gnathion

Gnathion (Gn) is a cephalometric and anthropometric landmark on the mandible used in craniofacial analysis. It is defined as the midpoint of the line segment joining pogonion (Pg), the most anterior point on the chin, and menton (Me), the lowest point on the chin, and lies on the midsagittal plane of the skull.

Pg marks the forward projection of the chin while Me marks the lowest point on the chin; Gnathion lies on the same chin region along the line connecting these two points. As a midsagittal reference, Gn is used to describe chin position and vertical chin dimension in cephalometric analyses, and it is frequently employed in orthodontic assessment and in planning craniomaxillofacial procedures. In modern practice, Gn coordinates can be obtained from radiographs or three-dimensional imaging and are used alongside other landmarks to characterize facial morphology and growth.

Etymology and context: the name Gnathion derives from the Greek gnathos, meaning jaw. The landmark is part of standard craniofacial nomenclature and is reported in radiographic, cephalometric, and 3D imaging analyses. While useful for describing chin position, exact definitions can vary between cephalometric analyses, so practitioners should refer to the specific methodology in use when comparing measurements.