Figure 17.1 (A) (i) Normal lip line, (ii) low lip line and (iii) high lip line. (B) Posed and spontaneous smiles. Greater facial movements are required for the generation of the spontaneous smile which produces greater upper lip elevation and tooth/gingival exposure. (C) Proclination of the maxillary incisors results in a reduction of tooth display at rest and during smiling. Retroclination will have the opposite effect. (D) The smile arc is shown in red. (E) The ideal relationship of the anterior maxillary gingival margins. (F) the ideal (i) embrasure and (ii) connector relationship.
Most patients seek orthodontic treatment to improve their smile aesthetics. With modern orthodontic and restorative techniques, it is possible to improve the appearance of the smile, assuming its individual components are understood. Knowledge of these components is also important for informed consent, as any anatomical limitations in achieving ideal aesthetics should be explained before commencing treatment. This chapter discusses the important components of a smile.
The lip line is the vertical relationship between the upper lip and the maxillary incisors during smiling. Ideally, the full length of the upper incisors and the interdental papillae should be visible during smiling. The lip line is high when a continuous band of gingival tissue is visible and low when less than 75% of the crown height of the central incisors can be seen (Figure 17.1A). The lip line in females is 1–2 mm higher than in males so it is acceptable for females to show 1–2 mm of gingivae anteriorly during smiling.
Many factors influence the lip line and amount of incisor display during rest and smiling:
(1) The type of smile
. The posed smile
is a voluntary
smile, not linked with emotion, that is fairly reproducible. An example of a posed smile is the smile elicited when someone is asked to smile for a photograph. The spontaneous smile
is an involuntary
smile, linked with emotion, where there is maximal elevation of the upper lip (Figure 17.1B
). An example of a spontaneous smile is the smile elicited when somebody is told a funny joke. It is important to assess both the posed and spontaneous smile during examination as the amount of incisor and gingival shown in the latter is greater.
(2) Elevation of the upper lip
. There is individual variation in upper lip elevation during smiling (mean = 7–8 mm). Excessive elevation, also termed hypermobility, results in a hig/>
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