To test the null hypothesis that there is no effect of maxillary incisor labiolingual inclination and anteroposterior (AP) position on smiling profile esthetics in young adult females.
A facial smiling profile photograph of a Chinese woman with a normal profile, a Class I occlusion, and a Class I skeletal pattern was digitized. The digital image was modified to obtain four series comprising 29 smiling profiles. The sample of individuals rating these pictures comprised 21 orthodontic professionals and 66 undergraduates. Post hoc tests were done with the Student Newman Keuls method to analyze the data.
Significant differences (P < .001) were detected when each photograph's ratings were compared. The smiling profile with the highest score was the one with 5° lingual inclination, while the ones with 15° labial inclination or 4-mm retrusion had lower scores than the others. Maxillary incisor protrusion and lingual inclination were preferable compared with retruded or flared incisors. There was no significant discrepancy between the professional and nonprofessional groups in terms of their assessments.
The hypothesis is rejected. Both maxillary incisor labiolingual inclination and AP position play an essential role in the esthetics of the smiling profile. However, when formulating treatment plans, dentists should never underestimate the labiolingual inclination's influence on the smiling profile.
Facial esthetics, in particular profile esthetics, is not only one of the motives that encourages most patients to seek orthodontic care but it is also one of the most important objectives of dental treatment.1–3 Although orthodontic treatment is based mainly on occlusal relationships, great attention has recently been paid to obtaining optimal facial profile esthetics.4 The potential effect of orthodontic treatment on facial attractiveness is accepted by most dentists.5 The literature also contains noteworthy studies6–8 that have shown comparable improvement in posttreatment profiles. However, it has been suggested9 that an ideal occlusion outcome does not necessarily result in desirable dentofacial features. And orthodontic treatment that adheres strictly to a cephalometric standard does not necessarily meet esthetic principles.10 When it comes to facial esthetics, not only should the tooth alignment and occlusion be closely monitored, but a thorough evaluation of the soft tissue–hard tissue relationship should also be included.
Although the public is generally consistent with regard to what it believes constitutes an attractive face, public esthetic standards may well vary with time. In spite of the public's emphasis on facial esthetic improvement, a reliable means to evaluate whole facial attractiveness does not exist.5 Esthetic standards, which are gradually established by the mass media, have a direct effect on orthodontics, orthopedics, and orthognathics. Thus, it seems worthwhile to clearly understand the social preferences related to dentofacial attractiveness and smile “pleasantness.”
A smile is one of the most important facial expressions, and it is also indispensable in terms of expressing friendliness, approval, and appreciation.11,12 Recently, smiling esthetics, especially frontal smiling esthetics, have been frequently studied.13–17 The soft tissue profile, including nose, lip, and chin, has received close attention as well.18,19 In order to assist in hard tissue cephalometric analysis, these studies made every effort to seek a standard normative range of the soft tissue. However, there are few smiling profile esthetic studies.
Evaluating the face in smiling profile is an integral part of a complete orthodontic diagnosis. Maxillary incisor labiolingual inclination and anteroposterior (AP) position have a key effect on the appearance of the smiling profile. To improve the prediction of the most proper position of the maxillary incisors, many cephalometric and profilometric measurements have been suggested. These include Andrews and Andrews20 six elements of orofacial harmony, for which the patient's forehead is used as a stable landmark to decide the maxillary incisor AP position in smiling profile. However, there are no reports about the effect of the maxillary incisor labiolingual inclination on smiling profile esthetics. The aim of this study was to evaluate the effect of maxillary incisor labiolingual inclination and AP position on smiling profile esthetics in young adult females.
MATERIALS AND METHODS
Subject selection was restricted to the following criteria: (1) Class I occlusion and Class I skeletal pattern; (2) hard tissue cephalometric analysis (Winceph 7.0) within the normal range, as described in the West China Cephalometric Analysis; (3) soft tissue cephalometric analysis (including Ricketts' esthetic plane,21 Merrifield's z-angle,22 and measurement within the normal range); (4) facial angle and H angle within the normal range, as described by Holdaway,10 and nasolabial angle and maxillary lip angle within the normal range, as described by Arnett and Bergman23; (5) ideal maxillary incisor–to-forehead relationship, as described by Andrews and Andrews20; and maxillary central incisors' facial axial point (FA) on the Goal Anterior Limit Line (GALL).
A 25-year-old female graduate who met the above criteria was chosen from the West China College of Stomatology (Sichuan University). Her right lateral profile photographs were taken with a Nikon D100 digital camera under standard conditions. The first profile photo was taken with a natural facial expression, for use in the profilometric assessment. The second profile photo was taken with a full smiling expression, and a small, 100-mm ruler was fixed above the head of the subject on the facial sagittal plane. The smiling image would be used for the following computer-aided image alterations (Figure 1). Altering images of a single subject was done to control the background interference with facial attractiveness rating; this method has been suggested5 to be a successful means of studying variations in dental appearance.
The subject's repeatable smiling profile photograph was altered with the Photoshop CS2 (version 9.0) digital imaging program to obtain four series comprising 29 smiling profile photographs. The 100-mm ruler above the subject's head was used to quantify hard and soft tissue movements and was later digitally removed to give the subject a normal appearance.
The maxillary incisor labiolingual inclination was altered while FA was kept unchanged on GALL, as described by Andrews and Andrews.20 The maxillary incisor was inclined labially by 5°, 10°, and 15° and lingually by 5°, 10°, and 15°, respectively. There were seven images, including the original smiling profile photo, in the first series (Figure 2A).
The maxillary incisor was moved in a horizontal plane with the incisor AP position altered. The maxillary incisor was moved anteriorly by 1 mm, 2 mm, 3 mm, and 4 mm and posteriorly by 1 mm, 2 mm, 3 mm, and 4 mm, respectively. There were eight images in the second series (Figure 2B). For retrusive simulations, the maxillary lip was moved at labrale superius at 1∶2 to tooth movement; for protrusive simulations, the maxillary lip was moved at labrale superius at 1∶3 to tooth movement.24
The smiling profile photo with maxillary incisor 2 mm anterior was altered. The maxillary incisor was inclined labially by 5°, 10°, and 15° and lingually by 5°, 10°, and 15°, respectively, with FA 2 mm anterior to GALL. Another image was gained through alteration of the maxillary incisor labiolingual inclination with FA on GALL. There were seven images in the third series (Figure 2C).
The smiling profile photo with maxillary incisor 2 mm posterior was altered, just as in the third series. There were also seven images in the fourth series (Figure 2D).
After all of the alterations, four series comprising 29 smiling profiles were printed. Each series was fixed with an erasable 100-mm visual analogue scale. The visual analogue scale was anchored by the descriptors “Least Attractive” (0) and “Most Attractive” (100). Visual analogue scales have been found25,26 to provide valid, reproducible, and representative ratings of dental and facial appearance.
An orthodontic professional panel (14 men, 9 women) and a nonprofessional panel (33 men, 33 women) were selected to judge the profile photographs. The orthodontic professional panel consisted of orthodontists who practiced in the Orthodontic Department at the West China Stomatological Hospital. The nonprofessional panel consisted of undergraduates from Sichuan University. The undergraduates, all of whom were in their 20s, were categorized as the nonexperts. They could represent the younger generation, which contains the greatest potential in terms of patients seeking orthodontic treatment.
Rating of Photographs
Each judge received the profile photographs while seated and was asked to grade each profile based on his or her assessment of the facial attractiveness of the subject, with the help of the 100-mm visual analogue scales. Each judge was asked to rate the attractiveness of the photographs on whatever criteria he or she thought important. The smiling profile photographs in each series were randomized before rating according to a random number table. The same observer gave the instructions for each of the study's 87 sessions.
SPSS (version 13.0) was used to analyze the data. The means of the raw data were determined in order to determine whether there were specific preferences for smiling profiles. The raw data were also analyzed with one-way analysis of variance (ANOVA). The factors were panel (professional and nonprofessional) and photograph (29 variations). Post hoc tests were done using the Student-Newman-Keuls (SNK) method. The level of significance was set at .05 for all statistical tests, unless otherwise stated. All altered pictures were divided into five groups according to whether the ratings were statistically significant or not per SNK analysis.
The subject used for photographic alteration exhibited excellent adherence to the accepted hard and soft tissue normative values. Her profilometric values were within the normal range (Tables 1 and 2), and the crown axial line of her central incisors was on GALL. She also had the ideal maxillary incisor-to-forehead relationship, as described by Andrews and Andrews20 (Figure 1).
The means for the raw scores are summarized by panel and photograph in Table 3. Figure 3 represents the interaction bar plot, in which the x-axis represents the randomized photograph number and the y-axis represents the raw score. This graph shows the higher levels of acceptance for incisor protrusion and lingual inclination, compared with retruded or labially inclined incisors, in both panels.
No significant difference was found in attractiveness ratings between the two panels. As might be expected, significant differences (P < .001) were detected when the ratings of each photograph were compared (Table 4). All altered pictures were divided into five groups by SNK analysis.
Harmonious Smiling Profiles
The average scores of the relatively attractive group, Group 5 (Figure 4A), were all greater than 75, including numbers 9, 2, 16, 18, 1, and 10. The smiling profile with the highest score was the one with incisors with 5° of lingual inclination with FA on GALL (No. 9). The average scores of the acceptable group, Group 4 (Figure 4B), were all greater than 70, including numbers 19, 4, 17, and 25.
The harmonious smiling profiles above indicated that proper protrusion of maxillary incisors (FA ahead of GALL within 2 mm) would not damage the esthetics of the smiling profile if the incisors were upright. Maxillary incisor lingual inclination (within 10°) and a small degree of labial inclination were considered relatively esthetic as well.
Unharmonious Smiling Profiles
The average scores of the unattractive group, Group 1 (Figure 4C), were all less than or equal to 60, including numbers 21, 29, 22, 23, 7, and 8. The smiling profile with the lowest score was the one with incisors in 4 mm of retrusion (No. 21). The average scores of the relatively unattractive group, Group 2 (Figure 4D), were all lower than 65, including numbers 5, 11, 15, 14, and 12. The rest of the images belonged to the interim group, Group 3, for which the average score ranged between 65 and 70.
Those unharmonious smiling profiles above indicated that maxillary incisor retrusion of more than 1 mm would damage the smiling profile esthetics even if the incisors were upright. However, protrusion of less than 3 mm did not affect the smiling esthetics. All of the images showing 15° labial inclination of the upper incisors were considered less attractive without exception, while the ones with 10° lingual inclination were considered relatively esthetic. It was not difficult to draw the conclusion that maxillary incisor lingual inclination and protrusion were more acceptable than incisor labial inclination or retrusion.
The subject met the requirement of the relationship between the maxillary incisors and the forehead, as described in Element II of the six elements of orofacial harmony.20 Forehead was used as a landmark for assessing the AP position of the maxillary central incisors in smiling profile. The original photo had received a relatively high score, which caused us to think that the subject's smiling profile was esthetic.
Both images 29 (maxillary teeth in 2 mm of retrusion, with FA unchanged) and 28 (maxillary teeth in 2 mm of protrusion, with FA unchanged) did not belong to the relatively attractive or acceptable group, even though FA of the incisors was still on GALL. On the other hand, incisor protrusion of less than 3 mm did not affect the smiling esthetics. This finding indicates that although the AP position of the incisors was important to the facial harmony, a small amount of the anterior movement of the maxillary incisors would not damage the smiling profile esthetics. However, improper labiolingual inclination of the upper incisors could easily ruin the pleasing appearance.
Of all the factors related to a balanced smiling profile, one can easily be controlled by orthodontists—the labiolingual inclination of the maxillary incisors. The expression of the incisor labiolingual inclination was influenced by various factors. However, most reports published on this issue indicate a loss of torque control of as high as 100% of the prescribed value.27 Based on the available evidence, Gioka and Eliades27 suggested that a high-torque prescription should be selected to account for the lack of full expression of the prescribed torque that occurs clinically. However, Isıksal et al.4 found that although the inclination values of the maxillary incisors were statistically different between extraction and nonextraction groups, the difference did not affect smiling esthetics in either group. Furthermore, increasing the labial inclination would cause smiling esthetics to deteriorate. The use of a high-torque bracket system, particularly in nonextraction treatment with anterior crowding, when initial tooth torques are close to the desired angles, would be inappropriate.28 Increased maxillary incisor labial inclination might also flatten the smile arc and reduce incisor display, which would lead to negative esthetic consequences.29,30 Our study corroborates these findings of others. Without exception, all of the images with 15° labial inclination of the upper incisors were considered less attractive.
When it comes to the AP position of the maxillary incisors, the ratings also showed us that the raters had some tendency with regard to smiling profile esthetics. The attractiveness of the images was reduced with the increase in maxillary incisor retrusion. All the images with 2-mm retrusion were considered unattractive, in spite of the different labiolingual inclinations. Only one image with slight lingual inclination was acceptable. Many other studies also found that the fuller smile was more attractive.31 Schlosser et al.5 evaluated the effect of maxillary incisor AP relationship on smiling profile and found that the protrusion of the upper anterior teeth was more attractive than that of the retruded ones from an esthetic standpoint. This finding was consistent with that of our investigation. Thus, it is preferable to leave a normally protrusive maxillary dentition where it is, or else it is preferable to advance it rather than to retract the maxillary anterior teeth.
Furthermore, each individual is a unique entity. When making treatment plans, it is essential that practitioners aim not only to achieve a normative dentofacial index, but also to consider the objective of obtaining a balanced smiling profile. The jaw size, the original labiolingual inclination of the maxillary anterior teeth, the AP position, and the soft tissue should be evaluated cautiously. Those patients with a Class III face type should be taken much more seriously in terms of increasing the maxillary incisor labial inclination to compensate for the underdevelopment of the maxilla and the upper alveolar bone, because the small amount of labial inclination increase of the upper incisors would have great negative influence on the attractiveness of the smiling profile. On the other hand, many patients with Class II face type can be treated with satisfactory esthetics through either dental arch expansion or tooth extraction, because there is an acceptable range of protrusion in our society. This is especially true if expansion is managed so as not to produce excessive labial inclination, or if extraction spaces can be closed without retracting the incisors too greatly.32
As facial esthetics becomes a more important objective in orthodontics, a better understanding of the beauty “tendency” can make it easier for clinicians to obtain the optimal smiling profile for patients. Maxillary incisors should be angulated and positioned favorably with regard to other facial structures in order to maximize facial harmony.
A maxillary incisor that is upright or in slight lingual inclination is preferable, in spite of the AP position of the maxillary incisors.
Labial inclination of the upper incisors could easily ruin a pleasing smiling appearance.
Maxillary incisor protrusion is preferable to retruded incisors.
Element II of Andrews and Andrews six elements of orofacial harmony is a useful reference to the smiling profile esthetics in young adult women.
The study was supported by Technology Support Programs of Sichuan Province in China (2009–2011, NO. 2009SZ0164).
PhD, student-graduate, State Key Laboratory of Oral Diseases (Sichuan University); Department of Orthodontics, West China Stomatological Hospital, Sichuan University, Sichuan, PR China
MS, student-graduate, West China Stomatological Hospital; State Key Laboratory of Oral Diseases, Sichuan University, Sichuan, PR China
Professor and Chair, Department of Orthodontics, West China Stomatological Hospital; State Key Laboratory of Oral Diseases, Sichuan University, Sichuan, PR China