title: [Indications for non-extraction treatment of dental crowding with Damon appliance].
abstract: OBJECTIVE
  To analyze the indications for successful non-extraction correction of dental crowding with Damon appliance. METHODSú 19 patients with non-extraction orthodontic treatment were reviewed. They had Class I skeletal pattern and both arches were treated with Damon 3 or Damon MX appliances. According to the initial diagnosis before treatment (T1), 7 cases needed extraction, but they rejected it. After correction of crowding (T2), they were allotted into either successful group or unsuccessful group. The successful group contained those subjects in whom the Z angle at T2 was no less than 70 degrees or that of T1. Others were allotted into the unsuccessful group. The dental casts and cephalometric radiophotographs were analyzed at T1 and T2. The difference between the two groups was analyzed with SPSS15.0 software package for Student's t test.
  
  
  RESULTS
  There were 11 cases in successful group. All the 7 cases rejecting extraction were finally allotted into the unsuccessful group. No significant difference in upper arch perimeter and arch width was detected between the two groups at both T1 and T2. The upper and lower incisors and upper lip showed a more retruded position in successful group at T1, although they showed a similar amount of protrusion from T1 to T2 in both groups. The forward movement of lower lip was 3.4mm in the unsuccessful group, which was significantly larger than that of 1.6mm in successful group(P<0.05). Z angle decreased 10.7 degrees in the unsuccessful group, while no significant change was detected in the successful group. The Holdaway upper lip strain was comparable in two groups, but the successful group showed significantly less soft chin strain than unsuccessful group (P<0.05).
  
  
  CONCLUSIONS
  Damon appliance can not rescue extraction cases. Straight soft tissue profile and upright incisor position are prerequisite for non-extraction treatment. And a harmonious chin and lip position is the key leading to the successful non-extraction treatment with Damon appliance.
authors.affiliation: Department of Orthodontics, Ninth People's HospitalìCollege of Stomatology, School of Medicine, Shanghai Jiao Tong University, Shanghai, China. tangg@graduate.hku.hk
authors.forename: Guo-hua
authors.initials: GH
authors.lastname: Tang
authors.forename: Lei
authors.initials: L
authors.lastname: Zhang
authors.forename: Xiao-cen
authors.initials: XC
authors.lastname: Xu
authors.forename: Xuan
authors.initials: X
authors.lastname: Li
authors.forename: Feng-ting
authors.initials: FT
authors.lastname: Chu
mesh_terms: D002508:Cephalometry; D006801:Humans; D007180:Incisor; D008046:Lip; D008310:Malocclusion / Q000628:therapy*; D009967:Orthodontic Appliances