The subgingival calculus found below the gingival margin is characterized by:

Correct answer: B. Dark gray-black color, formed from components of sulcular fluid/blood

• A. Brown staining from coffee/tea is supragingival and extrinsic — not characteristic of subgingival calculus.
• B. Correct. Subgingival calculus is dark gray or black due to incorporation of hemoglobin breakdown products, blood components, and gingival fluid. It is denser, harder, and more firmly attached than supragingival calculus and forms from minerals in the gingival crevicular fluid.
• C. Yellow/white calculus is supragingival calculus, which forms from salivary minerals.
• D. Green calculus is typically from chromogenic bacteria and is supragingival.