title: [Clinical effect of premolar extraction with high torque self-locking appliances].
abstract: OBJECTIVE
  To analyze the clinical effect of extraction correction of patients with maxillary protrusion by using Damon high torque appliances.
  
  
  METHODS
  Forty patients with extraction of four first premolars due to orthodontic treatment were selected. They had protrusion of maxilla and were randomly divided into two groups. Both arches of Damon group were treated with Damon high torque appliances and MBT group were corrected with traditional MBT straight wire appliance; patients in two groups received sliding mechanics for adduction of upper anterior teeth. Cephalometric radiophotographs were analyzed before（T0）and after adduction of upper anterior teeth（T1）. The difference between the two groups was analyzed with SPSS15.0 software package.
  
  
  RESULTS
  The upper incisors showed a more retruded position in the two groups at T1,although they showed a similar amount in both groups. The backward movement of upper lip was 2.31mm in Damon group, which was significantly less than that of 2.81mm in MBT group(P<0.05). No significant difference in the first molar mesialization was detected between Damon group(2.33 mm) and MBT group(2.36mm) (P>0.05). For anterior teeth retraction, nasolabial angle (NLA) in MBT and Damon group were 107.44°and 106.33°, increase of NLA in MBT group was 9.17°,which was significantly larger than that of 7.22°in Damon group (P<0.05). U1-MxP in MBT and Damon were 110.61°and 114.11°. U1-MxP decreased 12.06°in MBT group, while significant change was deteced in Damon group of 7.61°(P<0.05).
  
  
  CONCLUSIONS
  Application of Damon high torque appliances in extraction treatment of maxillary protrusion patients yielded better control of the labial crown torque of anterior teeth, and avoided excessive lingual inclination of anterior teeth compared with MBT in adduction of upper anterior teeth.
authors.affiliation: Department of Orthodontics, Stomatology Hospital of Nantong City. Nantong 226001, Jiangsu Province,China. E-mail:csx11238@163.com.
authors.forename: Shuang-xi
authors.initials: SX
authors.lastname: Chen
authors.affiliation: Department of Orthodontics, Shanghai Ninth People's Hospital, College of Stomatology, Shanghai Jiao Tong University School of Medicine. Shanghai 200011,China.
authors.forename: Guo-hua
authors.initials: GH
authors.lastname: Tang
authors.affiliation: Department of Orthodontics, Shanghai Ninth People's Hospital, College of Stomatology, Shanghai Jiao Tong University School of Medicine. Shanghai 200011,China.
authors.forename: Yu-nan
authors.initials: YN
authors.lastname: Jiang
authors.affiliation: Department of Orthodontics, Stomatology Hospital of Nantong City. Nantong 226001, Jiangsu Province,China.
authors.forename: Yong-jia
authors.initials: YJ
authors.lastname: Gu
authors.affiliation: Department of Orthodontics, Stomatology Hospital of Nantong City. Nantong 226001, Jiangsu Province,China.
authors.forename: Ting
authors.initials: T
authors.lastname: Zhang
authors.affiliation: Department of Orthodontics, Stomatology Hospital of Nantong City. Nantong 226001, Jiangsu Province,China.
authors.forename: Mei-qin
authors.initials: MQ
authors.lastname: Gao
mesh_terms: D001641:Bicuspid; D002508:Cephalometry; D003748:Dental Equipment; D006801:Humans; D007180:Incisor; D008046:Lip; D008437:Maxilla; D008963:Molar; D019228:Tooth Crown; D014081:Tooth Extraction / Q000379:methods*; D014087:Tooth Movement Techniques; D019415:Torque