Oral Surgery · patient case question
If an implant is eventually planned in the mandibular posterior region, what is the minimum safe vertical distance between the implant apex and the superior border of the inferior alveolar canal?
Patient case: Exposed Bone After an Extraction
Patient: 68-year-old male
Chief Complaint: “The bone is showing where they pulled my tooth, and it smells bad.”
Background: Metastatic prostate carcinoma with bone metastases, on monthly intravenous zoledronic acid for 3 years. Tooth #30 extracted 10 weeks ago at another office. No history of head and neck radiation. Non-smoker.
Medications: Zoledronic acid IV monthly · Leuprolide · Calcium and vitamin D
Vital Signs: BP 132/80 mmHg · HR 76 bpm · RR 16 · T 99.1°F
Findings: A 15 mm area of exposed, necrotic-appearing bone at the #30 site with purulent drainage and surrounding erythema. No extraoral fistula. Teeth #29 and #31 are present, sound, and periodontally stable. The patient asks about replacing #30 with an implant once the site heals.
Show answer and explanation
Correct answer: C. 2 mm
- A. Incorrect. Half a millimeter falls well within the error range of any radiographic technique and offers no meaningful protection to the nerve.
- B. Incorrect. Five millimeters is more conservative than required and would unnecessarily restrict implant length in an atrophic ridge.
- C. Correct. A 2 mm safety zone is the accepted minimum. It accommodates radiographic magnification and distortion, surgical drill overrun, and anatomic variation in canal position, protecting against paresthesia of the lower lip and chin.
- D. Incorrect. Eight millimeters would eliminate implant placement as an option in most posterior mandibles.
Note: Related safety margins worth memorizing: 1.5 mm from an implant to an adjacent natural tooth root, 3 mm between two adjacent implants, and 1 mm of bone on the buccal and lingual plates.