title: Stress and displacement patterns in the craniofacial skeleton with rapid maxillary expansion: a finite element method study.
abstract: BACKGROUND
  The purpose of this finite element study was to evaluate stress distribution along craniofacial sutures and displacement of various craniofacial structures with rapid maxillary expansion (RME) therapy.
  
  
  METHODS
  The analytic model for this study was developed from sequential computed tomography scan images taken at 2.5-mm intervals of a dry young human skull. Subsequently, a finite element method model was developed from computed tomography images by using AutoCAD software (2004 version, Autodesk, Inc, San Rafael, Calif) and ANSYS software (version 10, Belcan Engineering Group, Downers Grove, Ill).
  
  
  RESULTS
  The maxilla moved anteriorly and downward and rotated clockwise in response to RME. The pterygoid plates were displaced laterally. The distant structures of the craniofacial skeleton--zygomatic bone, temporal bone, and frontal bone--were also affected by transverse orthopedic forces. The center of rotation of the maxilla in the X direction was somewhere between the lateral and the medial pterygoid plates. In the frontal plane, the center of rotation of the maxilla was approximately at the superior orbital fissure. The maximum von Mises stresses were found along the frontomaxillary, nasomaxillary, and frontonasal sutures. Both tensile and compressive stresses could be demonstrated along the same suture.
  
  
  CONCLUSIONS
  RME facilitates expansion of the maxilla in both the molar and the canine regions. It also causes downward and forward displacement of the maxilla and thus can contribute to the correction of mild Class III malocclusion. The downward displacement and backward rotation of the maxilla could be a concern in patients with excessive lower anterior facial height. High stresses along the deep structures and the various sutures of the craniofacial skeleton signify the role of the circummaxillary sutural system in downward and forward displacement of the maxilla after RME.
authors.affiliation: Department of Orthodontics and Dentofacial Orthopedics, Manipal College of Dental Sciences, Manipal, India.
authors.forename: Pawan
authors.initials: P
authors.lastname: Gautam
authors.forename: Ashima
authors.initials: A
authors.lastname: Valiathan
authors.forename: Raviraj
authors.initials: R
authors.lastname: Adhikari
mesh_terms: D019245:Compressive Strength; D003198:Computer Simulation; D003393:Cranial Sutures / Q000502:physiology*; D003799:Dental Stress Analysis / Q000379:methods* / Q000706:statistics & numerical data; D004548:Elasticity; D005147:Facial Bones / Q000502:physiology*; D020342:Finite Element Analysis; D005624:Frontal Bone / Q000502:physiology; D006801:Humans; D008954:Models, Biological; D010155:Palatal Expansion Technique; D011859:Radiography; D012886:Skull / Q000000981:diagnostic imaging; D013100:Sphenoid Bone / Q000502:physiology; D013701:Temporal Bone / Q000502:physiology; D013718:Tensile Strength