Testing // Fast Toothpaste Check © Based on Material by FHG, Germany
Researcher at Fraunhofer Institute for Mechanics of Materials IWM in Halle have developed a new process for testing the abrasive effect of toothpastes, allowing this ‘abrasivity’, as experts call it, to be compared and evaluated in the lab. They worked closely with the Microtribology Centre µTC in Karlsruhe on a new evaluation method. The abrasive effect of a particular toothpaste on tooth dentin depends on the hardness, amount and particle size of the abrasive additives it contains, such as silica or alumina. Abrasivity is measured as the RDA value (radioactive dentin abrasion), ranging from 30 to over 200. This value is determined via a complex process that involves testers brushing over radioactively marked dentin samples. The abraded material is then measured via the resultant radiati- on intensity of the toothpaste slurry. Not all experts agree on the validity of RDA values, as test results have been known to vary partly from lab to lab.
The researchers at the IWM have chosen an alternative method to this radiotracer system. "Our new approach enables us to determine realistic abrasion rates and characterize the interaction between brush, enamel and toothpaste. What’s more, our tests are less laborious than the time-intensive radiotracer procedures carried out by only a handful of laboratories worldwide," says Dr. Andreas Kiesow, team leader at the IWM. The scientist and his team have successfully managed to determine the abrasion of various toothpastes on a microscopic scale and to measure the friction values using microtribological experiments. "Until now, tribological values such as friction coefficient, did not exist" says Kiesow.
The researchers use human teeth as well as different toothpastes made by industrial partners for their experiments. These toothpastes were diluted with water and saliva in order to create a solution whose consistency corresponds to the mixture of toothpaste and saliva that is present when people brush their teeth. The friction and wear tests were each carried out with a single bristle – referred to as a monofilament. This is mounted in specialized tribological instruments, a microtribometer and a nanoindenter, and moved over the sample in both straight and circular motions, in the latter case up to 8000 times. Highly sensitive instruments then measure the depth of the resultant marks left on the surface of the tooth.