# Reproducibility and Accuracy of Two Facial Scanners: A 3D In Vivo Study
## 4 Discussion  
Currently, 3D facial scans are promising for assessing facial soft tissue morphology, offering high-resolution surface textures and quickly capturing detailed 3D images, which benefit pediatric facial development evaluation, analysis of pathological facial morphology, cosmetic and reconstructive procedures, orthognathic surgery, and orthodontic procedures [22; 23; 24]. Furthermore, the advancement of these new acquisition technologies has enabled the capture of high-quality images suitable for landmark detection, serving as an alternative to CBCT. This approach allows for the acquisition of sequential frames while minimizing the patient's exposure to radiation, which is a very important goal in the medical and orthodontic fields [12]. Despite the existing literature on the accuracy of individual 3D imaging systems, numerous options are available on the market, and inter-device repeatability still needs to be verified by analyzing scans from different devices and comparing their relative performances [25; 26]. This study aimed to compare the accuracy and reproducibility of the EinScan H2 with respect to the Vectra M3 3D Imaging System and to anthropometric measurements. Specifically, the goal was to compare the accuracy of the portable EinScan H2 with the previously validated static Vectra M3. The use of portable devices can facilitate their application in clinical practice, as they are more accessible than static devices [16]. Moreover, no existing research evaluates the accuracy of this scanner in relation to 3D cephalometric areas and points. These data, thoroughly analyzed in this study, represent a crucial aspect in the field of orthodontics and, for this reason, have been investigated in this manuscript. The analysis of linear measurements has been extensively investigated in the literature. The importance of these measurements lies in their ability to obtain a comparison between the two scanners, and particularly a direct comparison of them with real anthropometric measurements [27; 28]. In this regard, comparison of linear measurements on 3D facial scans with direct anthropometry measurements has proved they are reliable and repeatable, showing no significant differences (\(p>0.05\)). These findings are supported by the literature, confirming that the differences observed in linear measurements are not clinically relevant [13; 29; 30]. Considering point measurements, it was observed that all the points taken into consideration showed a difference between Vectra and Einscan within the range from 0.5 mm to \(-0.5\) mm. The only point that showed a greater millimetric difference was the subnasal point (0.73 mm). However, the literature confirms that the vertical orientation of the head can affect the scanning accuracy in certain areas, making it difficult to correctly scan certain cephalometric landmarks, thus justifying the greater millimetric deviation [31]. To maintain a natural head position, various modalities such as chin rest, head positioning devices, or digital orientation sensors, should be used to obtain a more stable head position and to prevent unwanted movements [32]. The analysis of superimpositions revealed that more than 70% of the averages of overlapping surfaces of the forehead, left cheek, right cheek, tip of nose, and chin areas fell within the highly reproducible band (0.5 mm to \(-0.5\) mm) when comparing the Vectra-Einscan scanners. The nose and the right and left cheeks had the highest average value (almost 80%) of the surface in the highly reproducible category. The chin and the forehead, instead, obtained the lowest values in the bands considered highly reproducible (respectively, 70.46% and 71.72% in the 0.5->0 and 0->-0.5 mm range). The poor reproducibility of the forehead can be explained by the fact that facial scanners encounter greater difficulties in capturing images with large curvatures compared to areas with defined angles [33].