With the exception of mammals, most animals are polyphyodonts – that is they continually replace their teeth throughout their lives.

Sharks have a tooth replacement process that works much like a conveyer belt from back to front. Crocodiles will renew each of their 70-odd teeth about 50 times.

No doubt we have two sets of teeth because baby teeth would seem inharmonious to an adult mouth, all strangely small with spread spaces in between.

Still, nowhere near as outrightly creepy as photos of newborns run through Faceapp to give them toothy smiles. Exclaimed as hilarious by many, it has an AI, cyborg, chicken growth hormone affect that brands itself into the backbrain to punch through a serene dream.

Interestingly, in both fossil and modern polyphyodonts, often the replacement teeth develop in groups of alternating waves known as ‘Zahnreihen’ – from the German for “tooth row”.

The tammar wallaby (Notamacropus eugenii), also known as the dama wallaby or darma wallaby, is a small macropod native to South and Western Australia. A wallaby, basically, is a macropod not big enough to be a kangaroo. Tammars live for 10 to 14 years, in mobs that usually number about 50. They’re nocturnal, live predominantly on grasses, and are very good swimmers although the Australian Swim Team will never be called that.

As a polyphyodont, the tammar wallaby is more precisely a diphyodont – which means it replaces its teeth only once – and in this case only the premolars. As far back as 1893, scientists noted unusual things about this Australian native’s tooth development.

This delayed emergence of first teeth suggests that Zahnreihen still occurs in modern mammals despite the evolutionary sacrifice made about 205 million years ago. It was during this early Jurassic period when it was all Sam Neill-lush and landscapey, mammals eschewed continuous tooth replacement.

For a biological system that was hundreds of millions years old, it was a major modification.

Would we change that now if we could?

Maybe.

Although technology now has us very close to being able to regrow our own teeth. And who knows what kind of jawline we might have ended up with to keep those pegs forever pegged.

Forever active in polyphyodonts, human dental lamina degrades after the second set of teeth develop. Dental lamina is the structure that appears at the beginning of tooth germ formation, is present for the whole development time, and only disappears with the completed eruption of the dental crown of the tooth into the oral cavity.

Like a spent firework.

Children usually have 20 baby primary teeth that erupt at about 6 months of age, and fall out over the course of childhood to be replaced by permanent teeth.

For some people however, just like dead mean don’t wear plaid, milk teeth don’t fall out. These teeth are known as retained primary teeth.
So why, for some adults, do their baby teeth not fall out?

Sometimes it’s because of tooth agenesis, or hypodontia where the permanent teeth are missing. Genetic dispositions, dental injuries and infections can all prevent teeth from erupting as they should. Its incidence shows in less than 1% of the Caucasian populace, with a higher prevalence reported in Asian populations.

Should there be concern for baby teeth that remain?

It depends.

Often a retained primary tooth will have a healthy crown, strong roots, and be supporting alveolar bone. In cases like that, it’s a tooth that shouldn’t be causing any problems. In fact, the European Journal of Prosthodontics and Restorative Dentistry published a review confirming that retained deciduous teeth have reasonable survival of two decades.

Still, there are associated oral issues as a result of agenesis.

There can be a degree of root resorption, infraocclusions, cavities, and periodontal bone loss. Extractions, bridgework and dental implants are options to discuss with your dentist should treatment become necessary.

It’s interesting that the tammar wallaby’s tooth replacement is as unconventional as that of fruit bats. Eidolon helvum’s unusual way of renewing teeth is that they emerge either in front, beside, or behind the primary tooth – and even split off from it.

What’s been realised in this wild wallaby tooth world, is that instead of the replacement premolars developing from the successional dental lamina, they are in fact deferred baby teeth of primary lamina.

It’s a discovery that broadens the possibilities of human biological tooth replacement.

With their unique and efficient propulsion, their flexible reproductive strategy and their drought-adapted metabolism, kangaroos and wallabies hold a special place in Australian culture and ecology. The research now focused on this anomaly of evolution in tammar teeth suggests we’re learning more about macropods than how to just tie me kangaroo down, sport.

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Note: All content and media on the Bacchus Marsh Dental House website and social media channels are created and published online for informational purposes only. It is not intended to be a substitute for professional medical advice and should not be relied on as health or personal advice.

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