Human teeth are home to many different types of bacteria. This diverse oral microbiome ranges from microbes that are benign or even beneficial to those that can do some serious damage to our teeth. Tooth decay, also known as cavities in the U.S., is the most common human disease in the world, caused by a bacterial infection. Oral bacteria ferment sugars in the mouth, proliferate, and secrete excessive acid which leads to a breakdown of enamel and demineralization of the tooth structure.