A variety of methods exist to quantify the abrasivity of the inorganic materials commonly used in dentifrices to impart cleaning properties. The industry standard relative dentine abrasion test (RDA) uses a radiotracer technique to quantify the mass of bovine dentine lost after 1500 brush strokes. Another technique (Einlehner), adapted from the paper industry, looks at the mass lost from a brass mesh after hundreds of thousands of revolutions of a mechanical apparatus. Yet another method (PAV) quantifies abrasion by measuring the gloss of a poly methyl-methacrylate (PMMA) plate after 300 brush strokes in the presence of a simple silica slurry or dentifrice.
Method:
In this study we abraded PMMA plates in accordance with the last of these three approaches but then examined the abraded surface using a state-of-the-art optical profilometer. The plates were abraded in the presence of inorganic particles with a variety of structures, compositions and particle sizes.
Result:
The profilometer data was found to correlate with the gloss of the abraded PMMA plates, which was expected. Unexpectedly, there was no evidence of mass loss from the PMMA plate for any of the inorganics studied. These findings were found to be consistent with a low stress, three-body abrasion model.
Conclusion:
The absence of mass loss was consistent with a micro-ploughing mechanism, whilst those techniques whose conditions produce a mass loss are likely to fit a micro-cutting model. Future studies will attempt to use optical profilometry to establish which of these models, if any, is appropriate for low brush strokes with a dentine substrate.