Why do teeth and microbes go together?

Every time you smile, chew a crunchy carrot or say a word clearly, your teeth are hard at work. But your mouth is also home to millions of living things so small that you cannot see them. These tiny living things are called microbes. Some of them are harmless, some are helpful and some can damage your teeth or make you ill. That is why Class 4 Science studies teeth and microbes together: looking after your teeth is really about keeping the wrong microbes under control.

Our two sets of teeth

Human beings grow two sets of teeth in their lifetime. The first set, the milk teeth, starts to appear when a baby is about six months old. These small teeth help a young child bite, chew and learn to speak. From around the age of six, the milk teeth loosen and fall out one by one, and the second set, the permanent teeth, pushes through to take their place. Permanent teeth have to last for the rest of your life. If one is lost, a new one will not grow in its place.

Four kinds of teeth

Look in a mirror and you will notice that your teeth are not all the same shape. Each kind has its own job, a bit like the different tools in a kitchen.

Inside a tooth

The part of a tooth you can see is the crown, and the hidden part fixed into the jawbone is the root. The crown is covered with enamel, a hard, shiny coating. Under the enamel is a yellowish layer called dentine, and right in the middle is the soft pulp, which holds blood vessels and nerves. Pink gums wrap around the base of each tooth and help hold it firmly.

How tooth decay happens

After we eat, tiny bits of food stay on and between our teeth. Microbes in the mouth feed on the sugar in these bits and form a sticky, colourless layer called plaque. As they feed, they make acid. Day after day, this acid slowly wears away the enamel until a small hole, called a cavity, forms. If the hole reaches the pulp, the tooth can hurt a lot. The good news is that tooth decay can be prevented.

What are microbes?

Microbes, or micro-organisms, are living things that can be seen only through a microscope. They are found almost everywhere: in air, water and soil, on our skin and inside our bodies. The main groups are bacteria, viruses, fungi, protozoa and tiny algae. Microbes grow and multiply very quickly when they have food, warmth and moisture.

Helpful and harmful microbes

Not all microbes are bad. Bacteria help us make curd and cheese, yeast (a fungus) makes bread soft and fluffy, and some fungi give us important medicines. Microbes in the soil break down dead plants and animals into rich compost that helps new plants grow.

Other microbes, which we often call germs, cause diseases such as the common cold, chickenpox, typhoid and cholera. Some microbes also spoil food, making it smell bad or grow fuzzy mould. Germs spread through dirty hands, dirty water, uncovered food, coughs and sneezes, and insects such as flies and mosquitoes.

Staying safe and healthy

This Teeth and Microbes worksheet for Class 4 turns these ideas into an island adventure on WitKnowLearn, with an online quiz, online activities and interactive games. Flip the cards, run the tests in the Microbe Lab, then play the games, do the science labs and try the challenges.