1. Understanding Cephalometric Angles and Distances

Accurate interpretation of cephalometric analyses begins with reliable reference planes. The following planes form the spatial foundation upon which all subsequent angular and linear measurements are constructed:

• Frankfort Horizontal Plane (FH): A line connecting the porion and orbitale; approximates the natural horizontal when the head is in an anatomical position.
• Sella–Nasion Plane (SN): Extends from the sella turcica to nasion; provides a stable cranial base reference.
• Nasion–Pogonion (N-Pog): Indicates anterior facial projection.
• Mandibular Plane (Go-Me): Formed by connecting gonion and menton; assesses mandibular growth direction.
• Lower Border Mandibular Plane: A tangent line along the inferior border of the mandible, often used in vertical skeletal assessment.

2. Skeletal Angular Measurements

These angles are critical in determining anteroposterior discrepancies and skeletal classifications:

• SNA Angle: Quantifies the maxillary position relative to the anterior cranial base.
• SNB Angle: Indicates mandibular projection in the sagittal plane.
• ANB Angle: Calculated as the difference between SNA and SNB; key in diagnosing Class I, II, or III skeletal patterns.
• FMA (Frankfort–Mandibular Plane Angle): Reflects vertical growth pattern; a steeper angle correlates with a hyperdivergent facial type.
• MP–SN (Mandibular Plane to S-N): An alternative indicator of vertical dimension and mandibular inclination.

Note: These angular values are sensitive to head posture during radiographic acquisition. Interpretation should account for this variability.

3. Dental Inclination Angles

The axial inclination of incisors to skeletal structures provides insight into dentoalveolar compensation and esthetic profile:

• U1 to SN: Evaluates maxillary incisor inclination relative to the cranial base.
• IMPA (Incisor Mandibular Plane Angle): Indicates lower incisor proclination in relation to the mandibular plane.
• FMIA: A complementary metric reflecting incisor inclination relative to the Frankfort plane.

These angles are frequently influenced by vertical skeletal morphology. For example, high-angle cases often exhibit more upright lower incisors due to functional adaptation.

4. Linear Measurements of Incisor Position

Linear metrics quantify the degree of incisor protrusion or retrusion and are critical in treatment planning:

• U1 to A-Pog: Measures the sagittal projection of the upper incisors in millimeters, relative to the skeletal profile.
• L1 to NB: Indicates the prominence of the lower incisors relative to the mandibular base.

These values guide decisions regarding extraction therapy, facial esthetics, and incisor retraction limits.

Conclusion

Cephalometric analysis is a cornerstone of evidence-based orthodontic diagnosis. Each angular and linear variable—whether skeletal or dental—contributes to a comprehensive understanding of craniofacial architecture and growth direction.

When interpreted holistically, these measurements not only inform mechanics but illuminate the patient’s individual growth narrative.