Most vertebrates have continuous tooth generation, meaning that lost teeth are replaced with new teeth. Mammals, however, including humans, have teeth that are generally only replaced once, when milk teeth are replaced with permanent teeth.

Researchers have now shown that continuous tooth generation can be induced in mammals. [...] As a result of stimulating this particular signalling, one mouse molar developed dozens of new teeth with normal dentin, tooth enamel and developing roots. The crowns were, however, simple and cone-shaped, unlike the typically more complex multiple cusps of mouse molars. [...]

It is reasonable to conjecture that the potential for continuous tooth generation may also have been retained in humans. Who knows: perhaps dentists in the distant future may be able to use this million-year-old regenerative potential to make their patients grow new teeth to replace lost ones.