Establishment of a reliable horizontal reference plane for 3-dimensional facial soft tissue evaluation before and after orthognathic surgery

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 imageswere superimposed. Two reference lineswere 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 fromreliable facial Ex and T landmarks. This plane is consistent and crosses the FH plane at 17.6 degrees.