Toothpaste is a complex product designed to deliver beneficial ingredients like fluoride and mechanically assist the cleaning process. The physical scrubbing power that removes food debris and plaque biofilm is provided by fine, insoluble particles known as abrasives. This mechanical action is often referred to as the “grit” of the toothpaste. It must be carefully balanced to ensure effective cleaning without causing damage to the tooth structure.
Quantifying Toothpaste Abrasiveness
The standardized method for measuring this scrubbing power is the Relative Dentin Abrasivity (RDA) value. RDA quantifies the potential of a toothpaste to wear down dentin, the softer tissue beneath the enamel layer, under controlled laboratory conditions. The test involves brushing a sample of dentin treated with a radioactive isotope using a slurry of the toothpaste being tested. The amount of radioactive material removed is measured and compared against a standard reference abrasive, which is assigned an RDA value of 100. A higher RDA number signifies greater abrasive potential. Low abrasivity is generally categorized as 0 to 70, medium range is 70 to 100, and a score above 100 is considered medium-high or high abrasivity.
The Function of Abrasive Agents
Abrasive agents are necessary because water and a toothbrush alone are insufficient to fully disrupt and remove the sticky layer of plaque. These particles act as a gentle scouring agent, mechanically helping the toothbrush bristles polish the tooth surface. This friction removes accumulated plaque biofilm and extrinsic stains caused by substances like coffee, tea, or tobacco.
Common abrasive materials include hydrated silica, calcium carbonate, and dicalcium phosphate. Hydrated silica is widely used due to its effectiveness and ability to be formulated with varying particle sizes to control abrasivity. Calcium carbonate is often less aggressive than some forms of silica. These agents scrub the tooth surface, ensuring a clean foundation for therapeutic ingredients like fluoride.
Dental Wear Risks and Safety Limits
While abrasives are necessary for cleaning, excessive mechanical action can lead to significant dental wear. Overly abrasive toothpastes can cause erosion of the enamel, the hard outer layer of the tooth, and expose the underlying dentin. This exposure can result in increased tooth sensitivity, as the microscopic tubules leading to the pulp are no longer protected.
High abrasivity also poses a risk to restorative dental work, such as fillings, veneers, and crowns, which can be damaged or prematurely worn down. To protect consumers, the American Dental Association (ADA) and the International Organization for Standardization (ISO) have established safety thresholds. The universally accepted maximum limit for daily-use toothpaste is an RDA of 250. This threshold ensures the toothpaste is safe for a lifetime of use, though excessive brushing force can worsen the risk of wear.
Choosing the Right Abrasivity Level
Selecting a toothpaste with the appropriate abrasivity level should be based on individual oral health needs. For the average user with healthy teeth and gums, a medium RDA value (70 to 130) provides an effective balance of cleaning power and safety. Individuals with exposed root surfaces, gum recession, or extensive dental restorations should opt for a low-abrasivity product with an RDA under 70. These formulas minimize wear on softer dentin and cementum.
Users aiming for the removal of heavy extrinsic stains may benefit from a higher RDA toothpaste, sometimes exceeding 100. These products should be used cautiously, possibly alternating with a low-abrasivity paste or for a limited duration. Individuals who use electric toothbrushes, which provide higher mechanical action, should also consider a lower-abrasivity toothpaste to compensate for the greater scrubbing motion.