In my country there's a saying that literally translates to " your teeth fall off [in your dreams], your relatives die". Now don't worry, it's not supposed to be some nasty foreshadowing of bad things to come, only a way for our subconscious to express feelings of helplessness and/or loss.
Experiencing loss of teeth or more rarely limbs in dreams happens quite often to people who have just lost or are losing someone dear to them, but psychologists also link it to situations of uncertainty, in which you see bad happenings unfold before you that you can't really do anything about. The most common cause of this being, as I said, the death of a loved one.
I personally believe this to be true because it would also make sense of what happened to me: a couple years ago I was sad because my dog was ill and we all knew he was probably going to die. About a week before he eventually passed away I remember having this dream in which I was on holiday in switzerland with my family but I didn't want to go skiing with them 'cause my teeth were ALL falling out of my mouth for no apparent reason. It was.... kinda awful
Dunno if this makes any sense to you but I just thought I'd throw in my 2 cents ^^"