title: Effects of palate depth, modified arm shape, and anchor screw on rapid maxillary expansion: a finite element analysis.
abstract: OBJECTIVE
  This study examined the effects of palate depth, modifications of the arm shape, and anchor screw placement in the mid-palatal area on rapid maxillary expansion (RME) using finite element (FE) analysis.
  
  
  METHODS
  Three-dimensional FE models were constructed that included the maxilla (cortical and cancellous bone), maxillary sinus, maxillary first molar and first premolar, periodontal membrane, and an RME appliance with arms, bands, and anchor screws. The expansion screws were activated 0.2mm transversely.
  
  
  RESULTS
  The deepest palate model had the smallest lateral displacement of the tooth and expansion of the mid-palatal suture and the greatest strain of the arm among the models with different palate heights. The model with a larger diameter arm had the smallest arm strain among the models with various arm shapes. The model with an anchor screw had the greatest lateral displacement of the tooth and expansion of the mid-palatal suture among all models.
  
  
  CONCLUSIONS
  For a deeper palate, the arm strain increased and the effect of RME decreased. Modified arm shapes such as a larger diameter arm, arms connected by a diagonal wire, a straight arm, and a shorter arm efficiently expanded the maxillary dental arch. Anchor screws increased the effect of RME, generated more and closer bodily movement of the tooth, and parallel expansion of the mid-palatal suture. The model with an anchor screw without arms decreased the displacement of the teeth compared to the models with arms, so the arms are necessary for effective RME.
authors.affiliation: Department of Orthodontics, Nihon University School of Dentistry, Tokyo, Japan.
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Matsuyama
authors.affiliation: Department of Orthodontics, Nihon University School of Dentistry, Tokyo, Japan motoyoshi.mitsuru@nihon-u.ac.jp.
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Motoyoshi
authors.affiliation: Department of Orthodontics, Nihon University School of Dentistry, Tokyo, Japan.
authors.forename: Niina
authors.initials: N
authors.lastname: Tsurumachi
authors.affiliation: Department of Orthodontics, Nihon University School of Dentistry, Tokyo, Japan.
authors.forename: Noriyoshi
authors.initials: N
authors.lastname: Shimizu
mesh_terms: D001641:Bicuspid / Q000473:pathology; D001863:Bone Screws; D003724:Dental Arch / Q000254:growth & development; D020342:Finite Element Analysis; D006801:Humans; D008437:Maxilla / Q000254:growth & development / Q000601:surgery*; D008953:Models, Anatomic; D008963:Molar / Q000473:pathology; D009967:Orthodontic Appliances; D010155:Palatal Expansion Technique / Q000295:instrumentation*; D010159:Palate / Q000473:pathology*; D014087:Tooth Movement Techniques