Cephalometric tracing and landmarks

January 10, 2015

Since its introduction, several methods of cephalometric analysis have been proposed by experts in this field. Among the more commonly known and used are Steiner analysis, McNamara analysis, Ricketts analysis, Eastman analysis, Downs analysis and Tweeds analysis. No method can be called superior to the other.

The success of analysis lies in accurate marking of the landmarks, the planes and the construction of angles and arcs. Comparing the values arrived at with normal values helps to understand the pattern of the person’s skeletal structure. If the values arrived at are compared to the same person’s pre-treatment cephalogram, then the effect of the treatment can be assessed.

Cephalometric Landmarks

Cephalometric landmarks are specific structures, dental and skeletal, that can be easily recognized on a radiograph. Once the basic skeletal and the soft tissues outlines have been traced, the landmarks are penciled in. The main landmarks in a lateral cephalogram with their symbols are:

• Sella Turcica (S)
• Nasion (Na)
• A-point (A)
• B-point (B)
• Pogonion (Pg)
• Gnathion (Gn)
• Menton (Me)
• Anterior Nasal Spine (ANS)
• Posterior Nasal Spine (PNS)
• Basion (Ba)
• Orbitale (Or)
• Gonion (Go)
• Articulare (Ar)
• Porion (Po)
• Pterygomaxillary Fissure (Ptm)

Cephalometric planes

Landmarks are used as reference points to construct lines known as planes.

1. Po – Or Line: this is the Frankfort Plane and corresponds to the true horizontal with the patient in upright position.
2. ANS - PNS Line: this is the maxillary plane. It helps to assess the tendency of the maxilla in relation to other planes.
3. Me - Go Line: this is the mandibular plane. It helps to study the incline of the mandible in relation to other planes.
4. S - N Line: this represents the frontal cranial base.
5. N - A Line: shows the position of the maxilla as relative to the cranial base.
6. N - B Line: shows the position of mandible in relation to the cranial base.
7. Upper Incisor (U1) Line: connects the incisal edge to the root apex of the prominent upper incisor.
8. Lower Incisor (L1) Line: connects the incisal edge to the root apex of the prominent lower incisor

Cephalometric angles

1. MMPA: The Maxilla to Mandibular Planes Angle shows the relation between the maxilla and the mandible. It also gives an understanding of face height as well as indicates the direction that future growth will take.
2. SNA: The Sella to Nasion to A point angle points out how the maxilla lies in relation to the cranial base and whether it protrudes or is deficient horizontally.
3. SNB: The Sella to Nasion to B point angle conveys how the mandible lies as compared to the cranial base. This reveals whether the mandible is prognathic or retrognathic.
4. ANB: The A point to Nasion to B point angle shows position of the maxilla and the mandible in respect to each other. It helps to measure the difference between the size of the jaw and its position.
5. UIA: The Upper Incisor Angle reveals the inclination of the upper incisor to the skeletal base.
6. LIA: The Lower Incisor Angle shows the inclination of the lower incisor to the skeletal base.

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