# Reproducibility and Accuracy of Two Facial Scanners: A 3D In Vivo Study
## 2 Materials and Methods  
### Scanning Phase  
After the approval from the Institutional Review Board of the Postgraduate School of Orthodontics of the University of Ferrara and acquiring informed consent, 20 volunteers--11 men and 9 women, mean age 26 years old--were selected for the study.  
The inclusion criteria were subjects who had completed growth. Exclusion criteria included men with beards, previous trauma to the facial area, facial esthetic surgery, or skin blemishes.  
Each participant was measured manually and scanned using the two devices--the EinScan H2 scanner (EIN) and the Vectra scanner (VEC)--on the same day.  
A skilled operator performed all the scans and the other two operators verified the correct processing of the 3D image.  
On the day of the scans, each participant was instructed to take off glasses they might have been wearing and to pull back their hair through a band to ensure proper visibility of the face and of the ears. [PERSON] et al.'s [13] methodology was employed, and six reference markers were placed on each subject's face at six cephalometric points (Figure 1, Table 1), using a special cross-shaped mold.  
\begin{table}
\begin{tabular}{p{113.8 pt} p{284.5 pt}} \hline
**Cephalometric Point** & **Definition** \\ \hline \multirow{3}{*}{Trichion (Tr)} & The most superior midline point on the forehead, located at the hairline where the forehead meets the scalp. It is anatomically situated at the junction of the frontal bone and the anterior hairline. \\ \cline{2-2}  & The midpoint of the junction between the forehead and the nose. It corresponds to the most anterior point on the profile where the nasal dorsum transitions into the glabella, which is the smooth area between the eyebrows. \\ \hline \multirow{2}{*}{Pronasion (Prn)} & The most projected point of the nasal tip, which is commonly referred to as the apex of the nose. \\ \cline{2-2}  & \\ \end{tabular}
\end{table}
Table 1: Definition of the six cephalometric points.  
Figure 1: Frontal photograph and facial scan of the subject with reference points in order from top to bottom: Tr (midline of hairline), Na\({}^{\prime}\) (point on soft tissue over nasion), Prn (soft tissue point on tip of nose), L–R Zyg (lateral point of zygomatic arches), Pog\({}^{\prime}\) (soft tissue over pogonion).  
To maintain a natural head position and prevent movement during the scan, participants were seated with backtests and instructed to keep their mouths closed, lips relaxed, and eyes closed, while a thorough quality control assessment ensured consistency in head position and facial expression [13,18].  
The first scan was conducted with the Einscan H2. The operator positioned the patient correctly in front of the camera, monitored the alignment on the computer screen, and moved the scanner around the subject's face while using color-coded lights to maintain the proper distance and ensure complete coverage.  
The second scan was performed with the Vectra M3, capturing three images--two at 45\({}^{\circ}\) angles and one frontal--20-30 cm below the subject's face. The device was connected to a laptop to ensure 3D reconstruction accuracy throughout the session.  
Given the importance of the light source and its temperature for accurate scanning and good image quality [19, 20, 21], all patients were scanned under a good direct light source, ensuring that the face was sufficiently and evenly illuminated.