4.1.3 Dental Problems⭐牙齿问题

A dental cavity is a hole in the tooth.

A cavity is caused by bacteria in the mouth.

Brushing your teeth frequently and regularly can help prevent cavities.

A cracked tooth can be caused by biting down on something hard.

Dentists treat a cracked tooth by covering it with a crown.

A dental X-ray is a picture of your teeth and gums.

An X-ray shows what can't be seen on the surface of the teeth and gums.

Braces are used by dentists to straighten teeth over a period of years.

Though braces are usually for children, they can also be used for adults with crooked teeth. 

To extract a tooth, means to remove it from the mouth.

Dentists have to pull hard to extract a tooth.

what is the painful process that often require a injection?

Dentists often inject something into the gum to block the pain during the extraction process.