An obscure word brought to my attention by A.Word.A.Day, thegosis was defined there as "grinding of teeth as a means of sharpening them"; the illustrative example suggested one might do this to prepare the teeth to be weapons. I always double check these things; my regular on-line dictionaries didn't have entries for thegosis, but an internet search turned up a page on thegotics, and defined thegosis as to whet or sharpen, or metaphorically to excite or provoke.
Thegosis is usually confused with bruxism, the involuntary, usually night-time, grinding of the teeth, but in fact, argues Dr R.G. Every, a Christchurch dentist, thegosis is innate genetically programmed behaviour which refines and refreshes the tooth surface. It is practiced by many vertebrate and invertebrate animals in order to hone the teeth for use as tools and/or weapons. Every's theory, claims this web page, has been largely ignored or misquoted, and thus "the entire literature on tooth-wear, including studies of the human dentition, and the dietary and behavioural conclusions derived from them is fundamentally flawed."
I have been drawing here from Kevin B Scally's webpage article, at