Factors that break wudhu

Making wudhu after sexual arousal

Q: I am a woman and suffer regular vaginal discharge. Sometimes after sexual arousal, I am certain that the discharge which is present is normal vaginal discharge because during arousal or sexual thoughts I didn't have any discharge nor there was climax nor any fulfillment nor any orgasm. Is wudhu sufficient to offer salaah?

Blood under one's toe nail

Q: My toe was hit by a heavy thing falling down and it caused some blood to emerge within the nail. I heard that blood on the surface was pure and I washed the toe and did not think about it. Weeks later I thought about this again when I saw the dried up blood in my nail (Note: some of the blood was within my nail so I cannot remove it, otherwise I would need to remove my nail!) and I don’t know if that counts as pure or impure. 

Food getting stuck in dental cavities

Q:

1. I have cavities in my tooth, and when I eat, food gets stuck. When I rinse my mouth or use miswak, it's still stuck. But when I brush my teeth, it easily comes out. Should I brush my teeth before I perform wudhu everytime I eat, or is it okay for the food to be stuck in the cavities?

2. Is it permissible to have dental fillings so that food doesn't get stuck, or is the filling regarded the same as stuck food? If it is permissible, is there any specific type which should be used as a filling? For example, the fillings come in gold, porcelain, a composite resin (tooth-colored fillings), and an amalgam (an alloy of mercury, silver, copper, tin and sometimes zinc).

3. Sometimes, the food eaten comes back to mouth unintentionally. When this happens, does wudhu break? What about fast?