I had an Australian dentist for a while and he always called it Calculus so I guess it's been around for a while. It's very confusing as I couldn't see what the link was to a mathematical term but good old Wikipedia came up with the answer
"The word comes from Latin calculus "small stone", from calx "limestone, lime",[1] probably related to Greek χάλιξ chalix "small stone, pebble, rubble"[2] which many trace to a Proto-Indo-European root for "split, break up".[3] Calculus was a term used for various kinds of stones. This spun off many modern words, including "calculate" (use stones for mathematical purposes), and "calculus", which came to be used, in the 18th century, for accidental or incidental mineral buildups in human and animal bodies, like kidney stones and minerals on teeth.[3]
Tartar, on the other hand, originates in Greek as well (tartaron), but as the term for the white encrustation inside casks, aka potassium bitartrate commonly known as cream of tartar. This came to be a term used for calcium phosphate on teeth in the early 19th century"
It looks like we are returning to the early 19th century!
Taz x