Cephalometrics: Landmarks and Analyses Explained Simply

Cephalometrics is the measurement of the head and face using a standardized side-view skull X-ray called a lateral cephalogram. By marking anatomical landmarks on this X-ray and measuring the angles and distances between them, orthodontists can tell exactly where the upper jaw, lower jaw and teeth sit relative to the skull, something no clinical examination can measure precisely.

It matters because two identical-looking buck teeth can have opposite causes: one from a forward upper jaw, one from a backward lower jaw, and the treatments are completely different. It separates dental problems (wrong tooth angles) from skeletal problems (wrong jaw positions) and predicts growth direction.

Key Concepts

• Sella (S) and Nasion (N): the pituitary fossa centre and the nose bridge; the S-N line is the stable cranial-base reference.
• Point A and Point B: the deepest points on the upper and lower jaw bone above the front teeth; they define the jaw relationship.
• Pogonion, Menton, Gonion: the chin tip, the lowest chin point and the jaw angle; used to trace the mandible.
• Frankfort Horizontal: the line from Porion (ear hole) to Orbitale (eye-socket rim).
• SNA, SNB, ANB: Steiner's core angles; SNA (82°) shows maxilla position, SNB (80°) the mandible, ANB (2°) the jaw discrepancy.
• Incisor angles: upper incisor to NA line (22°, 4 mm) and lower incisor to NB line (25°, 4 mm); show whether teeth are flared or upright.

Formulas

ANB = SNA − SNB. With SNA = 82° and SNB = 80°, ANB = 2°, a normal jaw relationship. ANB above 4° indicates a Class II skeletal pattern; below 0° indicates Class III. Assumption: the S-N plane is normally positioned; with an abnormal cranial base, ANB misleads and the Wits appraisal is used instead.

Tweed's triangle: FMA + IMPA + FMIA = 180°, where FMA is the Frankfort-mandibular plane angle (25°), IMPA the lower incisor to mandibular plane angle (90°), and FMIA the Frankfort to lower incisor angle (65°); exact by geometry. Downs' Y-axis (S-Gnathion to Frankfort, ~59°) indicates growth direction: larger values mean more vertical growth.

Worked Example

A tracing gives SNA = 84° and SNB = 78°. Step 1: ANB = 84 − 78 = 6°, a clear Class II skeletal discrepancy. Step 2: SNA is 2° above the 82° norm (maxilla slightly forward) while SNB is 2° below the 80° norm (mandible back), so both contribute but the mandible more. Step 3: upper incisor to NA = 28° (flared, norm 22°), lower incisor to NB = 30° (flared, norm 25°). Step 4: FMA = 30° (high, norm 25°), showing vertical growth. Conclusion: skeletal Class II with mandibular deficiency and vertical growth; in a growing patient this means a functional appliance plus vertical control, not extractions alone.

Common Misconceptions

• "Cephalometrics gives exact, unquestionable numbers." Wrong: landmark identification varies between tracers, and norms differ between populations.
• "One analysis is enough." Wrong: Steiner excels at jaw relationships, Tweed at incisor positioning, Downs at facial type; cross-check at least two.
• "Every brace patient needs a cephalogram." Wrong: it is reserved for skeletal discrepancies, surgical cases and growth assessment to limit radiation.

Real-World Applications

Steiner's, Tweed's and Downs' analyses are taught in every orthodontic program and used for jaw discrepancies and surgical orthodontics, where prediction tracings plan exact millimetres of jaw movement. Modern software auto-traces digital cephalograms, though the clinician still verifies every landmark.

Cephalometrics turns a side-view skull X-ray into measured jaw positions through landmarks like Sella, Nasion and A/B points, analysed with Steiner's angles, Tweed's triangle and Downs' measurements. It separates skeletal from dental problems and guides whether treatment should move teeth, redirect growth or reposition jaws surgically.