Tartar, sometimes called calculus, is plaque that has hardened on your teeth. Tartar can also form at and underneath the gumline and can irritate gum tissues. Tartar gives plaque more surface area on which to grow and a much stickier surface to adhere, which can lead to more serious conditions, such as cavities and gum disease.
Not only can tartar threaten the health of your teeth and gums, it is also a cosmetic problem. Because tartar is more porous, it absorbs stains easily. So if you are a coffee or tea drinker, or if you smoke, it is especially important to prevent tartar buildup.