A Voice in the Arena: Lip Trapping by Dr. Chad Foster

Categories: Orthodontics;
A Voice in the Arena: Lip Trapping  

The curious aesthetics of lip-trapping compensation in mandibular-deficient patients

by Chad Foster, DDS, MS, editorial director

Much attention is paid to the upper lip and the nasolabial angle as they relate to soft-tissue profile aesthetics, but the lower lip is obviously important to consider as well.

In some mildly mandibular deficient Class II patients with excess overjet, “lower lip trapping” (lower lip resting against upper incisors) occurs as compensation by the soft tissue, which to some degree can serve to “mask” the underlying hard-tissue deficiency. In some of these cases it can present as a favorable aesthetic profile compensation. Observe this in the two patients here, in both photos and cephalometric X-rays.

As the lower lip reaches and rolls forward, it not only gives a more forward (Class I) appearance of the lower lip—to visualize, cover everything below the lower lip of these two patients and assess profile—it also significantly increases the “projected” surface area of the lower lip vermilion display as the lip rolls forward and down.

In the two cases below, this sensitive lower lip position is wholly dependent on the AP position of the upper incisors, as evident on ceph. Most often in these cases, advancing the mandible is ideal, but if not an option (adult patients who decline surgery), special attention should be given to any amount of upper incisor retraction if attempting to dentally camouflage the skeletal disharmony—particularly if the upper incisors are in a good position. What do we expect to happen to this “masking” if the uppers come back at all? The lower lip is actively resting on the upper incisor; it is not passively positioned there, which more so would be the case in a normal mandible where mild upper incisor retraction might have less effect on the aesthetic AP position and vermilion display of the lower lip. As the upper incisors go back, so will the lower lip as it decompensates, which can be at the expense of the lower lip aesthetic presentation. Keep in mind that lower lip pressure on incisors is 2½ times that of upper lip pressure.1

Our treatment plans should consider not just fixing what is bad, but also protecting what is good. Sometimes nature has a subtle way of doing what is best in a compromised situation. I think this concept applies in how we should treat some unique presentations of overjet/lip trapping. Obviously, not in every case is lip trapping an aesthetic benefit! Often it can be quite unaesthetic. How it presents in each case is quite unique, which demands our unique appreciation of each individual presentation.

A Voice in the Arena: Lip Trapping
A Voice in the Arena: Lip Trapping

1. Southard, Thomas E., et al. “Orthodontics in the Vertical Dimension.” Wiley Blackwell, 2015

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