Toothbrushing with fluoride toothpaste can help prevent tooth decay. The prebiotic action of arginine can also help buffer the oral plaque pH, which helps to prevent tooth demineralization. Although their anticavity benefits are recognized, it’s unclear exactly how fluoride- and arginine-containing toothpastes affect the dental plaque microbiome. To learn more, researchers recently sequenced the dental plaque microbiomes of 26 patients with active cavities and 27 cavity-free patients who brushed their teeth with fluoride toothpaste for three months and then with fluoride+arginine toothpaste for six months. The fluoride toothpaste altered the expression of hundreds of genes and changed the microbiome composition and activity of patients with or without cavities. Specifically, it reduced the abundance of cavity-associated bacteria while increasing that of healthy bacteria. although it also increased the abundance of some gum disease-associated bacteria. The fluoride+arginine toothpaste further improved the dental plaque microbiome, decreasing the abundance of both cavity- and gum disease-associated bacteria and increasing the expression of genes that transform arginine into pH-buffering ammonia. Although the mechanisms need clarification, these findings reveal that a fluoride toothpaste promotes a healthy oral microbiome, and a toothpaste containing both fluoride and arginine could be even more effective in promoting a healthy microbiome, leading to better cavity prevention.