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Periodontics · single question

A patient presents with alveolar ridge loss in BOTH the buccolingual and apicocoronal dimensions. What is the Siebert classification?

  1. Class I
  2. Class III
  3. Class II
  4. Class IV
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Correct answer: B. Class III

  • A. Siebert Class I is loss of ridge WIDTH only — buccolingual (horizontal) loss with preserved height.
  • B. Correct. Siebert CLASS III is COMBINED loss — both buccolingual and apicocoronal. Memory aid: I = width, II = height, III = both. Class III defects are the most demanding and generally require block grafting or combined hard and soft tissue augmentation before implant placement.
  • C. Siebert Class II is loss of ridge HEIGHT only — apicocoronal (vertical) loss with preserved width.
  • D. There is no Class IV in the Siebert classification — it contains only three classes.

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