Periodontics · patient case question
The subgingival deposits are grey to black in colour. What accounts for this?
Patient case: Deep pockets on molars and incisors only
Patient: Female, 22 years old
Chief Complaint: “My front teeth feel like they are moving.”
Background: Healthy. No medications, no allergies, non-smoker. No family history recorded.
Vital Signs: BP 112/70 mmHg · HR 72 bpm · RR 15 · T 98.4°F
Findings: Probing depths 8–9 mm at first molars and 5–6 mm at incisors. Other sites are 2–3 mm. Plaque and calculus deposits are minimal relative to the destruction. Dark, hard subgingival deposits are visible after retraction.
Show answer and explanation
Correct answer: A. Breakdown of red blood cells from the inflamed sulcus
- A. CORRECT. Subgingival calculus is dark because it forms in a sulcus that bleeds. Blood enters the crevicular environment, haemoglobin degrades, and the resulting pigments are incorporated into the mineralising matrix, giving the grey-black to dark-brown colour. Supragingival calculus, forming in a bloodless environment, is whitish-yellow.
- B. Subgingival calculus is indeed denser and harder than supragingival calculus, but mineral density is not what makes it dark — blood pigment is.
- C. Dietary chromogens stain supragingival surfaces where saliva and food reach; they do not reach the base of a periodontal pocket.
- D. Chromogenic bacteria produce the black or green extrinsic stain seen along the cervical margins of children's teeth, which is a surface film, not calculus.