What does plaque harden into through the action of saliva?

Plaque hardens into calculus through the action of saliva. This process occurs when the minerals in saliva deposit into the soft plaque that forms on the teeth, transforming it into a hard substance known as calculus or tartar. Calculus adheres strongly to the tooth surface and can only be removed with professional dental cleaning. Understanding this process is crucial since plaque and calculus contribute to periodontal disease and other oral health issues if not managed properly.

Other options do not accurately represent the result of plaque hardening. Granulomas are a type of tissue response to inflammation, biofilm refers to a community of microorganisms that can form on various surfaces, and pathogenic bifidobacteria are specific types of bacteria that can be involved in gut health, but are not directly related to the hardening of dental plaque.