The beauty controversy has always existed since ancient times among various cultures and civilizations, and different strata of society. Despite their differences and disparities among groups, it seems that there was always an agreement towards seeking ideal proportions and ratios to define facial beauty. [14, 15] Over the years, people strived to define and quantify facial attractiveness; however, it is difficult to confine or determine the standards of beauty because it is relative rather than fixed or absolute. [15, 16] Additionally, the great and increasing influence of the internet and social media, and the developments in the dental and medical cosmetic sector are tremendously influencing people’s perception of beauty. [4, 15] Therefore, it seems essential to reassess the ideals of facial beauty and understand patients’ preferences for the purpose of providing the most favorable patient-centered treatment. Furthermore, several studies has focused on the role of dental and perioral esthetics in particular on the overall perception of facial aesthetic, signifying the important contribution of the dentistry in defining and understanding patients’ expectations, and in the optimization in the treatment planning. 
According to previous studies, it was found that the years of experience in the dental field influenced the perception of facial aesthetics among dentists and dental students. [16, 17] Evaluating dental students’ perception towards facial esthetics is thus essential given their central role in the treatment planning in the overall facial esthetics. Early understanding of facial esthetics analysis by dental students will enhance their judgement and therefore the quality of the treatment they provide in context of the overall facial appearance. To the best of our knowledge, only few studies have evaluated the perception of facial subunits between clinical and preclinical dental students. Therefore, the aim of this study was to assess the perception of ideal facial aesthetic subunits among preclinical and clinical dental students.
The morphometric questionnaire of various computer-generated facial features was constructed to determine the ideals of aesthetics among the students. The effect of hair, skin color, and eyes were eliminated through using a standard model and only one variable was changed each time. In contrary to the previous studies, we evaluated the earlier mentioned facial subunits in three different views: frontal view, 45 degrees view, and lateral view, which was a limitation in the previous studies. The students thus had a plenty of opportunity to evaluate each model thoroughly from different views, then they chose the most and least preferred characteristics in terms of the above-mentioned features among the 6 avatar models for each of the 6 modified facial features.
Results of our study have shown that the preclinical and clinical students agreed on the most and least attractive facial model for all features except for the jaw shape, see Table 2. Summary of the most attractive facial features and least attractive among all dental students is showed in Table 3, and Figs. 1–6. Model 2 was the most popular choice for most attractive jaw shape, however students in their clinical chose Model 4 as the most attractive jaw shape, but this was not significantly different (p = 0.222). The reason behind this may bey due to their dental education and the clinical exposure to patients which has raised their overall aesthetics awareness. [16, 17] When comparing the jaw shape in model 2, to model 4, it looks broader and more prominent, which indicates the preference of the students in their clinical years towards having slimmer jaw shapes. When it comes to the least attractive jaw shape, the preclinical students chose model 3 in contrast to the clinical students who choose model 5. Interestingly, the jaw shape in model 5 is broad and the jaw angles are more defined which is somewhat similar to the jaw shape in model 2 that was chosen by the preclinical student as the most attractive. This seems to be in accordance with the previous finding that the clinical dental students do not perceive the broad jaw as attractive. The preclinical students perceived model 3, which has a rounded, slightly retruded jaw with less significant jaw angles, as the least attractive jaw model. This shows that there is a tendency among the preclinical dental students to prefer the broad jaw shapes. Previous study by Samizadeh found that the asian population also had a preference of a reduced lower facial third width. [9, 18]
The chin shape is also an important factor in determining the attractiveness of the lower facial third and in establishing the overall desired profile shape. [3, 7, 11, 13] Both clinical and preclinical students have agreed on the most and least attractive chin shapes. Model 6 chin shape, which is of moderate length and protrusion, was perceived as the most attractive chin shape. In contrast, the least preferred chin shape was model 2, which appears longer and more protruded. This agrees with what was reported by Naini, that ratings for attractiveness decreased on average 0.47 for each 2.5-mm increase in chin height for female faces. [11, 13]
The centered position of the nose gives it a significant role in influencing both upper and lower facial beauty.  Model 1 was considered the most attractive nose shape by both clinical and preclinical students. The nose appears shorter, more scooped, less projected, with a slightly rotated tip compared to model 6, which was chosen by both clinical and preclinical students as the least attractive. According to Pearson and Adamson, the nasal profile with a slight scoop, slight over-rotation, and slight underproduction was preferred by the public and the rhinoplasty group, which agrees with our findings.  Samizadeh demonstrated also similar results with regard to nose shapes preference among Asian population. 
The lips are a key feature of the lower facial third reflecting youth and attractiveness. [2, 12, 15] Similar to most of the previous characteristics, preclinical and clinical dental students have agreed on the most and least attractive mouth shapes. The most attractive mouth or lip shape chosen was model 2, which represents a full, projected lips of moderate width and a short upper lip. On the contrary, model 6 was the least attractive mouth shape as selected by both groups. The lips in model 6 are thin, less projected with long upper lip. In contrary to the results reported by Ioi et al, which showed that a slightly retruded lip position was preferred by the dental students. 
The cheek bone constitutes a prime part of establishing the overall shape and attractiveness of the face. [9, 18] The two main parameters that were changing throughout the 6 models were the cheek bone prominence and the buccal fat size. Model 1, which represents a very prominent cheek bone with minimal or no buccal fat, was considered the most attractive cheek shape by all the students. However, model 3, representing a less prominent cheek bone with increased buccal fat "chubby cheeks", was the least attractive cheek shape as reported by all the students. However, Samizadeh reported that an oval facial shape with a smooth flow from the zygoma and cheek, jaw angle and jaw line, and the chin was reported to be the most attractive in their study. [9, 18]
Each facial subunit plays its own essential role in contributing to the overall facial profile shape. [6, 7, 16, 20] According to previous studies, most orthodontic treatments and orthognathic surgeries are directed towards enhancing the profile shape. [14, 16, 20] The results of our study showed that model 1 was considered the most attractive profile shape, which has a straight profile with moderate length among both groups. Similarly, a straight facial profile was the most preferred facial profile among different cultural backgrounds. [7, 14, 15] In contrast, the prognathic profile shape, which is slightly longer, as represented in model 2, was the least attractive profile shape as reported by all the students in our study. In agreement with Abu Arqoub and Al-Khateeb, who reported that the most attractive female facial profile was the one with a reduced facial height among Jordanian population. [14, 20]
One of the main limitations of our study is that most of our population were females, which restricted us from making a reliable and unbiased comparison between males and females. We recommend to conduct a large multi-university study, which evaluate these findings in more comprehensive approach. Our study showed that the dental students at Kuwait University have a perception of the facial esthetics that is largely in accordance with previously published studies. We recommend the introduction of detailed courses in the dental curriculum that focuses specifically on facial esthetics and its clinical analysis within a comprehensive approach.