Researchers testing a naturally occurring amino acid found in saliva say it could help make dental plaque less damaging — and potentially reduce the risk of cavities before they start.
In a small human clinical trial, scientists from Aarhus University found that arginine, an amino acid already present in the mouth, can alter dental plaque in ways that make it less acidic, structurally less harmful and more supportive of beneficial bacteria.
Arginine plays a key role in neutralizing acids produced when oral bacteria break down sugars. Those acids are a major driver of enamel erosion and dental caries. While laboratory studies have previously suggested arginine could influence plaque behaviour, this study examined its effects directly inside the human mouth.
The findings were published in the International Journal of Oral Science.
Testing plaque in real mouths
The study involved 12 participants with active tooth decay. Each received specially designed dentures that allowed researchers to grow and collect intact dental biofilms — the complex bacterial communities that form plaque — from both sides of the jaw.
Participants dipped their dentures into a sugar solution for five minutes, followed immediately by either arginine or distilled water as a placebo for 30 minutes. One treatment was applied to one side of the mouth and the other to the opposite side. The routine was repeated three times a day for four days, with arginine always applied to the same side.
“The aim was to investigate the impact of arginine treatment on the acidity, bacterial composition and carbohydrate structure of biofilms from patients with active caries,” said Professor Sebastian Schlafer of Aarhus University’s Department of Dentistry and Oral Health.
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Less acid after sugar exposure
To assess acidity within the biofilms, researchers used a pH-sensitive dye known as C-SNARF-4, which allowed them to measure pH levels at different depths of the plaque.
Biofilms treated with arginine maintained significantly higher pH levels — meaning lower acidity — at 10 and 35 minutes after exposure to sugar.
“Our results revealed clear differences in acidity,” said lead author Yumi C. Del Rey. “The biofilms treated with arginine were significantly more protected against acidification caused by sugar metabolism.”
Structural changes inside plaque
The team also examined the carbohydrate “scaffolding” of the biofilms using fluorescently tagged lectins, proteins that bind to specific sugars. Two major components — fucose and galactose — were analyzed because they are thought to contribute to the formation of acidic pockets within plaque.
Arginine-treated biofilms showed an overall reduction in fucose-based carbohydrates, which may make plaque less capable of trapping harmful acids. Researchers also observed a structural shift, with galactose-containing carbohydrates decreasing near the tooth surface and increasing toward the top of the biofilm — a change that could further limit acid damage to enamel.
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Shifting the oral microbiome
Using 16S rRNA gene sequencing, the researchers analyzed bacterial composition within the biofilms. While both arginine-treated and placebo samples were dominated by Streptococcus and Veillonella species, arginine reduced the presence of the mitis/oralis group of streptococci — bacteria that produce acid but generate little alkali.
At the same time, arginine slightly increased bacteria better equipped to metabolize arginine and raise pH levels, creating a more balanced microbial environment.
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Potential role in prevention
Taken together, the findings suggest arginine can make dental plaque less aggressive by lowering acidity, reshaping its structure and nudging the oral microbiome toward a healthier balance.
Because arginine is naturally produced by the body and found in dietary proteins, researchers say it could be safely incorporated into toothpastes or oral rinses, particularly for patients at higher risk of cavities — including children.
Larger clinical trials will be needed, but the study adds to growing evidence that leveraging naturally occurring compounds may offer a promising path in preventive dentistry.