3D CT Soft Tissue Craniofacial Analysis and Lip Morphology

Objective: To assess the soft tissue characteristics of Bangladeshi adults to formulate soft tissue 3D CT standards using Holdaway’s (HA) and lip morphology (LM) analyses. Another aim of this study was to assess the gender dimorphism of Bangladeshi population. Material and Methods: One hundred and seventeen (Eighty-five men and Thirty-two women) Bangladeshi adults have obtained their computed tomography (CT) scan at the Radiology Department for normal diagnosis. Craniofacial deformities were undetected in all cases. The CT images were prepared by a 3D imaging programming software (Mimics 11.02 Materialise). Parameters from the identified landmark points were measured in 3D through this software. Results: Upper lip thickness (ULT) (vermillion UL-A point) measurement was significant in HA and in LM analyses, upper lip protrusion (ULP) (Ls to Sn-SPog) measurement has demonstrated significant difference among both genders, where p-value was less than 0.05. Mean measurements of Bangladeshi adults were relatively comparable except the face convexity (FC) when compared with the HA cephalometric soft tissue values. Conclusion: By using HA and LM analyses, 3D CT soft tissue standards were established for Bangladeshi adults. Measurements for all parameters have remained equivalent with the HA standard data apart from the FC measurement. This consequently may demonstrate that the Bangladeshi population retains a convex shape with a slight protrusive lip or retruded chin.


Introduction
Mental prosperity, Social acknowledgement, and individual confidence are connected with physical appearance [1]. Therefore, appearance is one of the essential elements of the face. Somewhere in the range of 5000 years back, the antiquated Egyptians stated their attention towards beauty and aesthetics [2].
Asymmetrical human faces are not beautiful, though balanced facial appearance remains satisfactory unless constantly delightful [3]. For an individual, some components (age, culture, ethnic background and personality) may influence the meaning of an appealing and satisfying look [4]. Achieving utmost facial aesthetic is the supreme objective for orthodontic and maxillofacial specialists [5].
In the human body, the face is considered the most variable part. Variability is specified by the facial size and shape of an individual and significantly added by the relation of these facial profiles to one another.
Facial quantities like harmony and disparity must be determined quantitatively but sadly only described in words earlier [6]. By orthodontic analysis and treatment planning, the significance of soft tissue esthetics has been described by different investigators. Many studies showed that soft tissues that vary significantly in thickness remain the key consideration in deciding a subject's ultimate facial profile [7][8][9]. Therefore, solitary investigation of dental and skeletal forms might be insufficient, as different varieties of the soft tissues involved in the dento-skeletal structure. Since treatment procedures turn out to be more powerful, additional importance has been given on the soft tissues.
For lip posture assessment and the profile's aesthetic quality, few line analyses have been proposed [10]. Rickett's ''E'' line [11] is affected a lot through the development of the nose. Steiner's ''S'' line [12] disposes of a larger change in skin profile because of the development of the nose, though HA ''H'' line [8] gets the benefit of eliminating the impact of nasal development in the assessment of lip posture.
After the revelation of cephalometric in 1931, it has been popular as a fundamental clinical instrument for the assessment of dento-skeletal relationship in orthodontics [13]. Disappointingly, information acquired from the cephalometric radiographs has been related with few faults like geometric distortion and superimposition of structures on the radiographs [14]. Currently, three-dimensional (3D) imaging techniques, for example, cone-beam computed tomography (CBCT) and computed tomography (CT), have played a vital part in the dental field. Through these modalities, the orthodontists can imagine 3D pictures of craniofacial structures without including the superimposition of anatomical structures [15]. With various 3D imaging programming methods, 2D pictures can reproduce in 3D. These reproduced images can offer correct and precise information to study a basic craniofacial problem [16].

Subjects and Samples
This cross-sectional retrospective study included one hundred and seventeen Bangladeshi patients who performed their CT scans at the Radiology Department of Medinova Medical Services LTD. Patients performed their CT scans for reasons other than craniofacial difficulties (for example, migraines, serious cerebral pain, changes in mental status). The inclusion criteria for this study were age eighteen to sixty-five years, no history of plastic or reconstructive medical method and excellent quality CT volumetric data.
Subjects with craniofacial deformities, wounds, burns or scar tissues, cleft lip, cleft palate in the craniofacial zone, also patients with a history of orthodontic treatment were excluded from this study.
Written Informed consent was taken from each patient before having a scan and all consent forms were reviewed and permitted by the institution's ethical authority. Data were collected from the archive with the best possible consent from the authority for study uses. All research-related task in this study was executed CT scans were kept in Digital Imaging and Communications in Medicine (DICOM) format, stored in a personal computer and then introduced into the Mimics medical imaging software (version 11.02, Materialise, Leuven, Belgium). This software was also utilized to build three-dimensional (3D) images originated from two-dimensional (2D) cross-sectional images. A sequence of processes were performed on the CT data, for instance, thresholding, region growing, and editing.
3D image-segmentation utilizing Mimics software was availed to measure the parameters from the identified landmark points (Tables 1 and 2). First, CT data segmentation was performed to measure a region of interest for example, the outer craniofacial part or the inner part of the skull. CT images were converted to a "Mask" by means of a threshold technique in which a line on a 2D image (drawn using the "Profile Line" feature) acknowledged the particular threshold values that fluctuates within the line. In a 3D-CT reconstruction, the threshold level was used to decide the minimum density of material. This image was reformatted at a threshold value that separated soft tissue from bone and air. Region growing was performed to select simply the region of interest. The rest of the parts that shared the similar value of "mask" could be eliminated easily by utilizing the region growing technique to assure that the particular portion only was selected. Consequently, the 2D images were transformed into 3D images using the calculated 3D tool.
Measurements were done on the 3D images with help of other 2D views.    Total measurements were performed by a solo researcher in an ideal manner (Figure 1 and 2). All measurements were remade three times. After two weeks, the second measurements were carried out and the researcher was blinded to the results to control bias. For the third time, the similar blinding was done, which is two weeks after the second measurement. The averages of the three readings of each measurement were considered for statistical analysis with the particular end goal of controlling intra-examiner variation.

Results
The Kolmogorov-Smirnov test indicated that all data were generally distributed. Intraclass coefficient analyses revealed intra-examiner reliability values of 0.90-0.96. This demonstrated that the examiner was dependable in conducting the measurement. The study sample included eighty-five males and thirty-two females.
The soft tissue measurements, as well as normal values, were presented via HA and LM analyses in Tables 3 and 4 Table 5 presents the HA analysis. The face convexity of all populations was appeared to be higher than the HA established value. Table 6 shows the LM measures for different populations.

Discussion
The achievement of orthodontic treatment is mostly acknowledged by the variation picked up in the patient's facial look, which includes the soft tissue profile. In HA investigation [8,9], Frankfort horizontal (FH) plane was used as a basis of the perspective plane.
In this study, the correlations of the Bangladeshi genders were achieved by using the means and SD of the values. The soft tissue facial angle (STFA) and convexity angle (CA) were used to overview the concavity or convexity of the profile. In this study, the STFA was 88.89º in males, 87.78º in females and the CA was 3.62º in males, 3.66º in females, which demonstrated a tendency to straight profile steady with Class I classification.
Measurements of HA soft tissue of Bangladeshi subjects were compared with the HA cephalometric established soft tissue values [8,9]. For HA analysis, the present data were compared with the Saudis [31], Japanese [20], Chinese [19] and Palestinians [32] ( Wei [33] has established no remarkable gender dimorphism in angular measurements, also a more similar craniofacial method in both genders of Chinese subjects. The male profile has remained more or less larger in overall linear measurements. Cheng [34], in his investigation of Malaysian genders, found no major differentiation in angular measurements, though the linear measurements have remained smaller for females when compared to males. In the current study, simply the ULT (vermillion UL-A point) has demonstrated a significant difference (p<0.05). The current study has shown the Class I classification of soft tissue measurements. Burstone [7] has reported that lip lengths in normal adolescent girls have remained more than 3 mm lesser for upper lip (UL) and lower lip (LL) when compared to young men, which have suggested lip retrusion in normal adolescent girls. In this study, females lip lengths were also not nearly to the males. The length of the male nose in Malaysian Chinese population [23] has remained more prominent, yet the nose angles were pretty equivalent among the two genders. The current study also revealed comparable results with no significant difference. Malaysian Indian [25] also demonstrated a significant difference in nose prominence. Malaysian Chinese [23] and Malaysian Indians [25] chin tip were significantly greater in males.
This was a measurement of the anteroposterior prominence of the combined size and position of lower jaw covering the soft tissue. Yeong and Huggare [35], who measured the Singaporean Chinese population, have stated that adolescent females presented more prominent mandibular prognathism than adolescent men among which the growth spurt would have occurred.
In this study, lip morphology (LM) was also measured using cephalometric linear and angular analyses by reference to Steiner's S line [12] and Ricketts E-line [11]. LM measurements were also compared with Malaysian Chinese [23], Malaysian Malay [24], Nigerian [36], North Indian [26] and Pakistani [27] populations (  [12] and Ricketts E-line [11] deal with the relations of chin, lips and nose. Alcalde et al. [20] has presented that the UL and LL of the Japanese were anteriorly situated in all studies.
NA is significantly affected by orthodontics and surgical procedures. In the current study, this angle has revealed no gender dimorphism. The ILSA was marginally bigger in males when compared to the females.
Ioi et al. [37] similarly has established that female had smaller ILSA than males. The UL of the Malaysian Indian females has remained further protrusive, yet the LL has remained retrusive when compared with the E line [25]. Purmal et al. [23] has revealed in another study of Malaysian Chinese, that lips have remained more protrusive in females than males. Cheng [34] has indicated in his study that soft tissue morphology is affected by alveolar prognathism and thickness of the soft tissue profile. Lew et al. [19] has mentioned, this protrusion may appear misrepresented because the chin and nose have remained less prominent. NA was observed to be more acute in males when compared to the females [25]. This result has revealed as per the present study.

Conclusion
3D CT soft tissue norms have been established for Bangladeshi adults using HA and LM analyses.
Overall, the results of the current study equally accept the concept that every ethnic group has its standards depending on anthropological and morphological findings.
Regarding this study, there are few varieties in the soft tissue facial structure of the Bangladeshi normal subjects. These varieties ought to be thought-about to assure better diagnosis and treatment planning of the Bangladeshi subjects, especially during orthognathic surgery and orthodontic treatment planning.
Moreover, 3D digitization can be used together in clinical practice and research fields as it was proven to be precise and sensitive in obtaining the data.