Point A (subspinale): the maxilla reference in profile
Quick facts
- Definition
- Deepest point of the anterior concavity of the maxilla, between the anterior nasal spine and the alveolar ridge.
- Abbreviation
- Point A or subspinale, also called Downs' A.
- Associated measurement
- SNA angle (sella, nasion, point A), which indicates the anteroposterior position of the maxilla.
- Use
- Profile cephalometry, orthodontic and surgical planning, and reading of the midface.
Point A, or subspinale, is a cephalometric point. On the profile X-ray (lateral cephalogram), it marks the deepest point of the concavity at the front of the maxilla, between the anterior nasal spine and the alveolar crest, above the upper incisors. It serves as a reference for locating the maxilla in the anteroposterior direction.
How is point A used?
Cephalometry uses points, lines and angles to describe the relationship between the bones of the face. Point A is one of the most cited because, together with point B, it summarizes the relationship between the maxilla and the mandible.
| Measurement | What it relates | General reading |
|---|---|---|
| SNA | Skull base and point A | Position of the maxilla: more forward or more backward |
| SNB | Skull base and point B | Position of the mandible |
| ANB | Difference between SNA and SNB | Relationship between the two bases |
Reference values vary between authors, populations and ages, and the interpretation belongs to whoever makes the orthodontic or surgical diagnosis. Cephalometry is a tool for analyzing the skeleton and should be read together with the clinical exam.
Why does point A matter in HOF?
The orofacial harmonization (HOF) professional rarely measures point A, but uses the reasoning it represents.
- Midface and upper lip: the position of the maxilla supports the upper lip, the nasolabial fold and the base of the nose. A more posterior maxilla is usually associated with a more retracted lip and a look of lacking support.
- Relationship with point B: differences between the bony bases appear in Class II and Class III. They explain profiles in which the chin seems small or large, without the problem being in the chin.
- Realistic expectations: when the concern comes from a bony discrepancy, filler can help with appearance, but it does not replace orthodontic or surgical treatment.
- Nasolabial angle and subnasale: reading the nasolabial angle and the subnasale depends on the position of the maxilla.
How do you separate a bony cause from a soft-tissue cause?
The challenge is to identify whether the concern is bone (position of the maxilla or mandible), teeth (incisor inclination) or soft tissue (lip, fat, skin). The lateral cephalogram answers part of this. The clinical exam and standardized photos answer the rest.
Also called: subspinale, Downs' A point, A point.
Frequently asked questions
What is point A used for?
On the profile X-ray, it marks the position of the maxilla. Compared with point B (mandible), it indicates whether the relationship between the bony bases is balanced, retrusive or protrusive.