Mentolabial angle: lower lip and chin
- Nerve
- Highlighted area
Quick facts
- Definition
- Angle, seen in profile, between the tangent to the lower lip and the tangent to the chin, with its vertex at the mentolabial fold.
- Cited reference
- Values vary between authors and populations; ranges around 120 to 130 degrees appear often.
- Sharp angle
- Deep mentolabial fold, everted lower lip or prominent chin.
- Open angle
- Shallow fold, flat transition between lip and chin, common with a recessed chin and a tense lower lip.
- Relevance in HOF
- Helps decide between projecting the chin, treating the fold or working on the lower lip.
The mentolabial angle is the angle formed, in profile, between the line tangent to the lower lip and the line tangent to the chin, with its vertex at the deepest point of the mentolabial fold. It describes how the lower lip connects to the chin. A sharp angle indicates a deep fold and a projecting lower lip; an open angle indicates a flat transition, often with a recessed chin.
How is it measured?
On a standardized profile photo, with the head in natural position and the lips at rest:
| Line | Where it runs |
|---|---|
| Labial | From the most anterior point of the lower lip to the deepest point of the mentolabial fold |
| Mental | From the deepest point of the fold to the most anterior point of the chin (soft tissue pogonion) |
Reference values vary between authors and populations. Ranges around 120 to 130 degrees appear often in the orthodontic and surgical literature, but the number alone does not define harmony. The most anterior point of the chin is described under pogonion.
What does a sharp or open angle indicate?
| Situation | Angle | Common findings |
|---|---|---|
| Deep fold | Sharp | Everted lower lip, prominent chin, sometimes a deep bite |
| Flat transition | Open | Recessed chin, tense lower lip, mentalis contraction when closing the mouth |
| Balanced profile | Intermediate | Smooth, curved transition between lip and chin |
The angle also depends on the teeth and bones: the inclination of the lower incisors, the position of the mandible and the height of the lower third change the support of the lip. In cases of significant skeletal alteration, orthodontic or surgical assessment is part of the conversation.
Why does it matter in HOF?
- Recessed chin: an open angle, with retrogenia, suggests that chin filler may improve the relationship between lip and chin.
- Deep fold: treating only the fold, without looking at the chin and lip, can leave the profile out of proportion.
- Overactive mentalis: contraction of the mentalis muscle, with an "orange peel" chin, changes how the area reads. The topic is covered in mentalis toxin.
- Lower lip: enlarging the lower lip sharpens the angle; in someone who already has a sharp angle, this calls for caution.
How does it show up in the assessment?
- Profile at rest: the basis of the measurement; avoid photos with contracted lips.
- Lips closed with effort: if the mentalis contracts, there is lip tension to consider.
- Relation to other references: the nasolabial angle, the Ricketts line and the cervicomental angle complete the reading of the facial profile.
Also known as: labiomental angle, soft tissue mentolabial angle, mentolabial angle.
Frequently asked questions
What is the normal mentolabial angle?
There is no single value. Ranges around 120 to 130 degrees appear often in the orthodontic and surgical literature, but the numbers vary with the method, sex and ethnicity. The angle should be read together with the rest of the profile.
Are the mentolabial angle and the mentolabial fold the same thing?
No. The mentolabial fold is the depression between the lower lip and the chin. The mentolabial angle is the measurement, in profile, of the lines that pass through the lip and the chin, with its vertex at that fold.