A new method to orient a 3-dimensional facial model to natural head position: A preliminary report on accuracy and reproducibility

Objectives: To establish and validate a novel method to orient a 3-dimensional (3D) facial model to natural head position (NHP) in a stereophotogrammetric system using a 2-dimensional frontal full-face photograph of NHP.

Material and methods: Specific technique procedure was reported for our method, and in vitro model experiment was performed for accuracy test. A preliminary volunteer study was then planned for reproducibility test.

Results: The accuracy on a 3D-printed test model was within 0.15°. Within an observational cohort of 22 dental students, the angular deviations of different maxillofacial regions (e.g., central forehead, left and right zygomatic regions, apex of nose and mental region) were no more than 2° between the 3D NHP models acquired with a shorter time-interval (1 h from baseline) or a longer time-interval (7 days from baseline), which were all considered clinically insignificant. In addition, the angular deviations were significantly larger with a 7d-interval than with a 1h-interval, indicting a decline in 3D NHP reproducibility over short time duration.

Conclusion: The current method may represent a clinically useful protocol for recording and transferring 3D NHP in stereophotogrammetry.

Clinical relevance: It may provide reliable and meaningful reference information for evaluating craniofacial morphology, and be of clinical use in the diagnosis, treatment and follow-ups of patients with aesthetic or deformed craniofacial problems.