Crystal Forms in Calculus – Supragingival Calculus and Subgingival Calculus

Dental Calculus is calcified or calcifying mass that forms on the surfaces of the teeth. It is formed on the external surface from vital, tightly adherent, nonmineralized plaque. It is divided into 2 types based on it location on the tooth surface – Supragingival Calculus and Subgingival Calculus.

Supragingival Calculus Features:

• Above the Gingival margin
• It is usually Yellow and White in color
• It is formed from the Salivary secretions due to its location on the tooth and is composed of Salivary Proteins.
• 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:

Subgingival Calculus Features:

• It is located on the tooth surface below the margins of the Gingiva
• It is Brown, Black or Greenish-black in color due tot he gingival exudate
• It is formed due to the Gingival Exudate
• It consists of Sodium which increase with the depth of the pocket

Dental Calculus in simple terms can be called Mineralized Dental Plaque which is formed by the precipitation of mineral salts starting from the 1st to 14th day of plaque formation.

Composition of Dental Calculus:

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

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)

Calcification of Dental Plaque to convert to Calculus starts in separate foci on the inner surface of the plaque. These foci of mineralization gradually increase in size and coalesce to form a solid mass of calculus.