Yes, stingrays do, in fact, have teeth! Stingray teeth are small and flat. They are attached to the jaw by a structure which is called a tooth band. The tooth band holds all of the stingray’s teeth. A stingray employs these teeth to crush and grind crustaceans. The tooth bands line the upper and lower jaw and the stingray uses both bands to crush prey.
Divers occasionally find stingray teeth, mixed in with shark teeth, resting on the ocean floor. Crustaceans can have very hard shells, so occasionally the stingray will lose a tooth. Stingray teeth are replaceable in a similar manner to sharks teeth. New teeth are grown on the backside of the tooth band and will push forward to replace missing teeth. It takes a lot of work to crush a crustacean and a the jaw plates of a stingray are very strong.
A stingrays mouth is only visible from underneath. Inside the frown-like mouth lies the strong jaws and rows of teeth which rest on the tooth bands. So, while we cannot usually see them, it is true that stingrays do have teeth.