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Orthodontics · single question

Which of the following best describes a steep mandibular plane angle?

  1. Deep bite
  2. Short vertical facial height
  3. Class III malocclusion
  4. Open bite
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Correct answer: D. Open bite

The mandibular plane angle (Go-Gn to SN or FH) reflects the vertical facial pattern. A STEEP mandibular plane angle = HIGH angle facial type = long anterior face height = tendency toward OPEN BITE (teeth don't close anteriorly because the mandible grows in a downward and backward direction). A FLAT mandibular plane angle = LOW angle = deep bite tendency = short anterior facial height.
  • A. INCORRECT. Deep bite is associated with a FLAT (low) mandibular plane angle — short anterior facial height, horizontal mandibular growth pattern.
  • B. INCORRECT. Short vertical facial height is associated with a LOW (flat) mandibular plane angle, not a steep one.
  • C. INCORRECT. Class III malocclusion (prognathic mandible) is not specifically determined by the mandibular plane angle — it depends on the skeletal AP relationship (ANB angle).
  • D. CORRECT. A steep mandibular plane indicates a HIGH angle facial type with excessive vertical facial development. The mandible rotates downward and backward, creating a tendency for ANTERIOR OPEN BITE.

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