Three-dimensional evaluation of social smile symmetry

Three-dimensional evaluation of social smile asymmetry in patients with unilateral impacted maxillary canine: a 3D stereophotogrammetry study

OBJECTIVE

This study aimed to evaluate social smile asymmetry in patients with unilateral impacted maxillary canine on 3D stereophotogrammetric images.

MATERIAL AND METHODS

The 3D social smile images of participants with unilateral impacted maxillary canine (n:20) and without impaction as a control group (n:20) were included. The images were recorded with a hand-held 3D stereophotogrammetry device (Fuel3D® Scanify®) and Geomagic Essentials 2 reverse engineering software were used for analyses. After the orientation process of the 3D records, the tissues around the smile area were divided into five morphological regions: cheek, upper lip lateral and medial, and lower lip lateral and medial. The deviation margins in the negative and positive directions for the 95% mesh rate and the total percentages of meshes between - 0.5- and + 0.5-mm deviations were calculated. ICC, paired samples t test, independent samples t test, and the Mann-Whitney U test were used for statistical analyses.

RESULTS

In individuals with impacted canine, the amount of maximum positive deviation in the upper lip medial was 5.64 mm ± 1.46 and maximum negative deviation was - 4.6 mm ± 1.17. In the control group, mean of deviation limits for all parameters was less than 1.19 mm ± 2.62, while in individuals with unilateral impacted maxillary canine, the maximum value was 8.34 mm ± 2.23. The mesh percentage between - 0.5 and 0.5-mm deviations was over 95% in all morphological areas in the control group, while in the impacted canine group, the number of meshes within the specified deviation limits was less than 95%.

CONCLUSION

Individuals with unilateral impacted maxillary canine exhibit greater asymmetry in social smile compared to the control group, with the asymmetry being most prominent near the corners of the mouth and cheeks.

CLINICAL RELEVANCE

Amount of asymmetry was higher in impaction group compared to the control group in social smile. The quantification of a possible smile asymmetry due to the impacted canine is crucial for the diagnosis and treatment planning of orthodontic and/or orthognathic cases for ideal aesthetic results. Hence, smile asymmetry should not be overlooked and should be considered in diagnosis and treatment planning.

Correlation of social smile symmetry with facial symmetry

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.

Effect of the ethnic, profession, gender, and social background on the perception of upper dental midline deviations in smile esthetics by Chinese and Black raters

BACKGROUND

The purpose of this study was to compare the perception of upper dental midline deviation on the attractiveness of a smile among raters from different ethnicities, professions, genders, and ages and measure to what extent the presence or absence of the associated smiling structures influence the raters' evaluations.

METHODS

A male subject (26 years of age) with adequate smile characteristics was selected by 3 experienced orthodontists, and 561 raters from 2 different ethnic groups (281 Chinese raters and 280 Black raters) rated the subject's smile after the subject's upper dental midline was digitally altered from 0 to 5 mm using a 5-point Likert scale on 12 smile photographs divided into two groups: group 1, in the presence of smile related structures, two-thirds of the nose, lips, and chin (NLC), and group 2, in the absence of smile related structures, the lips only (L).

RESULTS

There were statistically significant differences (p < 0.05) between the two ethnicities, in 2 mm and 4 mm in-group NLC and 5 mm in-group L, as well as the raters' profession to each midline shift of both groups (NLC) and (L) for both ethnicities except for 0 mm. Regarding the role of associated smile structures, the smile photos were observed in the presence of smile-associated structures, and in its absence (NLC × L), statistically significant differences (p < 0.05) were found when the deviation was 5 mm among the Chinese raters; in 1 mm, and 4 mm among the Black raters. Among different genders, statistical differences were only reported (p < 0.05) for Chinese raters for 5 mm in NLC, while statistical differences were observed for 2 mm and 3 mm in NLC for Black raters. For age categories, differences were observed (p < 0.05) for 4 mm, 5 mm in NLC and 4 mm, and 5 mm in L for Chinese raters, while 5 mm in NLC and 1 mm in L for Black raters.

CONCLUSION

Perception of the upper dental midline deviations was influenced by the factors of ethnicity, profession, presence or absence of smile-associated structures, as well as the gender and age of the raters.

Relationship between smile type and periodontal phenotype: a clinical and tomographic cross-sectional study

OBJECTIVES

To evaluate the correlation between smile type (ST) and the periodontal phenotype (PP).

MATERIAL AND METHODS

Clinical and photographic examinations of 164 participants (48 men and 116 women, mean age 22.9 ± 4.6 years) were performed, including an evaluation of ST (high, average, and low), gingival phenotype (GP) by transparency of the periodontal probe (TRAN), keratinized tissue width (KTW), gingival architecture (GA), tooth shape (TS), and papilla height (PH). A subgroup of 70 participants underwent soft-tissue cone-beam tomographic examinations (ST-CBCT), in which GP, gingival thickness (GT), buccal bone thickness (BBT), and the distances from the gingival margin and cementoenamel junction to the buccal bone crest (GM-BBC and CEJ-BBC) were evaluated. The data were analyzed using one-way ANOVA, Student's t-test, and chi-square tests, with the level of significance set at 0.05.

RESULTS

High, average, and low STs were found in 31.7%, 56.7%, and 11.6% of the participants, respectively. Sex (p=0.001), GP evaluated using TRAN (p=0.021) and ST-CBCT scans (p=0.009), GA (p<0.001), and TS (p=0.001), were associated with STs. The prevalence of thin GP was: 63% in low, 50% in average, and 38% in high smile types. KTW (p=0.004), PH (p<0.001), GT at different landmarks (p<0.05), CEJ-BBC (p=0.017), and GM-BBC (p=0.001) were significantly different among STs. The highest GT and KTW were found in the high-smile group, average-smile presented the higher CEJ-BBC while GM-BBC and PH, were higher in low-smile group.

CONCLUSION

Periodontal phenotype components presented important difference over the smile types.

CLINICAL RELEVANCE

A detailed examination of smile types is an essential part of treatment planning, especially when the patient has high esthetic demands. Clinical and tomographic individual analysis of periodontal phenotypes over the smile types may be helpful for a case-by-case approach, and for the development of well-defined treatment protocols.

Landmark movement trajectory: A simple reference to understand the dominant muscle contraction in a dynamic smile expression

Insight into the roles of perioral muscles play in smiling is essential to the relevant esthetic and reconstructive treatment. This study analyzed specific landmarks' movement trajectories to understand the dominant muscle activity in smiling. Sixty volunteers (aged 18-45 years) were included, and standardized frontal view images were obtained by three-dimensional photogrammetry. Each image sequence frame was referenced and superimposed onto the neutral image. Six surface landmarks were digitized on each frame to form the entire movement trajectories from resting to maximal smile. The perioral muscles were divided into different groups according to the inserting position of muscular fibers and the contracting direction. The movement paths of landmarks were analyzed to find the major muscle groups involved. The dominant muscle groups throughout smiling were successfully identified by landmark trajectory analysis in all 60 volunteers. Zygomaticus major was the dominant force for the beginning of most smiles. Apart from the zygomaticus major, other perioral muscles played a dominant role throughout smile expression, including levator anguli oris, buccinator and risorius, depressor anguli oris, and the upward muscle group of the upper lip were all identified. Besides, a notable high percentage of smiles presented a mixed pattern, indicating the cooperation of several muscle groups during smiling. Landmark movement trajectory provides a simple reference to understand the dominant perioral muscles in smiling. It can help surgeons get more information for the dynamic treatment of smiles.

Evaluation of facial asymmetry by stereophotogrammetry in individuals with unilateral maxillary impacted canine

PURPOSE

The aim of this study is to compare the symmetry of the facial and dentoalveolar structures of patients with unilateral impacted maxillary canine teeth with a control group of individuals without impacted teeth using three-dimensional face scans.

METHODS

The study included 28 patients (10 females, 18 males) with unilateral impacted maxillary canine teeth and 28 patients (15 females, 13 males) without any impacted maxillary canine between 12 and 25 years of age. The 3dMDface™ (3dMD Inc., Atlanta, GA, USA) imaging system was used to obtain 3D face images. 3dMD Vultus® (3dMD Inc., Atlanta, GA, USA) software was used for the measurements.

RESULTS

According to the study findings, there were differences in linear measurements and volume measurements between the right and left sides of the face in patients with an impacted canine. However, these differences were not statistically significant. In patients with an impacted canine, surface differences between the right and left halves of the face were not found to be statistically different from the control group.

CONCLUSION

There was no difference in the amount of facial asymmetry between patients with unilateral maxillary impacted canine and patients with normal tooth alignment in the control group.

The Influence of Varying Gingival Display of Maxillary Anterior Teeth on the Perceptions of Smile Aesthetics

OBJECTIVES

The aim of the study was to investigate the influence of gingival display on perceived smile aesthetics and to compare aesthetic gingival display preference amongst dental professionals and lay people.

METHODS

This cross-sectional study was based on the analysis of quantitative data collected via questionnaires. Two sets of digitally altered smile images with variations of gingival amount and architecture displays were produced. Ranking order scale was used to record aesthetic preferences, from the most attractive to the least attractive.

RESULTS

There were 124 respondents (60 lay people, 32 general dentists [GDPs] and 32 orthodontists). Average smile line, tangent to the zeniths of maxillary anterior teeth, was found to be the most attractive gingival amount (53.2%, χ² = 144.15, p < 0.045) amongst lay people, GDPs and orthodontists. High smile line was ranked as the least attractive amount amongst all respondents (88.7%, χ² = 359.37 p < 0.002). Class III gingival outline, where all gingival levels are symmetrical and in line, was found as the most attractive gingival architecture (65.3%, χ² = 10.87 p < 0.001).

CONCLUSION

No particular amount of gingival display is universally perceived as attractive although high smile lines are generally disliked. Class III gingival architecture is the most preferred gingival archetype when excessive amount of maxillary gingiva is exposed.

CLINICAL SIGNIFICANCE

A general acceptance to smile line variations demonstrates that the harmony amongst all smile components is more important than merely focusing on a single ideal smile constituent. However, when designing the smile with an inherent high lip line, a Class III gingival architecture might be more preferable since it reduces the negative impact of excessive gingival display.

Three-dimensional prediction of nose morphology in Chinese young adults: a pilot study combining cone-beam computed tomography and 3dMD photogrammetry system

The nose is the most prominent part of the face and is a crucial factor for facial esthetics as well as facial reconstruction. Although some studies have explored the features of external nose and predicted the relationships between skeletal structures and soft tissues in the nasal region, the reliability and applicability of methods used in previous studies have not been reproduced. In addition, the majority of previous studies have focused on the sagittal direction, whereas the thickness of the soft tissues was rarely analyzed in three dimensions. A few studies have explained the specific characteristics of the nose of Chinese individuals. The aim of this study was to investigate the relationship between the hard nasal structures and soft external nose in three dimensions and to predict the morphology of the nose based on hard-tissue measurements. To eliminate the influence of low resolution of CBCT and increase the accuracy of measurement, three-dimensional (3D) images captured by cone-beam computed tomography (CBCT) and 3dMD photogrammetry system were used in this study. Twenty-six measurements (15 measurements for hard tissue and 11 measurements for soft tissue) based on 5 craniometric and 5 capulometric landmarks of the nose of 120 males and 120 females were obtained. All of the subjects were randomly divided into an experimental group (180 subjects consisting of 90 males and 90 females) and a test group (60 subjects consisting of 30 males and 30 females). Correlation coefficients between hard- and soft-tissue measurements were analyzed, and regression equations were obtained based on the experimental group and served as predictors to estimate nasal morphology in the test group. Most hard- and soft-tissue measurements appeared significantly different between genders. The strongest correlation was found between basis nasi protrusion and nasospinale protrusion (0.499) in males, and nasal height and nTr-nsTr (0.593) in females. For the regression equations, the highest value of R² was observed in the nasal bridge length in males (0.257) and nasal tip protrusion in females (0.389). The proportion of subjects with predicted errors < 10% was over 86.7% in males and 70.0% in females. Our study proved that a combined CBCT and 3dMD photogrammetry system is a reliable method for nasal morphology estimation. Further research should investigate other influencing factors such as age, skeletal types, facial proportions, or population variance in nasal morphology estimation.

Evaluation of the maxillary midline, curve of the upper lip, smile line and tooth shape: a prospective study of 140 Caucasian patients

Background

A number of reference patterns such as the interincisal line, curve of the upper lip, width of the smile or shape of the teeth have been studied in different populations. Determining the frequency of different smile aesthetic parameters in a European Caucasian population and exploring possible gender differences is important in order to obtain predictable treatment outcomes.

Methods

Photographs were obtained under resting and forced smiling conditions in 140 individuals (70 males and 70 females) with a mean age of 20.1 ± 4.3 years. Different variables were recorded, including the position of the maxillary interincisal midline in relation to the facial midline, the arc and width of the smile, and the shape of the teeth. The data were processed using the SPSS version 15.0 statistical package, with application of the chi-squared test and a confidence level of 95%. The statistical power was 80%, and the level of significance 5% (α = 0.05).

Results

A total of 94.3% of the sample presented a maxillary interincisal midline coinciding with the facial midline, and 80% had a consonant smile line. The curve of the upper lip was upwards in 47.1% of the cases, followed by a straight curve in 41.4%. Most of the subjects (84.3%) presented a medium smile line with tooth exposure to the second premolar (61.4%). There were no significant differences between males and females.

Conclusions

The integration of aesthetic criteria is needed in order to guarantee satisfactory and predictable dental treatment outcomes. There were no statistically significant differences between males and females. The maxillary interincisal midline coincided with the facial midline, with a consonant smile arc and a medium smile line, upward lip curve and oval tooth shape.

Comparison of smile esthetics among celebrities, dentists, and dental students in a Han Chinese population

STATEMENT OF PROBLEM

Various components of smile esthetics have been evaluated. However, whether these components affect smile esthetics in Han Chinese celebrities, dentists, and dental students is unknown.

PURPOSE

The purpose of this study was to evaluate the smile esthetics of celebrities, dentists, and dental students in a Han Chinese population.

MATERIAL AND METHODS

Frontal images of smiles were obtained from the Internet for the celebrity group, while images of dentists and dental students were collected for the dentist and dental student groups. The buccal and posterior corridor ratios, the alignment discrepancy between the commissural and interpupillary lines, the number of teeth revealed, the width ratio relative to the golden proportion, and the width-to-length ratios of maxillary anterior teeth were calculated by using a photo-editing software program. Statistical analysis was performed by using 2-way ANOVA and the Tukey HSD test (α=.05).

RESULTS

Eligible images were obtained for 81 celebrities, 83 dentists, and 78 dental students. The celebrities were found to have the highest buccal and posterior corridor ratios and reveal the least teeth in the smile among the 3 groups (all P<.001). The alignment discrepancy for celebrities was significantly less than that for dental students (P=.025). Moreover, the absolute difference of width ratios from the golden proportion was significantly different from 0 for all groups (all P<.001).

CONCLUSIONS

Significant differences were found in the smiles of Han Chinese celebrities, dentists, and dental students in regard to the buccal and posterior corridor ratios, the alignment discrepancy between the commissural and interpupillary lines, and the number of teeth revealed. Chinese celebrities tended to have a smile that displays to the second premolar, with a medium buccal corridor width.

Class II functional appliance treatment and dynamic three-dimensional mimic muscle evaluation

BACKGROUND

Functional appliances have skeletal and dentoalveolar treatment effects, but knowledge on their effect on facial expressions is limited.

OBJECTIVE

To analyse changes in facial expressions, using three-dimensional (3D) mimic muscle evaluation, in growing children with Class II malocclusion and large overjet, undergoing functional appliance treatment.

METHODS

Fifteen growing children with Class II division 1 malocclusion, selected prospectively, had dynamic 3D recordings of facial expressions prior to and 12 months after commencing functional appliance treatment. Facial expressions recorded were smile and lip pucker, and the movements of the oral commissures were analysed, as well as mouth width and its symmetry. A control group of fifteen age- and sex-matched growing children without immediate need for orthodontic treatment had similar recordings prior to and after a 12-month observation period.

RESULTS

In the treatment group, the Class II malocclusion in all children improved after 12 months of functional appliance wear. With regard to movements of the oral commissures, the initial recordings of the treatment group did not show any significant differences to the control group for neither smile nor lip pucker. Differences were noted however when looking at mouth width asymmetry, where this tended to become more symmetrical in the functional appliance treatment group, during rest and during smiling, while it became more asymmetrical in the untreated control group.

CONCLUSION

The use of removable functional appliances in children with Class II division 1 malocclusion may have a positive effect on mouth width symmetry when smiling, making it more symmetrical.

Lip position analysis of young women with different skeletal patterns during posed smiling using 3-dimensional stereophotogrammetry

INTRODUCTION

The aim of this study was to explore the internal relationship between posed smile characteristics, lip position, and skeletal patterns in young women.

METHODS

Fifty women between the ages of 20 and 30 years were enrolled and divided into 3 groups-vertical, average, and horizontal patterns- using the following parameters: FMA, GoGn-SN, and Jarabak ratio. Each subject was scanned in natural head position and with a posed smile. The interlabial gap, intercommissural width, and smile index were calculated. The frontal region was selected as the reference plane for superimpositions. The changes of the lip landmarks in the vertical, sagittal, and coronal directions were investigated.

RESULTS

The smile indexes were listed in the following sequence: vertical < average < horizontal. Significant differences were found in the interlabial gap among the 3 groups. Compared with the average and horizontal groups, the upper lip landmarks of the vertical group showed differences and changed more only in the vertical direction. However, the lower lip landmark showed no differences in any direction.

CONCLUSIONS

Different skeletal patterns have characteristic smile features. The vertical skeletal pattern affects upper lip movements because there is more space for upper-lip elevation. However, the vertical skeletal pattern has no effect on lower lip movement.

Development of three-dimensional facial expression models using morphing methods for fabricating facial prostheses

PURPOSE

It is essential to fabricate a best-fit three-dimensional (3D) facial prosthesis model capable of facial expressions. In order for the facial prosthesis to remain in position, especially around marginal areas subject to movement, a new method of making 3D facial expression models using time-series data allowing changes in facial expression by morphing technique was developed.

METHODS

Seven normal subjects and seven patients with nasal defects or nasal deformities participated in this study. Three distinct facial expressions (i.e., a neutral expression, smiled, and open mouthed) were digitally acquired with a facial scanner. Prepared template models were transformed to homologous models, which can represent the form as shape data with the same number of point cloud data of the same topology referring to the scanning data. Finally, 3D facial expression models were completed by generating a morphing image based on two sets of homologous models, and the accuracy of the homologous models of all subjects was evaluated.

RESULTS

3D facial expression models of both normal subjects and patients with nasal defects were successfully generated. No significant differences in shape between the scanned models and homologous models were shown.

CONCLUSIONS

The high accuracy of this 3D facial expression model in both normal subjects and patients suggests its use for fabricating facial prostheses.

Upper Lip Asymmetry During Smiling: An Analysis Using Three-Dimensional Images

Objective

The aim of this study was to use three-dimensional images to determine the presence of upper lip asymmetry at rest and during smiling in a group of individuals with no history of orthodontics or facial cosmetic surgery.

Methods

Standardized three-dimensional frontal resting and smiling images of 54 volunteers were analyzed using the 3dMDvultus software (3dMD, Atlanta, GA). Measurements were made from the soft tissue nasion, ipsilateral ala, subnasale, and menton to the right and left commissures of the lip. A 2.5 mm or greater difference between the right and left sides was defined as an asymmetry. The agreement on the presence or absence of asymmetry between the subjects' states of rest and smiling was determined by the McNemar's chi-squared test. Statistical significance was defined as p<0.05.

Results

Menton was the most stable facial landmark to evaluate the upper lip symmetry at rest and during smiling (p=0.002). Using menton as a landmark, only one of the 54 subjects showed asymmetry while resting, but 12 (22%) showed asymmetry when smiling.

Conclusion

As part of treatment planning for orthodontics or orthognathic surgery, patients should be evaluated for the upper lip symmetry during resting and smiling. The presence of asymmetry during smiling is a significant clinical problem that needs to be recognized so that patients can be informed about the effect it can have on the final esthetic result.