title: Association between facial growth pattern and facial muscle activity: A prospective cross-sectional study.
abstract: OBJECTIVE
  To evaluate the relationship between facial growth pattern and electromyography (EMG) of facial muscles: anterior temporalis, masseter, buccinators, orbicularis oris, mentalis and anterior digastric.
  
  
  METHODS
  The sample consisted of 77 subjects aged between 18-28 years (mean age 21.10±2.03), with dental Class I relationship, normal overjet and overbite, balanced facial profile, no signs of temporomandibular disorders, and no previous orthodontic treatment. Facial growth pattern was determined on the lateral cephalograms according to the Björk sum (sum of the N-S-Ar, S-Ar-Go, and Ar-Go-Me angles) dividing the sample into three groups: horizontal facial pattern group (24 subjects), normal facial pattern group (41 subjects), and vertical facial pattern group (12 subjects). The EMG of anterior temporalis, masseter, buccinator, orbicularis oris, mentalis and anterior digastric muscles were examined for each patient in the rest position and in functional positions (central maximum intercuspation, chewing on right side, chewing on left side and swallowing). Mean values and standard deviation of EMG were obtained and compared between the three groups.
  
  
  RESULTS
  At rest, the EMG of the masseter, orbicularis oris and anterior digastric were higher in the vertical facial pattern group compared with the other two groups, with a moderate positive correlation between the EMG of these muscles and the Björk sum (P<.01). In contrast, during central maximum intercuspation, the activity of the anterior temporalis, masseter and buccinator was significantly lower in the vertical facial pattern group compared with the two other groups, with a moderate negative correlation between the Björk sum and EMG in the maximum central intercuspation position of these muscles (P<.01).
  
  
  CONCLUSIONS
  A significant relationship was found between facial muscle activity and facial growth pattern. The findings suggest that the activity of masticatory and perioral muscles could play a role in the direction of the facial growth.
authors.affiliation: Department of Orthodontics, Faculty of Dentistry, Damascus University, Damascus, Syria. Electronic address: mabdullah001@hotmail.com.
authors.forename: Mohannad
authors.initials: M
authors.lastname: Alabdullah
authors.affiliation: Orthodontic Graduate Clinic, School of Dentistry, University of Alberta, Edmonton, Canada.
authors.forename: Humam
authors.initials: H
authors.lastname: Saltaji
authors.affiliation: Department of Oral Biology, Faculty of Dentistry, Damascus University, Damascus, Syria.
authors.forename: Hussein
authors.initials: H
authors.lastname: Abou-Hamed
authors.affiliation: Department of Orthodontics, Faculty of Dentistry, Damascus University, Damascus, Syria.
authors.forename: Mohamed
authors.initials: M
authors.lastname: Youssef
mesh_terms: D000293:Adolescent; D000328:Adult; D002508:Cephalometry / Q000379:methods; D002680:Chin / Q000033:anatomy & histology; D003430:Cross-Sectional Studies; D003679:Deglutition / Q000502:physiology; D003768:Dental Occlusion, Centric; D004576:Electromyography / Q000379:methods*; D005152:Facial Muscles / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008334:Mandible / Q000033:anatomy & histology; D008335:Mandibular Condyle / Q000033:anatomy & histology; D008406:Masseter Muscle / Q000502:physiology; D008409:Mastication / Q000502:physiology; D008445:Maxillofacial Development / Q000502:physiology*; D009295:Nasal Bone / Q000033:anatomy & histology; D009334:Neck Muscles / Q000502:physiology; D011446:Prospective Studies; D012658:Sella Turcica / Q000033:anatomy & histology; D013703:Temporal Muscle / Q000502:physiology; D014716:Vertical Dimension; D055815:Young Adult
keywords: EMG; Facial morphology; Growth pattern; Masticatory muscles; Perioral muscles