"Three-Toed (Bradypus variegatus) and Two-Toed (Choloepus hoffmanni) Sloths" by Dallas Krentzel;
used with permission under CC BY 2.0
For a long time, it was thought that sloths did not have teeth; in fact, they were once classified in the same grouping as anteaters--of the Edentata grouping, meaning "without teeth." Truth be told, sloths do have teeth... just not very many!
Sloths have only 10 upper teeth and 8 lower teeth. The most prominent teeth on a sloth are the two front teeth that they use to bite off their food. Their other teeth are flat and used for grinding up their food (mostly tree leaves)!