Background
Objectives
Material and methods
Study design
Sample size calculations
Selection criteria
Smile
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Step 1: Find an appropriate subject among three candidates. A male subject (26 years of age) with adequate smile characteristics was selected by three experienced orthodontists.
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Step 2: Capture a photo. The subject was photographed smiling indoors by a professional photographer with adequate light and black studio backdrops and two studio strobes, using a digital camera (EOS 1300D, Canon; Tokyo, Japan) fixed on a tripod and a standardized focus on a frontal pose of the subject in a sitting position. The subject was 5 feet away from the camera lens, with the subject's head in a natural posture.
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Step 3: Select an appropriate photo. Any photos displaying head rotations along the vertical axis with imprecise clinical marks without reasonable resolution were excluded. The same experienced orthodontists selected one photo among the best three photos.
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Step 4: Adjust the photos. The chosen photo was then subsequently imported to Adobe Photoshop (CS5.1, San Jose, Calif.) and was cropped and divided into two groups: group 1, which included two-thirds of the nose, lips, and chin (NLC), and group 2, which only included the smiling lips (L) [10]. Afterward, the photos were converted to black and white [26].
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Step 5: Alter the midline. Constant incremental changes in the upper dental midline were generated with the advancement of 1 mm each time, from 0 to 5 mm to the left side, to the facial midline (The center of the top lip or philtrum, employed as a representative of the facial midline).
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Step 6: Print the photo. Photos were designed and curated to replicate the subject's original scale and size (real size scale) [10]. The researcher assigns a code to each photograph, which is then printed on glossy paper and organized randomly in an album in the following order: 3, 2, 0, 5, 4, and 1 mm (Fig. 1) and (Fig. 2).
Questionnaire
Statistical analysis
Results
Study demographic
Overall raters | Chinese raters | Black raters | ||||
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Profession | n | mean age | n | mean age | n | mean age |
Orthodontists | 112 | 35.9 ± 5.5 | 56 | 36.8 ± 5.5 | 56 | 35 ± 5.5 |
G.Practitioners | 112 | 26.4 ± 5.2 | 56 | 25 ± 5.9 | 56 | 27.8 ± 3.8 |
Dental students | 112 | 22.1 ± 1.4 | 56 | 21.8 ± 1.1 | 56 | 22.4 ± 1.6 |
Art students | 113 | 22.6 ± 4 | 57 | 20.4 ± 3.3 | 56 | 24.9 ± 3.3 |
Laypersons | 112 | 26.1 ± 6 | 56 | 23.1 ± 4 | 56 | 20.2 ± 6.2 |
Total | 561 (100%) | - | 281 (50.1%) | - | 280 (49.9%) | - |
Gender | n | % | n | % | n | % |
Male | 279 | (49.7%) | 123 | (43.8%) | 156 | (55.7%) |
Female | 282 | (50.3%) | 158 | (56.2%) | 124 | (44.3%) |
Total | 561 | (100%) | 281 | (100%) | 280 | (100%) |
Age group | n | % | n | % | n | % |
18–30 | 425 | (75.8%) | 219 | (77.9%) | 206 | (73.6%) |
31–51 | 136 | (24.2%) | 62 | (22.1%) | 74 | (26.4%) |
Total | 561 | (100%) | 281 | (100%) | 280 | (100%) |
Smile
Questionnaire
Overall population and ethnic groups
Deviation | NLC scores for overall raters | L scores for overall raters | P-value | ||||||||||||
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(mm) | Male (n = 279) mean ± SD | Female (n = 282) mean ± SD | 18-30 years (n = 112) mean ± SD | 31-51 years (n = 112) mean ± SD | Chinese (n = 281) mean ± SD | Black (n = 280) mean ± SD | Male (n = 279) mean ± SD | Female (n = 282) mean ± SD | 18-30 years (n = 425) mean ± SD | 31-51 years (n = 136) mean ± SD | Chinese (n = 281) mean ± SD | Black (n = 280) mean ± SD | Across gender | Across age groups | Across ethnicity |
0 | 2.2 ± 0.9 | 2.2 ± 0.8 | 2.3 ± 0.9 | 2.2 ± 0.9 | 2.2 ± 0.8 | 2.3 ± 1.0 | 2.1 ± 0.8 | 2.2 ± 0.8 | 2.2 ± 0.8 | 2.2 ± 0.8 | 2.2 ± 0.8 | 2.2 ± 0.9 | n.s | n.s | n.s |
1 | 2.3 ± 0.9 | 2.2 ± 0.9 | 2.2 ± 0.9 | 2.5 ± 0.9 | 2.3 ± 0.9 | 2.3 ± 0.9 | 2.1 ± 1.0 | 2.3 ± 1.1 | 2.2 ± 1.0 | 2.3 ± 1.1 | 2.3 ± 1.0 | 2.1 ± 0.9 | n.s | * NLC | n.s |
2 | 2.3 ± 0.9 | 2.2 ± 0.9 | 2.3 ± 0.9 | 2.4 ± 0.9 | 2.2 ± 0.9 | 2.4 ± 0.8 | 2.2 ± 0.9 | 2.3 ± 0.8 | 2.2 ± 0.9 | 2.4 ± 1.1 | 2.3 ± 0.4 | 2.4 ± 1.0 | * NLC | n.s | * NLC |
3 | 2.5 ± 0.9 | 2.4 ± 0.9 | 2.5 ± 0.9 | 2.6 ± 0.9 | 2.5 ± 0.9 | 2.5 ± 0.8 | 2.3 ± 1.0 | 2.4 ± 1.0 | 2.4 ± 1.0 | 2.6 ± 1.1 | 2.4 ± 1.0 | 2.5 ± 1.0 | * NLC | * L | n.s |
4 | 2.5 ± 0.9 | 2.7 ± 0.9 | 2.6 ± 0.9 | 3.0 ± 1.0 | 2.6 ± 0.9 | 2.8 ± 1.0 | 2.6 ± 1.0 | 2.7 ± 1.2 | 2.6 ± 1.1 | 2.9 ± 1.1 | 2.7 ± 1.1 | 2.7 ± 1.1 | n.s | *NLC + L | * NLC |
5 | 2.6 ± 0.9 | 2.8 ± 0.8 | 2.7 ± 1.0 | 3.1 ± 0.9 | 2.7 ± 0.9 | 2.9 ± 1.1 | 2.6 ± 1.0 | 2.7 ± 0.9 | 2.7 ± 1.0 | 3.0 ± 1.1 | 2.6 ± 1.0 | 2.9 ± 1.0 | n.s | *NLC + L | * L |
Effect of profession
Deviation | NLC scores for Chinese raters | L scores for Chinese raters | p-value | |||||||||
(mm) | Orthodontists (n = 56) mean ± SD | G. Practitioners (n = 56) mean ± SD | Dental students (n = 56) mean ± SD | Art students (n = 57) mean ± SD | Layperson (n = 56) mean ± SD | Orthodontists (n = 56) mean ± SD | G.Practitioners (n = 56) mean ± SD | Dental students (n = 56) mean ± SD | Art students (n = 57) mean ± SD | Layperson (n = 56) mean ± SD | Across profession | NLC x L Results* |
0 | 2.2 ± 0.8 | 2.2 ± 0.8 | 2.2 ± 0.9 | 2.4 ± 0.8 | 2.0 ± 0.9 | 2.2 ± 0.8 | 2.2 ± 0.8 | 2.1 ± 0.9 | 2.3 ± 0.9 | 2.2 ± 0.8 | n.s | n.s |
1 | 2.6 ± 0.9 | 2.5 ± 1.0 | 2.0 ± 0.7 | 2.3 ± 0.9 | 2.0 ± 0.9 | 2.6 ± 0.9 | 2.2 ± 1.0 | 2.0 ± 0.7 | 2.3 ± 0.9 | 2.2 ± 0.9 | * NLC + L | n.s |
2 | 2.6 ± 0.9 | 2.3 ± 0.7 | 1.9 ± 0.8 | 2.1 ± 0.4 | 2.1 ± 0.9 | 2.6 ± 1.0 | 2.3 ± 0.8 | 2.0 ± 0.8 | 2.0 ± 0.9 | 2.3 ± 0.8 | * NLC + L | n.s |
3 | 2.6 ± 1.1 | 2.5 ± 0.9 | 2.5 ± 0.7 | 2.6 ± 1.0 | 2.2 ± 0.9 | 2.9 ± 1.1 | 2.1 ± 1.0 | 2.4 ± 0.8 | 2.4 ± 1.2 | 1.9 ± 0.7 | * NLC + L | n.s |
4 | 3.3 ± 0.8 | 2.7 ± 0.9 | 2.5 ± 0.8 | 2.5 ± 1.0 | 2.2 ± 0.9 | 3.2 ± 0.9 | 2.5 ± 0.9 | 2.7 ± 0.9 | 2.8 ± 1.6 | 2.3 ± 0.8 | * NLC + L | n.s |
5 | 3.1 ± 0.9 | 2.9 ± 0.8 | 2.7 ± 0.8 | 2.6 ± 0.9 | 2.3 ± 0.8 | 3.2 ± 0.8 | 2.5 ± 1.0 | 2.7 ± 0.9 | 2.5 ± 0.9 | 2.3 ± 1.0 | * NLC + L | * |
Deviation | NLC scores for Black raters | L scores for Black raters | p-value | |||||||||
(mm) | Orthodontists (n = 56) mean ± SD | G. Practitioners (n = 56) mean ± SD | Dental students (n = 56) mean ± SD | Art students (n = 56) mean ± SD | Laypersons (n = 56) mean ± SD | Orthodontists (n = 56) mean ± SD | G. Practitioners (n = 56) mean ± SD | Dental students (n = 56) mean ± SD | Art students (n = 56) mean ± SD | Laypersons (n = 56) mean ± SD | Across profession | NLC x L Results* |
0 | 2.3 ± 0.9 | 2.3 ± 0.8 | 2.5 ± 1.5 | 2.2 ± 0.8 | 2.2 ± 0.8 | 2.2 ± 0.8 | 1.9 ± 0.9 | 2.4 ± 0.8 | 2.1 ± 0.8 | 2.2 ± 0.9 | n.s | * |
1 | 2.6 ± 0.7 | 2.1 ± 1.0 | 2.5 ± 0.8 | 2.1 ± 0.9 | 2.3 ± 0.8 | 2.7 ± 1.0 | 1.5 ± 0.7 | 2.5 ± 0.8 | 2.2 ± 0.9 | 2.0 ± 0.8 | * NLC + L | * |
2 | 2.7 ± 0.8 | 2.3 ± 0.8 | 2.6 ± 1.2 | 2.3 ± 0.6 | 2.2 ± 1.1 | 2.6 ± 1.0 | 2.0 ± 0.9 | 2.5 ± 1.1 | 2.6 ± 0.9 | 2.1 ± 1.0 | * NLC + L | n.s |
3 | 2.8 ± 0.7 | 2.3 ± 0.8 | 3.0 ± 0.8 | 2.4 ± 0.8 | 2.2 ± 0.8 | 2.8 ± 0.8 | 2.4 ± 0.8 | 2.9 ± 0.9 | 2.1 ± 1.4 | 2.3 ± 1.0 | * NLC + L | n.s |
4 | 3.2 ± 0.8 | 2.9 ± 0.9 | 3.1 ± 0.9 | 2.5 ± 0.9 | 2.4 ± 1.1 | 3.4 ± 0.9 | 2.2 ± 0.9 | 3.5 ± 0.9 | 2.0 ± 0.8 | 2.2 ± 1.0 | * NLC + L | * |
5 | 3.4 ± 0.8 | 2.8 ± 0.9 | 3.5 ± 1.4 | 2.3 ± 0.8 | 2.3 ± 1.0 | 3.4 ± 0.8 | 2.5 ± 0.9 | 3.8 ± 0.8 | 2.4 ± 0.8 | 2.5 ± 0.8 | * NLC + L | n.s |
Associated smile structures
Gender
Deviation | NLC scores for Chinese raters | L scores for Chinese raters | p-value | |||||||
(mm) | Male (n = 158) mean ± SD | Female (n = 123) mean ± SD | 18–30 year (n = 219) mean ± SD | 31–51 year (n = 62) mean ± SD | Male (n = 158) mean ± SD | Female (n = 123) mean ± SD | 18–30 year (n = 219) mean ± SD | 31–51 year (n = 62) mean ± SD | Across gender | Across age |
0 | 2.2 ± 0.9 | 2.2 ± 0.8 | 2.3 ± 0.8 | 2.0 ± 0.8 | 2.1 ± 0.8 | 2.2 ± 0.8 | 2.2 ± 0.8 | 2.1 ± 0.9 | n.s | n.s |
1 | 2.3 ± 0.9 | 2.2 ± 0.9 | 2.2 ± 0.9 | 2.5 ± 1.0 | 2.1 ± 1.0 | 2.3 ± 1.1 | 2.2 ± 1.1 | 2.3 ± 0.9 | n.s | n.s |
2 | 2.3 ± 0.9 | 2.2 ± 0.9 | 2.2 ± 0.8 | 2.4 ± 1.0 | 2.2 ± 0.9 | 2.3 ± 0.8 | 2.2 ± 0.8 | 2.4 ± 1.0 | n.s | n.s |
3 | 2.5 ± 0.9 | 2.4 ± 0.9 | 2.4 ± 0.9 | 2.6 ± 1.1 | 2.3 ± 1.0 | 2.4 ± 1.0 | 2.3 ± 0.9 | 2.6 ± 1.2 | n.s | n.s |
4 | 2.5 ± 0.9 | 2.7 ± 0.9 | 2.5 ± 0.9 | 3.1 ± 1.0 | 2.6 ± 1.0 | 2.7 ± 1.2 | 2.6 ± 1.1 | 3.0 ± 1.1 | n.s | *NLC + L |
5 | 2.6 ± 0.9 | 2.8 ± 0.8 | 2.6 ± 0.8 | 3.0 ± 1.0 | 2.6 ± 1.0 | 2.7 ± 0.9 | 2.5 ± 0.9 | 3.0 ± 1.0 | * NLC | *NLC + L |
Deviation | NLC scores for Black raters | L scores for Black raters | p-value | |||||||
(mm) | Male (n = 158) mean ± SD | Female (n = 123) mean ± SD | 18–30 year (n = 206) mean ± SD | 31–51 year (n = 74) mean ± SD | Male (n = 158) mean ± SD | Female (n = 123) mean ± SD | 18–30 year (n = 206) mean ± SD | 31–51 year (n = 74) mean ± SD | Across gender | Across age |
0 | 2.3 ± 1.1 | 2.3 ± 0.8 | 2.3 ± 1.0 | 2.4 ± 0.9 | 2.2 ± 0.9 | 2.1 ± 1.0 | 2.1 ± 0.9 | 2.3 ± 0.8 | n.s | n.s |
1 | 2.3 ± 0.8 | 2.3 ± 0.8 | 2.2 ± 0.9 | 2.5 ± 0.8 | 2.2 ± 0.9 | 2.1 ± 1.0 | 2.1 ± 0.9 | 2.4 ± 1.0 | n.s | * L |
2 | 2.6 ± 1.0 | 2.3 ± 0.9 | 2.4 ± 1.0 | 2.4 ± 0.9 | 2.4 ± 0.9 | 2.4 ± 1.1 | 2.3 ± 1.0 | 2.4 ± 0.9 | * NLC | n.s |
3 | 2.7 ± 0.8 | 2.4 ± 0.9 | 2.5 ± 0.8 | 2.6 ± 0.8 | 2.5 ± 0.8 | 2.5 ± 1.3 | 2.5 ± 1.1 | 2.6 ± 0.8 | * NLC | n.s |
4 | 2.8 ± 0.6 | 2.8 ± 1.1 | 2.8 ± 1.0 | 3.0 ± 0.9 | 2.9 ± 1.1 | 2.6 ± 1.1 | 2.6 ± 1.1 | 2.8 ± 1.0 | n.s | n.s |
5 | 2.9 ± 1.1 | 2.8 ± 1.1 | 2.8 ± 1.2 | 3.1 ± 0.9 | 2.9 ± 0.9 | 3.0 ± 1.1 | 2.9 ± 1.0 | 3.0 ± 1.0 | n.s | * NLC |
Age (Social Background)
Association between deviations in NLC and L and the raters' mean values
Discussion
Conclusions
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• Perception of the upper dental midline deviations was influenced by the ethnicity, profession, presence or absence of smile-associated structures, as well as the gender and age of the raters.
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• This data can aid in analyzing the smiles of people of Chinese and Black origin. Nevertheless, in order to get sufficient outcomes, each case must be evaluated on an individual basis while taking the patient's expectations and preferences into account.