title: The effect of incremental lower lip advancement on oral pressure and EMG activity of the lower lip.
abstract: OBJECTIVE
  During orthodontic arch expansion, the teeth are displaced against the perioral soft tissues. This can affect the equilibrium of forces that are thought to act on teeth, with consequent implications for long-term stability. The aim of this study was to investigate the effect of incremental lower lip advancement on intraoral pressure and electromyographic (EMG) activity of the lower lip.
  
  
  METHODS
  Intraoral pressure and EMG activity was measured in 10 participants (2 males, 8 females; 22 years ± 7 months) as the lower lip was incrementally advanced using three custom-made vacuum-formed stents of differing labial thicknesses (0.5, 2.5, and 4.5 mm). A task paradigm including at rest recordings and maximal voluntary contraction was completed for each tray.
  
  
  RESULTS
  Resting lip pressure generated increased as the lower lip was advanced (P < 0.001). The EMG activity of the lower lip increased significantly (P < 0.001) only once the lip was advanced from 2.5 to 4.5 mm. For the pressure recordings, the response to incremental lip advancement showed considerable individual variation.
  
  
  CONCLUSIONS
  These findings suggest that the initial pressure increase on the lower incisors was mostly likely due to the inherent viscoelastic properties of the lower lip, while the pressure increase between the 2.5 and 4.5 mm advancement was due to increased muscle activity. Each individual also responded to lower lip advancement in a different yet subject-specific manner.
authors.affiliation: *Department of Oral Sciences and.
authors.forename: Hannah C
authors.initials: HC
authors.lastname: Jack
authors.affiliation: **Sir John Walsh Research Institute, Faculty of Dentistry, University of Otago, New Zealand, Dunedin, New Zealand.
authors.forename: Jules
authors.initials: J
authors.lastname: Kieser
authors.affiliation: *Department of Oral Sciences and.
authors.forename: Joseph S
authors.initials: JS
authors.lastname: Antoun
authors.affiliation: *Department of Oral Sciences and mauro.farella@otago.ac.nz.
authors.forename: Mauro
authors.initials: M
authors.lastname: Farella
mesh_terms: D000328:Adult; D004576:Electromyography / Q000379:methods; D005260:Female; D006801:Humans; D007180:Incisor / Q000502:physiology; D008046:Lip / Q000502:physiology*; D008297:Male; D009971:Orthodontics, Corrective; D011312:Pressure; D015607:Stents; D055815:Young Adult