Correlation of social smile symmetry with facial symmetry

BMC Oral Health (2023) 23:572 Abbasi et al. BMC Oral Health https://doi.org/10.1186/s12903-023-03260-z Open Access RESEARCH Correlation of social smile symmetry with facial symmetry Hoshyar Abbasi1, Amin Golshah2 and Soraya Seifodini3* Abstract Background This study aimed to assess the correlation of social smile symmetry with facial symmetry. Methods In this cross-sectional study, frontal view photographs were obtained from 169 eligible patients at rest and smiling with a camera at the level of their nose tip. Several landmarks were selected for facial symmetry and measured at rest and social smiling at the two sides of the face. The respective formula was used to calculate the asymmetry index (AI). The mean values for each AI were calculated, and the correlation between the criteria for a symmetric smile in a social smile with the criteria for facial symmetry, and the correlation between the difference in symmetry criteria at rest and social smiling with facial symmetry criteria were analyzed. Results Significant correlations were noted between Oc-b AI (smile) and Sn-B (rest) facial AI (P = 0.046), An-a (smile) AI and Gn-a (rest) facial AI (P = 0.002), An-b (smile) AI and Sn-b (rest) facial AI (P < 0.001), Pog-a (smile) and Sn-a (rest) facial AI (P < 0.001), Nt-a (smile) and Sn-a (rest) facial AI (P < 0.001), Nt-b (smile) and Sn-b (rest) facial AI (P < 0.001), Ph-a (smile) and Sn-a (rest) facial AI (P < 0.001), Ph-b (smile) and Sn-b (smile) facial AI (P = 0.007), Oc-b AI (difference) and Gn-b (rest) facial AI (P = 0.031), Oc-Pog (difference) AI and Gn-b (rest) facial AI (P = 0.041), An-b (difference) AI and Sn-b (rest) facial AI (P < 0.001), Nt-a (difference) and Sn-a (rest) facial AI (P = 0.006), Nt-b (difference) and Sn-b (rest) facial AI (P < 0.001), and Ph-b (difference) and Sn-b (rest) facial AI (P < 0.001). Conclusions A significant correlation exists between social smile symmetry and facial symmetry. Keywords Smiling, Facial Asymmetry, Orthodontics Introduction Esthetics is a philosophical, complex, and abstract concept. It can be a characteristic feature of humans, animals, locations, objects, or ideas, and creates a pleasant sense of satisfaction in the observers [1]. Improvement of smile esthetics is one of the most important motives for *Correspondence: Soraya Seifodini 1 Department of Oral and Maxillofacial Surgery, School of Dentistry, Kermanshah University of Medical Sciences, Shariati Street, Kermanshah 67139546581, Iran 2 Department of Orthodontic, School of Dentistry, Kermanshah University of Medical Sciences, Shariati Street, Kermanshah 67139546581, Iran 3 School of Dentistry, Kermanshah University of Medical Sciences, Shariati Street, Kermanshah 67139546581, Iran patients undergoing orthodontic treatment. Accordingly, creation of a beautiful smile along with a stable occlusion and efficient masticatory system is among the main goals of contemporary dentistry [2]. Smile design is currently an inseparable part of dental treatment planning. A successful outcome requires a correct understanding of the interactions of perioral facial structures such as the facial muscles, bones, temporomandibular joints, and also the gingiva and occlusion. A beautiful harmonious smile involves both facial and dental components [3]. Facial components include the facial hard and soft tissues, while dental components include the teeth and gingiva. Smile design should include assessment of both facial and dental components. Facial esthetics is determined based on the standard principles of esthetics which include optimal © The Author(s) 2023. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativeco mmons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Abbasi et al. BMC Oral Health (2023) 23:572 arrangement of facial components, their symmetry, and facial proportions. Treatment planning for enhancement of facial esthetics is a multi-disciplinary approach, involving orthodontics, orthognathic surgery, periodontal surgery, cosmetic dentistry, and plastic surgery [4]. Some patients have an asymmetrical smile due to asymmetrical tension of the smile muscles. Also, in some cases, facial esthetic indices particularly midline may be different in smiling and at rest. Thus, it is important to assess whether facial asymmetry is correlated with smile asymmetry or not. There are two features in the face that play a major role in smile design, namely the interpupillary line and the lips. As mentioned earlier, achieving a beautiful smile is one of the most important reasons for patients seeking dental treatment [5]. Knowledge about the features and details of the face in smiling position can help enhance facial esthetics. Smiles can be divided into two groups of social and enjoyment smiles [6]. A social smile is a voluntary and static facial expression, which involves the contraction of the levator muscles of the lip; the teeth and sometimes the gingiva are visible in a social smile [7]. According to Kiefer et al., [8] smile symmetry is a miniesthetic component of dentofacial analysis. A symmetrical smile is more attractive. Also, an asymmetrical smile can suggest the presence of skeletal asymmetry. People with a visibly asymmetrical face often have a low quality of life. Thus, facial plastic surgery and orthognathic surgical procedures aim to minimize and clinically correct facial asymmetries as much as possible [8]. In some cases, the midline at rest does not coincide with the midline in social smile due to lack of symmetry [9]. Many patients demand a beautiful or at least a normal smile. To achieve this goal, dental clinicians should be able to recognize and correct unesthetic features of the face and smile. Many researchers have addressed smile features in different populations, and have reported some criteria for a beautiful smile in the respective communities [10]. Coincidence of facial and dental midline is among such criteria [11]. Different methods are used for smile analysis [12]. The method proposed by Nakamura et al., [13] in 2001 (...truncated)