A new three-dimensional method of assessing facial volumetric changes after orthognathic treatment

Objective: To validate a new method of facial volumetric assessment that is dependent on the use of stereophotogram metric models and a software-based Facial Analysis Tool. Design: The method was validated in vitro with three-dimensional (313) models of a lifelike plastic female dummy head and in vivo with a male-subject head. Methods: Thirty facial silicone explants were added in the nasal and perioral regions of each head, and their volumes were obtained by three different algorithms. These were compared with the actual values obtained by a "water displacement" method. Results: The least mean error was found with the "tetrahedron formation" method followed by the "projection" method and the "back-plane construction" method. The error with the tetrahedron formation method was 0.071 cm(3) (95% confidence interval [CI]: -0.074 to 0.2161 cm(3)) with the in vitro models and 0.314 cm(3) (95% CI: -0.080 to 0.708 cm(3)) with the in vivo models. The increased volumetric assessment error observed in vivo was attributed to the registration procedure and possible changes in facial expression. Conclusions: These results encourage the use of this method in the 3D assessment of orthognathic surgical outcome, provided a standardized facial expression is used for image acquisition.