Figure 2-3. Calculus.
c. Subgingival Calculus. Subgingival calculus, harder and darker than
supragingival calculus, is located below the crest of the marginal gingiva and is not
visible upon oral examination. See figure 2-3. Subgingival calculus ranges from dark
brown to greenish-black in color, is flint-like in consistency, and is firmly attached to the
tooth surface. Location of subgingival calculus is determined by careful probing with an
explorer or by using the air syringe. The inorganic component is primarily calcium
phosphate (70 to 90 percent). The organic component (10 to 30 percent) contains no
salivary protein, only serum protein.