11 Oct 2012
There are various types of toothpaste available on the market. They
come as pastes and gels, there are some that guard against tooth decay
or protect teeth from acid attack, others that are designed for
sensitive teeth. But which toothpastes clean well? Which preserve the
tooth enamel? A new evaluation method sheds light on the subject.
Everyone wants to have beautiful teeth. After all, a perfect set of
teeth symbolizes health and youthfulness, and can even influence career
prospects. If having pristine teeth calls for thorough oral hygiene,
then how well or badly does a given toothpaste clean? How effective is
it? What should it contain in order not to damage the structure of the
teeth? Such questions are primarily of interest to manufacturers of
dental hygiene products, and answers are being delivered by researchers
from the Fraunhofer Institute for Mechanics of Materials IWM in Halle.
Through close collaboration with the Microtribology Centre µTC in
Karlsruhe they 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.
Dangerous abrasive effect
Cleaning particles are an important component of toothpastes. These
abrasives, as they are known, mechanically remove dental plaque.
Nevertheless, the paste should not be too strongly abrasive. Over the
years the abrasion can cause damage to the tooth enamel, which does not
regenerate itself. This damage is more visible and pronounced in the
soft dentin. The German Dental Association recommends that people choose
less abrasive toothpaste if the necks of their teeth are exposed.
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 radiation 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.
Determining abrasion rates with microtribological tests
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"
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. "Our findings reveal that the
RDA value of toothpastes correlates with the depth of abrasion; the
higher the value, the greater the abrasion. By analyzing the friction
value we also identified a clear relationship between the friction
behaviors of the bristle on the dental enamel and the abrasiveness of
the toothpaste", sums up Kiesow. The new process allows the researchers
to not only characterize the abrasion more quickly and simply, but also
to describe how different geometries of toothbrush filaments act upon
the surface of the tooth and how the bristle shape should ideally be
designed. The experts at IWM can use their know how to support
manufacturers of dental hygiene with product development. At the end of
the day it is the consumer who benefits most.