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Orthodontics · single question

The CENTER OF RESISTANCE of maxillary incisors that have experienced significant bone loss is located at the:

  1. CEJ
  2. Apical third of the REMAINING bone support
  3. Middle of the original root length
  4. Crown
Show answer and explanation

Correct answer: B. Apical third of the REMAINING bone support

  • A. Incorrect. The CEJ is the crown-root junction, not the CRes in any condition.
  • B. Correct. The CENTER OF RESISTANCE shifts APICALLY with bone loss. When significant alveolar bone has been lost, the CRes moves toward the APICAL THIRD of the REMAINING alveolar bone support — roughly at the middle of the remaining bone-supported portion of the root. This affects orthodontic force application in periodontally compromised patients.
  • C. Incorrect. The CRes in a tooth with NORMAL bone support is approximately at the middle of the root (or junction of cervical and middle thirds). However, this changes with bone loss.
  • D. Incorrect. The center of resistance (CRes) is never at the crown.

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