The oral microbiome includes all of the microbes living in your mouth, which includes those living on the hard surfaces of your teeth and the soft surfaces of your tongue and mouth walls. As soon as food enters your mouth the oral microbiome begins the digestion process before it even gets to your gut.
Your oral microbiome contributes to a range of health areas of your body. Directly it impacts your dental health, the gut microbiome and your ability to obtain nutrients and nourishment from food, however it also has impacts your cognition, mental health, and immune system. The impact your oral health has on the rest of your body can be studied through the contents of the oral microbiome.