The paradigm shift from occlusion to esthetics emphasizes the interplay between dental structures and the surrounding soft tissue envelope. The objective of this study was to quantify the ideal and maximum acceptable deviation for nine smile characteristics by using digital manipulation of hard and soft tissue smile components. Intraoral photographs were manipulated using Adobe® Photoshop® CS2 to alter buccal corridor, smile arc, gingival display, crown torque in maxillary canines and the posterior buccal segments. Smiles were placed in a gender neutral face showing nasal tip to mentolabial fold. Quask™ Form Artist was used to generate the survey, which was administered in Columbus, OH (n=43); Seattle, WA (n=41) and Boston, MA (n=40). An interactive interface allowed raters to move a slider to answer questions. Rater reliability was assessed for each variable.
We found that, in general, raters were reliable (K = 0.5-0.8). Survey location was not significant except for the finding that the West coast accepted a broader smile (1.5 mm buccal corridor) than the Midwest and East coasts where the buccal corridor was found to be too minimal at 6 mm.
Rater preference for ideal and the threshold of acceptability is outlined below.
1. SMILE ARC: Cusp tips of the maxillary 2nd molars were 7.2mm above the incisal edges of the maxillary central incisors.
2. SMILE ARC UNACCEPTABLE: >7.9mm and <2.6mm above the incisal edges.
3. BUCCAL CORRIDOR IDEAL: 5.8 mm each side (16%).
4. BUCCAL CORRIDOR UNACCEPTABLE: >9.4 mm (26%) and <2.9 mm (8%) of dark space.
5. GINGIVAL DISPLAY IDEAL: 2.1mm (-2.1mm gingival display) central incisor coverage by upper lip.
6. GINGIVAL DISPLAY UNACCEPTABLE: >3.6mm of gingival display and 4mm of incisal coverage.
7. CANINE TORQUE, IDEAL CORRIDOR: -1 degree considered ideal with acceptable range of +10 to -7 degrees.
8. CANINE TORQUE, LARGE CORRIDOR: -4 degrees considered ideal with acceptable range of +8 to -10 degrees.
9. POSTERIOR TORQUE, IDEAL CORRIDOR: +4 degrees considered ideal with acceptable range of +5 to -7 degrees.
10. POSTERIOR TORQUE, LARGE CORRIDOR: +6 degrees considered ideal with acceptable range of +5 to -8 degrees.
We concluded that, overall, the preference of raters in different locations was not clinically significant and that raters displayed a wide range of acceptability for canine and posterior tooth crown torque in both narrow and broad smiles. This is a reliable method for determining individual smile characteristic preferences. Due to the wide range of acceptability for the ideal and threshold values for most variables, clinicians must be aware of individual preferences for each specific patient and should probably avoid sensitization of patients to smile characteristic deviations that fall within the acceptable range. The findings of this study can be used by clinicians as both a guideline toward ideal orthodontic finishes and acceptable compromise.