Fonty
It's better if you don't use toothpaste and if you mouthwash with normal commercial preparations you can damage your throat which is more sensitive while fasting than when eating. The body will often take advantage of your not eating to replace the lining in there so it will be new soft flesh in there. And toothpaste can be absorbed if only slightly but more important it can stimulate the taste buds which will divert energy to the digestions system and increase your chance of getting cravings for something to eat. You could try bicarb, it might be less of a problem because it doesn't taste like any food, more like chalk. ;)
Andrew.