title: Lip curve changes in males with premolar extraction or nonextraction treatment.
abstract: OBJECTIVE
  This retrospective study was designed to compare the responses of the upper and lower lip curves in young growing males, to orthodontic treatment involving either four premolar extractions or the holding of the E-spaces without premolar extractions.
  
  
  METHODS
  Pre- and post-treatment lateral cephalograms of 67 premolar extraction and 30 nonextraction patients were assessed. The results were subjected to analysis of variance to search for statistically significant differences amongst the pretreatment variables and changes in depths of lip curves. Pearson's correlation coefficients were also calculated and stepwise regression analysis undertaken.
  
  
  RESULTS
  A wide range of lip curve behaviour was seen in individual patients within all groups. No significant differences were found in the change in depth of lip curve amongst the various extraction and nonextraction groups. The inherent morphology of the soft tissues appeared to be the greatest determinant of lip curve behaviour with treatment.
  
  
  CONCLUSIONS
  It would appear that neither premolar extraction nor nonextraction treatment, if based on appropriate diagnostic criteria and followed with competent clinical management, will necessarily lead to direct effects on lip curvature.
authors.affiliation: Orthodontic Unit, School of Dental Science, University of Melbourne, 711 Elizabeth Street, Melbourne 3000 Victoria, Australia.
authors.forename: Pei-Ti
authors.initials: PT
authors.lastname: Lin
authors.forename: Michael G
authors.initials: MG
authors.lastname: Woods
mesh_terms: D000293:Adolescent; D001641:Bicuspid / Q000601:surgery*; D002508:Cephalometry; D002648:Child; D002680:Chin / Q000033:anatomy & histology; D005145:Face; D005500:Follow-Up Studies; D006801:Humans; D007180:Incisor / Q000033:anatomy & histology; D008046:Lip / Q000033:anatomy & histology*; D008297:Male; D008310:Malocclusion / Q000628:therapy; D008311:Malocclusion, Angle Class I / Q000628:therapy; D008312:Malocclusion, Angle Class II / Q000628:therapy; D008334:Mandible / Q000033:anatomy & histology; D008437:Maxilla / Q000033:anatomy & histology; D012189:Retrospective Studies; D012690:Serial Extraction; D013027:Space Maintenance, Orthodontic