Two experimental methods to integrate intra-oral scans into 3D stereophotogrammetric facial images

Objectives: For this research two different ways for integrating intra-oral scans into three-dimensional (3D) stereophotogrammetric images are analyzed and compared to the gold standard method.

Materials and methods: A cross-sectional study was performed. For each patient a complete dataset was collected, which was used to generate 3D fusion models by three different methods: method A using cheek retractors, method B using a tracer and method C using full-skull CBCT. The experimental methods A and B were compared to the gold standard method C.

Results: A group of eighteen patients were included in this study. The translation (X, Y,Z), the euclidean distance and the rotation (roll, pitch, yaw) were calculated for both experimental methods A and B in comparison with the gold standard method C. Twelve out of fourteen measurements were clinically acceptable (below 2 mm or 2 degrees). Method A shows the highest deviation in the pitch-orientation for rotation (2.51 degrees, 95% CI [1.756 … 3.272]), while method B shows a higher deviation along the y-axis (1.85 mm, 95% CI [1.224 … 2.467]).

Conclusions: This study shows promising results of non-ionizing methods to integrate intra-oral scans into 3D stereophotogrammetric images. With improved accuracy in pitch in method A and translation along the Y-axis in method B, all measurements will be within the clinically acceptable threshold. However, since these two measurements exceed the clinically acceptable thresholds, the complete model positioning is less accurate. Therefore the main goal in further research should be to improve the accuracy of the pitch in method A and the translation along the Y-axis in method B. Additionally, for clinical use the biggest improvement could be gained by optimizing the clinical workflow and data processing.

Clinical relevance: By using a non-ionizing 3D fusion model instead of a conventional cephalogram for treatment planning, the ionizing dose during orthodontic treatment can be significantly reduced.