A clinical study shows that arginine, a natural amino acid, can reduce acidity in dental biofilms and alter their structure to protect against cavities. Researchers at Aarhus University tested the treatment on participants with active tooth decay, finding promising results after four days. The findings suggest arginine could enhance cavity-prevention products like toothpaste.
Sugar-loving bacteria in the mouth produce acids that erode tooth enamel, leading to cavities. These bacteria form dense dental biofilms on teeth, where acid production intensifies damage. Arginine, naturally present in saliva, helps counter this by enabling beneficial bacteria to produce alkaline compounds via the arginine deiminase system.
To test arginine's effects in the human mouth, a team led by Post.doc. Yumi C. Del Rey and Professor Sebastian Schlafer at Aarhus University in Denmark conducted a clinical study with 12 participants who had active tooth decay. Participants wore specially designed dentures to grow biofilms. Each day, they dipped the dentures in a sugar solution for five minutes, then treated one side with arginine for 30 minutes and the other with distilled water as placebo. This was repeated three times daily for four days, with arginine consistently on the same side.
"The aim was to investigate the impact of arginine treatment on the acidity, type of bacteria, and the carbohydrate matrix of biofilms from patients with active caries," explains Sebastian Schlafer, professor at the Department of Dentistry and Oral Health.
After four days, biofilms were analyzed. Using the pH-sensitive dye C-SNARF-4, researchers found arginine-treated biofilms had higher pH levels—indicating lower acidity—at 10 and 35 minutes after sugar exposure. "Our results revealed differences in acidity of the biofilms, with the ones treated with arginine being significantly more protected against acidification caused by sugar metabolism," says Yumi C. Del Rey, the first author.
Structural analysis with fluorescently labeled lectins showed reduced fucose-based carbohydrates in arginine-treated biofilms, potentially limiting harm. Galactose-containing carbohydrates shifted, becoming less abundant near the tooth surface and more toward the top, which may prevent acid buildup.
Bacterial DNA sequencing via 16S rRNA revealed shifts in microbial composition. Arginine reduced acid-producing Streptococcus mitis/oralis group while slightly increasing arginine-metabolizing streptococci, dominated overall by Streptococcus and Veillonella species. These changes made biofilms less aggressive.
The study, published in the International Journal of Oral Science in 2025, highlights arginine as a safe, natural option for cavity prevention, suitable even for children, possibly added to oral care products.
