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Implants · single question

If the distance from the alveolar bone to the inferior alveolar nerve (IAN) is 10 mm, what is the maximum implant length that can be used?

  1. 7 mm
  2. 10 mm
  3. 8 mm
  4. 9 mm
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Correct answer: C. 8 mm

A 2 mm safety margin must be maintained between the apex of the implant and the superior border of the inferior alveolar nerve canal. With 10 mm of available bone from the alveolar crest to the IAN, subtracting the 2 mm safety margin leaves 8 mm for the implant. Maximum implant length = Available bone height − 2 mm safety margin = 10 − 2 = 8 mm.
  • A. INCORRECT. 7 mm would leave 3 mm from the IAN — while safe, it is not the MAXIMUM length available.
  • B. INCORRECT. 10 mm would place the implant apex directly at the IAN — this would cause nerve damage.
  • C. CORRECT. Maximum implant length = 10 mm (bone height) − 2 mm (safety margin from IAN) = 8 mm. This is the longest implant that can be placed while maintaining adequate safety from the nerve.
  • D. INCORRECT. 9 mm would leave only 1 mm from the IAN — insufficient safety margin, risking nerve injury.

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