How much is green tea really good against tooth decay?

I heard that many times:

Green tea is good for cavity protection.

For example, it is written on this site (the first one googled):

1. Cavity prevention

Because green tea controls bacteria and lowers the acidity of saliva and dental plaque, it may be a useful tool in preventing cavities. A recent Egypt-based study tested people before and after they gave their mouths a five-minute rinse with green tea. The test subjects had less bacteria and acid in their mouths, as well as reduced gum bleeding. Other research has found that drinking green tea shows promise when it comes to preventing tooth decay.

But I never heard such a thing from some reliable source (my dentist doesn't know anything about that). The question has three parts really, they are:

1. Is green tea really good against cavity?
2. How much? Is it even worth mentioning?
3. Do you have some reliable source? (big medical research, world respected dentist, or something like these)