So - firstly, the teeth falling out dream is actually one of the most common recorded dreams!

Nextly, there are lots of other reality checks that can be tried. Changing the light doesn't usually work - at all - in dreams. Try looking at your hands, putting a finger on your palm to see if it goes all the way through. Try jumping to see if you float or if you fall normally. Try reading something, looking away, and looking back again to see if it's changed. Try doing the same with digital clocks. Nose pinch reality check works as well, but for me personally, normally just a glance at my oddly bulbous hands will assure me that I am dreaming. Good luck