Medically reviewed by Edmund Khoo, DDSMedically reviewed by Edmund Khoo, DDS Calculus, or tartar, is a hardened substance that forms on teeth. A calculus bridge occurs when this calculus stretches ...

(via Numberphile) This video features Swagat Saurav Mishr discussing the research of Professor P.P.Divakaran, and the very early history of calculus in India.