Three-dimensional natural head position reproduction using a single facial photograph based on the POSIT method

We developed a new method to record and reproduce the three-dimensional natural head position (NHP) from a single photograph of a patient's face using a pose from orthography and scaling with iterations (POSIT) algorithm. We attached 4-mm spherical ceramic markers to the patient's face as feature points. A frontal photograph of the patient's NHP was taken using an ordinary digital camera parallel to the global horizon. Computed tomography (CT) was then performed on the patient with the markers. The ceramic marker positions were determined in the 2D image and corresponded to points in the 3D model. The 3D rotation matrix determined using the feature points via the POSIT method was applied to the CT model to reproduce the NHP. A skull phantom was used to evaluate the accuracy and reproducibility of the developed method. The degree difference (°) between the true and POSIT orientations in the roll, pitch, and yaw directions was quantified as the error. The mean accuracy was -0.04 ± 0.15°, -0.17 ± 0.50°, and -0.02 ± 0.37° in the roll, pitch, and yaw directions, respectively. The method developed was highly reproducible during intra-observer and inter-observer variation analyses. The accuracy of the method was clinically acceptable, and the procedure was time- and cost-effective. This method is accurate and inexpensive; additionally, it does not affect the patient's lip position, and we expect it to be routinely used during orthognathic surgery.