title: Root shortening in patients treated with two-step and en masse space closure procedures with sliding mechanics.
abstract: OBJECTIVE
  To investigate the comparative amount of root shortening between two-step and en masse space closure procedures.
  
  
  METHODS
  Fifty-two patients were selected from a pool of patients satisfying the following inclusion criteria: no evidence of resorption on the pretreatment panoramic radiographs; no dental trauma; no dilacerations of incisor roots, anodontia, or impacted canines; complete root formation at the start of treatment; intact and caries-free incisors; no endodontically treated incisors; Angle Class I or II malocclusion; extraction of four first premolars; and space closure with moderate anchorage. Patients received treatment with either a two-step or an en masse procedure to close the extraction spaces after alignment and leveling with the same preadjusted appliances. Root shortening of the maxillary and mandibular incisors was evaluated on panoramic radiographs, taken before and after space closure, and measured in millimeters. Distortion of measurements caused by panoramic radiographs was corrected by using special metal rods ligated to brackets. Statistical comparisons of root shortening between space closure procedures were investigated with the two-sample t test.
  
  
  RESULTS
  No difference was found in the amount of root shortening between space closure procedures. The average root shortening of maxillary central and lateral incisors was 0.43 +/- 0.12 mm and 0.58 +/- 0.10 mm, respectively, and that of mandibular central and lateral incisors was 0.23 +/- 0.07 mm and 0.22 +/- 0.06 mm, respectively.
  
  
  CONCLUSIONS
  No difference should be expected in root resorption between two-step and en masse space closure procedure.
authors.affiliation: Department of Orthodontics, Tongji University, Shanghai, China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Huang
authors.forename: Xu-Xia
authors.initials: XX
authors.lastname: Wang
authors.forename: Jun
authors.initials: J
authors.lastname: Zhang
authors.forename: Chao
authors.initials: C
authors.lastname: Liu
mesh_terms: D000293:Adolescent; D001641:Bicuspid / Q000601:surgery; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007180:Incisor / Q000000981:diagnostic imaging*; D008297:Male; D008311:Malocclusion, Angle Class I / Q000628:therapy; D008312:Malocclusion, Angle Class II / Q000628:therapy; D008334:Mandible / Q000000981:diagnostic imaging; D008437:Maxilla / Q000000981:diagnostic imaging; D009811:Odontometry / Q000379:methods; D052280:Orthodontic Anchorage Procedures; D016910:Orthodontic Brackets; D019516:Orthodontic Space Closure / Q000009:adverse effects* / Q000295:instrumentation / Q000379:methods; D009969:Orthodontic Wires; D011862:Radiography, Panoramic; D012391:Root Resorption / Q000000981:diagnostic imaging / Q000209:etiology*; D012690:Serial Extraction; D014092:Tooth Root / Q000000981:diagnostic imaging*