title: Natural reference structures in the human maxilla: a systematic search in children with tantalum implants.
abstract: OBJECTIVE
  The aim of the study was to locate stable natural reference structures (NRS) in the maxilla as seen on lateral cephalometric radiographs.
  
  
  METHODS
  Retrospective radiographic analysis.
  
  
  METHODS
  Paired serial lateral cephalometric radiographs of 27 children (aged 7·1-13·5 years at the initial radiograph and a mean interval of 3·9 years between radiographs) with a minimum of three Björk-type tantalum implant markers in the left maxilla were examined for the presence of NRS. The pairs of radiographs were converted to digital image format, superimposed and registered using stable implants. Potential NRS were located by visual examination of the superimposed images and tested for morphological and spatial stability using automated computer-based analysis employing cross-correlation.
  
  
  RESULTS
  NRS were detected in 24 of the 27 subjects (median: 4; range: 1-9 NRS). The number of NRS was statistically significantly negatively correlated with the interval between the radiographs (rrank = -0·422; P = 0·03), but not significantly correlated with the age at the initial radiograph (rrank = 0·23; P = 0·26). Those NRS found above the nasal floor were both morphologically and spatially stable over periods of several years. The most conspicuous of these were the mid-portion of the anterior contour of the zygomatic process beyond 9 years of age and the junction of the corticated walls of the infra-orbital canal with the internal surface of the maxilla.
  
  
  CONCLUSIONS
  This study has demonstrated the existence of several NRS visible on the lateral cephalometric image of the maxillae. The most prominent NRS should be sufficient in most cases to permit accurate orientation of serial cephalometric radiographs.
authors: Stephen
authors: S
authors: Springate
mesh_terms: D000293:Adolescent; D059925:Anatomic Landmarks / Q000000981:diagnostic imaging*; D001672:Biocompatible Materials / Q000737:chemistry; D001846:Bone Development / Q000502:physiology; D002508:Cephalometry / Q000379:methods*; D002648:Child; D057918:Fiducial Markers; D005500:Follow-Up Studies; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008437:Maxilla / Q000000981:diagnostic imaging* / Q000254:growth & development; D009915:Orbit / Q000000981:diagnostic imaging; D011859:Radiography; D012189:Retrospective Studies; D013635:Tantalum / Q000737:chemistry; D015050:Zygoma / Q000000981:diagnostic imaging
chemical_list: D001672:Biocompatible Materials; D013635:Tantalum
keywords: cephalometrics; maxilla,; maxillary growth,; natural reference structures,; tantalum implants,