Biology

Gilla:		Dela:

Video

Materials

• 1 piece of cardboard
• 1 pair of scissors
• Modeling clay
• Plastic wrap

Short explanation

The function of your teeth is to divide the food into smaller parts before you swallow it. The front teeth are sharp and can cut and chop the food. The back teeth are flat and grind the food.

Long explanation

Humans are diphyodont, which means we get two sets of teeth during our lives. The first set of teeth - the deciduous teeth - begins to break through the gums around the age of 6 months and before the age of 32 months you usually have them all. By then each quadrant, i.e. each half of the lower jaw or upper jaw, contains: 2 incisors, 1 canine and 2 molars. This makes a total of 20 baby teeth.

The second set of teeth - the permanent teeth - replaces the deciduous teeth between about 6 and 12 years of age and during this time humans have both deciduous and permanent teeth mixed. What happens during the replacement is that the forming permanent teeth inside the jaw press on the roots of the baby teeth, which causes the roots to break down and be absorbed by the permanent teeth. This loosens the baby teeth and thus they can also remain if a permanent tooth is not formed underneath (which is quite common).

In an adult, each quadrant normally contains 2 incisors, 1 canine, 2 premolars and 2-3 molars. This makes a total of 28-32 permanent teeth.

The most posterior molar that may not develop in each quadrant is called the wisdom tooth. In Homo sapiens ancestors, natural selection favored a larger brain, which probably required the jaws to shrink to make room for it. The wisdom teeth did not really fit anymore and they started to cause problems (pressing on the gums, getting crooked etc.). Because dental problems before modern dentistry could actually lead to death, natural selection has lead to the fact that many people today never develop wisdom teeth.

In summary, the teeth are there to divide the food, which is the first step in the digestive system. But the different teeth also have their own anatomy and function. With the help of your dental impression, you can take a closer look at how anatomy and function are connected. The incisors have a sharp edge which cuts the food into pieces, much like when a pair of pliers cuts something. The canines have a sharp "spike", with which you can hold the food while you tear off pieces (suitable if you eat tough meat for example). Thanks to their two "spikes", the premolars also have the ability to hold the food while you tear off pieces. At the same time, they are also good at crushing and grinding the food between them when you chew. The molars are fully designed to crush and grind the food between them, which you can see from their flat chewing surfaces.

Experiment

You can turn this demonstration into an experiment. This will make it a better science project. To do that, try answering one of the following questions. The answer to the question will be your hypothesis. Then test the hypothesis by doing the experiment.

• What differences are there between your teeth and the teeth of a friend of the same age?
• What differences are the between your teeth and the teeth of an older person?
• What differences are the between your teeth and the teeth of someone with all their baby teeth?
• Are there more similarities between your and a close relative's teeth, compared to someone you are not related to?
• What are the differences between the teeth in your upper jaw and lower jaw?

Variations

If you find it uncomfortable to put so much modeling clay in your mouth, you can make an impression of one quadrant at a time.

If you want, you can use salt dough instead of modeling clay. You make salt dough by mixing 2 parts flour, 1 part water and 1 part salt into a smooth dough. You can also add food coloring. The advantage of salt dough is that you can dry it in the oven for 1-2 hours at 100 °C (200 °F), making it hard. When hard, you can also paint it.

Regardless of whether you use modeling clay or salt dough, you can make a plaster model of your teeth. Buy a plaster mix and follow the instructions on the package. Pour the plaster mixture onto the dental impression you have made (but first shape an edge around it so that the plaster does not spill).

Gilla:		Dela: