Fantasizing about the opposite gender

Q:  

1. I am confused about the types of zina. I am aware that looking at a male, whether it's a picture or physically, is considered as zina. Also, fantasizing about a male is zina. But, is fantasizing about an imaginary male also a zina?

2. When people read romance novels, they get aroused, and eventually, discharge. Is wudhu or ghusl necessary?

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?

Masturbation

Q: After urinating, when rinsing the private area with a hand shower, the pressure of the water is satisfying. Sometimes, I get really aroused, which follows a discharge. Is this counted as masturbation? Do I have to perform ghusl?