my idiot's guide to dreams says that it could mean insecurity about how we are perceived by others or it could mean the feeling of loss of power over our dreams or choices. it can be a little more complicated then that, though. the book is "The Complete Idiot's Guide to Interpreting Our Dreams" it's in Alpha Books collection. neat book
Old people says that, if you dream about falling your tooth, you will die or someone in your family will die. But there is no scientific explanation that those sayings are true. Don't be afraid if you dreamed like that. Just always pray before you sleep.