Toothpaste abrasivity

Abrasion is one part of tooth wear

Non-carious tooth wear is loss of tooth structure without bacterial decay. Three processes are usually separated for description even though they interact in a mouth: abrasion is mechanical wear by an outside object or substance; erosion is chemical dissolution by non-bacterial acid; and attrition is tooth-to-tooth contact. A groove at the gumline is therefore not a signature that identifies one cause. Occlusal loading, acid, brushing and abrasive slurry can all contribute.

Toothpaste is the dominant source of abrasion during normal toothbrushing experiments. The toothbrush carries the slurry and changes the force and contact pattern, but water and a brush alone generally remove far less hard tissue. The clinically important question is not whether a paste abrades at all, because it must polish to clean, but whether the combined exposure is appropriate for the surface being cleaned.¹⁴

Enamel and dentin are not interchangeable substrates. Enamel is highly mineralized and far more wear resistant. Dentin, and the thin cementum over a root, become relevant after gum recession or cervical wear exposes them. The same brushing system that is uneventful on sound enamel can be a poor choice for an exposed root.

What the abrasive system is doing

Common dentifrice abrasives include hydrated silicas, calcium carbonate, calcium phosphates, alumina, sodium bicarbonate and, in some products, charcoal. A name on an ingredient list cannot predict performance. Abrasion depends on particle hardness, shape, size distribution, concentration, aggregation, solubility and how those particles interact with binders, surfactants and water in the finished paste.⁴

This is why “contains silica” is not a useful verdict. In a study of 26 retail dentifrices, RDA values ranged from 36 to 269 and stain-removal scores ranged from 25 to 138. Products with strong stain removal were often, but not always, more abrasive. Some abrasive systems cleaned efficiently at lower RDA, demonstrating that cleaning and wear are related without being locked together.⁴

What RDA measures, and what it leaves out

Relative dentin abrasivity was developed as a controlled comparison. In the established radiotracer method, prepared dentin is irradiated, brushed with a standardized slurry and the radioactivity released from removed dentin is compared with a reference abrasive assigned a value of 100. Profilometry-based methods instead measure changes in the surface profile. ISO 11609 standardizes dentifrice requirements and test methods; the ADA uses an RDA ceiling of 250 for its Seal of Acceptance.¹²

Reference

RDA 100

ADA Seal ceiling

RDA 250

Measures

Dentin, in vitro

The ADA’s interpretation is deliberately two-sided. With proper technique, lifetime use of a dentifrice at or below 250 is expected to produce limited dentin wear and virtually no enamel wear. At the same time, the ADA states that values below 250 should not be used quantitatively to rank toothpaste safety.¹ A paste at 120 is more abrasive than one at 60 in that assay; it is not thereby “twice as damaging” in a mouth.

RDA leaves out the toothbrush, force, time, frequency, dilution by saliva, acid exposure, pellicle, individual anatomy and whether the contact surface is enamel, dentin, cementum or a restoration. It also says nothing directly about surface roughness. Different methods can rank products differently, especially at the more abrasive end, and RDA and relative enamel abrasivity can diverge sharply.³⁸¹⁷

The correct use of RDA is quality control and rough comparison under one standardized test. The incorrect use is a color-coded internet chart that turns every value into a diagnosis. Published numbers can also outlive the formulation they measured.

Why whitening creates the trade-off

Extrinsic discoloration sits on the acquired pellicle and outer tooth surface. Intrinsic color comes from within enamel and dentin. Abrasives can remove the first; they cannot bleach the second. Whitening dentifrices may supplement polishing with peroxide, enzymes, citrate, pyrophosphates or hexametaphosphate, or use optical pigments such as blue covarine, but the abrasive system remains central to many formulations.⁵

A controlled laboratory study separated chemical exposure from brushing in six whitening dentifrices. The chemical-only treatment did not produce significant color differences; the chemo-mechanical treatment did, and whitening correlated with abrasive level (r² = 0.80). Under those conditions, the action was mainly mechanical stain removal.⁶

Clinical evidence confirms that whitening pastes can improve the appearance of extrinsic stain. A systematic review and meta-analysis found better stain and shade-guide outcomes than regular dentifrices, but rated the evidence low to moderate and found more reported adverse effects. White strips produced greater whitening in the small direct comparisons. Those adverse-effect data do not measure long-term hard-tissue loss, so they should not be used as proof of abrasion.⁷

What direct abrasion studies found

The evidence does support concern about some products. In a 2016 brushing-machine study of root dentin, three silica-based whitening pastes produced mean wear of 7.59 to 8.86 µm, compared with 2.89 and 2.94 µm for two regular pastes under the same 2,500-cycle protocol.⁹ These are comparative laboratory results, not a forecast that a user loses that depth over an equivalent calendar period.

In an erosion-abrasion model, some whitening pastes increased wear of acid-challenged bovine root dentin while others performed similarly to a regular control or to erosion alone. The authors’ clinical conclusion was narrow and appropriate: some whitening dentifrices deserve caution in patients with exposed roots.¹⁰

Other studies show why the category cannot be treated as a verdict. A 2023 simulation found the charcoal whitening product caused the most dentin wear, while a blue optical whitening paste did not differ significantly from a regular paste; all tested products remained within the study’s accepted abrasivity range.¹¹ A 2024 study found peroxide whitening pastes at RDA-PE 19 to 46 and silica whitening pastes at 80 or 111 after 4,000 strokes. Particle concentration, not the word “whitening,” was the significant formulation factor.¹²

Activated charcoal is equally variable. Twelve charcoal toothpastes measured from RDA 24 to 166 and relative enamel abrasivity 0 to 14, broadly overlapping ordinary commercial dentifrices.¹³ One charcoal product can be abrasive; the category is not uniformly so. “Natural” describes origin, not tribology.

Who has the narrower safety margin

The strongest case for choosing a less abrasive formula is exposed root dentin. In a simulated non-carious cervical lesion model, higher-abrasivity slurries produced faster and greater root-surface volume loss at advanced brushing intervals. The authors specifically advised lower-abrasivity dentifrices after root exposure.¹⁵

Acid narrows the margin further by partially demineralizing the surface before mechanical contact. Dietary acids, gastric reflux and recurrent vomiting are different exposures, but each can leave mineralized tissue more susceptible to wear. Reviews conclude that abrasive dentifrices may increase surface loss on eroded teeth, while emphasizing that most of the evidence comes from laboratory and in situ models rather than long clinical trials.¹⁶

Technique still matters. Increasing force, duration and frequency increases cumulative contact; brush stiffness and head geometry alter how that force reaches a cervical surface. A lower-RDA paste does not make forceful scrubbing harmless, just as a pressure sensor does not rescue an unnecessarily abrasive formulation. The variables multiply rather than substitute for one another.

Clinically, the reasons to ask for an individual assessment are visible recession, a wedge-shaped or scooped defect near the gumline, progressive sensitivity, a history of erosive tooth wear, frequent acidic drinks, reflux or an eating disorder. These findings do not prove toothpaste caused the damage. They identify a mouth in which avoidable abrasion is a poor bargain.

A defensible way to choose

• Choose for the problem you have. If the issue is removable coffee or tea stain, a whitening paste may help. If the tooth itself is darker, repeated polishing is the wrong mechanism.
• Treat the exact product as the evidence unit. Do not infer abrasivity from “whitening,” “charcoal,” “natural” or one ingredient. Ask for a current RDA result measured on the current formulation.
• Interpret RDA as one variable. A documented lower-abrasivity paste is a reasonable precaution for exposed roots or active wear, but numbers below 250 are not a universal ladder from dangerous to safe.
• Reduce force before chasing products. Use a soft brush and light pressure. A powered brush with a pressure warning can make excessive force visible; our review of powered toothbrushes covers that evidence.
• Address acid separately. A different toothpaste cannot neutralize the clinical importance of repeated dietary or gastric acid exposure. Reflux, recurrent vomiting and progressive erosion deserve professional care.

None of this is an argument for brushing with water alone or abandoning toothpaste. Normal oral hygiene prevents disease, and reviews conclude that its benefits substantially exceed the possible side effects. The argument is narrower: cleaning does not improve without limit as abrasivity rises, and someone with a vulnerable surface should not pay for stain removal with avoidable tissue loss.¹⁴

Where the evidence is weak

Abrasivity research has an unavoidable translation problem. Controlled machines are good at isolating product differences, but people do not brush polished slabs with fixed loads in standardized slurry. Laboratory cycles are sometimes described as equivalent to a number of months or years; that conversion should be read as protocol shorthand, not a literal clinical clock.

There is no long-term randomized trial assigning people to high- and low-abrasivity pastes and measuring irreversible tooth loss for decades. Such a trial would be slow, confounded by technique and acid exposure, and ethically difficult once wear emerged. The evidence is therefore a chain: standardized abrasion measurements, mechanistic erosion-abrasion work, shorter in situ experiments and clinical observation of multifactorial lesions. It is enough to justify risk reduction, not enough to calculate an individual’s future loss from an RDA number.³

Product studies are also time-specific. Formulations change while names and packaging stay familiar, and some influential whitening reviews and dentifrice tests have authors or funding from oral-care manufacturers. Reference 5 was authored from Unilever Oral Care; reference 4 was performed at a commercial dental-products testing laboratory. Those facts do not invalidate the methods or results, but they belong beside them.