A diphyodont is any animal with two successive sets of teeth, initially the
"deciduous" set and consecutively the "permanent" set. Most mammals are diphyodonts as to chew their food they need a strong, durable and complete set of teeth.
contrast with polyphyodonts, whose teeth are constantly replaced. Diphyodonts also differ from monophyodonts which are animals who have only one set of teeth that do not change over a long period of growth.
In diphyodonts the number of teeth that are replaced varies from species to species. In humans a set of twenty deciduous teeth, or "milk teeth", are replaced by a completely new set of thirty-two adult teeth.
Polyphyodonts include most toothed fishes, many reptiles such as crocodiles and most other vertebrates, mammals being the main exception. New, permanent teeth grow in the jaws, usually
under or just behind the old tooth, from stem cells in the dental lamina. Young animals typically have a full set of teeth when they hatch; there is no teeth change in the egg. Within days, tooth replacement begins, usually in the back of the jaw continuing
forward like a wave. On average a tooth is replaced every few months.
In anatomy, a heterodont is an animal which possesses more than single tooth morphology. For example, members of this group generally possess incisors, canines, premolars, and molars. The presence of heterodont dentition is evidence of some degree of feeding/hunting specialization
in a species. In contrast, homodont dentition refers to a set of teeth that possess the same tooth morphology.