The cephalometric plane extending from GONION to MENTON is the:

Correct answer: D. Mandibular plane

• A. The OCCLUSAL PLANE passes through the occlusal contacts of the posterior teeth and the incisal overlap.
• B. FRANKFORT HORIZONTAL runs from PORION (superior external auditory meatus) to ORBITALE (inferior orbital rim) and serves as the standard horizontal reference.
• C. The FACIAL PLANE runs from NASION to POGONION and is used to evaluate anteroposterior chin position.
• D. CORRECT. The MANDIBULAR PLANE is drawn along the inferior border of the mandible, defined in the Steiner analysis from GONION (the constructed point at the angle of the mandible) to MENTON (the most inferior point of the bony chin). Its inclination is a primary indicator of vertical facial pattern: a STEEP mandibular plane angle indicates a hyperdivergent, long-face, open-bite tendency, while a FLAT angle indicates a hypodivergent, short-face, deep-bite tendency.

Note: The mandibular plane angle carries treatment implications: high-angle patients resist bite opening and respond poorly to extrusive mechanics, while low-angle patients have strong musculature and deep bites that are harder to open. Assess it before planning vertical mechanics.