Cephalometric characteristics of postorthodontic female patients with attractive and unattractive frontal posed smiles
To identify differences in skeletal, dental, and soft-tissue morphology between postorthodontic patients with attractive and unattractive frontal posed smiles. The attractiveness of close-up photographs of frontal posed smiles in 100 adult female patients after conventional orthodontic treatment was evaluated by 20 dental students (10 men, 10 women) using a visual analogue scale. Posttreatment cephalograms of the 20 patients with the most attractive smiles (attractive group; mean age 23.75 ± 3.35 years) and the 20 patients with least attractive smiles (unattractive group; mean age 23.11 ± 4.45 years) were selected, and 41 measurements were made and compared between groups using the Mann-Whitney U-test (P < .05). When compared with the attractive group, the unattractive group exhibited greater values for sella-nasion plane to mandibular plane, palatal plane to mandibular plane, anterior facial height, lower facial height, and lower facial height/anterior facial height as skeletal measurements; for occlusal plane to sella-nasion plane, palatal plane to occlusal plane, and maxillary central incisor to palatal plane as dental measurements; and for lower face, upper lip length, and upper lip superior to palatal plane as soft-tissue measurements. Cephalometric analysis revealed that postorthodontic Japanese female patients with unattractive frontal posed smiles are characterized by a hyperdivergent skeletal pattern with extruded maxillary incisors and a steep occlusal plane, accompanied by a longer upper lip than patients achieving attractive posed frontal smiles.ABSTRACT
Objectives:
Materials and Methods:
Results:
Conclusions:
INTRODUCTION
One goal of orthodontic treatment is to refine quality of life by achieving physical and mental health, including not only the functional occlusal relationship of teeth with a balanced skeletal pattern but also the improvement of facial esthetics.1,2 Attention to smile evaluations in facial esthetics has recently been increasing in orthodontic diagnosis.3 Among several previously proposed evaluations of frontal smile, buccal corridor,4,5 smile line or smile arc,4,6–10 and amount of exposure of maxillary gingiva or gummy smile6,11 have become essential items in current orthodontic diagnosis.3,12
To create esthetically improved smiles for individual patients after orthodontic treatment by setting optimized treatment goals, the relationship between the evaluation results of facial esthetics and lateral cephalometric analysis has been investigated.6,8,11,13,14 Işıksal et al.15 found a weak but significant negative correlation only between the smile attractiveness of postorthodontic patients in close-up photographs and the degree of labial inclination of the maxillary incisor in cephalometric analysis. In contrast, Oh et al.16 obtained significant but relatively weak relationships between the facial attractiveness of a set of full-face photographs and some vertical and anteroposterior skeletal measurements in cephalometric analysis. Other studies have observed a significant influence of the skeletal pattern on the size of the buccal corridor5 and smile arc classification,10 but no significant association has been observed with gummy smile evaluations.11 Therefore, based on findings from those previous studies, no agreement has been reached regarding the morphological characteristics needed to achieve an attractive smile after orthodontic treatment.
The purpose of the present study was to compare skeletal, dental, and soft-tissue morphologies by lateral cephalometric analysis between postorthodontic patients with attractive and unattractive frontal posed smiles from the Japanese population.
MATERIALS AND METHODS
This study was approved by the ethics committee of Nippon Dental University (Tokyo, Japan; approval T2015-41).
Sample size was estimated to have an effect size of 0.702, according to a previous study14 using G*power version 3.1 statistical software (Heinrich Heine Universität Düsseldorf Experimentelle Psychologie, Düsseldorf, Germany). Analysis revealed that the required minimum sample size for each group was 13 to detect this effect size with 0.8 power at 5%.
Orthodontic Patients
A total of 100 female patients who had undergone orthodontic treatment, including control of second molars, and were aged younger than 30 years old at the completion of active treatment in Nippon Dental University Hospital were selected. Patients with cleft lip or cleft palate or who had undergone orthognathic surgery were excluded. Within 1 month after active treatment, lateral cephalograms using the same machine (CX-150SK; Asahi-Roentgen, Kyoto, Japan) and frontal photographs with a posed smile from a standardized distance of 150 cm were taken.12
Photos of patients smiling appropriately were scanned using a flatbed scanner (GT-X970; Epson, Tokyo, Japan) and then converted into 2000-dpi monochrome TIFF images that depicted only the area around the lips to reduce confounder effects of background features such as nose, cheeks, chin, and hair type9,17 and to protect the personal information of patients.
To evaluate selected images, 10 male and 10 female students (mean age 20.65 ± 2.41 years) enrolled at Nippon Dental University who had not yet completed a course in smile esthetics in orthodontics were selected as evaluators. Selected images were printed with a 100-mm visual analogue scale.17 The length of the visual analogue scale was measured twice using digital calipers (NTD12-15CX; Mitutoyo, Kawasaki, Japan), and the mean value was used. The 100 images were ranked according to the mean of the visual analogue scale evaluations of smile attractiveness for each image.12 The minimum age was set as 17 years with consideration of growth of the female patients and excluded patients ranked as 8th, 12th, and 87th. The image qualities of the lateral cephalograms for these patients were evaluated by two orthodontists (Y. K. and K. A.). The 20 patients with the most attractive smiles (ranked from 1st to 25th, with the exclusion of the 6th, 15th, and 16th) were defined as the attractive group, and the 20 patients with the least attractive smiles (ranked from 72nd to 100th, with the exclusion of the 73rd, 74th, 75th, 81st, 82nd, 84th, 85th, and 90th) were defined as the unattractive group with appropriate image quality according to the consensus agreement of the two orthodontists (Table 1). Further details of the sampling process were described in a previous article.12
Control Participants
A control group was employed to demonstrate the ethnic norm for Japanese patients as a reference. Two orthodontists initially selected approximately 100 male and female participants with normal occlusion18 from a total population of approximately 4000 students at Nippon Dental University and other related schools. These individuals were selected based on the following inclusion criteria for the initial selection process: age ≥18 years without previous orthodontic treatment; absence of congenital craniofacial anomalies including cleft lip and/or palate; straight profile without strain on the lips; normally erupted permanent teeth from second molar to second molar in the maxillary and mandibular arches with class I relationships without anterior or posterior crossbite and no obvious asymmetry in the dental arch; overbite and overjet ranging from 1 to 4 mm; crowding and space <2 mm; absence of teeth with abnormally shaped crowns; absence of rotated, displaced, impacted, transposed, or prolonged retained deciduous teeth; and healthy periodontal tissue.
The purpose of the present study, the protocol, and the potential risk due to radiation exposure were explained in writing, and approximately 50 females agreed to participate and provided informed consent. Facial photographs (frontal, lateral, three-quarter view at rest, and frontal, three-quarter view at posed smile) and lateral cephalograms of these participants were taken at Nippon Dental University Hospital using the same X-ray machine and camera under identical settings. Image quality was also confirmed by the two orthodontists. Subsequently, the participants meeting the following criteria were further selected: gingival exposure at maxillary anterior teeth in a frontal posed smile photograph of 0 to 2 mm and symmetrical lip morphology and absence of abnormality at rest and at frontal posed smile photographs.
Finally, 20 individuals were selected as the control group (Table 1). All participants in both groups were selected from the same ethnic population in Japan.
Cephalometric Analysis
Lateral cephalograms of orthodontic patients and controls were scanned using the same flatbed scanner as 150-dpi monochrome images in JPEG format. Magnification was automatically adjusted to 1:1, and 41 measurements (14 skeletal, 13 dental, and 14 soft-tissue components) selected based on previous studies11,13–17 were measured using Dolphin Imaging version 11.5 software (La Jolla, Calif; Figures 1–3, Table 2). Cephalograms were taken in the intercuspal position with relaxed lips and facial muscles. Therefore, the position of the mandible and soft-tissue morphology may have differed from those observed during posed smile. Cephalograms were analyzed twice with an interval of at least 1 month by one evaluator (Y. K.), and the mean of the two measurements was used.
Citation: The Angle Orthodontist 88, 6; 10.2319/092017-631.1
Citation: The Angle Orthodontist 88, 6; 10.2319/092017-631.1
Citation: The Angle Orthodontist 88, 6; 10.2319/092017-631.1
Cephalometric Superimposition
The x–y coordinates of the reference points for each patient were exported as text data and imported into Excel 2013 (Microsoft Corporation, Redmond, Wash). All reference points for each patient were individually translated at Sella as the origin and rotated on the Sella-Nasion (SN) line at 7° above the constructed horizontal plane. Medians of the x–y coordinates for all reference points were calculated for each group and superimposed.19,20
Reliability Tests
To calculate and examine intraexaminer errors of cephalometric measurements, 10 cephalograms (five from each patient group) were randomly selected and reanalyzed at an interval of at least 2 weeks by one evaluator (Y. K.). For interexaminer errors, the same cephalograms were reanalyzed by another orthodontist using the same general clinical procedure without a calibration session. Method error was calculated using Dahlberg's formula.21 Maximum intra- and interex-aminer error values were 0.57° (Z angle) and 1.04° (nasolabial angle) for angular measurements, 0.37 mm mandibular central incisor to nasion-point B (L1 to NB) and 0.30 mm (L1 to NB) for linear measurements, and 0.24% (lower facial height/anterior facial height) and 0.26% (lower facial height/anterior facial height) for ratio measurements.
Statistical Analysis
Statistical analysis was performed using SPSS for Windows version 24.0 software (IBM, Armonk, NY). The results of all cephalometric measurements were tested for normality of distribution using the Kolmogorov-Smirnov test. Significant differences from normal distributions were obtained for two cephalometric measurements from the unattractive group (upper lip protrusion and upper lip to E-line), so the medians and interquartile ranges were calculated for each measurement, and the nonparametric Mann-Whitney U-test was used for comparisons between the two patient groups. The significance level was set at 5%.
RESULTS
Skeletal antero-posterior measurements showed no significant differences between the groups. In skeletal vertical measurements, the unattractive group showed significantly larger SN to mandibular plane, palatal plane to mandibular plane, anterior facial height, lower facial height, and lower facial height/anterior facial height when compared with the attractive group (P < .05; Table 3).
For dental anterior-posterior measurements, no significant differences between groups were found. In vertical dental measurements, the unattractive group showed significantly larger occlusal plane to SN, palatal plane to occlusal plane, and maxillary central incisor (U1) to palatal plane than the attractive group (P < .05; Table 3).
In the antero-posterior soft-tissue measurements, no significant difference was seen between patient groups. In soft-tissue and dental vertical measurements, lower face, upper lip length, and upper lip superior to palatal plane were larger in the unattractive group than in the attractive group (P < .05; Table 3).
Using median values of the x–y coordinates of reference points for cephalometric measurements, morphological characteristics were graphically compared between patient groups using superimposed images as shown in Figure 4.
Citation: The Angle Orthodontist 88, 6; 10.2319/092017-631.1
DISCUSSION
Although the smile attractiveness of postorthodontic patients without severe skeletal discrepancies was evaluated from frontal close-up photographs depicting only the area around the lips, significant hyperdivergent tendencies were observed in the unattractive group but not in the attractive group. These findings supported the result of a previous study performed in China.16 However, they did not agree with results from the United States16 and Turkey.15 Such inconsistencies may be attributable to ethnic or cultural differences.16,22,23 Hyperdivergent tendencies are often observed after conventional orthodontic treatment in patients after adolescence,24 and prevention with appropriate treatment options is therefore necessary.25–27 Although hyperdivergent tendencies were observed in the present study, it was not possible to determine whether these were present before treatment. In addition, to create an attractive smile, surgical orthodontic treatment including maxillary impaction osteotomy28 could be recommended as a possible treatment alternative for specific cases with a severe hyperdivergent skeletal pattern.4,11,29
In dental and soft-tissue measurements, significantly larger vertical distance from the palatal plane to the maxillary central incisor edge and longer upper lip length (both approximately 2–3 mm on average) were observed in the unattractive group when compared with the attractive group. This extruded maxillary central incisor and adaption of the upper lip may be attributable to compensation for the hyperdivergent skeletal pattern of the unattractive group.30,31 Although the vertical positions of the maxillary incisors and upper lip are also important factors affecting jaw function and pronunciation, when considering smile esthetics these findings could also be associated with the larger amount of gingival exposure during posed frontal smile or gummy smile in the unattractive group evaluated in the previous study.12 However, the causes of gummy smile include not only the extruded maxillary incisor11 but also the shorter length of the upper lip at rest and when smiling32 and muscular hyperactivity in elevating the upper lip when smiling.10,11,33 Therefore, in addition to the skeletal, dental, and soft-tissue morphologies, activity of the perioral and facial muscles creating the smile could represent another important factor when investigating this issue in future studies.
Although the present study did not evaluate the smile arc, the relationship to the sagittal cant of the occlusal plane has been discussed in previous studies.4,8 Most studies found that ideal consonant and excessive smile arcs were more acceptable than a flat or reversed smile arc.4,6,7,29,34–36 An unfavorable flat smile arc was observed more frequently in patients with a hypodivergent skeletal pattern.10 In contrast, the present study evaluated naturally obtained variations among postorthodontic patients, revealing an approximately 2° to 3° steeper occlusal plane in the unattractive group than in the attractive group. Batwa et al.37 found the most suitable occlusal plane angles to true horizontal for creating an attractive smile were 10° and 15° for patients' and dentists' judgments, respectively, and suggested that a flat occlusal plane angle would be unattractive, as might an overly steep occlusal plane. Therefore, to create an appropriate smile arc as part of an attractive frontal smile, it is considered important to identify excessively inclined occlusal planes during treatment planning and avoid tooth movement that does not produce the desired esthetic results.
CONCLUSIONS
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Cephalometric analysis revealed that unattractive frontal posed smiles in postorthodontic Japanese females are characterized by a hyperdivergent skeletal pattern with extruded maxillary incisors and steep occlusal plane, accompanied by a longer upper lip when compared with patients achieving attractive posed frontal smiles. To provide individual patients with the most esthetically pleasing smile possible, the importance of avoiding a severe hyperdivergent skeletal pattern should be considered during diagnosis and treatment.
Cephalometric analysis, skeletal. CHP indicates constructed horizontal plane.
Cephalometric analysis, dental.
Cephalometric analysis, soft tissue.
Average morphological features by cephalometric analysis in the attractive and unattractive groups.
Contributor Notes