Patient Selection

The subjects enrolled in this study were recruited from the Graduate Orthodontic Clinic during a routine posttreatment appointment (ie, final records or retention check). Each adult subject (≥18 years old) reviewed and signed a consent form created in accordance with guidelines of the Health Sciences Institutional Review Board (IRB). Each subject under the age of 18 years reviewed and signed a child's assent form, and a legal guardian reviewed and signed a consent form in accordance with the IRB. Each subject also reviewed and completed a consent form created by the university in accordance with the Health Insurance Portability and Accountability Act for the use and disclosure of protected health information. None of the subjects received compensation for their participation.

To be included in the study, patients had to present with the following characteristics: (1) age ranging from 12 to 20 years; (2) Caucasian ancestry; (3) orthodontic treatment completed within the previous 6 months; (4) absence of missing or malformed teeth; and (5) a complete set of diagnostic posttreatment records, including study models, panoramic radiograph, and intra- and extraoral photographic series.

The protocol used in this investigation required that 48 subjects be recruited to satisfy the design of the Q-sort. A test was performed to determine the power of this sample size with respect to correlation tests (Type I error = 0.05). For a bivariate normal distribution and a sample size of 48, a test of H₀: P = 0 (ie, the correlation coefficient under the null hypothesis) was found to have a power of 0.80 to detect a linear correlation of r = 0.38. Thus, the default sample size for the Q-sort procedure was deemed adequate for purposes of testing for correlation.

Image Capture

All photographs were taken by 1 of 2 staff photographers. The extraoral photographic series included photographs of the subject in repose, during smiling, and in profile. For the purpose of the current study, only the extraoral smiling photographs were used. A Canon EF 35 mm SLR camera (Canon USA Inc., Lake Success, NY) was mounted to a frame set at a fixed distance of 36 inches between the lens and the subject. The camera was connected to a 1-strobe lighting source that illuminated the subject indirectly from a flash that reflected off a photographic umbrella. Before taking the smiling image, the photographer instructed the subject to “smile.” The reproducibility of the posed smile derived from static photograph has been demonstrated by Ackerman et al.4 Each image was captured on Kodak EV-100 slide film (Eastman Kodak Co., Rochester, NY).

The film was developed and the 2-in × 2-in slides were scanned using the Nikon Super Coolscan 4000 ED (Nikon Inc., Melville, NY) and imported directly into a commercially available image editing software program (Adobe Photoshop 7.0, Adobe Systems Inc., San Jose, CA). Each slide was scanned at maximum dots per inch to enhance the image quality. A 3-in × 5-in template was created to standardize the size and location of each image. Images were opened in Photoshop, and the template was superimposed on top of the image (Figure 1). The smile images were enlarged until the outer commissures of the lips matched the vertical tick-marks inset three-quarters of an inch from the border of the template. The smiling images were then positioned so that the maxillary incisal edges coincided with the horizontal line of the template.

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After enlarging and positioning the images, the portion of the image outside the template was cropped. The resulting images were edited further in Photoshop using the healing brush tool to remove blemishes, skin irregularities, or other extraneous marks that could influence the rater when evaluating the image. Images were labeled with a unique 4-digit number chosen randomly. Once the editing was complete, each image was compressed to approximately 150 KB and saved as a JPEG file.

Rater Selection

Both orthodontists and parents of orthodontic patients rated the smile images. The orthodontic panel was comprised of 25 full- and part-time orthodontic faculty members recruited from the University of Michigan Graduate Orthodontic Program. This panel consisted of 15 male and 10 female orthodontists whose clinical experience ranged from 1 to 35 years, with an average of 17 years. Their ages ranged from 29 to 64 years, with an average age of 46 years. Sixteen of the panelists were certified by the ABO. Of the 25 orthodontic raters, 13 were graduates of the University of Michigan and two had received their orthodontic specialty training internationally.

The nonorthodontic panel comprised 20 parents whose children were currently undergoing orthodontic treatment in the Graduate Orthodontic Clinic. This panel consisted of 12 women and eight men whose ages ranged from 36 to 52 years, with an average of 43 years. Of the 20 parent panel members, nine had undergone orthodontic treatment themselves.

Because a related study has shown that orthodontists and lay panelists score smile images in a similar way with regard to the level of attractiveness,5 the findings of the two groups of raters were pooled (N = 45) for the purpose of this study.

The Q-Sort method

The Q-Sort method, originally proposed by Stephenson in 1953,6 represents an alternative approach that generates a valid 9-category ordinal ranking of large samples based on a variety of subjective criteria. The Q-sort method uses a progressive forced-choice winnowing of the sample to create a quasinormal distribution, in this instance rating smile images on an esthetic scale from “least pleasing” to “most pleasing.” Although originally intended for a sample size of 96, the Q-sort technique has been applied to samples of 48 to rank items according to complex, subjective criteria.7

Panelists were asked to apply the Q-sort technique to rate the attractiveness of the series of 48 subjects on the smile images captured with clinical photography. Rating sessions for the parents coincided with consecutively scheduled orthodontic appointments, while the rating sessions for the orthodontists occurred sporadically over a 2-month period.

Each panelist was asked to select and organize groups of images in a specific order (Figure 2). From the 48 images, the two least and most attractive smiles were identified and placed into their respective columns. The raters then selected the four least and most attractive smiles, followed in a similar manner by the five and then the eight smile photographs from each extreme, leaving the 10 smiles presumably of neutral attractiveness. Each rater was also asked to survey the distribution and establish a cutoff point between two columns separating “unattractive” from “attractive” smiles.

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The assignment of scores to each Q-sort distribution is depicted in Figure 2. The X-axis represents the score assigned to each photograph in a given group; and the Y-axis, the number of subjects. Each of the nine groups of images were given a score ranging from 0, for the two images with the least perceived attractiveness, to 8, for the two images with the greatest perceived attractiveness. The scores each subject received from the various judges were averaged to generate each subject's overall Q-score for the smile captured with clinical photography.

The cutoff point separating the unattractive and attractive images was also given a numeric value. For example, a line drawn between columns 2 and 3 on the Q-sort distribution was given a score of 2.5 (Figure 2), which represented the esthetic boundary for that panel member. The cutoff points received from the various judges were averaged to generate the overall demarcation between attractive and unattractive images.

ABO Grading System Assessment

One of the investigators (Dr Jamieson, a calibrated grader and a director of the ABO) scored the posttreatment dental casts and panoramic radiographs of all subjects according to the guidelines of the ABO Objective Grading System.1 Specifically, study models were evaluated according to the following characteristics: alignment, occlusal contacts, marginal ridges, occlusal relationships, buccolingual inclination, overjet, and interproximal contacts; panoramic radiographs were evaluated for root parallelism. The individual component and combined scores generated from the ABO Objective Grading System of each subject served as a measure of each subject's occlusal outcome.

Statistical Analysis

Standard descriptive statistics (means, standard deviations, and ranges) were calculated for age and for Q-sort scores, esthetic boundary cutoff scores, and components of the ABO Objective Grading System. The relationship between the occlusal outcome and perceived smile attractiveness of the subjects was evaluated by means of a Pearson product-moment correlation. Specifically, the individual component and total combined scores of the ABO Grading System were evaluated against the average combined Q-scores of smiles captured with clinical photography. Logistic regression was used to evaluate whether the individual component or total combined scores of the ABO Grading System could predict whether a smile would be attractive or unattractive.

The Type I error rate for all statistical tests was set at 0.05. All statistical tests were performed with the aid of a statistical software program (SPSS; Statistical Package for the Social Science for Windows, version 12.0, Chicago, Ill).