Calculus (also known as tartar) is hardened plaque that has been left on the tooth for a while and cannot be brushed away by the toothbrush. Accumulation of calculus can lead to gum disease which can cause tooth loss. Therefore, it is imperative to visit your dentist or hygienist to have a professional clean regularly (usually 6-monthly) to prevent the progression of gum disease. Oral hygiene at home is also very important. Your dentist will also coach you in the best technique of brushing and flossing so as to keep your teeth as clean as you can in between your 6 monthly visits.