title: Determination of forces on a split palatal screw after rapid maxillary expansion.
abstract: OBJECTIVE
  Aim of this study was to develop a finite element model of the forces that patients with rapid maxillary expansion bear and to validate it by a mechanical test.
  
  
  METHODS
  Computer-aided design models of the metallic screw and polymeric splint were modelled and discretized. Two forces were generated and considered independently: F1 at the temporary molar (2.5 N) and F2 at the permanent molar (2.5 N). The results of the finite element analysis were used to define the strain values which the anterior and posterior arms of the rapid maxillary expansion appliance bore as a linear function of F1-F2 by calculating the strain-force coefficient δij. Two strain gauge rosettes were attached to an appliance which was placed in an XY motorized stage to reproduce the same forces used in the finite element analysis. Once the system was validated, the matrix was inverted to determine forces F1 and F2 that a group of 40 patients underwent (median age 8.33 years, standard deviation 1.86 years) for 75 days, using their strain values. The parents of the patients activated a quarter turn (0.20 mm) twice a day until 50% transversal overcorrection was achieved.
  
  
  RESULTS
  Finite element analysis showed that the effects of the forces on stress at the location of the arms were notably different. There was a satisfactory correlation between finite element analysis predictions and in vitro values. Dissipation of F1 and F2 in patients was predicted to be 62.5 and 80%, respectively, after 75 days of retention.
  
  
  CONCLUSIONS
  These results back the finite element analysis model for force prediction.
authors.affiliation: Orthodontics Unit 5305, Odontostomatology Department, HUBc, University of Barcelona, Planta 2, Pavelló de Govern, C/FeixaLlarga SN, L'Hospitalet de Llobregat, 08907, Barcelona, Spain. valentingarcia2@gmail.com.
authors.forename: Valentin Javier
authors.initials: VJ
authors.lastname: García
authors.affiliation: Department of Materials Engineering, Applied Mechanics and Construction, University of Vigo, Lagoas-Marcosende, 36310, Vigo, Spain.
authors.forename: Rubén
authors.initials: R
authors.lastname: López-Cancelos
authors.affiliation: Applied Physics Department, Applied Physics Unit, EEI, University of Vigo, Lagoas-Marcosende, 36310, Vigo, Spain.
authors.forename: Antonio
authors.initials: A
authors.lastname: Riveiro
authors.affiliation: Department of Materials Engineering, Applied Mechanics and Construction, University of Vigo, Lagoas-Marcosende, 36310, Vigo, Spain.
authors.forename: Rafael
authors.initials: R
authors.lastname: Comesaña
authors.affiliation: Department of Materials Engineering, Applied Mechanics and Construction, University of Vigo, Lagoas-Marcosende, 36310, Vigo, Spain.
authors.forename: Josep Maria
authors.initials: JM
authors.lastname: Ustrell I Torrent
authors.affiliation: Orthodontics Unit 5305, Odontostomatology Department, HUBc, University of Barcelona, Planta 2, Pavelló de Govern, C/FeixaLlarga SN, L'Hospitalet de Llobregat, 08907, Barcelona, Spain.
authors.forename: Khaled
authors.initials: K
authors.lastname: Kasem
authors.affiliation: Department of Materials Engineering, Applied Mechanics and Construction, University of Vigo, Lagoas-Marcosende, 36310, Vigo, Spain.
authors.forename: Aida
authors.initials: A
authors.lastname: Badaoui
authors.affiliation: Human Anatomy and Embryology Unit 5304, HUBc, University of Barcelona, Pavelló de Govern, C/FeixaLlarga SN, L'Hospitalet de Llobregat, 08907, Barcelona, Spain.
authors.forename: Mª Cristina
authors.initials: MC
authors.lastname: Manzanares-Céspedes
authors.affiliation: Human Anatomy and Embryology Unit 5304, HUBc, University of Barcelona, Pavelló de Govern, C/FeixaLlarga SN, L'Hospitalet de Llobregat, 08907, Barcelona, Spain.
authors.forename: Patricia
authors.initials: P
authors.lastname: Carvalho-Lobato
mesh_terms: D001863:Bone Screws; D002648:Child; D003198:Computer Simulation; D017076:Computer-Aided Design; D000078331:Correlation of Data; D004867:Equipment Design; D020342:Finite Element Analysis; D006801:Humans; D008432:Mathematical Computing; D010155:Palatal Expansion Technique / Q000295:instrumentation*
keywords: Finite element analysis; Forces; Rapid maxillary expansion; Strain gauges