Technically, most frogs have teeth, just only in the upper jaw and none in the lower jaw (with one exception having re-evolved lower jaw teeth in apparent defiance of Dollo's Law). Toads have completely lost their teeth in both upper and lower jaws.

Interestingly, their teeth are unique. Unlike most animals, where the tooth is a single, whole structure, in frogs the tip and base of each tooth are connected by a layer of fibrous connective tissue. When most animals shed teeth, the whole tooth comes out, but frogs lose only the tips. Only modern and extinct amphibians have teeth like this