Impact of incisor display and lower lip height on aesthetic perception and age estimation

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Materials and Methods: Smile photographs were digitally modified to simulate different proportions of incisor exposure combined with reduced or unaltered lower lip vermilion height. A total of 162 evaluators (orthodontists, dentists, and laypersons) rated attractiveness using a 10-point visual analog scale and estimated the apparent age range. The differences between groups were tested by Kruskal-Wallis, chi-square and repeated measures ANOVA, and a linear regression was performed, with p<0.05 as statistically significant. Results: Greater maxillary incisors exposures were considered more attractive by all groups. However, the lower lip vermilion height did not significantly influence esthetic perception or age estimation. Orthodontists were more critical compared to dentists and laypersons. An increase in mandibular incisor exposure was correlated with the attribution of a more advanced apparent age. Older laypersons tended to be more tolerant of smiles showing greater mandibular incisor exposure. Conclusions: These findings suggest that the proportion of maxillary and mandibular incisor exposure plays a significant role in the perception of smile attractiveness and age estimation. Clinical significance: The results not only contribute to our understanding of smile esthetics but also have direct implications for clinical practice in orthodontics and esthetic dentistry, guiding treatment planning and patient communication. smile esthetics incisor exposure aging orthodontics Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 INTRODUCTION Smile esthetics has gained significant attention in the last decades due to the recognition among professionals of the importance of understanding laypersons' perception, since these are potential dental patients [ 1 , 2 ]. Their views on smile characteristics that affect esthetics should be valued, as they may influence treatment needs ranking and orthodontic planning [ 2 , 3 ]. Orthodontists typically have a more critical esthetic evaluation of various smile and occlusal characteristics compared to laypersons and other dental professionals [ 4 , 5 ], and their recognition of patients’ perception is fundamental. Previous research indicates that incisor exposure affects smile esthetics [ 5 , 6 ]. Ideal maxillary incisor exposure in young individuals is reported to be around 3 to 5 mm at rest and 10 mm during a posed smile [ 7 , 8 ]. With aging, the upper lip tends to become more flaccid, and the height of the lip vermilion, particularly in the lower lip, tends to decrease [ 9 – 12 ]. Additionally, maxillary incisor exposure decreases while mandibular incisor exposure increases proportionally in both males and females [ 7 , 11 , 13 – 15 ]. Consequently, smiles often change into a shorter and wider shape [ 16 ]. Orthodontic treatment can influence the final position of incisors, requiring special care when altering their vertical position through extrusion or intrusion. Such changes can impact incisor exposure and overall smile esthetics [ 8 , 14 ]. Aging has also been reported as influencing the perception of smile esthetics, with younger age groups preferring smiles with greater incisor exposure and older individuals preferring less incisor display [ 17 ]. However, there is a notable lack of studies evaluating the esthetic perception of different proportions of maxillary and mandibular incisor exposure in the smile and whether these differences influence perceived age when assessed by professionals and laypersons. The primary objective of this study was to investigate the perception of smile attractiveness among orthodontists, dentists, and laypersons, concerning varying incisor exposure proportions coupled with reduced or unaltered lower lip vermilion height. The secondary objective was to assess whether changes in the percentage of maxillary/mandibular incisor exposure and alterations in the lower lip vermilion height impact the perceived age range of the smile’s owner. METHODS This research project was approved by the Research Ethics Committee of Antonio Pedro University Hospital at Universidade Federal Fluminense, Niteroi, Brazil (CAAE #70685923.1.0000.5243). Written informed consent was obtained from the two photographic models and from the research participants. This study utilized an extra-oral frontal smile photograph with half-open mouth of a 24-year-old female volunteer, with no considerable facial asymmetry. We also used an intra-oral frontal photograph with half-open mouth of a 22-year-old female volunteer with a history of orthodontic treatment and a normal occlusion. Both photographic models provided written informed consent before the use of their images in the study. The photographs were modified using GIMP 2.10.32 free and open-source software (The GIMP Development Team, Berkeley, California, USA). The extra-oral frontal smile photograph was standardized by removing distracting factors such as skin signs, irregularities and spots. In the resulting image, the edited side was mirrored to ensure smile symmetry. The dentition part within the smile area was cropped, and the lower lip was cropped in all its extension by a 1mm-strip to create an additional smile with a shorter-vermilion lower lip. The intra-oral frontal photograph was also edited by mirroring the right side to ensure symmetry. This intra-oral image was then layered behind the extra-oral cropped one and proportioned to it according to measurements taken clinically in the smile and teeth from the model, allowing for subsequent image manipulation. Ten images were created with alterations in the vertical position of the intra-oral photograph, displaying varying proportions of upper incisors (Ui) and lower incisors (Li) exposure: 100% of Ui exposure (100Ui), 80% of Ui exposure and 20% of Li exposure (80Ui-20Li), 60% of Ui exposure and 40% of Li exposure (60Ui-40Li), 40% of Ui exposure and 60% of Li exposure (40Ui-60Li), and 20% of Ui exposure and 80% of Li exposure (20Ui-80Li), for both unaltered and reduced lower lip scenarios (Fig. 1 ). The amount of incisor exposure was calculated in pixels, by measuring the amount of vertical display of right central maxillary and mandibular incisors and calculating the percentage of each to the vertical distance between the lower border of the upper lip and the upper border of the lower lip, all measured over a line passing through the middle of the maxillary right incisor crown. Using Qualtrics XM online survey platform (Qualtrics, Provo, Utah, USA), participants first previewed the 10 images assembled, then evaluated them individually in random order. Smile attractiveness was assessed for each image using a digital version of a 10-point wide visual analog scale (VAS), with endpoints representing “most unattractive” at zero on the left and “most attractive” at 10 on the right. The participant could slide the cursor to mark any point along the scale and the score was registered with two decimal places. Participants were also asked to estimate the age range of the smile’s owner for each image, with three possible answers in a multiple-choice design: less than 30 ( 50). The link for the online questionnaire was sent to evaluators that fulfilled the inclusion criteria, who responded between January and April of 2024. Each image was coded for subsequent analysis of the results. Evaluators were divided in three groups with the following inclusion criteria: 1) the orthodontists should be either orthodontic residents or specialists in Orthodontics; 2) the dentists should have a university degree in Dentistry, but no training in Orthodontics; and 3) laypersons should have completed high school and be above 18 years of age. All 162 volunteers signed an online informed consent form. The sample size was calculated to determine the number of evaluators needed for the research, considering α of 5% and β of 20%, the standard deviation from a previous study [ 18 ], and a minimum detectable difference of 1 score. This resulted in a sample size of 54 participants per group, totaling 162 individuals. A total of 18 participants were invited to retake the questionnaire after a one-month interval to estimate the method’s reliability. Statistical analysis Data were analyzed using the Jamovi Project (2024). jamovi (Version 2.5) [Computer Software]. Retrieved from https://www.jamovi.org . Differences in age values and sex distribution among groups of evaluators were tested using the Kruskal-Wallis and chi-square tests, respectively. Scores attributed to each image were visually represented through boxplots and means and standard deviations calculated. A repeated measures ANOVA, followed by Tukey’s post-hoc test, were used to assess differences in scores attributed for each image, considering the group of evaluators as a factor. Frequencies of the age ranges chosen by the evaluators for each image were presented in bar plots, with intergroup differences assessed using chi-square tests. The Friedmand test with the Durbin-Conover pairwise multiple comparison method was used for intragroup comparison of the different images and the Kruskal-Wallis test with the Dwass-Steel-Critchlow-Fligner pairwise multiple comparison method was used for intergroup comparison to examine median differences, considering age range chosen as a categorical variable. A linear regression analysis was performed to test the influence of the evaluators’ age, sex ang group on the scores attributed to each image. Intraclass correlation coefficient (ICC) was used to measure reliability of the method. A p-value below 0.05 was regarded as statistically significant. RESULTS A total of 162 participants completed the questionnaire, comprising 54 orthodontists (43 females and 11 males, mean age 34.22 ± 9.12 years), 54 dentists (37 females and 17 males, mean age 36.26 ± 9.69 years), and 54 laypersons (35 females and 19 males mean age 36.15 ± 10.23 years). No statistically significant differences were observed in age (p = 0.103) or sex distribution (p = 0.210) between the groups. The ICC value was 0.826, confirming reliability of the measures. Table 1 presents the mean attractiveness scores assigned to each image by the evaluators. The highest scores were given to images with 100 and 80% of upper incisor exposure. Mean scores decreased progressively for Images with 60%, 40%, and 20% upper incisor exposure, with statistically significant differences noted among them. Comparisons between images with reduced versus unaltered lower lips, with the same extent of incisor exposure, revealed a statistically significant difference only for the image with 100% upper incisor exposure across all groups of examiners (mean difference of 1.2 for orthodontists, 1.12 for dentists and 1.03 scores for laypersons), with higher scores for unaltered lips. Statistically significant differences were observed between orthodontists and laypersons for images of reduced lips with 60%, 40% and 20% upper incisor exposure. Similarly, orthodontists differed markedly from the other two groups of examiners in images showing unaltered lips with 60%, 40% and 20% upper incisor exposure. Orthodontists always graded the images with lower scores (Fig. 2 ). Figures 3 to 6 illustrate the frequency distribution of perceived age assigned to each image by the combined examiner groups and by each group separately. Images with 100% or 80% upper incisor exposure and both reduced or unaltered lower lips were mostly associated with individuals under 30 by 68.5 to 92.6% of the evaluators. Conversely, images with 60%, 40% or 20% upper incisor exposure displayed marked differences between orthodontists and dentists and between orthodontists and laypersons. Most orthodontists attributed the 60Ui-40Li images with individuals aged between 30 and 50 years, and images 40Ui-60Li and 20Ui-80Li with individuals over 50. In contrast, the majority of dentists attributed all images to the under-30 age category, with the percentage attributions for the 30–50 and above-50 age categories increasing proportionally to the greater exposure of lower incisors. Laypersons predominantly associated the 60Ui-40Li and 40Ui-60Li images with the under 30 age category, while the 20Ui-80Li images were more frequently attributed to the 30–50 year age range. Table 2 presents the intragroup and intergroup statistical differences in age attribution. According to Table 3, the linear regression analysis indicated a statistically significant influence of the age factor on the attractiveness scores for both images with 80% of lower incisors exposure and the image with 60% of lower incisor exposure and unaltered lips (Fig. 7 ). Older individuals tended to assign higher scores to these images with a greater percentage of lower incisor exposure. The participants’ sex did not significantly influence the scores. The orthodontist group difference from the laypersons influenced the scores in most images, except for images of 100% of Ui exposure and 80% of Ui exposure combined with unaltered lips. DISCUSSION The present study provides novel insights into the perception of smile attractiveness and age estimation based on varying proportions of maxillary and mandibular incisor exposure, coupled with changes in lower lip vermilion height. The methods determined for this study included the analysis of only the smile portion of the face to avoid distractions from unrelated areas, similar to other research [ 6 , 17 , 19 – 22 ]. The online Qualtrics platform was selected due to its ease of access and established performance in other published studies [ 23 – 25 ]. Considering the value of 5 on the 0-to-10 VAS as a threshold for unattractive/attractive [ 26 ], our results indicate that maxillary incisor exposure has a significant impact on the perception of smile attractiveness. Higher exposure (100Ui and 80Ui-20Li) was consistently assessed as attractive by the three groups of evaluators (laypersons, dentists, and orthodontists). As the proportion of mandibular incisor exposure increased, the perception of attractiveness decreased, and the images with higher mandibular incisor exposure (40Ui-60Li and 20Ui-80Li) were considered unattractive by all groups. These findings suggest a universal preference for smiles with more maxillary incisor visibility, which may be related to youth, health, and esthetics [ 11 , 13 ]. The reduction in lower lip vermilion height did not significantly influence esthetic perception or age estimation in any evaluator group. The only images with similar proportions of incisor exposure that showed differences between altered and unaltered lips were those with 100% upper incisor exposure. This may be due more to the increased gingival margin in the image with reduced lips than to the difference in lower lip dimensions, as this effect was not significant in any other proportions. In young individuals, the expected proportion of upper to lower lip vermilion height ranges between 55% and 90% [ 3 , 7 , 10 , 12 , 16 , 27 – 30 ]. However, the literature describes a decrease in the vermilion height of the lower lip as a consequence of aging, while the upper lip does not appear to undergo as significant a decrease [ 9 – 12 ]. If a lower lip with increased vermilion height could distract observers from the unesthetic appearance of increased lower incisor exposure associated with aging, that would be valuable information for lip augmentation treatments aimed at esthetic enhancement. Nevertheless, our findings suggest that even a lower lip with increased vermilion height and a more youthful appearance could not diminish the unesthetic impact of increased lower incisor exposure in the smile. This consideration should be made carefully when planning such treatments. Additionally, a lower lip with decreased vermilion height did not impact age perception as much as the extent of lower incisor exposure. Our study demonstrates that the proportion of maxillary to mandibular incisor exposure plays a significant role in age estimation. Younger individuals typically display exclusively maxillary incisors or a very small proportion of mandibular incisors during smiling [ 31 ]. This finding is consistent with the literature, which suggests that age-related changes in incisor exposure are a common phenomenon [ 7 , 11 , 13 – 15 ]. However, we must consider that the amount of incisor exposure may vary depending on the situation, such as during smiling, speaking, or between static and dynamic scenarios [ 11 , 20 ]. Furthermore, our results indicate that older laypersons tend to be more accepting of smiles with greater mandibular incisor exposure, still perceiving them as relatively esthetic. This finding highlights the potential influence of the evaluator's age on the perception of smile attractiveness and the importance of considering individual preferences in treatment planning. Similar to other studies, orthodontists were more critical in the smile esthetic analysis than dentists and laypersons [ 4 , 22 , 32 , 33 ]. Therefore, communication between professionals and patients is extremely important in the treatment planning phase to balance expectations and ensure that the professional considers the patient’s esthetic preferences and chief complaint. Considering the clinical relevance and practical applicability of the present study, knowledge of laypersons’ perceptions may guide orthodontists’, prosthodontists’, and general practitioners’ conduct when planning vertical changes to the anterior teeth during dental treatment [ 4 , 11 ]. A careful analysis of incisor exposure during smiling, at rest, and during speech should be considered, as these changes may impact the esthetic facial aspect and age appearance [ 11 , 20 ]. Additionally, professionals may use this information to enhance their communication with patients, aiming to align expectations with clinically achievable outcomes. Our findings underscore the important role of incisor display in shaping esthetic judgments and age attribution across different groups of evaluators, including orthodontists, dentists, and laypersons. The results not only contribute to our understanding of smile esthetics, but also have direct implications for clinical practice in orthodontics and esthetic dentistry, guiding treatment planning and patient communication. The approach of digitally altering incisor exposure and lower lip dimensions in virtual photographs allowed for a systematic investigation of these variables. Limitations of this study include the use of digitally manipulated static photographs, which does not fully represent the dynamic nature of a smile. Additionally, the teeth, lips and skin used in the images were characteristically from a young model, which may have influenced the esthetic and age perception. The subjectivity of esthetic evaluation may also be considered a limiting aspect, and the VAS was used to reduce this bias. Future research should include a more diverse sample of models with different facial characteristics to confirm these results in different populations. Dynamic smile assessment can also be employed to add to the existing knowledge. CONCLUSION A considerably greater proportion of upper incisors exposure (100% or 80%) in smiles was consistently considered more attractive by all evaluator groups. Greater proportions of lower incisors exposure in the smile (60% or 80%) were considered unattractive by all groups. Orthodontists were more critical and assigned lower scores compared to dentists and laypersons. An increase in lower incisors exposure was consistently correlated with the attribution of an older apparent age to the smiles. Among the evaluators, particularly in the laypersons’ group, older individuals tended to give higher scores to smiles that showed more exposure of the lower incisors than younger individuals. Declarations Acknowledgements: All the authors declare no conflict of interest. The authors assure no commercial or financial interest in the products or companies mentioned in this study. Conflict of interests: All authors declare no financial and non-financial conflict of interests. Ethical Approval: This research project was approved by the Research Ethics Committee of Antonio Pedro University Hospital at Universidade Federal Fluminense, Niteroi, Brazil (CAAE #70685923.1.0000.5243). Informed Consent: Written informed consent was obtained from the two photographic models and from the research participants. 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DOI: 10.1016/j.jds.2022.11.030 Tables Tables 1 to 3 are available in the Supplementary Files section Additional Declarations No competing interests reported. Supplementary Files Table1.xlsx Table2.xlsx Table3.xlsx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6457217","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":452793973,"identity":"9bc2bb85-3024-47ab-a0ae-b130144c6297","order_by":0,"name":"Juliana Do Espirito Santo Russo","email":"","orcid":"","institution":"Fluminense Federal University","correspondingAuthor":false,"prefix":"","firstName":"Juliana","middleName":"Do Espirito Santo","lastName":"Russo","suffix":""},{"id":452793974,"identity":"b7bd39ce-57c1-4e4e-9a35-f0db93185d17","order_by":1,"name":"Rafael Cunha Bittencourt","email":"","orcid":"","institution":"Fluminense Federal University","correspondingAuthor":false,"prefix":"","firstName":"Rafael","middleName":"Cunha","lastName":"Bittencourt","suffix":""},{"id":452793975,"identity":"a9d810bf-736a-4493-ab2a-3d0edb2ad256","order_by":2,"name":"Daniella Mascarenhas Calixto Barros","email":"","orcid":"","institution":"Fluminense Federal University","correspondingAuthor":false,"prefix":"","firstName":"Daniella","middleName":"Mascarenhas Calixto","lastName":"Barros","suffix":""},{"id":452793976,"identity":"52d3ba91-b2cd-4992-b3cf-8f564db35359","order_by":3,"name":"Rebeca Passeri de Almeida","email":"","orcid":"","institution":"Fluminense Federal University","correspondingAuthor":false,"prefix":"","firstName":"Rebeca","middleName":"Passeri","lastName":"de Almeida","suffix":""},{"id":452793977,"identity":"d5b0c496-d6f7-4454-8621-27b4391c761b","order_by":4,"name":"Diego Coelho Lorenzoni","email":"","orcid":"","institution":"Fluminense Federal 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Mattos","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA9ElEQVRIiWNgGAWjYDACdiDmMYDxKiQYGxgYH3wAkrgBM0wLG4h1BqSF2XAGYS0MUC2MbQyEtfA3Mz+TeFNgF80/v//gw5/zLGQbJJIZGxh33MOpReIwm5nkHIPk3BnHmJmNebdJGEO0nCnGqcWAmcFMmseAObfhGDObNOM2icQGifzjDxjbEvBoYf8G1FKfOx+oRfLnHJAWkC14tfCAbDmcuwGoRYK3gQgtEod5ii3nGBzP3Xgs2diY55iEcRvPY8aGxDO4tfC3t2+88eZPde68wwcfPvxRUyfbzw605eMO3FowARuIIEXDKBgFo2AUjAJMAAD+CE0s94w7iQAAAABJRU5ErkJggg==","orcid":"","institution":"Fluminense Federal University","correspondingAuthor":true,"prefix":"","firstName":"Claudia","middleName":"Trindade","lastName":"Mattos","suffix":""}],"badges":[],"createdAt":"2025-04-15 17:53:29","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6457217/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6457217/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":82602785,"identity":"a1b6404b-7b78-4250-b157-881621ae8e1c","added_by":"auto","created_at":"2025-05-13 09:51:47","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":7307755,"visible":true,"origin":"","legend":"\u003cp\u003eSmiles following manipulation of maxillary and mandibular incisor exposure; reduced vermilion height of the lower lip on the left column and unaltered lower lips on the right column. \u003cstrong\u003eA\u003c/strong\u003e and \u003cstrong\u003eB\u003c/strong\u003e, 100% upper incisor exposure with no lower incisor display (100Ui); \u003cstrong\u003eC\u003c/strong\u003e and \u003cstrong\u003eD\u003c/strong\u003e, 80% of vertical incisor exposure are from the upper incisors and 20% from the lower (80Ui-20Li); \u003cstrong\u003eE\u003c/strong\u003eand \u003cstrong\u003eF,\u003c/strong\u003e 60% of vertical incisor exposure are from the upper incisors and 40% from the lower (60Ui-40Li); \u003cstrong\u003eG\u003c/strong\u003e and \u003cstrong\u003eH\u003c/strong\u003e, 40% of vertical incisor exposure are from the upper incisors and 60% from the lower (40Ui-60Li); \u003cstrong\u003eI \u003c/strong\u003eand \u003cstrong\u003eJ\u003c/strong\u003e, 20% of vertical incisor exposure are from the upper incisors and 80% from the lower (20Ui-80Li).\u003c/p\u003e","description":"","filename":"Fig1.png","url":"https://assets-eu.researchsquare.com/files/rs-6457217/v1/e6289063d2af523aaffd6b69.png"},{"id":82601543,"identity":"8480fc70-5b04-477f-876c-f699b412d58f","added_by":"auto","created_at":"2025-05-13 09:43:47","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1364355,"visible":true,"origin":"","legend":"\u003cp\u003eBoxplots illustrating statistical differences (*) among groups of examiners (orthodontists, dentists and laypersons) for each image of \u003cstrong\u003eA\u003c/strong\u003e, thinner lips, or \u003cstrong\u003eB\u003c/strong\u003e, thicker lips.\u003c/p\u003e","description":"","filename":"Fig2.png","url":"https://assets-eu.researchsquare.com/files/rs-6457217/v1/99c9fdcb6588a30f104c358b.png"},{"id":82601548,"identity":"ddfda996-5e74-43ae-95c5-c32e5205128e","added_by":"auto","created_at":"2025-05-13 09:43:47","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1164777,"visible":true,"origin":"","legend":"\u003cp\u003eBar plot showing the distribution of attributed age ranges (\u0026lt;30, 30-50, \u0026gt;50) for each image with thinner or thicker lips, combining data from all examiners.\u003c/p\u003e","description":"","filename":"Fig3.png","url":"https://assets-eu.researchsquare.com/files/rs-6457217/v1/9e551de32f0b8a44f57b9959.png"},{"id":82601559,"identity":"305d45ed-b9b0-4451-81bb-86b396d049e7","added_by":"auto","created_at":"2025-05-13 09:43:48","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1150703,"visible":true,"origin":"","legend":"\u003cp\u003eBar plot showing the distribution of attributed age ranges (\u0026lt;30, 30-50, \u0026gt;50) for each image with thinner or thicker lips among orthodontists.\u003c/p\u003e","description":"","filename":"Fig4.png","url":"https://assets-eu.researchsquare.com/files/rs-6457217/v1/969c1de9eb5e6e3f88fbf7c5.png"},{"id":82601551,"identity":"7a13cccc-7fb0-4d5c-abf0-e4154820f856","added_by":"auto","created_at":"2025-05-13 09:43:47","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1120917,"visible":true,"origin":"","legend":"\u003cp\u003eBar plot showing the distribution of attributed age range (\u0026lt;30, 30-50, \u0026gt;50) for each image with thinner or thicker lips among dentists.\u003c/p\u003e","description":"","filename":"Fig5.png","url":"https://assets-eu.researchsquare.com/files/rs-6457217/v1/074111738a6a970f2a3690ac.png"},{"id":82601571,"identity":"abadb8b5-345c-4135-ab41-96b915837888","added_by":"auto","created_at":"2025-05-13 09:43:48","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1129554,"visible":true,"origin":"","legend":"\u003cp\u003eBar plot showing the distribution of attributed age range (\u0026lt;30, 30-50, \u0026gt;50) for each image with thinner or thicker lips among laypersons.\u003c/p\u003e","description":"","filename":"Fig6.png","url":"https://assets-eu.researchsquare.com/files/rs-6457217/v1/7f266d1223746a00ecec3128.png"},{"id":82601545,"identity":"5ec0f94f-98e2-43f9-828c-a2172a93c5bf","added_by":"auto","created_at":"2025-05-13 09:43:47","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":5713,"visible":true,"origin":"","legend":"\u003cp\u003eLinear regression scatterplots showing that, particularly for the group of laypersons, older people tended to give higher scores to these images with a higher percentage of lower incisor exposure.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-6457217/v1/40d5d919b57fb7504a00a714.png"},{"id":88281779,"identity":"32fe695f-2a3e-4756-b669-43c1a4a19772","added_by":"auto","created_at":"2025-08-04 20:31:44","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":13384976,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6457217/v1/df1e2f52-8db7-44d0-913b-96e9c76ee369.pdf"},{"id":82601546,"identity":"ce37c505-a85c-423d-8e0c-e8dce9e13229","added_by":"auto","created_at":"2025-05-13 09:43:47","extension":"xlsx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":10621,"visible":true,"origin":"","legend":"","description":"","filename":"Table1.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-6457217/v1/9e3bbbb9aad728f1e8ff4dfa.xlsx"},{"id":82601552,"identity":"972315ba-868e-4a37-b50f-a46b7d88345b","added_by":"auto","created_at":"2025-05-13 09:43:47","extension":"xlsx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":11234,"visible":true,"origin":"","legend":"","description":"","filename":"Table2.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-6457217/v1/05cd478e39b458f2a9755fc7.xlsx"},{"id":82602784,"identity":"17a050d5-5c10-4357-afef-3d071eab6db9","added_by":"auto","created_at":"2025-05-13 09:51:47","extension":"xlsx","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":10722,"visible":true,"origin":"","legend":"","description":"","filename":"Table3.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-6457217/v1/76be3b35ba8fa0d3a1f91c6f.xlsx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Impact of incisor display and lower lip height on aesthetic perception and age estimation","fulltext":[{"header":"INTRODUCTION","content":"\u003cp\u003eSmile esthetics has gained significant attention in the last decades due to the recognition among professionals of the importance of understanding laypersons' perception, since these are potential dental patients [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Their views on smile characteristics that affect esthetics should be valued, as they may influence treatment needs ranking and orthodontic planning [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Orthodontists typically have a more critical esthetic evaluation of various smile and occlusal characteristics compared to laypersons and other dental professionals [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], and their recognition of patients\u0026rsquo; perception is fundamental.\u003c/p\u003e \u003cp\u003ePrevious research indicates that incisor exposure affects smile esthetics [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Ideal maxillary incisor exposure in young individuals is reported to be around 3 to 5 mm at rest and 10 mm during a posed smile [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. With aging, the upper lip tends to become more flaccid, and the height of the lip vermilion, particularly in the lower lip, tends to decrease [\u003cspan additionalcitationids=\"CR10 CR11\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Additionally, maxillary incisor exposure decreases while mandibular incisor exposure increases proportionally in both males and females [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan additionalcitationids=\"CR14\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Consequently, smiles often change into a shorter and wider shape [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eOrthodontic treatment can influence the final position of incisors, requiring special care when altering their vertical position through extrusion or intrusion. Such changes can impact incisor exposure and overall smile esthetics [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAging has also been reported as influencing the perception of smile esthetics, with younger age groups preferring smiles with greater incisor exposure and older individuals preferring less incisor display [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. However, there is a notable lack of studies evaluating the esthetic perception of different proportions of maxillary and mandibular incisor exposure in the smile and whether these differences influence perceived age when assessed by professionals and laypersons.\u003c/p\u003e \u003cp\u003eThe primary objective of this study was to investigate the perception of smile attractiveness among orthodontists, dentists, and laypersons, concerning varying incisor exposure proportions coupled with reduced or unaltered lower lip vermilion height. The secondary objective was to assess whether changes in the percentage of maxillary/mandibular incisor exposure and alterations in the lower lip vermilion height impact the perceived age range of the smile\u0026rsquo;s owner.\u003c/p\u003e"},{"header":"METHODS","content":"\u003cp\u003e This research project was approved by the Research Ethics Committee of Antonio Pedro University Hospital at Universidade Federal Fluminense, Niteroi, Brazil (CAAE #70685923.1.0000.5243). Written informed consent was obtained from the two photographic models and from the research participants.\u003c/p\u003e \u003cp\u003eThis study utilized an extra-oral frontal smile photograph with half-open mouth of a 24-year-old female volunteer, with no considerable facial asymmetry. We also used an intra-oral frontal photograph with half-open mouth of a 22-year-old female volunteer with a history of orthodontic treatment and a normal occlusion. Both photographic models provided written informed consent before the use of their images in the study.\u003c/p\u003e \u003cp\u003eThe photographs were modified using GIMP 2.10.32 free and open-source software (The GIMP Development Team, Berkeley, California, USA). The extra-oral frontal smile photograph was standardized by removing distracting factors such as skin signs, irregularities and spots. In the resulting image, the edited side was mirrored to ensure smile symmetry. The dentition part within the smile area was cropped, and the lower lip was cropped in all its extension by a 1mm-strip to create an additional smile with a shorter-vermilion lower lip. The intra-oral frontal photograph was also edited by mirroring the right side to ensure symmetry. This intra-oral image was then layered behind the extra-oral cropped one and proportioned to it according to measurements taken clinically in the smile and teeth from the model, allowing for subsequent image manipulation.\u003c/p\u003e \u003cp\u003eTen images were created with alterations in the vertical position of the intra-oral photograph, displaying varying proportions of upper incisors (Ui) and lower incisors (Li) exposure: 100% of Ui exposure (100Ui), 80% of Ui exposure and 20% of Li exposure (80Ui-20Li), 60% of Ui exposure and 40% of Li exposure (60Ui-40Li), 40% of Ui exposure and 60% of Li exposure (40Ui-60Li), and 20% of Ui exposure and 80% of Li exposure (20Ui-80Li), for both unaltered and reduced lower lip scenarios (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The amount of incisor exposure was calculated in pixels, by measuring the amount of vertical display of right central maxillary and mandibular incisors and calculating the percentage of each to the vertical distance between the lower border of the upper lip and the upper border of the lower lip, all measured over a line passing through the middle of the maxillary right incisor crown.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eUsing Qualtrics XM online survey platform (Qualtrics, Provo, Utah, USA), participants first previewed the 10 images assembled, then evaluated them individually in random order. Smile attractiveness was assessed for each image using a digital version of a 10-point wide visual analog scale (VAS), with endpoints representing \u0026ldquo;most unattractive\u0026rdquo; at zero on the left and \u0026ldquo;most attractive\u0026rdquo; at 10 on the right. The participant could slide the cursor to mark any point along the scale and the score was registered with two decimal places. Participants were also asked to estimate the age range of the smile\u0026rsquo;s owner for each image, with three possible answers in a multiple-choice design: less than 30 (\u0026lt;\u0026thinsp;30), from 30 to 50 (30\u0026ndash;50), or above 50 (\u0026gt;\u0026thinsp;50). The link for the online questionnaire was sent to evaluators that fulfilled the inclusion criteria, who responded between January and April of 2024. Each image was coded for subsequent analysis of the results.\u003c/p\u003e \u003cp\u003eEvaluators were divided in three groups with the following inclusion criteria: 1) the orthodontists should be either orthodontic residents or specialists in Orthodontics; 2) the dentists should have a university degree in Dentistry, but no training in Orthodontics; and 3) laypersons should have completed high school and be above 18 years of age. All 162 volunteers signed an online informed consent form.\u003c/p\u003e \u003cp\u003eThe sample size was calculated to determine the number of evaluators needed for the research, considering α of 5% and β of 20%, the standard deviation from a previous study [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e], and a minimum detectable difference of 1 score. This resulted in a sample size of 54 participants per group, totaling 162 individuals.\u003c/p\u003e \u003cp\u003eA total of 18 participants were invited to retake the questionnaire after a one-month interval to estimate the method\u0026rsquo;s reliability.\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eData were analyzed using the Jamovi Project (2024). \u003cem\u003ejamovi\u003c/em\u003e (Version 2.5) [Computer Software]. Retrieved from \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.jamovi.org\u003c/span\u003e\u003cspan address=\"https://www.jamovi.org\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e. Differences in age values and sex distribution among groups of evaluators were tested using the Kruskal-Wallis and chi-square tests, respectively. Scores attributed to each image were visually represented through boxplots and means and standard deviations calculated. A repeated measures ANOVA, followed by Tukey\u0026rsquo;s post-hoc test, were used to assess differences in scores attributed for each image, considering the group of evaluators as a factor. Frequencies of the age ranges chosen by the evaluators for each image were presented in bar plots, with intergroup differences assessed using chi-square tests. The Friedmand test with the Durbin-Conover pairwise multiple comparison method was used for intragroup comparison of the different images and the Kruskal-Wallis test with the Dwass-Steel-Critchlow-Fligner pairwise multiple comparison method was used for intergroup comparison to examine median differences, considering age range chosen as a categorical variable. A linear regression analysis was performed to test the influence of the evaluators\u0026rsquo; age, sex ang group on the scores attributed to each image. Intraclass correlation coefficient (ICC) was used to measure reliability of the method. A p-value below 0.05 was regarded as statistically significant.\u003c/p\u003e \u003c/div\u003e"},{"header":"RESULTS","content":"\u003cp\u003eA total of 162 participants completed the questionnaire, comprising 54 orthodontists (43 females and 11 males, mean age 34.22 \u0026plusmn; 9.12 years), 54 dentists (37 females and 17 males, mean age 36.26 \u0026plusmn; 9.69 years), and 54 laypersons (35 females and 19 males mean age 36.15 \u0026plusmn; 10.23 years). No statistically significant differences were observed in age (p\u0026thinsp;=\u0026thinsp;0.103) or sex distribution (p\u0026thinsp;=\u0026thinsp;0.210) between the groups.\u003c/p\u003e\n\u003cp\u003eThe ICC value was 0.826, confirming reliability of the measures.\u003c/p\u003e\n\u003cp\u003eTable\u0026nbsp;1 presents the mean attractiveness scores assigned to each image by the evaluators. The highest scores were given to images with 100 and 80% of upper incisor exposure. Mean scores decreased progressively for Images with 60%, 40%, and 20% upper incisor exposure, with statistically significant differences noted among them.\u003c/p\u003e\n\u003cp\u003eComparisons between images with reduced versus unaltered lower lips, with the same extent of incisor exposure, revealed a statistically significant difference only for the image with 100% upper incisor exposure across all groups of examiners (mean difference of 1.2 for orthodontists, 1.12 for dentists and 1.03 scores for laypersons), with higher scores for unaltered lips.\u003c/p\u003e\n\u003cp\u003eStatistically significant differences were observed between orthodontists and laypersons for images of reduced lips with 60%, 40% and 20% upper incisor exposure. Similarly, orthodontists differed markedly from the other two groups of examiners in images showing unaltered lips with 60%, 40% and 20% upper incisor exposure. Orthodontists always graded the images with lower scores (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e\n\u003cp\u003eFigures \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e to \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e illustrate the frequency distribution of perceived age assigned to each image by the combined examiner groups and by each group separately. Images with 100% or 80% upper incisor exposure and both reduced or unaltered lower lips were mostly associated with individuals under 30 by 68.5 to 92.6% of the evaluators. Conversely, images with 60%, 40% or 20% upper incisor exposure displayed marked differences between orthodontists and dentists and between orthodontists and laypersons. Most orthodontists attributed the 60Ui-40Li images with individuals aged between 30 and 50 years, and images 40Ui-60Li and 20Ui-80Li with individuals over 50. In contrast, the majority of dentists attributed all images to the under-30 age category, with the percentage attributions for the 30\u0026ndash;50 and above-50 age categories increasing proportionally to the greater exposure of lower incisors. Laypersons predominantly associated the 60Ui-40Li and 40Ui-60Li images with the under 30 age category, while the 20Ui-80Li images were more frequently attributed to the 30\u0026ndash;50 year age range. Table 2 presents the intragroup and intergroup statistical differences in age attribution.\u003c/p\u003e\n\u003cp\u003eAccording to Table 3, the linear regression analysis indicated a statistically significant influence of the age factor on the attractiveness scores for both images with 80% of lower incisors exposure and the image with 60% of lower incisor exposure and unaltered lips (Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e). Older individuals tended to assign higher scores to these images with a greater percentage of lower incisor exposure. The participants\u0026rsquo; sex did not significantly influence the scores. The orthodontist group difference from the laypersons influenced the scores in most images, except for images of 100% of Ui exposure and 80% of Ui exposure combined with unaltered lips.\u003c/p\u003e"},{"header":"DISCUSSION","content":"\u003cp\u003eThe present study provides novel insights into the perception of smile attractiveness and age estimation based on varying proportions of maxillary and mandibular incisor exposure, coupled with changes in lower lip vermilion height. The methods determined for this study included the analysis of only the smile portion of the face to avoid distractions from unrelated areas, similar to other research [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan additionalcitationids=\"CR20 CR21\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. The online Qualtrics platform was selected due to its ease of access and established performance in other published studies [\u003cspan additionalcitationids=\"CR24\" citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eConsidering the value of 5 on the 0-to-10 VAS as a threshold for unattractive/attractive [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e], our results indicate that maxillary incisor exposure has a significant impact on the perception of smile attractiveness. Higher exposure (100Ui and 80Ui-20Li) was consistently assessed as attractive by the three groups of evaluators (laypersons, dentists, and orthodontists). As the proportion of mandibular incisor exposure increased, the perception of attractiveness decreased, and the images with higher mandibular incisor exposure (40Ui-60Li and 20Ui-80Li) were considered unattractive by all groups. These findings suggest a universal preference for smiles with more maxillary incisor visibility, which may be related to youth, health, and esthetics [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe reduction in lower lip vermilion height did not significantly influence esthetic perception or age estimation in any evaluator group. The only images with similar proportions of incisor exposure that showed differences between altered and unaltered lips were those with 100% upper incisor exposure. This may be due more to the increased gingival margin in the image with reduced lips than to the difference in lower lip dimensions, as this effect was not significant in any other proportions. In young individuals, the expected proportion of upper to lower lip vermilion height ranges between 55% and 90% [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan additionalcitationids=\"CR28 CR29\" citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. However, the literature describes a decrease in the vermilion height of the lower lip as a consequence of aging, while the upper lip does not appear to undergo as significant a decrease [\u003cspan additionalcitationids=\"CR10 CR11\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. If a lower lip with increased vermilion height could distract observers from the unesthetic appearance of increased lower incisor exposure associated with aging, that would be valuable information for lip augmentation treatments aimed at esthetic enhancement. Nevertheless, our findings suggest that even a lower lip with increased vermilion height and a more youthful appearance could not diminish the unesthetic impact of increased lower incisor exposure in the smile. This consideration should be made carefully when planning such treatments. Additionally, a lower lip with decreased vermilion height did not impact age perception as much as the extent of lower incisor exposure.\u003c/p\u003e \u003cp\u003eOur study demonstrates that the proportion of maxillary to mandibular incisor exposure plays a significant role in age estimation. Younger individuals typically display exclusively maxillary incisors or a very small proportion of mandibular incisors during smiling [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. This finding is consistent with the literature, which suggests that age-related changes in incisor exposure are a common phenomenon [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan additionalcitationids=\"CR14\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. However, we must consider that the amount of incisor exposure may vary depending on the situation, such as during smiling, speaking, or between static and dynamic scenarios [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFurthermore, our results indicate that older laypersons tend to be more accepting of smiles with greater mandibular incisor exposure, still perceiving them as relatively esthetic. This finding highlights the potential influence of the evaluator's age on the perception of smile attractiveness and the importance of considering individual preferences in treatment planning.\u003c/p\u003e \u003cp\u003eSimilar to other studies, orthodontists were more critical in the smile esthetic analysis than dentists and laypersons [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. Therefore, communication between professionals and patients is extremely important in the treatment planning phase to balance expectations and ensure that the professional considers the patient\u0026rsquo;s esthetic preferences and chief complaint.\u003c/p\u003e \u003cp\u003eConsidering the clinical relevance and practical applicability of the present study, knowledge of laypersons\u0026rsquo; perceptions may guide orthodontists\u0026rsquo;, prosthodontists\u0026rsquo;, and general practitioners\u0026rsquo; conduct when planning vertical changes to the anterior teeth during dental treatment [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. A careful analysis of incisor exposure during smiling, at rest, and during speech should be considered, as these changes may impact the esthetic facial aspect and age appearance [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Additionally, professionals may use this information to enhance their communication with patients, aiming to align expectations with clinically achievable outcomes.\u003c/p\u003e \u003cp\u003eOur findings underscore the important role of incisor display in shaping esthetic judgments and age attribution across different groups of evaluators, including orthodontists, dentists, and laypersons. The results not only contribute to our understanding of smile esthetics, but also have direct implications for clinical practice in orthodontics and esthetic dentistry, guiding treatment planning and patient communication. The approach of digitally altering incisor exposure and lower lip dimensions in virtual photographs allowed for a systematic investigation of these variables.\u003c/p\u003e \u003cp\u003eLimitations of this study include the use of digitally manipulated static photographs, which does not fully represent the dynamic nature of a smile. Additionally, the teeth, lips and skin used in the images were characteristically from a young model, which may have influenced the esthetic and age perception. The subjectivity of esthetic evaluation may also be considered a limiting aspect, and the VAS was used to reduce this bias.\u003c/p\u003e \u003cp\u003eFuture research should include a more diverse sample of models with different facial characteristics to confirm these results in different populations. Dynamic smile assessment can also be employed to add to the existing knowledge.\u003c/p\u003e"},{"header":"CONCLUSION","content":"\u003col\u003e\n \u003cli\u003eA considerably greater proportion of upper incisors exposure (100% or 80%) in smiles was consistently considered more attractive by all evaluator groups.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eGreater proportions of lower incisors exposure in the smile (60% or 80%) were considered unattractive by all groups.\u003c/li\u003e\n \u003cli\u003eOrthodontists were more critical and assigned lower scores compared to dentists and laypersons.\u003c/li\u003e\n \u003cli\u003eAn increase in lower incisors exposure was consistently correlated with the attribution of an older apparent age to the smiles.\u003c/li\u003e\n \u003cli\u003eAmong the evaluators, particularly in the laypersons’ group, older individuals tended to give higher scores to smiles that showed more exposure of the lower incisors than younger individuals.\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll the authors declare no conflict of interest.\u003c/p\u003e\n\u003cp\u003eThe authors assure no commercial or financial interest in the products or companies mentioned in this study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interests:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors declare no financial and non-financial conflict of interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical Approval:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research project was approved by the Research Ethics Committee of Antonio Pedro University Hospital at Universidade Federal Fluminense, Niteroi, Brazil (CAAE #70685923.1.0000.5243).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eInformed Consent:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWritten informed consent was obtained from the two photographic models and from the research participants.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that no funds, grants, or other support were received during the preparation of this manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eParrini S, Rossini G, Castroflorio T, Fortini A, Deregibus A, Debernardi C. 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Perceptions of Jordanian laypersons and dental professionals to altered smile aesthetics.\u0026nbsp;\u003cem\u003eEur J Orthod.\u003c/em\u003e 2011;33(4):450-456. DOI: 10.1093/ejo/cjq100\u003c/li\u003e\n \u003cli\u003eAckerman MB, Brensinger C, Landis JR. An evaluation of dynamic lip-tooth characteristics during speech and smile in adolescents.\u0026nbsp;\u003cem\u003eAngle Orthod.\u003c/em\u003e 2004;74(1). DOI: 10.1043/0003-3219(2004)074\u0026lt;0043:AEODLC\u0026gt;2.0.CO;2\u003c/li\u003e\n \u003cli\u003eDuarte MEA, Machado RM, da Motta AFJ, Mucha JN, Motta AT. Morphological simulation of different incisal embrasures: Perception of laypersons, orthodontic patients, general dentists and orthodontists.\u0026nbsp;\u003cem\u003eJ Esthet Restor Dent.\u003c/em\u003e 2017;29(1):68-78. DOI: 10.1111/jerd.12272\u003c/li\u003e\n \u003cli\u003eMachado RM, Duarte MEA, da Motta AFJ, Mucha JN, da Motta AT. Variations between maxillary central and lateral incisal edges and smile attractiveness.\u0026nbsp;\u003cem\u003eAm J Orthod Dentofacial Orthop.\u003c/em\u003e 2016;150(3):425-435. DOI: 10.1016/j.ajodo.2016.02.022\u003c/li\u003e\n \u003cli\u003eBahaman L, Bashkail F, Alghamdi A, Alhazmy A. Assessing patients\u0026rsquo; preferences for preventive dental care: A discrete choice experiment.\u0026nbsp;\u003cem\u003eCureus.\u003c/em\u003e 2023;15(8):1-7. DOI: 10.7759/cureus.44028\u003c/li\u003e\n \u003cli\u003eGasparello GG, et al. Orthodontics social media, perceptions of science- and non-science-based posts among orthodontists, dentists, students and laypeople.\u0026nbsp;\u003cem\u003ePLoS One.\u003c/em\u003e 2023;18(9):1-11. DOI: doi.org/10.1371/journal.pone.0286927\u003c/li\u003e\n \u003cli\u003eAlhadidi A, Paniagua B, Cook R, Tyndall D, Baqain Z, Cevidanes LH. The use of a custom-made virtual template for corrective surgeries of asymmetric patients: proof of principle and a multi-center end-user survey.\u0026nbsp;\u003cem\u003eInt J Comput Assist Radiol Surg.\u003c/em\u003e 2019;14(3):537-544. DOI: 10.1007/s11548-018-1858-8\u003c/li\u003e\n \u003cli\u003eSchabel BJ, McNamara JA Jr, Franchi L, Baccetti T. Q-sort assessment vs visual analog scale in the evaluation of smile esthetics.\u0026nbsp;\u003cem\u003eAm J Orthod Dentofacial Orthop.\u003c/em\u003e 2009;135(4):S61-S71. DOI: 10.1016/j.ajodo.2007.08.019\u003c/li\u003e\n \u003cli\u003eSito G, Consolini L, Tr\u0026eacute;vidic P. Proposed guide to lip treatment in Caucasian women using objective and measurable parameters.\u0026nbsp;\u003cem\u003eAesthet Surg J.\u003c/em\u003e 2019;39(12):NP474-NP483. DOI: 10.1093/asj/sjz026\u003c/li\u003e\n \u003cli\u003eHwang K, Kim YS, Kim H. Perceptions of attractive and healthy-looking lips.\u0026nbsp;\u003cem\u003eJ Craniofac Surg.\u003c/em\u003e 2019;30(2):596-603. DOI: 10.1097/SCS.0000000000005070\u003c/li\u003e\n \u003cli\u003eIoi H, Kang S, Shimomura T, Kim SS, Park SB, Son WS, et al. Effects of vermilion height on lip esthetics in Japanese and Korean orthodontists and orthodontic patients.\u0026nbsp;\u003cem\u003eAngle Orthod.\u003c/em\u003e 2014;84(2):239-245. DOI: 10.2319/041613-293.1\u003c/li\u003e\n \u003cli\u003eJang KS, Bayome M, Park JH, Park KH, Moon HB, Kook YA. A three-dimensional photogrammetric analysis of the facial esthetics of the Miss Korea pageant contestants.\u0026nbsp;\u003cem\u003eKorean J Orthod.\u003c/em\u003e 2017;47(2):87-99. DOI: 10.4041/kjod.2017.47.2.87\u003c/li\u003e\n \u003cli\u003eDe Paiva TT, Machado RM, Motta AT, Mattos CT. Influence of canine vertical position on smile esthetic perceptions by orthodontists and laypersons.\u0026nbsp;\u003cem\u003eAm J Orthod Dentofacial Orthop.\u003c/em\u003e 2018;153(3):371-376. DOI: 10.1016/j.ajodo.2017.07.018\u003c/li\u003e\n \u003cli\u003eZhang M, et al. Subjective evaluation of facial asymmetry with three-dimensional simulated images. \u003cem\u003eBMC Oral Health.\u003c/em\u003e 2023;23(1):1-14. DOI: 10.1186/s12903-023-03167-9\u003c/li\u003e\n \u003cli\u003eCheng JH-C, et al. Factors affecting perception of laypeople and dental professionals toward different smile esthetics. \u003cem\u003eJ Dent Sci.\u003c/em\u003e 2023;18(2):739-746. DOI: 10.1016/j.jds.2022.11.030\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTables 1 to 3 are available in the Supplementary Files section\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"smile esthetics, incisor exposure, aging, orthodontics","lastPublishedDoi":"10.21203/rs.3.rs-6457217/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6457217/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eObjective:\u003c/strong\u003e This study investigated the perception of smile attractiveness and age estimation based on different proportions of maxillary and mandibular incisor exposure, combined with changes in lower lip vermilion height.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMaterials and Methods:\u003c/strong\u003e Smile photographs were digitally modified to simulate different proportions of incisor exposure combined with reduced or unaltered lower lip vermilion height. A total of 162 evaluators (orthodontists, dentists, and laypersons) rated attractiveness using a 10-point visual analog scale and estimated the apparent age range. The differences between groups were tested by Kruskal-Wallis, chi-square and repeated measures ANOVA, and a linear regression was performed, with p\u0026lt;0.05 as statistically significant.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults: \u003c/strong\u003eGreater maxillary incisors exposures were considered more attractive by all groups. However, the lower lip vermilion height did not significantly influence esthetic perception or age estimation. Orthodontists were more critical compared to dentists and laypersons. An increase in mandibular incisor exposure was correlated with the attribution of a more advanced apparent age. Older laypersons tended to be more tolerant of smiles showing greater mandibular incisor exposure.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusions: \u003c/strong\u003eThese findings suggest that the proportion of maxillary and mandibular incisor exposure plays a significant role in the perception of smile attractiveness and age estimation.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eClinical significance: \u003c/strong\u003eThe results not only contribute to our understanding of smile esthetics but also have direct implications for clinical practice in orthodontics and esthetic dentistry, guiding treatment planning and patient communication.\u003c/p\u003e","manuscriptTitle":"Impact of incisor display and lower lip height on aesthetic perception and age estimation","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-05-13 09:43:42","doi":"10.21203/rs.3.rs-6457217/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"b26b83d2-800b-4f65-8b0f-7fdc827e3250","owner":[],"postedDate":"May 13th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-08-04T20:23:22+00:00","versionOfRecord":[],"versionCreatedAt":"2025-05-13 09:43:42","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6457217","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6457217","identity":"rs-6457217","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}