calculus

n.; pl. calculi

1) a stone: a hard pebble-like mass formed within the body, particularly in the gall bladder (see gallstone) or anywhere in the urinary tract (see cystolithiasis, nephrolithiasis, staghorn calculus). Calculi in the urinary tract are commonly composed of calcium oxalate and are usually visible on X-ray examination. Some of these stones cause pain if they cause obstruction and prevent urine flow in the ureter or kidney, or by direct irritation of the bladder. Stones passing down a duct (such as the ureter) cause severe colicky pain. Most stones pass spontaneously, but some need to be broken into smaller pieces, usually by extracorporeal lithotripsy, and the remainder by endosurgical techniques (see litholapaxy) or rarely by open surgery. Calculi may also occur in the ducts of the salivary glands.

2) a calcified deposit that forms on the surface of a tooth as it is covered with dental plaque. Supragingival calculus forms above the gingivae (gums), principally in relation to the openings of the salivary gland ducts. Subgingival calculus forms beneath the crest of the gingivae. Calculus hinders the cleaning of teeth and its presence contributes to gingivitis and periodontal disease.