Cephalometric Analysis Explained: Landmarks, Measurements, and How AI Tracing Works

Cephalometric analysis turns a lateral skull X-ray into numbers: a set of angles and distances that describe how the jaws relate to the skull base, how they relate to each other, and where the teeth sit within them. Those numbers anchor orthodontic diagnosis — they're how "the lower jaw looks small" becomes a measurable, trackable, defensible finding.

The landmarks

Everything starts with landmarks — defined anatomical points identified on the lateral ceph. The core set every analysis builds on:

• Sella (S) — center of the sella turcica; one end of the cranial base reference line.
• Nasion (N) — the frontonasal suture; the other end of the S-N reference line.
• A point — deepest concavity of the anterior maxilla; represents the maxillary basal bone.
• B point — deepest concavity of the anterior mandible; represents the mandibular basal bone.
• Pogonion, Menton, Gnathion — the chin: most anterior, most inferior, and the midpoint between them.
• Gonion — the angle of the mandible, used for mandibular plane construction.
• ANS / PNS — anterior and posterior nasal spine, defining the palatal plane.
• Incisor landmarks — tips and apices of the most prominent upper and lower incisors.

The measurements that drive diagnosis

Skeletal — how the jaws relate

• SNA — is the maxilla forward or back relative to the cranial base? (Norm ≈ 82°)
• SNB — the same question for the mandible. (Norm ≈ 80°)
• ANB — the difference: the single most-cited number for sagittal jaw discrepancy. Roughly, ANB above ~4° suggests a skeletal Class II pattern, below ~0° suggests Class III.
• Mandibular plane angles (SN-MP, FMA) — vertical pattern: high-angle (open-bite tendency) versus low-angle (deep-bite tendency) growth.

Dental — where the teeth sit

• U1-SN / U1-NA — upper incisor inclination: proclined, normal, or retroclined.
• L1-MP (IMPA) — lower incisor inclination relative to the mandibular plane; critical when planning whether crowding gets resolved by proclination, IPR, or extraction.
• Interincisal angle — the relationship between upper and lower incisors.

No single number diagnoses anything. The skill is reading the pattern — a Class II ANB with retroclined lower incisors plans very differently from the same ANB with proclined ones.

The traditional workflow — and its cost

Manual tracing means identifying 15–25 landmarks by hand, constructing reference planes, and measuring angles — historically on acetate over a lightbox, more recently by clicking points in software. Done carefully it takes 15–30 minutes per case, and studies of inter-examiner reliability consistently show meaningful variation between clinicians on the harder landmarks (porion and the incisor apices are notorious).

What AI tracing actually changes

AI cephalometric tracing trains a model on thousands of expert-traced films to propose landmark positions automatically. Published comparisons show AI placement accuracy comparable to the variation between trained clinicians for most landmarks — which makes it an excellent first draft.

The workflow that respects both the speed and the responsibility looks like this:

1. AI proposes every landmark on the uploaded ceph in seconds.
2. The clinician verifies — each point reviewed, dragged where needed. This step is not optional; the doctor owns the diagnosis.
3. Measurements compute from the verified positions and recalculate live if a point moves.
4. The analysis lands in the patient record, next to the photos, exam, and treatment plan — not in a separate application's export folder.

The net effect isn't that the computer does the analysis — it's that the clinician spends their minutes on judgment (verifying hard landmarks, reading the pattern) instead of mechanics (clicking 25 points from scratch). That's the design behind AI cephalometric analysis in OrthoRecords.

Practical notes for better cephs

• Natural head position matters — a tipped head changes soft-tissue read and some angular relationships.
• Teeth in occlusion, lips at rest unless your protocol specifies otherwise.
• Trace what you can see — when bilateral structures double-image, conventions (bisecting) should be applied consistently across a patient's films.
• Compare like with like — progress comparisons mean superimposing analyses taken with the same conventions, which is far easier when every film for the patient lives in one record.