Dental plaque calcifies when calcium phosphate begins depositing in it. Under normal conditions, the oral fluids are saturated with calcium and phosphate, which is important for maintaining sound enamel. However, this abundance of mineral ions also contributes to calculus formation on the tooth surface (i.e., calcification of plaque biofilm). The amount and type of calcium phosphate salts present vary greatly but include brushite, octacalcium phosphate (OCP), tricalcium phosphate (TCP) and apatite. While supragingival calculus forms from saliva, subgingival calculus forms either from saliva or crevicular fluid. Dental calculus that forms from crevicular fluid can contain heme and some breakdown products which make it pigmented. It is called serumnal calculus. Calculus forms most readily in areas which are adjacent to the openings of the salivary ducts, where the calcium phosphate in saliva is least stable. In populations with poor oral hygiene, supragingival calculus can be extensive and result in gingival recession. Calculus formation can be controlled by adding mineralization inhibitors to dentifrices and mouthrinse. The chemical agents used most often for calculus control in dentifrice are described briefly below.71
Pyrophosphate. Phosphate is a ubiquitous chemical group found in biological systems. As shown in (Figure 16), two phosphate groups combine chemically to form a molecule called pyrophosphate (P2O74-).
Pyrophosphate occurs naturally in saliva and plays a role in inhibiting calculus formation. These molecules chelate calcium (Figure 17), slowing the rate of nucleation (crystal formation) and calcification of plaque. The pyrophosphate binds to calcium in a growing crystal, essentially slowing further crystal growth at that site and effectively decreasing calculus build-up (Figure 18). Original Crest® Tartar Control dentifrice contained 3.3% pyrophosphate. It was the first tartar control dentifrice introduced to the market, and the first tartar control dentifrice to receive the ADA Seal of Acceptance.72,73
Figure 16. Pyrophosphate.
Two phosphate groups combine to form pyrophosphate.
Figure 17. Pyrophosphate.
Negatively charged pyrophosphate molecules bind (chelate) positively charged calcium ions.
Figure 18. Anticalculus Action.
Pyrophosphate inhibits calculus formation by inhibiting calcium phosphate deposition in plaque.
Figure 19. SHMP Hydrolysis.
(A) SHMP is a polyphosphate created from a chain of repeating phosphate units. (B) The hydrolysis or breakdown of SHMP proceeds to single phosphate molecules, although many intermediate products are also produced.
Figure 20. Gantrez® Calcium Chelation.
Video 7. Formation of Calculus.
Video 8. Mechanism for Calculus Protection.