3 D stereophotogrammetry facial analysis of Angle I subjects : gender comparison

Objective: The aim of this study was to establish reference parameters for facial analysis in subjects with Angle’s Class I occlusion by means of stereophotogrammetry, comparing men and women. Material and method: Twenty-six healthy young adults with Angle’s Class I occlusion volunteered to participate in the study, 15 males and 11 females, ages between 18 and 30 years old (22 years ± 5). These subjects were clinically examined to verify their type of occlusion. Twenty-five landmarks were performed in soft tissue, and those subjects underwent image capturing by the stereophotogrammetry technique, using the apparatus Vectra (M3-Canfield®). The following variables were measured in those images: naso-labial angle (C-Sn-Ls); (N-Prn -Pg); (N-Sn-Pg); mentolabial (Li-Ps-Pg); growth angle (T-Go-Pg), cheek area (T, Zy, Chk, Ch, Gn, Go), hemifaces’ areas (T, Zy, Ft, Tr, N, Prn, C, Sn, Ls, Sto, Li Ps, Gn, Go), lip area, bilaterally (Ls, Cph, Ch, Li, Sto), and linear measurements of the lips and jaw. Result and conclusion: The data were compared between genders (Student’s t-test), and no statistically significant differences between groups (p>0.05) were found. Despite the limitations of this study, it is possible to conclude that, as there were no differences between men and women for the studied variables (angular, linear, and area), the data of the total sample (Class I) should be used as reference parameters in future studies. Additionally, the 3D stereophotogrammetry technique has proven to be a new possibility for facial analysis, which might be employed in several areas of dentistry. Descriptors: Photogrammetry; imaging three-dimensional; dental occlusion.


INTRODUCTION
Facial analysis is essential for the diagnosis and treatment planning of different dental procedures, such as for example, orthognathic surgery and visualization of craniofacial malformations.The development of techniques that seek to ensure this type of analysis has been proposed, among them the one that stands out the most is the 3D stereophotogrammetry 1 .This technique consists of a rapid method for acquisition of images in a non-invasive and safe manner, reducing the need for exposure to radiation.Image acquisition is performed by cameras positioned at different angles, and a software produces a three-dimensional digital image of the individual's face.These images precisely represent the soft tissues of the face, since it is not necessary that there is contact with the skin's surface.This technique can be widely used both in the dental area, as well as in the medical field for the diagnosis, planning and comparison of the results obtained 2,3 .
The 3D image acquisition system and facial sculptor Vectra M3 (Canfield Scientific, Fairfield, NJ) consists of two capsules including three cameras (one color and two black and white) and a projector in each capsule.The system captures images in two dimensions of the individual's face and reconstructs them three-dimensionally.These 3D images can be processed, analyzed, manipulated and measures 4,5 .The possibility of handling the 3D image in different directions (front, side, inferior-superior, superior-inferior) allows several types of analysis of soft tissue are performed, among them we can highlight the measurement of linear distances, angles and areas.Furthermore, it is possible to superimpose these images before and after treatment, for example, orthognathic surgery, which also allows the patient to view these results 5 .
Knowledge of the occlusion is of paramount importance for many areas in Dentistry, among which stand out the oral rehabilitation, restorative dentistry, orthodontics and functional orthopedics of the jaws.The majority of the analyses that are carried out for plans dental interventions are based on images of hard tissues (x-rays, computed tomography, cephalometries).However, it is important to point out also the importance of evaluating the soft tissue, because this represents the facial appearance of each individual.
Therefore, the objective of this study was to establish reference parameters for the analysis of facial soft tissue of subjects Class I Angle by means of the 3D stereophotogrammetry technique (Vectra M3 -Liphook, United Kingdom®), comparing men and women.

Study Design
This was a cross-sectional observational study.

Research Participants
A group of 26 healthy volunteers (11 women and 15 men, were recruited for this study.Their ages ranged between 18 and 30 years (22 years ± 5).Inclusion criteria were: occlusion in Angle Class I and presence of at least 26 teeth in the mouth.We excluded individuals who had missing teeth, patients with central or peripheral neurological disorders, or who have suffered tumors, trauma in the region of head / neck and orthognathic or plastic surgery.Patients were also excluded who were undergoing orthodontic treatment, users of partial or full dentures, and subjects with presence of accentuated horizontal and/or vertical overlaps and maxilla-mandibular discrepancies.
All participants were informed about the ethical aspects related to this research and were asked to sign the Informed Consent.This study was approved by the Research Ethics Committee of School of Dentistry of Ribeirão Preto (FORP/USP), according the protocol 08874612.3.0000.5419.

Procedures Performed
The research participants were submitted to clinical dental care performed by a dental surgeon trained and calibrated, with the objective to evaluate the occlusal conditions and the verification of the existence of the Class I Angle.Initially, a band was positioned on the participant's head with the purpose to secure their hair and ensure better visualization of the face.The skin was cleaned with sterile gauze soaked in 70% alcohol, in order to remove any impurities, oiliness and makeup.Reference Points were marked on the facial surface of the participants using black eyeliner (Boticário®), previously established by Ferrario et al. 6 and Sforza et al. 1 .
The data obtained were analyzed by means of descriptive statistics, in order to establish average and standard deviation of linear distances, angles and areas, the Students T Test was also employed for comparison between genders, after checking the normality of the data, in which a 5% level of significance (Bioestat 5.0).

RESULT
The values of the mean and standard deviation for each variable evaluated are distributed in Tables 1, 2, 3 and 4, and Table 1 shows the angles T-Go-Pg , C-sn , N-Prn-Pg , N-Sn-Pg and Li-Sl -Pg, Table 2 shows the values of the areas of the cheeks, facial hemispheres and lips, in Table 3 the values for the lips (upper and lower distances and distance from the lip midline) and in Table 4 the values of linear measurements of the mandible.It is important to point out that for all variables were considered each gender and the total sample (Class I).
Regarding the analyzed angles, the biggest difference observed between the mean values in the comparison between genders was for the convexity angle of facial soft tissue profile without the nose (N-Sn-Pg), for which men achieved an average of 161.9 (± 3.8) and 166 women (± 4.0), although not statistically significant.For the other values of angles was found great proximity between men and women, being that no statistically significant differences were obtained in the comparison between genders for any variable (p>0.05)(Table 1).
Considering Table 2, it is possible to check that there was no statistically significant difference between men and women in the  areas of cheek and facial hemispheres.For the right hemiface, the p value was 0.98 and for the left hemiface was 0.65.While for the right cheek area of the p value was 0.09 and the left cheek was 0.08.As for the lip area, the p value for the right side was 0.31 and 0.19 for the left side.
Tables 3 and 4 contain data concerning the descriptive statistical analysis of the data of lips and linear measurements of the mandible (mean and standard deviation) for men, women, and total sample (Class I).The measures relating to the lips were considered: distance top right, distance top left, distance bottom right, distance bottom left and away from the lip midline and measures concerning the linear distances of the mandible are Go-Gn, Go-T and sum of Go-Gn and Go-T.

DISCUSSION
The scientific and technological advances, techniques such as laser scanning, MRI, ultrasound, scan for contact and stereophotogrammetry offer significant changes in the diagnostic process, because they are considered non-invasive methods of facial analysis 5,7,8 . .The data previously analog have gone digital, and opened up the possibility of fast acquisition, accurate and without radiation, with its information while being archived for future analyzes, moreover can be shared easily with patients and other professionals 2,5,[9][10][11] .Stereophotogrammetry is a conservative method for individuals submitted to imaging, not to issue any type of radiation 12 .Doctors Table 1.Mean and standard deviation of angles T-Go-Pg (growth), C-Sb-Ls (nasolabial), N-Prn-Pg (convexity of soft profile facial with nose), N-Sn-Pg (convexity of soft profile face without nose) and Li-Sl -Pg (mentolabial) for both genders and total sample (Class I)    and dental surgeons must consider the risks and benefits to the patient in obtaining craniofacial images, current research is attempting to reduce unnecessary x-ray exposure, especially in children 13 .
In several clinical applications, virtual reproductions of morphology can help professionals during the diagnosis and planning of medical procedures and treatments 12 .The system used in this study enables the overlay of images captured from the individual with the image obtained by means of computed tomography and, thus increasing the accuracy of images and measurements.Naudi et al. 14 and Schendel et al. 15 verified this hypothesis and confirmed the great applicability of 3D imaging, as well as their superposition.This new method is promising, in that it assist with more accuracy the planning of surgical treatments. .Metzler et al. 16 e Tzou et al. 17 compared the validity of threedimensional stereophotogrammetry with other imaging systems, which proved to be an effective reliable and fast method.The software allows for tissue modifications to promote the planning and visualization of the possible post-operative.The same can be found in this study, being that this method does not provide any changes in soft tissues of the face, since the device does not come in contact with the face of the individual to perform the image capture, which would result in changes to the measurements.It also allows the measurement of linear distances, area, and volume and it is possible view the images from different angles.
The apparatus for facial analysis in 3D (Vectra M3) have a high cost and need for a suitable location, with space reserved specially for their installation without temporary changes.Thus, the facial analysis in 3D is still limited to laboratories of universities and research centers 8,18 .
The images obtained from individuals are standardized and can be saved for later evaluation of cases and form a database for future comparisons.These images allow modifications that facilitate preoperative planning, and a "vision" of post-operative patients.Thus, it allows great applicability, especially in Dentistry as in cases of orthognathic surgery 14,15,[19][20][21][22][23] .
According to Brons et al. 24 and Metzler et al. 16 the speed in the pictures capture speed significantly reduces possible distortions due to the individual drive, which facilitates work done with children.There is no need for contact with the facial surface, thus prevents changes in soft tissues, which could cause errors in direct measurement 2,7 .

Figure 1 .
Figure 1.Reference Points marked facial in the midline and bilaterally in the face prior to the acquisition of three-dimensional images.

Figure 2 .
Figure 2. Marking of the hemiface area, growth angle T-Go-Pg, the lip area and linear distances of the lips for viewing of the Vectra®-3D dimensional image processing software.

Table 2 .
3ean and standard deviation of the areas of the cheeks, lips and hemifaces for both sides of the face (D for right and E for the left), considering men, women and total sample (Class I), measured in cm3 * Students T Test, comparison between genders, adopting a 5% significance level.

Table 3 .
Mean and standard deviation of the variables related to his lips: upper right distance, distance upper left, lower right distance, left smaller distance and distance from the lip midline (LML), considering both genders and the total sample (Class I)

Table 4 .
Mean and standard deviation of the variables concerning the linear distances of the mandible: Go-Gn, Go-T and the sum of Go-Gn and Go-T (D for right-hand side and E for the left-hand side), considering both genders and the total sample