Observation of the smile is important for the orthodontist to analyze its characteristics. However, direct measurement will allow the orthodontist to evaluate the lip-tooth relationship during movement and at rest. Measurement of the resting and dynamic lip-tooth position is necessary to smile visualization because this will help translate the smile characteristics into quantifiable terms needed to develop the orthodontic treatment plan.
The required frontal measurements at rest are the following:
– Philtrum height: measured in millimetres from subspinale to the most inferior portion of the upper lip on the vermilion tip
– Commissure height: measured from a line constructed from the alar bases through the subspinale and then from the commissures perpendicular to this line
– Interlabial gap: the distance in millimetres between the upper and lower lips
– Amount of incisor display at rest
On the other hand, the required frontal measurements of the posed smile are the following:
– Amount of incisor display on smile
– Crown height and width. In most references, the central incisors are specified to have approximately an 8:10 width/ height ratio.
– Gingival display (if present)
– Smile arc: 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.