title: Establishment of a Reliable Horizontal Reference Plane for 3-Dimensional Facial Soft Tissue Evaluation Before and After Orthognathic Surgery.
abstract: BACKGROUND
  This study aims to demonstrate the reliability of our proposed facial reference system in the horizontal axis using 3-dimensional photogrammetry and to find a correlation between this plane and the Frankfurt horizontal (FH) plane.
  
  
  METHODS
  Forty-one patients were enrolled. Three-dimensional facial images were taken before and 6 months after orthognathic surgery. Superimposition was carried out, and differences in landmark position were evaluated. Two constant landmarks were selected to construct a reference system within a standardized reference frame. Cone-beam computed tomography and 3-dimensional facial images were superimposed. Two reference lines were identified, and the angle between these lines was calculated.
  
  
  RESULTS
  For landmark reliability, 5 landmarks [gnathion, nasion, exocanthion (Ex), endocanthion, and tragion (T)] were constant. Two landmarks (Ex and T) were selected to construct a reference system within a standardized reference frame. For angular measurement, the mean angle between this reference plane and the skeletal FH plane was 17.6 ± 2.0 degrees. There was no statistical difference between sex, side, and preoperative/postoperative timing of photography.
  
  
  CONCLUSIONS
  Our proposed reference plane is constructed from reliable facial Ex and T landmarks. This plane is consistent and crosses the FH plane at 17.6 degrees.
authors.affiliation: From the *Division of Plastic Surgery, Siriraj Hospital, Mahidol University, Bangkok, Thailand; †Plastic and Reconstructive Surgery and Craniofacial Research Center, Chang Gung Memorial Hospital, Chang Gung University; and ‡Craniofacial Research Center, Chang Gung Memorial Hospital, Taoyuan, Taiwan.
authors.forename: Peerasak
authors.initials: P
authors.lastname: Chortrakarnkij
authors.forename: Daniel
authors.initials: D
authors.lastname: Lonic
authors.forename: Hsiu-Hsia
authors.initials: HH
authors.lastname: Lin
authors.forename: Lun-Jou
authors.initials: LJ
authors.lastname: Lo
mesh_terms: D000293:Adolescent; D000328:Adult; D059925:Anatomic Landmarks; D054893:Cone-Beam Computed Tomography; D005145:Face / Q000033:anatomy & histology*; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D056948:Orthognathic Surgical Procedures; D010780:Photogrammetry; D012016:Reference Values; D015203:Reproducibility of Results