Video transcript: What can a New Zealand reptile tell us about false teeth?

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September 2010

Music in background.

Dr Neil Curtis
We are interested in how people know how hard to fight and how they stop themselves from fighting too hard. Of course, we eat lots of different types of food and food can be very complicated. We are aware that people have a special ligament between their teeth and their tooth sockets which judges how much force is being applied to food items.

So food like these sweets can illustrate that very well because they have got a hard outer shell but are soft inside. So as Susan is biting down on the sweet, there are signals going from her teeth and, in particular, the ligament between the teeth and her tooth sockets telling her how hard she can bite without breaking her teeth. But there are animals that don't have any of this ligament so we have investigated one of these animals to see how they are controlling their bite force.

So the animal we decided to study is the tuatara. This is a skull of a tuatara. If we look along the upper jaw we can see the tooth row and the teeth are fused to the bone so there is no obvious boundary between the teeth and the bone. There are no sockets and there is no ligament so this animal must be using other receptors in the skull in order to judge how hard it needs to bite. We placed the specimen material in a high resolution micro CT scanner. This takes a lot of very detailed x-rays. We then upload these x-rays into a computer and use the computer to build the model. So once we have the computer model with the representation of muscles we can make the jaws move. By allowing the jaws to move we can see the different roles each of the muscle groups is performing. Whether it be opening the jaws, closing the jaws or shearing the jaws forward. Tuatara lack the periodontal ligament  that we have and that we use to gauge how hard to bite but from the model we can tell that there is a nervous system operating, perhaps receptors in the jaw joint.

Some humans have dental implants which, as you can see from this model, are screwed into the jaw bone and, therefore, they also lack periodontal ligaments just like the tuatara. This gives us an analogous situation.