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One of the goals of orthodontic treatment is creating beautiful smiles. We enhance the smile by correcting the relationship of the teeth to the surrounding gums and lips. Hence, we focus our evaluation on three aspects of the smile: the vertical relationship of the lips to the teeth, the transverse dimension of the smile and the smile arc.
Vertical tooth-lip relationships
It is important to display most of the crowns of the upper front teeth on a social smile. The guideline is that at least 75% of the crown should be seen when the patient smiles, and exposure of all the crown and some gingiva is both aesthetic and youthful. Obviously, the goal of treatment should be to position the teeth relative to the upper lip and gums so that they are displayed on smile within these guidelines. Inadequate or excessive display of gingiva on smile is not esthetically pleasing and youthful. Excessive display of maxillary gingiva on smile must be evaluated carefully because of the natural tendency of the upper lip is to lengthen with increasing age (Proffit, W. et al., Contemporary Orthodontics 5th edition, 2007).
Transverse Dimension of the Smile
In narrow or collapsed upper arch, the smile may also appear narrow, which is less appealing. Transverse expansion of the narrow maxillary arch improves the appearance of the smile (Proffit, W. et al., Contemporary Orthodontics 5th edition, 2007).
The Smile Arc
The smile arc is defined as the relationship of the curvature of the incisal edges of the maxillary incisors and canines to the curvature of the lower lip in the posed smile. The ideal smile arc has the maxillary incisal edge curvature parallel to the curvature of the lower lip. Evaluation of anterior smile esthetics must include both static and dynamic evaluations of the profile, frontal, and 45° views to optimize both dental and facial appearance in orthodontic planning and treatment (Sarver, 2001).
An asymmetric smile sometimes is a patient's major concern. It is possible that this is due to more eruptions of the teeth or different crown heights on one side, and if so repositioning the teeth or changing the gingival contours should be included in the treatment plan (Proffit, W. et al., Contemporary Orthodontics 5th edition, 2007).
Treatment plans for problems relating directly to the appearance of the teeth fall into three major categories: 1) reshaping teeth to change tooth proportion and/or correct "black triangles" between the teeth; 2) orthodontic preparation for restorations to replace lost tooth structure and correct problems of tooth shade and color; and 3) reshaping of the gingiva (Proffit, W. et al., Contemporary Orthodontics 5th edition, 2007).