Point B (supramentale): the mandible reference in profile
Quick facts
- Definition
- Deepest point of the anterior concavity of the mental symphysis, between the alveolar ridge and the pogonion.
- Abbreviation
- Point B or supramentale.
- Associated measurements
- SNB (position of the mandible) and ANB (difference between maxilla and mandible).
- Use
- Profile cephalometry, orthodontic and surgical planning and reading of the lower third.
Point B, or supramentale, is a cephalometric point located at the front of the mandible. On the profile X-ray, it corresponds to the deepest point of the concavity between the alveolar ridge of the lower incisors and the bony chin, at the mental symphysis. It is the counterpart of point A, on the maxilla.
How is point B used?
Point B serves to describe the anteroposterior position of the mandible relative to the skull base. It takes part in two measurements that have become almost a common vocabulary in orthodontics.
| Measurement | Calculation | General reading |
|---|---|---|
| SNB | Angle between sella, nasion and point B | Position of the mandible in profile |
| ANB | SNA minus SNB | Relationship between maxilla and mandible |
| Wits | Distance between projections of A and B on the occlusal plane | Alternative to ANB |
Reference values vary between authors and populations, and the interpretation belongs to whoever makes the diagnosis. In general terms, an increased ANB is associated with a Class II relationship, and a reduced or negative ANB with a Class III one. See cephalometry.
Why does it matter in HOF?
The chin is one of the most requested areas in harmonization. Many complaints of a "small chin" originate in the relationship between the bony bases, and not only in the chin.
- Retrogenia and micrognathia: in cases of retrogenia (a recessed chin) or micrognathia, point B is set back relative to the maxilla, and the profile looks "chinless". Filler can adjust the appearance, within limits.
- Pogonion and point B: the pogonion is the reference for chin projection in soft tissue. Point B gives the bony position just above it and helps explain the transition between the lower lip and the chin.
- Expectations: a patient with a major bony discrepancy needs to know that harmonization is complementary, and that correcting the base may require orthodontics or surgery.
- Mentolabial sulcus: the depth of the groove between the lower lip and the chin depends on bone and soft tissue.
How do you talk to the patient?
Technical vocabulary does not help in the office, but the idea does: the chin is part of a larger structure. Explaining that "your chin sits a little behind the line of your lips because of the position of the bone" makes the conversation clearer than promising an effect with no basis.
Also called: supramentale, B point.
Frequently asked questions
What is the difference between point B and the pogonion?
Point B is the concavity above the chin, in the alveolar part of the symphysis. The pogonion is the most forward point of the bony chin. The two describe the mandible in different ways.