Beauty is a trendy topic as reflected by the number of papers published recently, or at any time, in reputable journals [1,2,3,4,5,6]. A beautiful appearance can have positive effects on self-confidence, mental health, social status, physical attractiveness, career success, academic success, intelligence, the level of happiness, or choice of spouse [1,2,3,4,5, 7].

Smile is a crucial factor to facial beauty [8]. It is the most important feature in facial attractiveness after the eyes [1,2,3,4,5, 8]. A warm smile is the universal language of kindness, and attracts affection and positive feedback and can even hide facial imperfections to some extent [1,2,3,4,5]. A beautiful smile is often the main complaint in dentistry, and patients usually evaluate the results of treatment based on positive changes in their smile [1, 3,4,5, 9]. Smile analysis includes the following factors: evaluation of the smile arch, gingival appearance, gingival beauty, examination of the buccal corridor space, and the fit between the dental and facial midlines [1, 2, 10, 11].

The perception of beauty is affected by many factors that can influence the subjective standards of observers, such as people’s culture, personal experiences, and the profession among others [1,2,3,4,5, 11]. Therefore, what is desirable from the point of view of dental aesthetics may be completely irrelevant to the patient’s point of view [1,2,3,4,5, 12]. Therefore, the classification of aesthetics into pleasant, acceptable, and unpleasant requires a calibration and a proper communication between the patient and the dentist [1, 3,4,5, 13].

Besides subjective factors related to the observer, anatomic factors of the observed face may matter as well. Dental and soft tissue feature affect esthetics in orthodontic treatment, although it is not clear which factors have the greatest impact on smile attractiveness at the end of the treatment [1,2,3,4,5, 12]. Many studies have been conducted to understand preferences of ordinary people and dentists toward the beauty factors of a smile [1,2,3,4,5].

The extent of gingival display is one of the factors that affect the beauty of a smile [1, 6, 9, 13, 14]. People who show too much gingiva in the upper jaw when they smile are called gummy smile [1, 6, 9, 13, 14]. This issue can decrease self-confidence and even cause psychological problems for people, making them seek treatment [15]. Although controversy exists over the normal level of gingival display, usually the display of maxillary incisors along with 1 to 2 mm of gingival margin is considered normal [16].

The width of the buccal corridor is another factor that may affect the attractiveness of a smile. A wide smile might be more attractive than a narrow one as far as it is not exaggerated [2, 8,9,10, 17,18,19]. Recently, some orthodontists refer to the buccal corridor as a negative space that should be limited by expanding the width of the maxilla. On the other hand, as it has been well shown in prosthetics, the lack of a buccal corridor space is one of the characteristics of artificially looking teeth [20].

An important point in smile esthetics is that most studies in this regard are limited to the mouth, neglecting the effect of the facial shape on the attractiveness of the smile [6]. The appearance of the face is an important factor in understanding the beauty of a smile. Therefore, the appearance of the face should be considered in the orthodontic treatment plan [17, 19]. When it comes to the combination of the 3 factors ‘facial forms with gingival displays and buccal corridor sizes’, there is no study in the literature.

Since there was no study on the effects of the combination of facial heights with gingival displays and buccal corridor sizes, we conducted this study. Its aim was to find the combined effects of gingival display and the width of the buccal corridor in each of the three facial shapes (long, normal, and short) on facial / smile esthetics from the perspectives of orthodontists versus general dentists verus laypeople. Moreover, the most appealing combinations of gingival displays and the widths of the buccal corridor and facial forms were comparatively determined for orthodontists, maxillofacial surgeons, and laypeople (and all of them combined). The null hypotheses were no effects of the abovementioned anatomical features as well as the judges' ages, sexes, and expertise on their esthetic preferences.