Calculus is composed of 70-80 % of Inorganic component which is mainly Crystalline in Structure. The four main crystal forms and their percentages are as follows:

  1. Hydroxyapatite: 58%
  2. Magnesium Whitlockite: 21%
  3. Octacalcium Phosphate: 12%
  4. Brushite: 9%

Generally, 2 or more crystal forms are typically in a sample of calculus. Hydroxyapatite and Octacalcium Phosphate are detected most frequently i.e 97% to 100% of all supragingival calculus.

  1. Brushite: More common in the Mandibular Anterior region
  2. Magnesium Whitelockite: More common in the Posterior region

Crystal forms in sub gingival and supra gingival calculus

Differences in Composition of Crystals between Supra Gingival and Sub Gingival calculus:

The inorganic composition of subgingival calculus is similar to that of supragingival calculus, with some differences.

Supragingival to Subgingival Crystal Ratio:

  1. Hydroxyapetite: Supragingival = Subgingival (Supragingival calculus has more than subgingival calculus)
  2. Magnesium Whitlockite: Supragingival > Subgingival (Supragingival calculus has equal to Sub gingival calculus)
  3. Octacalcium Phosphate: Supragingival < Subgingival (Supragingival calculus has less than subgingival calculus)
  4. Brushite: Supragingival < Subgingival (Supragingival calculus has less than subgingival calculus)