This current study investigated which angle of canine inclination (angle between canine tooth axis (CA-line) and the line between the lateral canthus and the ipsilateral labial angle (EM-line)) is perceived to be most attractive in a smile. The second objective was to determine whether laymen and dental experts share the same opinion. A Q-sort assessment was performed with 48 posed smile photographs to obtain two models of neutral facial attractiveness. Two sets of images (1 male model set, 1 female model set), each containing seven images with incrementally altered canine and posterior teeth inclinations, were generated. The images were ranked for attractiveness by three groups (61 laymen, 59 orthodontists, 60 dentists). The images with 0° inclination, that is CA-line (maxillary canine axis) parallel to EM-line (the line formed by the lateral canthus and the ipsilateral corner of the mouth) (male model set: 54·4%; female model set: 38·9%), or -5° (inward) inclination (male model set: 20%; female model set: 29·4%) were perceived to be most attractive within each set. Images showing inward canine inclinations were regarded to be more attractive than those with outward inclinations. Dental experts and laymen were in accordance with the aesthetics. Smiles were perceived to be most attractive when the upper canine tooth axis was parallel to the EM-line. In reconstructive or orthodontic therapy, it is thus important to incline canines more inwardly than outwardly.

Test statistic valuesFrequency 0 100 200 300 60 70 80 90 100 110 Figure S1.Histograms for the values of the L 3 -statistic, considering 4 objects, 60 judges per group, W=0.82, under various scenarios (1,000 simulated data sets each). Bandwidth is equal to 1 in all histograms. In each iteration, the value of the L 3 -statistic for a three-group combination with newly generated groups under the same parameters was calculated. The scenarios in detail: One group with three transpositions in fixed ranking (light-gray), one group with two transpositions in fixed ranking (dark-gray), one group with a single transposition in fixed ranking (white), all groups have the same fixed ranking (black), maximum of L 3 for 4 objects (gray diamond).