The role of oral nitrate-reducing bacteria in the prevention of caries: A review related to caries and nitrate metabolism

Circulating nitrate is actively absorbed by salivary glands and secreted into the oral cavity, where it is reduced to nitrite by oral nitrate-reducing bacteria. This process has previously been considered harmful because nitrate and nitrite can promote the formation of potentially carcinogenic N-nitrosamines. However, recent studies have shown that nitrate may have other physiological functions, and it can serve as a precursor for the systemic production of nitric oxide and perform nitric oxide (NO)-like functions, such as promoting vasodilation, regulating metabolic diseases, alleviating senescence, and protecting the digestive system. Inside the oral cavity, nitric oxide is likely to inhibit sensitive species as part of the non-specific oral immune system. Exogenous administration of nitrate can maintain a balance in the pH of saliva. Oral nitrate-reducing bacteria can control the progression of caries by metabolizing lactic acid and reducing its accumulation, which is beneficial to the homeostasis of the oral microecology. In the current manuscript, we reviewed nitrate-reducing bacteria and their nitrate-metabolizing functions during the development of caries. Furthermore, we listed the effects of probiotics and dietary modification, which may be a promising method to prevent the occurrence of caries. We believe that this review provides novel ideas for the prevention of caries and treatment in clinical settings.