Why can't humans grow a third set of teeth?

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If we break a bone, it repairs itself over time. So, why can’t we grow a third set of teeth?

Have you ever wondered why, unlike our bones, our teeth don’t just repair themselves when they break?

Fillings, crowns and root canals, it’s all fairly cringey to even think about.

The truth is, hanging onto our 32 pearly whites is one of life’s missions that many of us will fail.

In fact, tooth loss is the most common organ failure there is.

By the time we’re over the age of 65, about one in five of us will have lost all of our natural teeth.

And Professor Alastair Sloan from the University of Melbourne says it can make a huge difference in someone’s life.

“It does have an impact on people's lives. You can't chew properly. Therefore it affects your diet. You will have psychosocial issues. You won't have a good smile.”

Toothaches can kill

Many people ignore the warning signs when something might be wrong with their teeth. More than 70,000 Aussies end up in hospital each year from an untreated dental infection.

And those numbers may not demonstrate the scale of the problem because dental disease can lead to conditions like heart disease, Alzheimer's, even death.

German fashion designer Hugo Boss died from a tooth abscess and it was one of the leading causes of death before antibiotics existed.

“What we do know is that untreated dental disease does create some big problems that require significant treatment, “ Professor Sloan says.

Despite the risks, no one really likes going to the dentist.

What sharks can teach us

Science may be able to save our smiles and also spare us from a painful trip to the dentist.

In labs right around the world scientists have been exploring ways we can avoid the dreaded drills and painful procedures.

And scientists have been getting some inspiration from sharks.

“They almost have rows of teeth behind each other. So if a tooth is lost, then the tooth behind it, or the developing tooth behind and gets pushed forward to take its place,” Professor Sloan says.

Humans and sharks share the same basic genetic ability to grow teeth. But unlike sharks, humans don’t have an endless supply.

Professor Sloan says, “Sharks give us that insight into how you might be able to manipulate those genes and those stem cells to regenerate dental tissue.”

Using stem cells could be a hairy issue

Associate Professor Munira Xaymardan from the University of Sydney believes the key to regrowing human teeth will be in taking an adult stem cell from the gums and converting it into its embryonic state then using RNA technology to instruct the cell to become a tooth.

Scientists have already successfully grown teeth in toothless mice. The trick will be doing it in a human mouth.

But telling those stem cells what to do is difficult. Get it wrong and you might end up growing not teeth, but something else entirely. 

“Yeah. So that's one of the risks of using very early stem cells, we need to know exactly what molecule to put in. So they grow into something else, right? They will not be sweat glands or a hair piece or something like that,” Associate Professor Munira Xaymardan says.

Growing a sweat gland or a tuft of hair in your gums could be a slight problem.  

Still, Munira is optimistic that research around the world will lead to human teeth being grown inside people’s mouths in the next decade.

“The technology is growing really fast and developing really fast. So my answer will be, yes, it's just a matter of time that we can actually master tissue growth cues and understand how organs generate and regenerate.”

But for now, the best saviour for your smile is a toothbrush and some floss.

And swapping out the sweet treat for some fruit.