Samples selection
This study was carried out at the Department of Stomatological Hospital of Chongqing Medical University, China after the ethical approval and study protocol was approved (CQHS-REC-2021001). Written informed consent for the participation in the study and the publication of their identifying images in an online open-access publication platform has been obtained from all subjects. We confirm that all methods were performed in accordance with the relevant guidelines and regulations.
The CBCT and 3D facial scan images of 20 orthognathic patients (ten women) were used. Two types of image were taken at the same time for diagnostic purposes. All patients underwent the same surgery procedure-maxillary Le Fort I osteotomy and mandibular bilateral sagittal splint ramus osteotomy to treat skeletal class III malocclusion, which were performed by a same surgeon from the above hospital. Patients with congenital syndromes, systematic diseases, cleft lip /palate, temporomandibular joint disorder or facial trauma were excluded.
Data acquisition
CBCT (KaVo Dental Gmb H, USA; 80 mA, 8.9-second scan time) scans were acquired at a 0.4 mm* 0.4 mm* 0.4 mm voxel size level and set at a matrix of 400 × 400 pixels in each CT slice and a 0.25 mm slice thickness. The CBCT data were then stored into a specialized computer in Digital Imaging and Communications in Medicine (DICOM) format, and were converted in to 3D models for measurement with a 3D reconstruction software, Mimics 19.0, (Materialise, Leuven, Belgium). To obtain the optimal facial soft tissue models, the threshold values for Hounsfield units(HU)were set as -718 to -177 HU and smooth procedure was performed. After these processes, the 3D facial soft tissue images reconstructed by CBCT were obtained.
The facial scanner Morpheus 3D (Morpheus, Gyoung-gi, Korea) was used for 3D facial surface scan, which emitted white structured light to the patient and fine texture of facial skin can be obtained. Other parameters of this device included a scan time of 0.8 seconds, a scan accuracy of 0.1mm and an image resolution of 1024x768 ppi. After scanning process, the images were then auto-synthesized by the MDS software of the device (Morpheus, Gyoung-gi, Korea), and the 3D facial scan models were obtained.
Variables measurement
11 soft tissue landmarks and 15 linear and angular measurement variables were used in this study (Figure 1, Figure 2 and Table 1). Landmarks location and variables measurement were performed in CBCT model and 3D facial scan models respectively using a mouse-driven graphics cursor in 3D view. To assess the intra-observer reproducibility, the first author located the landmarks twice at an interval of 2 weeks, and the intra-class correlation (ICC) analysis was performed at 95% confidence intervals. All variables were measured twice in two-week interval by the same operator, and the mean of the two measured values was used for final statistical analysis.
Table 1
Definition of landmarks and measurements in this study
Item
|
Definition
|
Cm
Sn
Sbal (L/R)
|
The uppermost point of the nasal columella
The midpoint of the turning between the skin of the upper lip and the root of the nasal columella
The turning point of philtrum crest and nasal columella (Left side/Right side)
|
Cph (L/R)
|
The highest point of the arch of the upper lip (Left side/Right side)
|
Ch (L/R)
|
The outermost point of the oral cleft junction (Left side/Right side)
|
Ls
Li
|
Midpoint of the vermilion border of the upper lip
Midpoint of the vermilion border of the lower lip
|
Length of PC(L/R)
Width of the mouth
Vermilion thickness of UL
Vermilion thickness of LL
Protrusion angle of UL
Protrusion angle of LL
Angle of UM (L/R)
Angle of LM (L/R)
Angle of CB (L/R)
Central angle of CB
Nasolabial angle
|
Distance from Sbal to Cph (Left side/Right side)
Distance from ChL to ChR
Distance from Ls to Stmo
Distance from Li to Stmo
∠ChL-Ls-ChR
∠ChL-Li-ChR
∠Cph-Ch-Stmo (Left side/Right side)
∠Cph-Ch-Stmo (Left side/Right side)
∠Ch-Cph-Ls (Left side/Right side)
∠CphL-Ls-CphR
∠Cm-Sn-Ls
|
PC, the philtrum crest; UL, the upper lip; LL, the lower lip; UM, the upper mouth; LM, the lower mouth; CB, the Cupid’s bow. |
Statistical analysis
The data of this study were analyzed using SPSS 26.0 software (IBM Co., Armonk, NY, USA) and MedCalc Software (version 20.009, Ostend, Belgium) For qualitative evaluation, the Shapiro-Wilk Test was applied to analyze the distribution characteristics of the data and the Bland-Altman plots was used to analyze the equivalence between measurements derived from these two kinds of model. To determine the equivalence of the 2 methods, the line of equality (difference=0) must contain entirely within the 95% confidence interval of their mean difference. To quantify specific deviation of CBCT measurements from facial scanner, the results of the latter were set as a benchmark, and mean absolute difference(MAD) and relative error magnitude(REM) for each variable were calculated. The calculation was performed as follows:
![](https://myfiles.space/user_files/58895_8739fc6c57c1c19a/58895_custom_files/img1628659933.png)