Processes contributing to the formation of dental calculus

Dental calculus is a petrified plaque biofilm. Calculus removal requires professional scaling procedures as a result of its physical hardness and strong attachment to the teeth. The aim of this paper is to review chemical (MD, Ca, P, F), physical (hardness, adhesive strength), ultrastructural (SEM, TEM), and clinical data on calculus in order to provide perspective on the roles that adhesion and cementation play in tartar development. SEM, TEM and microradiographic analyses of deposits in cross section show that calculus mineralizes in successive layers of varying thickness. Chemical analysis shows that plaque mineralization occurs rapidly (on a clinical time scale, < 2 wks on average) with the formation of calcium phosphate crystals contributing up to 80% of the weight of deposits. Although calculus adheres strongly to the teeth (up to 4,000 kN.m^‐2 in attachment force) the hardness measures only 10–20% of sound enamel (20–40 Vickers Hardness Numbers). The clinical formation of calculus (measured as the area coverage on the teeth) follows a rapid course, levelling off after 2–3 months. Crystal growth inhibitors reduce the maximum plateau of calculus coverage but do not alter the mineral composition of mature deposits. These findings support the view that calculus formation is strongly affected by the adhesion of mineralizing plaques onto existing deposits. Maximum tooth coverage with supragingival calculus is affected by the time period of cementation of plaque layers (influenced by plaque formation and mineralization rates) and average frictional forces (mastication/ toothbrushing) acting on appositional layers. Tartar control action by current technologies can be thought of as “antiadhesive”; in the sense that lengthened time periods of plaque petrification permit cleansing of softer deposits by patients using normal hygiene methods. The development of technologies for the “complete”; control of calculus development must take into account the strong role of adhesion/cementation in tartar formation.

Key words:

• Tartar
• dental calculus
• hardness
• mineralization
• petrification
• plaque
• adhesion