title: Three-dimensional reproducibility of natural head position.
abstract: BACKGROUND
  Although natural head position has proven to be reliable in the sagittal plane, with an increasing interest in 3-dimensional craniofacial analysis, a determination of its reproducibility in the coronal and axial planes is essential. This study was designed to evaluate the reproducibility of natural head position over time in the sagittal, coronal, and axial planes of space with 3-dimensional imaging.
  
  
  METHODS
  Three-dimensional photographs were taken of 28 adult volunteers (ages, 18-40 years) in natural head position at 5 times: baseline, 4 hours, 8 hours, 24 hours, and 1 week. Using the true vertical and horizontal laser lines projected in an iCAT cone-beam computed tomography machine (Imaging Sciences International, Hatfield, Pa) for orientation, we recorded references for natural head position on the patient's face with semipermanent markers. By using a 3-dimensional camera system, photographs were taken at each time point to capture the orientation of the reference points. By superimposing each of the 5 photographs on stable anatomic surfaces, changes in the position of the markers were recorded and assessed for parallelism by using 3dMDvultus (3dMD, Atlanta, Ga) and software (Dolphin Imaging & Management Solutions, Chatsworth, Calif).
  
  
  RESULTS
  No statistically significant differences were observed between the 5 time points in any of the 3 planes of space. However, a statistically significant difference was observed between the mean angular deviations of 3 reference planes, with a hierarchy of natural head position reproducibility established as coronal > axial > sagittal.
  
  
  CONCLUSIONS
  Within the parameters of this study, natural head position was found to be reproducible in the sagittal, coronal, and axial planes of space. The coronal plane had the least variation over time, followed by the axial and sagittal planes.
authors: Tri-Service Orthodontic Residency Program, Lackland AFB, San Antonio, TX 78236-5551, USA.
authors: Diana W
authors: DW
authors: Weber
authors: Drew W
authors: DW
authors: Fallis
authors: Mark D
authors: MD
authors: Packer
mesh_terms: D000293:Adolescent; D000328:Adult; D002508:Cephalometry / Q000295:instrumentation; D054893:Cone-Beam Computed Tomography; D006257:Head / Q000000981:diagnostic imaging*; D006801:Humans; D021621:Imaging, Three-Dimensional; D008137:Longitudinal Studies; D011187:Posture; D015203:Reproducibility of Results; D055815:Young Adult