Calculus formation occurs in the presence of...?

Calculus formation, also known as tartar, occurs when plaque, a sticky film of bacteria that forms on teeth, is mineralized by the saliva. Saliva contains minerals such as calcium and phosphate, which precipitate and combine with the organic components of plaque over time, leading to the hardening process that creates calculus.

The presence of both plaque and saliva is crucial for this process to occur. Plaque provides the organic matrix that attracts minerals from the saliva, initiating the calcification process. Without plaque to begin with, calculus cannot form, and while saliva alone contains the necessary minerals, it does not lead to calculus formation without the presence of plaque. Therefore, the correct answer encompasses the critical interplay between both substances.