Which Bacteria Causes Cavities? Looking Inside Your Mouth You probably know that bacteria in your mouth cause cavities, plaque, and tooth decay. And you also probably know that proper at-home care such as brushing and flossing is the best way to prevent cavities and more serious problems. (Combine with regular dental check-ups and professional cleanings for best results!) However, most species of bacteria are relatively harmless to our oral health; [...]