Sella-Nasion Plane
Also written as: SN — Sella-Nasion
A cephalometric reference plane drawn from the sella turcica to the nasion, used as a baseline for angular measurements of jaw position.
Full Definition
The sella-nasion (SN) plane connects two cranial landmarks—sella (the centre of the pituitary fossa) and nasion (the frontanasal junction)—and serves as a relatively stable cranial base reference in lateral cephalometric tracing. Many standard angular measurements, such as SNA and SNB, are expressed relative to this plane. Editors proofing cephalometric analysis sections must verify that the plane is correctly identified and that derived angle values are reasonable (e.g., SNA ≈ 82°). Deviations from standard values indicate skeletal discrepancies central to the manuscript's argument. The abbreviation SN should be spelled out on first use in most clinical publications.
Usage
Usage note: Always expand 'SN plane' on first use; do not confuse with 'SNB angle,' which measures mandibular position relative to this plane.
In Context
- "All angular measurements in the study were referenced to the sella-nasion plane to ensure consistency across subjects." — Cephalometric methods section
- "The SN plane is considered a reliable, reproducible baseline despite minor individual variation in cranial base morphology." — Textbook chapter draft