Cheat Sheet - Cephalometric Tracing and Landmarks
1. The 5 Functional Units
A good cephalometric landmark must (1) be identified accurately on a ceph, and (2) represent a known part of one of the five functional units of the craniofacial complex:
- The cranium and cranial base
- The skeletal maxilla and nasomaxillary complex
- The skeletal mandible
- The maxillary teeth and alveolar process
- The mandibular teeth and alveolar process
2. Landmark Table
| Landmark | Region | Definition | How to locate / trace it |
|---|---|---|---|
| Sella (S) | Cranial base | Centre of the bony crypt (sella turcica) of the sphenoid that houses the pituitary; posterior end of anterior cranial base. Stable — does not change after age 7. | Draw the contour of the depression extending anteriorly & posteriorly over the edges of the concavity, mark S in the centre; extend the line forward along the floor of the anterior cranial base to aid superimposition. |
| Nasion (N/Na) | Cranial base | Anterior end of the fronto-nasal suture (junction of nasal & frontal bones); front end of anterior cranial base. | Draw the outer surface of the nasal & frontal bones past the junction, draw the suture between the bones, mark N where the lines intersect. |
| Porion (P) | Cranial base | Most superior point of the external auditory meatus (machine porion). | Identify the top of the external auditory meatus outline. |
| Orbitale (Or) | Cranial base | Lowest point on the inferior bony orbital rim (average both sides). | Trace the orbital rims; if both sides visible separately, locate the point halfway between. Don’t confuse the dotted line behind the orbit with the rim. |
| ANS | Maxilla | Tip of the anterior nasal spine; most anterior point of the nasal floor. | Trace the superior & inferior surfaces of the ANS and mark its tip. |
| Point A | Maxilla | Deepest (innermost) point on the premaxillary contour between ANS and the incisor; junction of skeletal maxilla and dentoalveolar process. | Follow the external bone contour downward toward the upper incisor and mark A at the depth of the concavity. |
| PNS | Maxilla | Tip of the posterior nasal spine (palatine bone); junction of hard & soft palate. | Trace the inner contour of the anterior maxillary alveolus, continue posteriorly along the roof of the mouth to the end of the bony outline; mark the end as PNS. |
| Point B | Mandible | Deepest point on the anterior mandibular contour between incisor and bony chin. | Trace the bony chin incl. inner symphysis, follow upward toward the incisor, mark B at the depth of the concavity. |
| Pogonion (Pg) | Mandible | Most anterior point of the bony chin. | Mark the forward-most point of the chin outline. |
| Menton (Me) | Mandible | Most inferior point of the symphysis. | Mark the lowest point of the symphysis outline. |
| Gnathion (Gn) | Mandible | Midpoint of inferior chin contour, halfway between Pg and Me (bisector of mandibular & facial planes). | Mark the point midway between Pg and Me on the chin contour. |
| Gonion (Go) | Mandible | Most outward/everted point at the junction of ramus and body (centre of gonial-angle curvature). | Follow the lower border posteriorly around the angle and up the posterior ramus; mark the centre of the curvature. |
| U1 / L1 | Dentition | ==U1 = maxillary central incisor tip; L1 = mandibular central incisor tip.== | Mark the incisal tip of each central incisor. |
| U6 / L6 | Dentition | ==U6 = maxillary 1st molar mesial cusp tip; L6 = mandibular 1st molar mesial cusp tip.== | Mark the mesial cusp tip of each first molar. |
Note: When drawing lips and incisor teeth, get the root inclination correct.
Tracing pitfalls
- Orbitale: don’t confuse the dotted line behind the orbit with the orbital rim.
- Superimposition: do NOT register at Nasion — N drifts forward with growth. Register at S.
3. Reference Planes
| Plane | Defined by | Use |
|---|---|---|
| SN | Sella–Nasion | Inclination of the anterior cranial base; reference arm for SNA/SNB. |
| Frankfort / FH | Orbitale–Porion | True-horizontal estimate. |
| Palatal plane (PP) | ANS–PNS | Maxillary base. |
| Occlusal plane (OP) | Along occluding surfaces of molars/premolars | Reference for occlusion. |
| Mandibular plane (MP) | Go–Gn (Go–Me in some) | Mandibular base. |
| Y-axis (growth axis) | S–Gn | Path of downward-forward facial growth. |
4. Construction Lines to Draw (Workbook Protocol)
Begin analysis by drawing the five horizontal planes:
- SN — extended posteriorly beyond S
- True horizontal — perpendicular to true vertical, through Or
- Palatal — ANS–PNS, extended beyond PNS
- Occlusal — along molar/premolar surfaces, extended
- Mandibular — Go–Gn, extended posteriorly
Then:
- Drop a true vertical (N-perpendicular) from Nasion, parallel to the plumb chain.
- Draw a dashed true-vertical segment through points A and B.
- Draw the long axes of the maxillary and mandibular incisors.
Acetate setup: rough side up, exactly over the film, face oriented to the right; tape so top & right edges coincide.
5. Superimposition Registration (Quick Reference)
| Type | Register on | Notes |
|---|---|---|
| Overall (cranial base) | S–N line at S | S is stable after age 7; Nasion drifts forward with growth — do NOT register at N. Shows jaws + soft-tissue profile vs cranial base. |
| Maxillary | Lingual contour of the palate (behind upper incisors) + keep palatal plane (ANS–PNS) level | Do NOT make teeth coincide. Isolates maxillary tooth movement vs maxilla. |
| Mandibular | Three internal landmarks: lingual contour of the symphysis, the inferior alveolar (mandibular) canal (IAN), and the crypt of the unerupted 3rd molar | Internal structures don’t move as the mandible grows — do NOT rely on Go–Gn (surface remodels). Isolates mandibular tooth movement vs basal bone; also shows condylar growth & gonial remodelling. |
Sources: Level II Unit B Summary—integrated, L4 Level II Unit B, Workbook, 02 - Cephalometric Tracing Techniques