Ask Mr Brain...all will be explained

PUBLISHED : Thursday, 29 April, 1999, 12:00am
UPDATED : Thursday, 29 April, 1999, 12:00am

Why are wisdom teeth called 'wisdom teeth'? JACKY Wisdom teeth, or third molars, are the last teeth to develop. They are called 'wisdom teeth' because they usually appear during a person's late teens or early 20s - the 'age of wisdom'.

The jaws of modern humans are often not large enough to accommodate the four wisdom teeth, which is why they cause more problems than other teeth. In fact, in nine out of 10 people, at least one wisdom tooth remains underneath the gum due to lack of space.

When a wisdom tooth is blocked from growing properly, it is called an 'impacted' wisdom tooth. A tooth may be partially impacted, meaning it is crooked and breaks through the gum only partially, or it may fail to break through at all and remains totally impacted.

However, problems can occur with few or no symptoms. As wisdom teeth develop, their roots become longer and the jawbone becomes more dense. Thus, as people grow older, it becomes more difficult to remove their wisdom teeth and complications can arise. So dentists may recommend the removal of wisdom teeth even if they are not causing problems yet, especially for young adults.

Is it true that some pigs have tusks? There are 16 pig species, native to Europe, Africa and Asia.

Domestic pigs do not have tusks but most pigs that live in the wild do. Some pigs have a pair of upturned or curving tusks, such as warthogs, babirusas and wild boars.

The babirusa is a hairless pig which has tusks that grow upwards through its snout and curve towards its eyes.

When foraging, the male does most of the rooting, while females and young follow behind and feed on unearthed items.

Pigs use their heads and tusks as weapons. The shape of a pig's head and tusks reflects the way it fights.

The wild boar tries to slash its rival's shoulders with sharp tusks, and has matted hair on its shoulders for protection. Warthogs, which have large growths, or warts, around the face, clash head-on and try to injure their opponent's head with wide, curving tusks.

Who invented plastic? The first important plastic, celluloid, was discovered by American inventor John Hyatt in 1869. It is a mixture of cellulose nitrate (manufactured from plant cellulose), camphor and alcohol. It was used as a cheap substitute for ivory but is very inflammable.

However, modern plastics did not really get underway until 1909, when Belgian-born American chemist L H Baekeland produced a thermosetting (cannot be resoftened by heating) resin from phenol and formaldehyde.

The new substance - named Bakelite after its inventor - was widely used for making radios, telephones and electric insulators.

At first Bakelite was often used for simple shapes before designers realised the 'plastic' properties of the new material would allow it to be moulded into any shape.