Accuracy of RGB-D camera-based and stereophotogrammetric facial scanners: a comparative study

Objectives: This study aimed to evaluate and compare the accuracy and inter-operator reliability of a low-cost red -green-blue-depth (RGB-D) camera-based facial scanner (Bellus3D Arc7) with a stereophotogrammetry facial scanner (3dMD) and to explore the possibility of the former as a clinical substitute for the latter.Methods: A mannequin head was selected as the research object. In the RGB-D camera-based facial scanner group, the head was continuously scanned five times using an RGB-D camera-based facial scanner (Bellus3D Arc7), and the outcome data of each scan was then imported into CAD software (MeshLab) to reconstruct three-dimensional (3D) facial photographs. In the stereophotogrammetry facial scanner group, the mannequin head was scanned with a stereophotogrammetry facial scanner (3dMD). Selected parameters were directly measured on the reconstructed 3D virtual faces using a CAD software. The same parameters were then measured directly on the mannequin head using the direct anthropometry (DA) method as the gold standard for later comparison. The accuracy of the facial scanners was evaluated in terms of trueness and precision. Trueness was evaluated by comparing the measurement results of the two groups with each other and with that of DA using equivalence tests and average absolute deviations, while precision and inter-operator reliability were assessed using the intraclass correlation coefficient (ICC). A 3D facial mesh deviation between the two groups was also calculated for further reference using a 3D metrology software (GOM inspect pro).Results: In terms of trueness, the average absolute deviations between RGB-D camera-based and stereo-photogrammetry facial scanners, between RGB-D camera-based facial scanner and DA, and between stereo-photogrammetry facial scanner and DA were statistically equivalent at 0.50 +/- 0.27 mm, 0.61 +/- 0.42 mm, and 0.28 +/- 0.14 mm, respectively. Equivalence test results confirmed that their equivalence was within clinical re-quirements (<1 mm). The ICC for each parameter was approximately 0.999 in terms of precision and inter -operator reliability. A 3D facial mesh analysis suggested that the deviation between the two groups was 0.37 +/- 0.01 mm.Conclusions: For facial scanners, an accuracy of <1 mm is commonly considered clinically acceptable. Both the RGB-D camera-based and stereophotogrammetry facial scanners in this study showed acceptable trueness, high precision, and inter-operator reliability. A low-cost RGB-D camera-based facial scanner could be an eligible clinical substitute for traditional stereophotogrammetry.Clinical Significance: The low-cost RGB-D camera-based facial scanner showed clinically acceptable trueness, high precision, and inter-operator reliability; thus, it could be an eligible clinical substitute for traditional stereophotogrammetry.