D-institut [creativecommons license] via Wikimedia CommonsTooth growth in mammals is restricted to a single row, whereas non-mammalian vertebrates, such as sharks, grow multiple rows of teeth. Until recently, the mechanisms that enabled or restricted iterative tooth development were not well understood. Understanding these regulatory mechanisms may hold benefits for humans—we don’t need multiple rows of teeth, but being able to reactivate the tooth development pathway later in life may offer a strategy for regenerating teeth lost to tooth decay or gum disease.