Polyphydont

A polyphyodont is an animal whose teeth are continuously replaced. Most toothed fishes are polyphyodonts. Diphyodonts, on the other hand, are characterized by having only two successive sets of teeth. Reptiles and most other vertebrates are also polyphyodonts, mammals being the main exception. Mammals chew their food. This requires a strong set of firmly attached, strong teeth and a "full" tooth row with no gaps. [1]

Manatees and elephants are unusual among mammals because they are polyphyodonts, as opposed to most other mammals who replace their teeth only once in their lives (diphyodont). The new teeth emerge from the back of the jaw and are sometimes referred to as “Marching Molars”. [2]