Smile characterization by U.S. white, U.S. Asian Indian, and Indian populations

With growing demand for high esthetic standards, dentists must understand patient perception and incorporate their preferences into treatment. However, little is known about how cultural and ethnic differences influence esthetic perception.

The purpose of this study was to determine whether differences in ethnic background, including the possibility of assimilation, affected a layperson's perception of esthetic and smile characteristics.

A survey was developed containing images that were digitally manipulated into a series of barely perceptible steps, changing 1 smile parameter to form a strip of images that displayed that parameter over a wide range. Data were collected with a customized program which randomly displayed a single image and allowed the subject to use the mouse to adjust an on-screen slider according to displayed instructions, that is, "Please move the slider to select the image you find to be most ideal"; or "Please move the slider to select the first image that you find unattractive." A convenience sample (n=288) comprised of U.S. whites, U.S. Asian Indians, and Indians living in India was surveyed. This sample provided a power of .86 to detect a difference of ±1.5 mm. Subjects evaluated images showing the smile arc, buccal corridor, gingival display, vertical overlap, lateral incisal step, maxillary midline to midface, and maxillary to mandibular midline. Rater reliability was assessed with the Fleiss-Cohen weighted Kappa (Kw) statistic and corresponding 95% confidence interval after each question was repeated in a random sequence. Choice differences due to ethnicity were assessed with a multiple randomization test and the adjusted P value with the step-down Bonferrroni method of Holm (α=.05).

The Kw for the 17 variables in all 3 groups ranged from 0.11 for ideal vertical overlap to 0.64 for ideal buccal corridor space. Overall reliability was fair to moderate. Differences attributed to ethnicity were demonstrated between the Asian Indians and U.S. whites. Differences attributed to assimilation were demonstrated between U.S. Asian Indians and Asian Indians. Differences between U.S. Asian Indians and U.S. whites can be instructive and demonstrate the relative power of ethnicity and assimilation. A difference between these groups shows the power of ethnicity and no difference between these groups shows the power of assimilation. The ratings of the Asian Indians and the U.S. whites showed a clinically significant difference for Ideal Buccal Corridor and Maximum Smile Arc. There were no significant differences between the U.S. Asian Indians and Asian Indians. There were clinically significant differences between the U.S. Asian Indians and U.S. whites only for Ideal Buccal Corridor.

Ethnicity had a significant effect on the esthetic choices for Buccal Corridor and Smile Arc. There is no conclusive evidence for assimilation.