title: Variability of the inclination of anatomic horizontal reference planes of the craniofacial complex in relation to the true horizontal line in orthognathic patients.
abstract: BACKGROUND
  The purpose of this study was to assess the reliability of the Frankfort horizontal (FH), sella-nasion horizontal, and optic planes in terms of their variabilities in relation to a true horizontal line in orthognathic surgery patients.
  
  
  METHODS
  Thirty-six consecutive presurgical orthognathic patients (13 male, 23 female; age range, 16-35 years; 30 white, 6 African Caribbean) had lateral cephalometric radiographs taken in natural head position, with a plumb line orientating the true vertical line, and the true horizontal line perpendicular to the true vertical. The inclinations of the anatomic reference planes were compared with the true horizontal.
  
  
  RESULTS
  The FH plane was found to be on average closest to the true horizontal, with a mean of -1.6° (SD, 3.4°), whereas the sella-nasion horizontal and the optic plane had means of 2.1° (SD, 5.1°) and 3.2° (SD, 4.7°), respectively. The FH showed the least variability of the 3 anatomic planes. The ranges of variability were high for all anatomic planes: -8° to 8° for the FH, -8° to 15° for the sella-nasion horizontal, and -6° to 13° for the optic plane. No significant differences were found in relation to patients' sex, skeletal patterns, or ethnic backgrounds.
  
  
  CONCLUSIONS
  The clinically significant variability in the inclinations of anatomic reference planes in relation to the true horizontal plane makes their use unreliable in orthognathic patients.
authors.affiliation: Postgraduate student, Department of Orthodontics, St George's Hospital and King's College London Dental Institute, London, United Kingdom.
authors.forename: Ameen M
authors.initials: AM
authors.lastname: Zebeib
authors.affiliation: Consultant orthodontist and honorary senior lecturer, Kingston and St George's Hospitals and St George's Medical School, London, United Kingdom. Electronic address: Farhad.Naini@yahoo.co.uk.
authors.forename: Farhad B
authors.initials: FB
authors.lastname: Naini
mesh_terms: D000293:Adolescent; D000328:Adult; D059925:Anatomic Landmarks / Q000473:pathology*; D063405:Anatomic Variation; D002508:Cephalometry / Q000706:statistics & numerical data*; D004424:Ear Canal / Q000473:pathology; D005123:Eye / Q000473:pathology; D005147:Facial Bones / Q000473:pathology*; D005260:Female; D006801:Humans; D008297:Male; D009295:Nasal Bone / Q000473:pathology; D009915:Orbit / Q000473:pathology; D056948:Orthognathic Surgical Procedures / Q000379:methods*; D012016:Reference Values; D015203:Reproducibility of Results; D012658:Sella Turcica / Q000473:pathology; D012886:Skull / Q000473:pathology*; D055815:Young Adult