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:
- Hydroxyapatite: 58%
- Magnesium Whitlockite: 21%
- Octacalcium Phosphate: 12%
- 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.
- Brushite: More common in the Mandibular Anterior region
- Magnesium Whitelockite: More common in the Posterior region
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:
- Hydroxyapetite: Supragingival = Subgingival (Supragingival calculus has more than subgingival calculus)
- Magnesium Whitlockite: Supragingival > Subgingival (Supragingival calculus has equal to Sub gingival calculus)
- Octacalcium Phosphate: Supragingival < Subgingival (Supragingival calculus has less than subgingival calculus)
- Brushite: Supragingival < Subgingival (Supragingival calculus has less than subgingival calculus)