[Neil Pariser]

Neil Pariser  asked the Naked Scientists:
   
With all the talk about stem cells today, can you tell me if there is any research looking to grow a third or 4th generation of teeth?  Also - why do we only get two sets...milk teeth and adult???
 
Sharks can grow them forever!!!
  
Neil Pariser
New City, New York
What do you think?

[chris]

This is evolution. The primary or deciduous dentition (milk teeth) are much smaller and less numerous than the adult teeth; as such they can fit into a smaller jaw more readily, can be grown and deployed at lower resource cost and more rapidly.

But they are also softer and less resilient than adult teeth. Also, as the jaw grows, more than doubling in size as a person develops, more teeth are needed to fill the space and also to cope with tougher and bulkier food items that are required to sustain a bigger person.

Nature has compromised with two sets of teeth. The secondary dentition that replaces the milk teeth is bulkier, harder and there are more teeth. Historically these teeth have proved adequate to enable a person to survive beyond child-bearing age, which is the selection point controlling our evolution. As such, there is no reproductive advantage to having any more teeth beyond our secondary dentition, so it has never happened.

[evan_au]

is any research looking to grow a third or 4th generation of teeth?

Yes, researchers have been looking at this.
But a tooth is a very complex structure, with many differentiated cell types involved, so it is hard to make a tooth from already-differentiated cells. And it would need to be implanted into a suitable environment in the jaw, which doesn't really exist when an adult has a tooth pulled.

Perhaps as a child, instead of putting your tooth under a pillow to get a coin from the tooth fairy, you should have dropped it in liquid nitrogen so the stem cells could be extracted decades later, and save yourself thousands of dollars getting an artificial tooth.

Of course, initially, any teeth grown from stem cells will cost a lot more than an artificial tooth!
..and there is always the scary specter of the artificially-grown tooth becoming cancerous...

[MayoFlyFarmer]

If humans lived longer, or lost/damaged teeth at a higher rate, I would imagine that we would have evolved to replace teeth more than once during our lifespans. Give how we live, there just wasn't any/enough evolutionary pressure for more teeth than we have.

[Karen W.]

Okay, I have a friend whom I adore. He  is a musician both vocal and multi instrumental...He has two sets of teeth. He is now around 40 years old. We have talked on a few occasions about this, as it is something he wants to rid himself of. Now, he only has an extra set on the top, which seem the same size as the front teeth. There is just a second row behind the front row. We have both wondered why this happens, and how common it is? He had his first set, just like we did, then lost those, then grew his first adult teeth, but with them grew a third upper set. We worry if pulling them out would it affect his vocals, not having that extra row?  Pertaining to this question, How or why did he get a 3rd set If we were not set up to receive an extra set be it evolution or space accommodation in our jaw line.. Is it possibly a genetic thing that he received these extra teeth?

[MayoFlyFarmer]

Karen, is your friend a shark by chance? 

[Karen W.]

LOL nope.. no shark! LOL I often wondered if they were his baby teeth never fallen out but I guess his fell out as per any everyone else's.. So I have nothing but curiosity about why this occurred in him.

[chris]

What does it look like? Pretty weird presumably?

[Karen W.]

Well Chris, when you look at him straight on you cannot see them, only the front set! He had to show me the second set. He has an incredible voice and is a singer/ saxaphonist. So when he tips his head back and opens his mouth you can see the whole front row from where molars start forward..then you see directly behind them another full sized set, they are slightly crooked but are wrapped right behind his first upper set. JUST LIKE THE FRONT...We were trying to do some announciating practice, while working on his tongue placement behind his teeth, that is when he told me, and showed me. He has a small speech impediment..He wants to get them all pulled but I wonder if it would effect his vocals or Sax playing?
I also wonder if its a DNA thing or fluke..or what may have caused him to have a second row...