Why do we have wisdom teeth?

Tegan Taylor: How wise are you, Norman?

Norman Swan: You know, when I was a kid, I was quite taken with the story of King Solomon.

Tegan Taylor: You wanted to cut a baby in half?

Norman Swan: Well, no, but this whole idea of wisdom…you have your three wishes, what should you wish for? All these things that you used to do when you're a kid, like your first cherry of the season you're supposed to make a wish, so I would always wish for wisdom, but it just shows you how useless wishes are because…

Tegan Taylor: That is actually incredibly wholesome, the idea of baby Dr Norman Swan wishing for wisdom. And so many people trust you now, it's actually a really lovely

Norman Swan: Well, maybe the wish came true, maybe old Solly up here was listening.

Tegan Taylor: Yeah. How many wisdom teeth do you have though? Did you wish for those?

Norman Swan: I have a full complement, four.

Tegan Taylor: I have two, but only because…

Norman Swan: You've got two? I always knew you were a bit deficient.

Tegan Taylor: Deficient?! I had three, and then they had to take one out because it was coming in the wrong way. And the other two, they actually took my molars out and my wisdom teeth grew down. And so on my right side of my mandible, the moving part of your jaw, I have what's called third molar agenesis, which meant that my wisdom tooth never generated there.

Norman Swan: And this is the topic of today's What's That Rash?.

Tegan Taylor: Sure is. I am moderately wise health reporter Tegan Taylor, on Jagera and Turrbal land.

Norman Swan: And I'm the complete idiot Dr Norman Swan, coming to you from Gadigal land.

Tegan Taylor: And, Norman, today's question is from a very special question asker, it's actually from our producer Shelby, and I reckon…look, Shelby, come in, you need to read it for yourself.

Norman Swan: Yes, come in from the control room, do it yourself, you can't get out of this one. So Shelby, thanks for coming in.

Shelby Traynor: Yes.

Norman Swan: And meet our What's That Rash? audience directly.

Shelby Traynor: Hi, guys.

Norman Swan: Shelby is the person you've got to thank for What's That Rash? because she actually makes it happen. Why the question about wisdom teeth? And what is the question?

Shelby Traynor: Because I'm in pain, Norman.

Norman Swan: Oh no! Now you tell us.

Tegan Taylor: And it wasn't just us?

Shelby Traynor: No, my wisdom teeth are trying to come in. I thought I'd made it to the point where they wouldn't, but they're trying to come in, and they hurt. And I'm wondering why in the world am I dealing with this pain? They're not doing anything for me except giving me a massive dental bill, which I don't want to pay.

Norman Swan: Okay, so I think the question is, why the heck have I got wisdom teeth? What are they all about?

Shelby Traynor: Yeah. And what happens if I just leave them? Will I be okay?

Norman Swan: Okay.

Tegan Taylor: Well, Shelby, I think it's time for us to do a deep dive.

Shelby Traynor: Great.

Norman Swan: Let's go. Look, this is one of those what turns out to be quite a typical What's That Rash? question which is a simple question; what is it? And it uncovers this Doctor Who TARDIS of information,

Tegan Taylor: Any opportunity that we get to talk about human evolutionary biology is my favourite. And this is such a good one because obviously this has evolved for some reason. It's been passed on through the generations of humans for some reason. And yet they seem to cause us nothing but a world of hurt these days. Was there ever a time when having wisdom teeth was a survival advantage for humans? That's why it would have been passed down, it's what got people to be able to reproduce and pass those genes on.

Norman Swan: Well, as much as you can ever know in evolution, the answer is yes. And by looking at comparative animal populations, and you look at the paleopathological record, essentially these are third molars, so these are the third molars at the back of your mouth. They appear, at least in us, relatively late, in late adolescence, maybe your early 20s they start to appear.

Tegan Taylor: They actually don't even start forming in your mouth until you're about seven years old.

Norman Swan: Yes. Now, whether that's an evolutionary thing or not is another matter. Let's go back to where you've got well-formed third molars, which probably in their time didn't cause problems, and this is when we animals had larger mouths to chew roots, nuts…basically we were not eating refined soft foods, and you needed more teeth and a bigger mouth to get through it all and grind it all up. And whereas now you probably barely use your third molars, your wisdom teeth, if indeed you've got them. But the fact of the matter is, at the moment we just don't use that part of our mouth very much for chewing, whereas when we ate unprocessed diets, we needed to have those teeth there.

Tegan Taylor: Yeah, I think humans, Homo sapiens as we currently exist, are pretty relatively new kids on the block. And there's a lot of things that we have that are hangovers from lifestyles that we no longer enjoy.

Norman Swan: Yeah, and if you think of the pictures you've seen of other versions of the Homo species, they had much bigger jaws. So their jaws were actually really quite big, and, as we've evolved, our jaws have become smaller and smaller. And that's the problem for the wisdom tooth is that there's less and less space for the wisdom tooth to break through.

Tegan Taylor: So are we saying that wisdom teeth are sort of like an evolutionary hangover?

Norman Swan: Yes, and that's why Shelby's got a problem is that Shelby's got a mouth with wisdom teeth coming through that's not big enough to take the wisdom teeth, and it gets impacted against other teeth there at the back of the mouth, and you get inflammation, you get infection, you can even get dental decay in the next teeth and create that problem. But the other fascinating thing I discovered, which I didn't know, but I think you did, to some extent, Tegan, is the genetics of wisdom teeth.

Tegan Taylor: Yeah, I do have a story about the genetics of wisdom teeth from within my own family. So my sisters-in-law are identical twins, and it's the whole thing, they share dreams, and they talk about how similar they are. But when it came to having their wisdom teeth taken out when they needed to, they discovered when they did the X-rays that they had a different number of wisdom teeth to each other. One of them had the full set, and one of them only had three. And that blew my mind because you think, well, these people are genetically identical, so surely they have the same dental record. And then I looked into it and actually it's not common, but it isn't out of the question that, yes, identical twins can have different numbers of wisdom teeth. So as much as there is a genetic component, it's not only genetics.

Norman Swan: No, there's more to it than that. It's also in terms of your ethnic background. So, Bangladeshis have about a 38% incidence of what's called third molar agenesis. In other words, not producing wisdom teeth. Koreans it's 41%. India, rather than Bangladesh, it's 11%. 100% of indigenous Mexicans have third molar agenesis.

Tegan Taylor: So they just don't get wisdom teeth?

Norman Swan: They just don't get wisdom teeth, and it varies a lot around the world.

Tegan Taylor: That is crazy. They're obviously more evolved than us. So when there's not room in the mouth, they can get impacted, like you said, they can cause dental problems and they can cause pain, like Shelby said, which is why so many people do have them removed. What goes into the decision to remove a wisdom tooth or let it stay put?

Norman Swan: Well, that's a debate amongst dentists. So I think there's little debate amongst dentists that if you are getting pain, if you're getting inflammation, you're getting infection, you've had an abscess, or you're damaging the molars next to the wisdom tooth, those are indications that you're probably better off without it. The debate is should you…given that impacted third molars is really common, you know, some studies have impaction in up to 70% of the population, it's just a big problem out there in the community. But should everybody have their third molars out, their wisdom teeth out, to prevent the problem arising and to give more space in the mouth for the other teeth to develop? And I think a lot of people come down on the side of this is an unnecessary operation, you should really only have it done if you've got problems, because the surgery to remove it is not necessarily totally benign.

Tegan Taylor: It's a bit like having your tonsils out or whatever, there needs to be a good enough reason to go past the status quo and intervene, that 'first do no harm' sort of thing.

Norman Swan: Yes. So, for example, if you need to dissect the bone away to remove the tooth, which is the complete removal of the wisdom tooth, and you go in and you dissect away the bone so you can get in and remove the tooth with its roots completely, in some people that can be very close to really important nerves. And if those nerves get damaged, you can end up with a disability in your face. So again, not entirely benign. Surgeons will know if they're worried about that in terms of the anatomy of the face. And what they can do with some people is what we call a coronectomy, which is the remove the top of the wisdom tooth, but the underlying bone is intact. So in most experienced hands of oral surgeons, no problems, but you do run that risk, so you shouldn't have it done unnecessarily.

Tegan Taylor: What did people used to do in the olden days? I think I always thought that wisdom teeth were there to kind of be like, well, you're probably going to have some of your teeth fall out of your head anyway, so here's some extras just in case. But it doesn't sound like that is the case?

Norman Swan: Well, I think some dental historians believe that in times gone by we were eating a much tougher diet. This is not the Palaeolithic diet, but even almost within living memory, you're eating a much tougher diet, the meat would have been tougher, you'd have been eating the crusts on bread. And you may well have actually had a much healthier mouth developing than now. So, are we seeing more wisdom tooth impaction now with our soft namby-pamby diet than we used to have when…?

Tegan Taylor: What, when men were men and women were women? What is this?

Norman Swan: That's right, and chewing on jerky at breakfast time.

Tegan Taylor: Is this another thing we can pin on the Industrial Revolution?

Norman Swan: I think it's another thing we can pin on the soft food…I mean, the fast-food industry.

Tegan Taylor: I think it must be fairly easy to fact-check this, Norman. We have dental records for people who lived before 100 years ago. Is there evidence that people had their wisdom teeth through to adulthood a couple of generations ago?

Norman Swan: What we know from the paleopathological record is that…and again, this varies, but they have found preserved bodies from thousands of years ago, and in these bodies the bones are the best-preserved part, including the teeth and you can tell what they ate, where they found impacted wisdom teeth, so it's not a new thing, they did get them and people probably died in pain. And one of the drivers for early dentistry was pain relief.

Tegan Taylor: So we now have anaesthetics, which is lovely. And we have antibiotics, which is even better. What does wisdom tooth removal look like these days? You sort of hinted at it before,

Norman Swan: Yeah, two main operations really, one is complete removal, which really requires dissection, removal of some of the bone, it varies a lot. And then either removal of the tooth in separate parts or as a whole, usually in separate parts, so you get it completely removed. Versus the coronectomy, which I don't think is done that often, where you just shave off the surface of the tooth and leave the underlying tooth in there, because the surgeon's worried about pranging a nerve in taking it out.

Tegan Taylor: So, Norman, to summarise the answer to Shelby's question in one or two sentences, basically wisdom teeth have been useful to us historically, maybe less so these days. And it's not just a question of ripping them out willy-nilly, there's got to be a reason to take them out.

Norman Swan: That's right, if you've got symptoms, see your dentist, have a chat about it. It doesn't have to come out, this is just discomfort, but probably there's a bit of imperative if you've got infection going on or an abscess, but talk to your dentist, and there's no point in putting up with pain if you don't have to.

Tegan Taylor: Well, I think we might need to bring Shelby back in and get her verdict. Did we answer your question, Shelby?

Shelby Traynor: Yes. And grossed me out.

Tegan Taylor: Yeah, I think that was probably a little terrifying in parts. How are you feeling now about your impending wisdom tooth journey?

Shelby Traynor: Not good. I don't feel like I have much of an option though. I don't really want to live in pain forever, so…

Norman Swan: Yeah, you don't want to be dug up in a thousand years…the 'Shelby Mouth'…

Tegan Taylor: Have future historians judging you.

Shelby Traynor: Yeah, I don't want to become a scientific case study that we talk about on this show.

Norman Swan: The biggest question is whether the ABC pays you enough to have your wisdom teeth out. But that's a story for another What's That Rash?.

Tegan Taylor: Well, thank you, Shelby, for your question. And if you, friends, have a question, you can email us, thatrash@abc.net.au. Or if you have a weird tooth story, I would actually really love to be properly grossed out by people's tooth stories. One of our colleagues had a friend who used to make jewellery out of people's teeth. I don't even know whose teeth they were, but they were so creepy. So if you reckon you can top creepy tooth jewellery, I want to hear about it, thatrash@abc.net.au.

Norman Swan: Tell everybody you know about this fabulous new podcast called What's That Rash? and get them to subscribe.

Tegan Taylor: And you can also tell them (and yourself) to follow us @ABChealth on Instagram, which is also a channel where you can ask us your questions.

Norman Swan: And you can see me making myself up and you can see Tegan getting delayed onset muscle soreness.

Tegan Taylor: All that and more @ABChealth on Insta. And we'll see you next week.