Saliva, a heterogeneous fluid containing simple proteins, glycoproteins, electrolytes, small organic molecules and compounds transported from the blood, constantly bathes the teeth and the oral mucosa. It acts as a cleansing solution, an ion reservoir and a buffer. In addition to its host-protective properties, saliva could serve as first line defence against free-radical mediated oxidative stress, since the process of mastication and digestion of ingested foods promotes a variety of reactions, including lipid peroxidation. Moreover, during gingival inflammation, the flow of gingival crevicular fluid increases change in the composition of saliva with products from inflammatory response; this, in turn, could play some role in controlling and/or modulating oxidative damages in the oral cavity. This is the reason why the antioxidant capacity of saliva has attracted increasing interest, and led to the development of techniques suitable for of the antioxidant capacity of saliva.
Here, we review current peer-reviewed literature concerning the nature and characteristics of free radicals, reactive oxygen species, pro-oxidants and antioxidants present in saliva, especially its pro-oxidant and anti-oxidant characteristics, as well as current methods for assessing the antioxidant capacity of saliva. In the last decade, several methods were developed for assaying the antioxidant activity of saliva, indicating the increasing interest of researchers and clinicians. Unfortunately, systematic studies of saliva are still lacking, even in healthy populations.