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Periodontics · patient case question

At #19 the probing depth is 4 mm and the gingival margin lies 1 mm CORONAL to the CEJ. What is the clinical attachment level?

Patient case: Periodontal bone loss assessed on radiograph and at surgery

Patient: Female, 52 years old

Chief Complaint: “My gums have pulled back and my back teeth feel loose.”

Background: Irregular dental attendance. Former smoker. No relevant medical history.

Vital Signs: BP 126/78 mmHg · HR 74 bpm

Findings: Radiographs show angular loss of the crestal bone on the mesial of #30, the crest sloping apically away from the CEJ rather than running parallel to it. At #19, a periodontal probe calibrated in millimetres reads 4 mm in the sulcus, and the gingival margin sits 1 mm CORONAL to the CEJ. A surgical photograph after flap reflection shows an interproximal defect in which the bone is lost between two adjacent roots while the facial and lingual plates remain.

  1. 5 mm
  2. 3 mm
  3. 6 mm
  4. 4 mm
Show answer and explanation

Correct answer: B. 3 mm

  • A. 5 mm results from ADDING the 1 mm instead of subtracting it. Addition is correct only when there is true RECESSION, with the margin apical to the CEJ.
  • B. CORRECT. CAL is measured from the CEJ to the base of the pocket. When the gingival margin is CORONAL to the CEJ — overgrowth or oedema rather than recession — that overlying distance is SUBTRACTED: CAL = probing depth − distance from CEJ to gingival margin = 4 − 1 = 3 mm. Recorded conventionally, a coronal margin is a NEGATIVE recession value, and CAL = PD + (−1) = 3 mm.
  • C. 6 mm does not follow from any correct handling of these two numbers.
  • D. 4 mm is the probing depth itself. Probing depth equals CAL only when the gingival margin sits exactly AT the CEJ, which is not the case here.

Note: Fix the sign convention and the arithmetic follows every time. CAL = probing depth + recession. Margin APICAL to the CEJ (recession) is a POSITIVE value and is added. Margin CORONAL to the CEJ (enlargement or oedema) is a NEGATIVE value and is subtracted. CAL, not probing depth, is what measures true destruction.

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