A trephine is a surgical instrument with a cylindrical blade. They may be specially designed for obtaining a cylindrical shaped core of bone that can be used for tests and bone studies, cutting holes in bones (i.e., the skull) or for cutting out a round piece of the cornea for eye surgery.
A wood figurine of dentist, holding tooth extracting forceps behind his back, from the early 20th century German set of doctors with inscription: "Bin nich herzlos, ziehe schmerzlos" Translation: "I'm not heartless, I pull painless"