A clinical trial from Aarhus University found that rinsing with arginine after sugar exposure measurably reduced acid levels in dental biofilms from patients with active caries. The study, published in the International Journal of Oral Science, included 12 participants fitted with custom dentures that allowed intact biofilm collection from both sides of the jaw. One side received arginine rinses three times daily; the other received distilled water as a placebo. After four days, arginine-treated biofilms showed higher pH values at 10 and 35 minutes post-sugar exposure, measured using a pH-sensitive fluorescent dye. Arginine also changed the carbohydrate structure of the biofilms: fucose-based components decreased overall, and galactose-containing carbohydrates shifted away from the tooth-facing base of the biofilm. At the bacterial level, arginine reduced the proportion of acid-producing streptococci in the mitis/oralis group while slightly increasing streptococcal species that metabolize arginine and produce alkaline compounds. Together, these changes made the biofilms less acidic and structurally less harmful. The researchers propose that arginine could be added to toothpaste or oral rinses as a low-risk adjunct to existing caries-prevention approaches. Because arginine occurs naturally in saliva and dietary proteins, it is considered safe for broad use, including in children.