Milk inhibits tooth discoloration in chlorhexidine treatment

Dental Tribune International

Thu. 18. January 2024

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HALLE, Germany: Antiseptic mouthrinses containing chlorhexidine commonly cause tooth discoloration after eating or drinking during treatment. A study by the Fraunhofer Institute for Microstructure of Materials and Systems IMWS in Halle explored the extent to which certain beverages can prevent this discoloration in patients undergoing chlorhexidine treatment. The study’s findings suggest a simple solution for dental professionals to recommend to their patients during the treatment period: adding milk when drinking tea or coffee.

Dr Sandra Sarembe, the research scientist at Fraunhofer IMWS who led the study, explained the biochemical processes behind tooth discoloration in a press release: “The changes in colour can occur because the positively charged chlorhexidine sticks to the negatively charged surfaces in the mouth—i.e., saliva, gingiva and enamel—and remains there for a long period of time. In contrast to proteins—an element of dental plaque, which the substance prevents from forming—dye molecules bind very easily to chlorhexidine. And the stronger or more permanent the binding, the more likely it is to cause discoloration.” She added: “The active ingredient chlorhexidine itself does not have any colouring properties.”

The researchers examined a total of 11 beverages with varying pH values—since the pH value influences the binding of dye molecules to chlorhexidine—and colour properties. These beverages included diet lemonade, ginger tea, coffee and black tea, and trials were conducted both with and without milk. Water served as the reference point.

Daily mechanical tooth cleaning was replicated in a toothbrushing simulator. (Image: Fraunhofer IMWS)

The study is the first of its kind to examine the extent to which various liquids can cause discoloration during chlorhexidine treatment in such detail. The researchers developed a model to closely mimic the oral environment, utilising dental crowns exposed cyclically to artificial saliva, 0.2% chlorhexidine mouthwash and the different beverages. This cycle was repeated 28 times to simulate a typical 14-day chlorhexidine usage period. Additionally, daily mechanical tooth cleaning with water and toothpaste was replicated using a toothbrushing simulator.

Discoloration of teeth becomes less durable with added milk

The study’s findings revealed that the consumption of beverages high in dye molecules during chlorhexidine treatment leads to the formation of persistent surface layers on teeth. “As expected, black tea and red wine caused the most noticeable discoloration; coffee or beer ranked somewhere in the middle. The deposits were much easier to remove by brushing with toothpaste compared to water alone, but this did not alter the overall ranking in terms of the severity of the discoloration,” said Dr Sarembe.

(a) After drinking pure black tea during chlorhexidine treatment, significantly stronger staining can be seen under the scanning electron microscope in comparison with (b) drinking the beverage diluted with milk. (Image: Fraunhofer IMWS/Haleon)

“It was interesting to observe that, by diluting black tea and coffee with milk, the structure of the resulting layer of discoloration changes and becomes significantly less durable,” she continued. Therefore, an essential recommendation for dental professionals is to advise patients to add milk to their coffee and tea when undergoing chlorhexidine treatment.

The study was commissioned by the consumer healthcare company Haleon, and the results have not been published.