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Orthodontics · single question

A patient has an ANB angle of 6 degrees. What skeletal relationship does this indicate?

  1. Class I skeletal relationship
  2. Class II skeletal relationship
  3. Class III skeletal relationship
  4. A vertical growth pattern with no anteroposterior discrepancy
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Correct answer: B. Class II skeletal relationship

  • A. Class I is ANB of roughly 0–4 degrees, centred on 2.
  • B. CORRECT. The ANB angle measures the anteroposterior relationship of the maxilla (point A) to the mandible (point B) relative to nasion. Normal is approximately 2 ± 2 degrees. ANB GREATER than about 4 degrees indicates a CLASS II skeletal pattern — the maxilla positioned forward relative to the mandible, from maxillary prognathism, mandibular retrognathism, or both. At 6 degrees this is a definite Class II.
  • C. Class III is ANB BELOW 0 degrees (negative), indicating the mandible is positioned forward relative to the maxilla.
  • D. ANB is purely an anteroposterior measurement. Vertical pattern is assessed by other measures — the SN-MP angle, FMA, and the Jarabak ratio.

Note: Complementary values: SNA normal 82 ± 2 (maxillary position), SNB normal 80 ± 2 (mandibular position), ANB = SNA − SNB. Wits appraisal is a useful cross-check when nasion or the cranial base is atypically positioned.

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