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Implants · patient case question

What is the maximum implant length that can be used?

Patient case: Implant length above the inferior alveolar nerve

Scenario: There is 10 mm of bone available from the crest to the INFERIOR ALVEOLAR NERVE.

  1. 7 mm
  2. 10 mm
  3. 8 mm
  4. 9 mm
Show answer and explanation

Correct answer: C. 8 mm

  • A. 7 mm would be safe but is not the MAXIMUM length permitted, which is what the question asks.
  • B. A 10 mm implant would place the apex directly against the canal with no safety margin at all, risking paresthesia or permanent nerve injury.
  • C. Correct. A SAFETY ZONE of at least 2 mm is maintained between the implant apex and the superior border of the inferior alveolar canal. With 10 mm of available bone, 10 − 2 = 8 mm is the longest implant that respects that margin.
  • D. 9 mm leaves only a 1 mm margin — inadequate to allow for radiographic distortion, measurement error and surgical over-preparation.

Note: Other implant safety distances worth memorising: at least 1.5-2 mm between an implant and an ADJACENT NATURAL TOOTH; at least 3 mm BETWEEN TWO IMPLANTS; at least 1 mm of bone on the buccal and lingual aspects.

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