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Orthodontics · single question

Orthodontic (forced) eruption to extrude a tooth should proceed at approximately what rate?

  1. 2 mm per week
  2. 2 mm per month
  3. 1 mm per month
  4. 1 mm per week
Show answer and explanation

Correct answer: C. 1 mm per month

  • A. 2 mm per week is far beyond any accepted rate and would produce mobility, resorption and pulpal injury.
  • B. 2 mm per month outpaces bone and attachment remodelling and risks root resorption and relapse.
  • C. CORRECT. Slow forced eruption of roughly 1 mm per month allows the alveolar bone and gingival attachment to migrate coronally WITH the tooth. This is what you want when you are trying to bring sound tooth structure above the crest for a ferrule.
  • D. 1 mm per week (about 4 mm per month) is rapid extrusion — used deliberately only when you want the tooth to move WITHOUT the bone following, and it must be combined with weekly fibrotomy.

Note: Two different techniques with opposite goals: SLOW extrusion (~1 mm/month) brings bone and gingiva along and is used to regenerate a deficient ridge; RAPID extrusion with fibrotomy leaves the attachment behind and is used to expose crown margin without altering gingival levels.

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