title: The relationship between estimated and registered natural head position.
abstract: OBJECTIVE
  To study the inherent relationship between registered and estimated natural head position and further explore the nature of natural head position.
  
  
  METHODS
  Thirty-one pretreated patients were included in this study. Both registered natural head position (RNHP) and estimated natural head position (ENHP) were obtained. For RNHP, mirror orientation was used to help to adjust the subject's head position. For ENHP, two approved standard photographs were studied by the assessors before estimation. Correlation analysis was used to analyze the relationship between two angles: Rphoto/Rxray and Ephoto/ Eray.
  
  
  RESULTS
  A significant correlation was found between RNHP and ENHP, both on the photographs and on the cephalograms.
  
  
  CONCLUSIONS
  There is a strong correlation between RNHP and ENHP. RNHP is the subjective perception of the subject and gets some objective meaning by mirror orientation. ENHP is the subjective perception of assessors and gets objective meaning by a standardization session in advance. The mirror orientation of RNHP and the advance standard study of ENHP are crucial for validity and accuracy of NHP as an extracranial reference plane.
authors.affiliation: Peking University, School and Hospital of Stomatology, Department of Orthodontics, Beijing, China.
authors.forename: Jiuhui
authors.initials: J
authors.lastname: Jiang
authors.forename: Tianmin
authors.initials: T
authors.lastname: Xu
authors.forename: Jiuxiang
authors.initials: J
authors.lastname: Lin
mesh_terms: D002508:Cephalometry / Q000379:methods; D005145:Face / Q000000981:diagnostic imaging; D006257:Head / Q000000981:diagnostic imaging*; D006801:Humans; D010781:Photography; D011187:Posture; D011859:Radiography