Cephalometric planes and lines

Measuring linear values

  • Posterior facial height (AFP) – Distance from the Ar point to the mandibular plane, in a tangence with the mandibular ramus posterior border (Merrifield, 1989).
  • Anterior facial height (AFA) – Distance between the Me point and its ortogonal projection over the palatine plane. The palatine plane is traced by joining ENP and ENA points (Merrifield, 1989).
  • Facial Height Index (IAF) – set by the AFP/AFA ratio (Horn, 1992).

Measuring angular values

  • a) FMA – Angle formed by the intersection of the Frankfurt horizontal plane (PHF) with the mandibular (MD). The Frankfurt horizontal plane was traced by joining points Po and Or. The mandibular plane by the mandible body inferior border tangent, going through point Me (Tweed; 1954).
  • b) SNA – Angle formed by the intersection of the Saddle-Nasion and Nasion-A lines (Riedel; 1952).
  • c) SNB – Angle formed by the intersection of the Saddle-Nasion and Nasion-B lines (Riedel; 1952).
  • d) ANB – Angle formed by the intersection of the Nasion-A and Nasion-B lines (Riedel; 1952).
  • e) Angle Z – Formed by the intersection of the Frankfurt horizontal plane with the Pg point tangent line and the most anterior lip (Merrifield; 1966).
  • f) Y axis angle – Formed by the Y axis, from point (S) to point Gn, with the Frankfurt horizontal plane (Downs; 1948).
  • g) SN-GoGn Angle – Formed by the intersection of the mandibular plane (GoGn) with the S-N line.
  • h) IMPA angle – mandibular plane intersection with the lower central incisive long axis


Source: Comparative cephalometric study

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