title: Lip closing force of Class III patients with mandibular prognathism: a case control study.
abstract: BACKGROUND
  To compare the lip closing force of patients with mandibular prognathism to that of patients without dentofacial anomalies.
  
  
  METHODS
  The subject group included 62 female patients of Class III relationship with mandibular prognathism. The control group been comprised of 71 patients of Class I relationships without skeletal deformities. Maximum lip closing force and average lip closing force were measured using a Y-meter. Student's t-test was carried out to analyse the differences between the groups. Correlation and stepwise multiple linear regression analyses were performed to analyse the relationship between lip closing force and craniofacial morphology.
  
  
  RESULTS
  The lower lip closing force of subjects with mandibular prognathism was significantly greater than that of patients in the control group (P < 0.001), while the upper lip closing force showed no difference (P > 0.05). The lower lip closing force of patients with mandibular prognathism was strongly correlated with IMPA (Lower Incisor - Mandibular Plane angle, P < 0.001) and FMA (Frankfort Plane-Mandibular Plane angle, P < 0.001). Multiple regression equations: (MaxLL) = 12.192 - 0.125 * (IMPA) + 0.082 (FMA); (AveLL) = 9.112 - 0.091 * (IMPA) + 0.054 (FMA).
  
  
  CONCLUSIONS
  The lower lip closing force was markedly increased in Class III patients with mandibular prognathism and was strongly correlated with lower incisor position and mandibular plane angle.
authors.forename: Sihui
authors.initials: S
authors.lastname: Chen
authors.forename: Ying
authors.initials: Y
authors.lastname: Cai
authors.affiliation: Department of Orthodontics, Laboratory of Oral Biomedical Science and Translational Medicine, School of Stomatology, Tongji University, Middle Yanchang Road 399, Shanghai, P, R, China. orthodboy@126.com.
authors.forename: Fengshan
authors.initials: F
authors.lastname: Chen
mesh_terms: D002508:Cephalometry; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008046:Lip / Q000503:physiopathology*; D008334:Mandible / Q000002:abnormalities*; D008445:Maxillofacial Development; D011378:Prognathism / Q000175:diagnosis / Q000503:physiopathology*; D012189:Retrospective Studies; D012720:Severity of Illness Index