What the terms actually describe
SNA and SNB are angles from Steiner's cephalometric analysis, each formed between three points traced on a lateral (side-view) skull X-ray:
- Sella (S) — the center of the pituitary fossa, deep inside the skull.
- Nasion (N) — the junction of the nasal and frontal bones.
- Point A / Point B — the deepest points on the bony curve of the upper jaw (maxilla) and lower jaw (mandible).
SNA measures how far forward the maxilla sits relative to the cranial base; SNB does the same for the mandible. The difference between them, ANB, is used to classify skeletal Class I, II, or III jaw relationships — the same recession/protrusion question the Ricketts E-line and gonial angle pages also touch, from different angles.
Where it comes from
SNA and SNB were introduced by American orthodontist Cecil C. Steiner in his 1953 paper "Cephalometrics for You and Me," published in the American Journal of Orthodontics. Steiner's analysis remains one of the most widely taught cephalometric systems in orthodontic education today — a diagnostic and surgical-treatment-planning tool, not a beauty scale.
Commonly cited norms are SNA around 82 degrees and SNB around 80 degrees, each with roughly a 2-degree spread.
Why it can't be read from a photo
This is the central limitation, and it's a bigger problem than the usual population-norm caveat: Sella, Nasion, and points A and B are bony landmarks inside the skull. None of them is visible in a photograph, a side-profile selfie, or a webcam frame — only on an actual radiograph, traced by someone qualified to read one.
Estimating SNA or SNB "by eye" from a photo isn't a simplified version of the measurement; it's a different activity that happens to share a name with it, since the reference points it depends on simply aren't there to measure.
Why the quoted "ideal" also doesn't generalize
Even for someone with an actual radiograph, the commonly cited 82°/80° figures come from Steiner's original, largely Caucasian reference sample. Later population-specific cephalometric studies — on Indian, Arab, Malay, and Vietnamese samples, among others — found meaningfully different average SNA and SNB values, with several of those papers stating outright that applying one population's norms to another isn't appropriate.
That's the same caution this site applies to any single quoted "ideal" figure, the same point made about the golden ratio face template and the Ricketts E-line.
Where this fits next to what Mogalytics actually reads
Mogalytics does not compute or display SNA, SNB, or ANB. Its six-measurement composite reads live from a front-facing camera feed, and the closest measurement in the same skeletal-projection family is:
- Jaw ratio — jaw height relative to face height, read frontally from visible soft tissue, not skeletal projection from a radiograph.
Jaw ratio and SNA/SNB both speak to how the jaw and midface relate to each other, but they're measuring different things with different instruments — one is a live camera-based proportion, the other is a clinical X-ray angle. Mogalytics makes no claim of parity between the two, or with any clinical cephalometric or radiographic analysis. See the accuracy page for the general limits of any camera-based reading.
Related reads
SNA/SNB sits alongside the other clinically-sourced terms this site covers, plus the closest of the six live measurements. If you're auditing the rest:
- Jaw ratio — the closest camera-read analog, a frontal soft-tissue proportion rather than a skeletal X-ray angle.
- Ricketts E-line — another side-profile orthodontic standard with population-specific norms, measured from a photo rather than a radiograph.
- Gonial angle — another side-profile-only term Mogalytics doesn't compute directly.
- Chin-to-philtrum ratio — a different lower-face ratio in the same jaw family, read frontally.
- Accuracy — what a camera-based reading can and can't tell you, generally.