Polished to perfection

Dentists use special polish to make teeth shiny white again. A new measuring technique determines the effect of dental care products and helps to optimize them so they polish the rough tooth surfaces until they are perfectly smooth, but preserve the tooth enamel.

Brush your teeth twice a day! Any child knows these days that regular tooth care is the only way to banish the bacteria that cause caries. Yet sometimes that is not enough. The tooth surface wears down and gets uneven – and the problem is that dental plaque adheres particularly well to a rough surface. Dentists therefore offer professional cleaning services, removing plaque and discoloration with abrasive prophylactic pastes. This renders the tooth surface beautifully smooth, making it difficult for bacteria to gain a foothold. Yet there is a risk that the polishing treatment will also grind away precious tooth enamel and dentin at the exposed necks of teeth. The manufacturers therefore have to find the happy medium when developing their prophylactic pastes: The pastes should be just abrasive enough to remove superficial discoloration and plaque, but preferably not wear down the tooth enamel.

Until now, scientists lacked any realistic objective measuring techniques to assess tooth abrasion caused by chewing and by the effect of toothpastes. A leading manufacturer of dental hygiene products asked the Fraunhofer Institute for Mechanics of Materials IWM in Freiburg, one of whose specialties is the analysis and visualization of surface roughness, to help them develop new prophylactic pastes. The effectiveness of a prophylactic paste has so far been measured by how well the granules that it contains are able to smoothen a rough surface. The test is performed by first roughening tooth enamel or denture materials such as ceramics and titanium to a precisely defined value with an aggressive grinding material. But this does not truly reflect reality, as chewing wears out different materials at different rates. The new measuring method developed by the IWM researchers, a kind of chewing simulation, takes this factor into account. As the experts led by Dr. Raimund Jaeger, head of the Biomedical Materials and Implants department, discovered when comparing pastes and subsequently analyzing the surfaces, some pastes polish the surface but also unnecessarily ablate the tooth material, producing slight grooves on the tooth surface. The ideal paste, on the other hand, polishes so lightly that only the roughness is eliminated while the tooth enamel is hardly ground at all. “Obviously, every case is different,” says Jaeger. “Teeth with particularly heavy plaque or discoloration will need a more abrasive paste.” Normally, however, a gentler prophylactic paste will do the job. Thanks to the IWM researchers, the manufacturer has now been able to optimize the formulation.