A point (A) — this is the point of deepest concavity on the anterior profile of the maxilla. It is also called subspinale. This point is taken to represent the anterior limit of the maxilla and is often tricky to locate accurately. However, tracing the outline of the root of the upper central incisor first and shielding all extraneous light often aids identification. The A point is located on alveolar bone and is liable to changes in position with tooth movement and growth.

Anterior nasal spine (ANS) — this is the tip of the anterior process of the maxilla and is situated at the lower margin of the nasal aperture.

B point (B) — the point of deepest concavity on the anterior surface of the mandibular symphysis. The B point is also sited on alveolar bone and can alter with tooth movement and growth.

Gonion (Go) — the most posterior inferior point on the angle of the symphysis. This point can be ‘guesstimated’, or determined more accurately by bisecting the angle formed by the tangents from the posterior border of the ramus and the inferior border of the mandible .

Menton (Me) — the lowest point on the mandibular symphysis.

Nasion (N) — the most anterior point on the frontonasal suture. When difficulty is experienced locating nasion, the point of deepest concavity at the intersection of the frontal and nasal bones can be used instead.

Orbitale (Or) — the most inferior anterior point on the margin of the orbit. By definition, the left orbital margin should be used to locate this point. However, this can be a little tricky to determine radiographically, and so an average of the two images of left and right is usually taken.

Pogonion (Pog) — the most anterior point on the mandibular symphysis.

Porion (Po) — the uppermost outermost point on the bony external auditory meatus . This landmark can be obscured by the ear posts of the cephalostat, and some advocate tracing these instead

Posterior nasal spine (PNS) — this is the tip of the posterior nasal spine of the maxilla. This point is often obscured by the developing third molars, but lies directly below the pterygomaxillary fissure.

Sella (S) — the midpoint of the sella turcica.

SN line — this line, connecting the midpoint of sella turcica with nasion, is taken to represent the cranial base.

Frankfort plane — this is the line joining porion and orbitale. This plane is difficult to define accurately because of the problems inherent in determining orbitale and porion.

Mandibular plane — The line joining gonion and menton. This is only one of several definitions of the mandibular plane, but is probably the most widely used. Other definitions can be found in the publications listed in the section on further reading.

Maxillary plane — the line joining anterior nasal spine with posterior nasal spine. Where it is difficult to determine ANS and PNS accurately, a line parallel to the nasal floor can be used instead.

Functional occlusal plane — a line drawn between the cusp tips of the permanent molars and premolars (or deciduous molars in mixed dentition). It can be difficult to decide where to draw this line, particularly if there is an increased curve of Spee, or only the first permanent molars are in occlusion during the transition from mixed to permanent dentition. The functional plane can change orientation with growth and/or treatment, and so is not particularly reliable for longitudinal comparisons.

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