA
authors.lastname: Maurage
authors.forename: Alain
authors.initials: A
authors.lastname: Duhamel
authors.forename: Joël
authors.initials: J
authors.lastname: Ferri
mesh_terms: D000328:Adult; D002508:Cephalometry; D005146:Facial Asymmetry / Q000000981:diagnostic imaging / Q000473:pathology* / Q000601:surgery*; D005260:Female; D006801:Humans; D008297:Male; D008310:Malocclusion / Q000000981:diagnostic imaging / Q000473:pathology* / Q000601:surgery*; D008406:Masseter Muscle / Q000737:chemistry* / Q000000981:diagnostic imaging / Q000601:surgery; D018485:Muscle Fibers, Skeletal / Q000737:chemistry*; D018995:Myosin Heavy Chains / Q000032:analysis*; D056948:Orthognathic Surgical Procedures; D010641:Phenotype; D011859:Radiography; D013194:Staining and Labeling; D018709:Statistics, Nonparametric; D014716:Vertical Dimension
chemical_list: D018995:Myosin Heavy Chains