Oh, no!You've got a cavity.Your teeth are the hardest things in your body, yet tiny germs are able to make holes in them.A hole in your tooth is called a cavity, and once you have one, only a dentist can come to the rescue.The key is to prevent cavities from forming in the first place.Every day, there's a battle going on in your mouth.Acids and bacteria attack your teeth and plaque builds up.Your body has superheroes--your saliva--that try to fight...