Plaque is the accumulation of bacteria, microorganisms and their products which sticks to the tooth surfaces.
Dental plaque is soft and easily removed by brushing and flossing the teeth.
Calculus is dental plaque that has mineralized. Calculus can form when plaque is not removed from the tooth surfaces. This plaque becomes old and eventually forms into calculus. Calculus can form above or below the gumline. Calculus cannot be removed by brushing and flossing.