Implants · patient case question
What is the minimum safe distance between an implant apex and the inferior alveolar canal?
Patient case: Implants, Peri-implantitis, and a Regeneration Question
Patient: 59-year-old male
Chief Complaint: Review of two implants placed four years ago, and assessment of a defect on tooth #6.
Background: Former smoker. History of treated periodontitis. Irregular maintenance attendance.
Medications: None
Vital Signs: BP 130/82 mmHg · HR 74 bpm · RR 16 · T 98.4°F
Findings: Implant at site #19: 6 mm probing depth with bleeding and suppuration, 2 mm of radiographic crestal bone loss. Tooth #6 has a NARROW three-walled intrabony defect on its MESIAL surface, 6 mm deep, with the tooth firm and vital. Posterior mandibular ridge is being assessed for a further implant.
Show answer and explanation
Correct answer: B. 2 mm
- A. 10 mm would preclude posterior mandibular implants in the great majority of patients.
- B. CORRECT. A minimum of 2 mm of vertical clearance is maintained between the implant apex and the superior border of the inferior alveolar canal. This margin absorbs the cumulative error of radiographic magnification, surgical guide fit and drill depth, and protects against the heat generated during osteotomy preparation. Violating it risks permanent paraesthesia or dysaesthesia of the lower lip and chin.
- C. 5 mm is unnecessarily conservative and would exclude implants in many atrophic posterior mandibles where they can be placed safely.
- D. 0.5 mm is well within the combined margin of measurement and surgical error and offers no real protection.
Note: Companion figures to know: 1.5–2 mm from an implant to an adjacent natural TOOTH; 3 mm between two adjacent IMPLANTS; and at least 1 mm of bone circumferentially, preferably 2 mm on the buccal. Use CBCT for posterior mandibular planning — a panoramic film alone is not adequate.