Among the aspects of the face often overlooked during esthetic procedures are the lips of a patient. In reality, the lips create the frame for the teeth just like a picture frame does for a piece of art. I’m sure many of you have taken a photograph to a frame shop and have evaluated multiple frames to see what looks best. You’re able to note that as certain parameters of the frame are changed, so is the appearance of the artwork. This is also true for smiles.

lip symmetry smiling dentistry

As a general rule, I evaluate two primary areas concerning the lips: the way they move (what I will call symmetry) and their thickness or fullness. In this day and age, it is of course necessary to determine if the patient has any plans to alter their lips for the following evaluation to have value in planning treatment. If they do have plans to use fillers, or any other procedure that alters the lips, I would prefer they be done prior to the dental procedures.

Upper lip symmetry in a full smile

My first evaluation begins with viewing the upper lip as it moves from rest to a full smile. Is it symmetrical in its movement, or does one side rise further up than the other? Research has shown that around 30 percent of adults have some form of lip asymmetry, so it is very common. The challenge is that if one side rises further up, it means that side will show more tooth and potentially more gingival display in a full smile.

It is possible to improve this asymmetry unilaterally with Botox, ensuring the higher side doesn’t move as much, but most patients don’t choose the Botox correction. In reality, what this means is that we need to counsel the patient about how common this finding is and that it simply means they will always have a slight asymmetry to their smile. In other words, I don’t let the upper lip asymmetry alter my tooth position choices or gingival levels.

​Smile symmetry in the lower lip

My next evaluation is to watch the lower lip move from rest to a full smile, again looking for symmetry. If the lower lip is asymmetric in its movement, it can be problematic for the tooth position ultimately chosen.

As dentists, we often talk about using the interpupillary line as a reference for leveling the incisal plane-occlusal plane, but the eyes are quite a distance from the edges of the teeth; it is actually quite difficult to look at the eyes and teeth at the same time.

In addition, it is not uncommon for a patient to have significant asymmetry in the levels of one eye relative to the other. I find the most important thing determining the incisal plane is not the interpupillary line, but the relationship of the teeth to the lower lip; a pleasing smile line, if you will.

lip symmetry esthetics dentistry
FIG 1: This patient has symmetric upper and lower lips and a pleasing, level smile line.

This becomes challenging if the lower lip is asymmetric, as creating what you perceive as a level occlusal plane relative to the eyes can create an unattractive smile line relative to the lower lip. In these instances, the lip does alter how I position the teeth.

The role of asymmetry in treatment planning

lip asymmetry facial esthetics
FIG 2: This patient has a maxillary reconstruction with anterior veneers and posterior crowns.

In the figure above, the patient's lower lip has a significant asymmetry during a full smile, going up much more on the left and down on the right. My original diagnostic wax-up and provisional restorations were done parallel to her interpupillary line, but it became clear almost immediately after the provisional restorations were placed that it wasn’t a pleasing incisal plane in relation to her lower lip.

I modified the provisional, shortening the left lateral, canine and premolars until in a full smile the relationship was more pleasant. A model of the corrected provisional was then sent to the laboratory to communicate the correct tooth position. Obviously in shortening the teeth visually, it is still necessary to maintain an acceptable functional relationship. The teeth don’t follow her lip exactly because the amount of lip asymmetry is too great for that, but they do have a pleasant relationship to the lip.   

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Commenter's Profile Image Gerald Benjamin
September 7th, 2013
The significance and power of the direct resin mockup at the consultation appointment is frequently overlooked by dentists. The placement of resin on the incisal edges would have allowed the dentist, patient and ceramicist to precisely and predictably KNOW where the edges needed to be placed in relation to the asymmetrical movement of the lips. The results in this case are fabulous. A careful examination would reveal that the attention paid to the asymmetric lips resulted in a slight reverse smile which neither a negative nor a detraction in this case. Many years ago Frank and I had a discussion in which it was agreed that the more attractive your patient is, the less the small negatives in the final results matter. It is rare that we can 'get away with' a reverse smile but this case demonstrates that it can be done! Fabulous results