Specialty Minerals Calcium Carbonates in Toothpaste and Oral Care Products
Precipitated calcium carbonates (PCC) and ground calcium carbonates (GCCs) are used in general purpose toothpastes, specialty dentifrices, and other oral care products. PCC functions as a moderate-to-mild abrasive, a less expensive filler, and as a thickener or bodying agent when using smaller or high surface area PCCs. Because calcium carbonate is insoluble in water, it can only be used in opaque products, not in clear gels.
Calcium Carbonate: The Moderate to Mild Abrasive
The abrasivity of a mineral particle depends on two factors—its particle size and the basic hardness of the mineral.
Within a given mineral type, the smaller a particle, the less abrasive it will be; the larger, the more abrasive. Calcium carbonates used in various toothpastes range from 0.7 to 10 microns with the grade chosen partially depending on the degree of abrasiveness desired for the product.
The basic abrasivity of a mineral can be indicated by giving its Moh’s Hardness number. The Moh’s Hardness Scale runs from 1 to 10. The hardness of talc, the softest mineral, is defined as 1. The hardness of a diamond, the hardest mineral, is defined as 10.
As you can see from the graph, it is not a linear scale, but more exponential. Therefore, a mineral with a hardness of 6 is not twice as abrasive as a mineral with a hardness of 3, but is about 8 times as hard.
Calcite is the pure mineral form of calcium carbonate. While the pure mineral itself has a Moh’s Hardness of 3, the limestone rocks in which it is found also contain some quartz, or silica, giving ground limestones or GCCs Moh’s values around 4. PCCs have silica removed during manufacturing, so its Moh’s value is closer to 3. For comparison, silica has a Moh’s value of 6.
Calcium carbonates are considered moderately abrasive, less abrasive than precipitated silicas, but abrasive enough to provide good cleaning.
A Range of Abrasivities
One test for abrasivity is the Einlehner Abrasion test where a bronze mesh is exposed to a 10-percent slurry of the abrasive material for a given number of revolutions, and the weight loss of the screen measured. The higher the loss, the more abrasive the particles used in the slurry. Three of Specialty Minerals Inc. (SMI) calcium carbonates were tested by this method with the following results:
The larger, ground carbonate resulted in the largest metal loss, while the fine particle-sized PCC showed the least.
When formulating a toothpaste with calcium carbonate as the abrasive, the strongest cleaning action will result when using a GCC. For products for everyday use, a GCC or a larger-particled PCC is fine.
Some dentifrices are designed for bridgework, dentures and other forms of artificial teeth which are made from polymers much softer than natural tooth enamel. If a highly abrasive material like silica is used on these synthetic teeth, then they can be worn away too quickly. Here, a smaller-particled PCC would be necessary. The same is true for toothpastes for people with sensitive teeth. Abrasion of the remaining tooth enamel must be minimized, so a small PCC would be the best choice.
Specialty Minerals Calcium Carbonates for Toothpastes
Mildest abrasion applications: ViCALity Albafil® PCC, a 0.7 micron-sized PCC, will be the mildest, yet effective abrasive. ViCALity Albaglos® PCC, a mixture of 85 percent ViCALity Albafil® PCC and 15 percent 3-micron ViCALity® Heavy PCC, will be slightly more abrasive because of the presence of the larger particle in the blend. The small particle size, and resulting higher surface areas, will provide body or thicken the toothpaste formulation potentially reducing the amount of more expensive thickeners.
Moderate abrasion applications: We recommend ViCALity® Heavy (3 microns) or Extra Heavy (4.5 microns) PCCs made in the U.S. or Sturcal™ L PCC (6 microns) made in the U.K.
Moderate abrasion with thickening: The ViCALity® Extra Light, Calopake® Extra Light, and Sturcal™ F and H PCC products have needle shaped, open structures which result in higher surface areas. With particle sizes ranging from 2 to 4 microns, they function effectively as moderate abrasives and the high surface areas will add thickening. The chart below shows an example of viscosities achieved in slurries of ViCALity® Extra Light PCC:
Moderately high abrasion applications: Food grade Vicron® ground limestones such as 25-11 (5.5 microns) or 41-8 (8 microns) grades are typically used. These GCCs are a bit larger than the PCCs and a bit harder. They are excellent in opaque toothpastes for the general population.