RDA — what toothpaste abrasivity indicates and when it truly matters

“RDA 70”, “low RDA”, “toothpaste with an RDA below 100”. This abbreviation is appearing on an increasing number of tubes and in more and more rankings, usually without explanation. Yet, it is one of the few numbers in the world of toothpastes that is backed by a standardized measurement method. It is worth knowing what it measures and what it does not.

What is RDA?

RDA (Relative Dentin Abrasivity) is the relative abrasivity of a toothpaste against dentin. It is measured in a laboratory: dentin is radioactively labeled, brushed with toothpaste for a set number of strokes, and the amount of material lost is checked compared to a reference toothpaste assigned a value of 100. The method dates back to the 1970s and is currently part of the ISO 11609 standard for toothpastes.

The scale is conventional: water itself has an RDA of about 4, baking soda about 7, and most toothpastes fall between 50 and 150. The upper limit permitted by the standard is 250; toothpaste exceeding this value cannot be sold as a product for daily use.

What RDA says and what it doesn't

It says how strongly a toothpaste abrades dentin under laboratory conditions. It does not say how strongly it abrades enamel (which is a different, much harder material and has a separate indicator, REA), nor how it will behave in your mouth with your pressure, your toothbrush, and your saliva. Pressure force and bristle hardness have a greater impact on abrasion than the difference between RDA 70 and 110.

An important caveat: below 250, there is no proven “safety scale”. Studies do not show that a toothpaste with an RDA of 60 protects teeth better than a toothpaste with an RDA of 120 for a person with healthy enamel. Anything below the limit is considered safe with proper brushing technique. Low RDA is a precaution, not clinical evidence.

When does low RDA matter?

In three situations where you are scrubbing something softer than enamel:

• Exposed dentin. When gums recede and expose the tooth necks, the toothbrush hits the dentin, which is several times softer than enamel and absorbs abrasion like a sponge. Here, abrasives really make a difference, especially after an acidic meal when the surface is softened.
• Hypersensitivity. Exposed dentin tubules are painful; a strong abrasive makes it difficult to close them and can worsen the problem. More in the article what for tooth sensitivity.
• Freshly after whitening. For several days after the procedure, enamel behaves as if it were demineralized. Common sense dictates using a mild toothpaste then, preferably with hydroxyapatite; leave aggressive “whitening” toothpastes for later or not at all, because they won't change the color of the tooth anyway.

Additionally, there is one technical rule that works regardless of the toothpaste: a soft toothbrush, light pressure, and after an acidic meal, wait half an hour before brushing.

Why do so few manufacturers provide RDA?

Because the measurement is expensive, performed in only a few laboratories worldwide, and the result is not required on the label. Brands that provide it usually have a vested interest: either they want to show a low value or they are explaining a high one. The absence of a number does not mean the toothpaste is aggressive. It means it is unknown, in which case we look at the type of abrasive in the INCI: hydrated silica and calcium carbonate are standard, while activated charcoal and larger amounts of soda increase abrasion.

How it looks in our selection

We only provide values declared by the manufacturers:

• ANNAGIO Intense Fresh Effect: RDA 70, the lowest declared value in our selection.
• Davids: the manufacturer states an RDA of 101–111 depending on the variant; Charcoal + Peppermint is in the upper part of the range.
• BOKA, Ollie, PrevDent, LEBON, Laro, LyDenti: manufacturers do not provide RDA values or the data is inconclusive, so we do not list them. In their INCI, they all contain mild abrasives (hydrated silica, calcium carbonate, kaolin); BOKA and PrevDent are also marketed by the manufacturers for people with hypersensitivity.

If you have receding gums or hypersensitivity, start with the hypersensitivity toothpaste collection: that is where we have gathered toothpastes with hydroxyapatite and potassium nitrate, designed with exposed dentin in mind.

Frequently asked questions

Does a low RDA toothpaste clean worse?

Not necessarily. Cleaning is primarily the work of the toothbrush and the detergent; abrasives help with plaque and discoloration. A toothpaste with an RDA of 70 used with good technique cleans better than a toothpaste with an RDA of 150 used for 30 seconds.

Do whitening toothpastes have high RDA?

Often, but not always. Some base “whitening” on abrasives (high RDA), others on enzymes or hydroxyapatite (low). The name on the tube says nothing; the ingredients do.

Does RDA also apply to children's toothpaste?

Yes, the same scale. Children's toothpastes usually have low abrasivity because the enamel of primary teeth is thinner. BOKA Kids uses the same mild abrasives as the adult toothpastes.

Sources: Hefferren J.J., “A laboratory method for assessment of dentifrice abrasivity”, Journal of Dental Research 1976; ISO 11609:2017 “Dentistry — Dentifrices — Requirements, test methods and marking”; American Dental Association, materials on toothpaste abrasivity (RDA and 250 limit); manufacturer materials (annagio.de, davids-usa.com).