The Benefits of Abrasives
Abrasives provide the cleaning power in toothpastes. They give toothpaste a slightly gritty texture designed to polish teeth and remove plaque, food remnants, and stains.
The most commonly used abrasives are hydrated silica, calcium carbonate, aluminum oxides, and various phosphates of calcium, or aluminum. Calcium carbonate is the compound of which chalk is made, but the form used in toothpaste is not simply ground up chalk. The compound is chemically reformed into finer particles than those found in chalk. Likewise, sand contains pure silica, but the form used in toothpaste is gentler than that in sand. Harsher abrasives include anhydrous dicalcium phosphate, zirconium silicate, crystalline silica, and pumice. Those abrasives are commonly used by the dentist to remove tartar and stains. Some European toothpastes even contain abrasives made of tiny granules of hard plastic.
Most abrasives used in toothpaste pose no harm to teeth because tooth enamel is made almost entirely of hydroxyapatite, a form of calcium phosphate that is about as hard as the mineral topaz or the steel in most knives.
But toothpastes designed to remove tough stains, such as those from tobacco and coffee, may contain harsher abrasives than do regular brands. Some experts say that the frequent use of highly abrasive toothpastes over many years has the potential to damage tooth enamel.
Harsher abrasives may also contribute to the loss of cementum at the base of the teeth. Cementum is a thin layer of calcium, magnesium, and phosphorus that covers the dentin (the main material of which teeth are composed) below the gum line. If the cementum is worn away—from overly vigorous brushing or the aging process—the sensitive dentin is exposed. Repeated brushing with harsh abrasives may also wear away exposed dentin, increasing sensitivity.