Summer,
I am really sorry that I haven't really got useful advice but wanted to say that I feel your pain as Grace has been the same for a few weeks (she is 8.5 months) having previously been fine at self settling in her cot. There are tears from me most evenings at the moment.
I have been trying to use CC; it worked initially but no longer seems to for us as if I try it, she tends to scream to the point of vomiting

I do think it could be teeth, although I have spoken to the HV with whom I get on really well and she thinks it is much more likely separation anxiety.
She recommended something called the 'disappearing chair' which is the next thing I think I will try. She said to put DD to bed, but remain in the room, on a chair, and just sit there or read a magazine or something until DD drops off. Each night, move further away from her until outside of the door. I am not sure if this will work for me as I think Grace would just want to play, but perhaps it may be worth a shot?
I do hope things improve soon; sleep issues are so hard.
Em xx