title: Mechanical load exerted by PET-G aligners during mesial and distal derotation of a mandibular canine : An in vitro study.
abstract: BACKGROUND
  The six force-moment (F/M) components exerted by aligners of different thickness during simulated mesiorotation and distorotation of a mandibular canine were studied.
  
  
  METHODS
  An acrylic mandibular model with a separated right canine mounted on a hexapod via a 3D F/M sensor was used. Duran+®aligners (Scheu Dental, Germany) of thickness 0.5, 0.625, and 0.75 mm were fabricated on plaster models with the measurement tooth in its neutral position. The F/M values were recorded during progressive mesiorotation or distorotation of tooth 43 in 1° steps up to ±15°, corresponding to 0.5 mm displacements of the tooth's interdental contacts. Each rotation step included renewed seating of the aligner on the acrylic model. Three aligners were tested three times each for each thickness and direction of rotation.
  
  
  RESULTS
  The median rotational moments for the 0.5 mm aligner and 15° distorotation of tooth 43 was 27.49 Nmm (interquartile range, IQR 1.45 Nmm). The corresponding values for the 0.625 and 0.75 mm aligners were 41.04 Nmm (IQR 5.62 Nmm) and 42.48 Nmm (IQR 2.17 Nmm), respectively. The average rotational moments for distorotation were 15% higher than for mesiorotation (p = 0.01). Relatively high collateral F/M components, specifically an intrusive force and labiolingual and mesiodistal tipping moments, were observed.
  
  
  CONCLUSIONS
  To avoid overloading of periodontal structures, derotation of lower canines should be limited to 10° per setup step, leading to rotational moments of about 15 Nmm. The mechanical behavior of the 0.625 and 0.75 mm aligners were similar; thus, it may be omitted from the aligner sequence. Further studies are required to investigate specific aligner modifications or attachments for minimizing collateral F/M components or unwanted movements, respectively, during canine derotation.
authors.affiliation: Department of Orthodontics, University of Ulm, Albert-Einstein-Allee 11, 89081, Ulm, Germany. fayez.elkholy@uni-ulm.de.
authors.forename: F
authors.initials: F
authors.lastname: Elkholy
authors.affiliation: Department of Prosthodontics, University of Ulm, Ulm, Germany.
authors.forename: B
authors.initials: B
authors.lastname: Mikhaiel
authors.affiliation: Department of Orthodontics, University of Ulm, Albert-Einstein-Allee 11, 89081, Ulm, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Schmidt
authors.affiliation: Department of Orthodontics, University of Ulm, Albert-Einstein-Allee 11, 89081, Ulm, Germany.
authors.forename: B G
authors.initials: BG
authors.lastname: Lapatki
mesh_terms: D000818:Animals; D003481:Cuspid / Q000502:physiology*; D004285:Dogs; D005858:Germany; D006801:Humans; D003765:Models, Dental; D016382:Orthodontic Appliance Design; D009968:Orthodontic Appliances, Removable; D012399:Rotation; D014087:Tooth Movement Techniques / Q000379:methods*; D016474:Weight-Bearing / Q000502:physiology*
keywords: Aligner; Canine derotation; Force; Moment; Orthodontic appliances; Thermoplastic appliance