An esthetic evaluation of lip-teeth relationships present in the smile

Abstract

This study was initiated in an attempt to obtain some information about two questions: (1) Are the smiles of orthodontically treated patients as attractive as those of persons with “normal occlusion”? (2) What relationship between the lips and teeth, if any exists, should the orthodontist consider in positioning the anterior teeth during orthodontic treatment?Forty subjects, twenty with orthodontically treated occlusions and twenty with “normal occlusions,” were evaluated. There were ten male and ten female subjects in each group. Standardized black and white photographs of their smiles, with the areas surrounding the smiles masked out, were evaluated by a panel of ten men and ten women. No photographs of the smiles of patients prior to orthodontic therapy were used.Five basic components of each smile were studied: (1) the smile line ratio, that is, the congruency of the arc of curvature of the upper border of the lower lip and the arc of curvature of the incisal edges of the upper anterior teeth; (2) the smile symmetry ratio, whether or not the lips on each side of the smile midline were symmetrical with each other; (3) the buccal corridor ratio, the ratio of the width between the canine teeth to the width of the smile; (4) the height of the upper lip, determined by the relationship of the upper lip to the gingival margin of the upper central incisor; and (5) the curvature of the upper lip, whether or not the corners of the smile were above, even with, or below the midline of the upper lip.The following observations were made: 1.1. As a result of the panel members' evaluations, orthodontically treated subjects had significantly poorer smile scores than the subjects with “normal occlusion.”2.2. The smile line ratio appeared to be of importance to an attractive smile, and the most attractive smile displayed a smile line ratio of 1.00 to 1.25 or near perfect harmony between the arcs of curvature of the incisal edges of the upper incisors and the upper border of the lower lip.3.3. The smile symmetry ratio was revealed in this study to be important to a good smile, since no smiles that were asymmetrical had high smile scores.4.4. The buccal corridor ratio appeared to be of no significance to an attractive smile.5.5. The height of the upper lip to the upper central incisor influenced the rating of the smile, the most attractive smiles having the upper lip at the height of the gingival margin of the upper central incisor.6.6. In the subjects studied, the upper lip curvature was most desirable when the corners of the smile were above the midline of the upper lip. However, those smiles in which the corners of the smile were below the midline of the upper lip were attractive if they possessed the most desirable relationships of each of the other components.Further evaluation of these and other components of the smile should lead to the development of a “smile index,” so that the orthodontist may be better able to give the patient an “ideal smile” which would be an expression of the optimum in facial esthetics for that individual.