Bless you for trying to help your SIL. I ended up with Atypical Trigeminal Neuralgia after some weird dental work with a young, inexperienced dentist. Things only worsened from there. This is common...Check out a book called "Striking Back," written by a neuro and TN expert which describes these dental cases in detail.

Anyway, a good website to check out is called livingwithtn.org

There isTN 1 or TN 2 or atypical. TN 1 is worse (IMHO) and often requires brain surgery called an MVD. The good thing is that if successful, it can last a very long time or even bring permanent relief. But since it was after dental work (kinda common actually) it is a little more likely to be ATN.

After one of the worst years of my life with extraordinary pain, I am better....NOT cured by any means, but I am more myself.

My medication routine, and I understand this works for others with ATN is as follows:
Desipramine (pills)
Compounded cream applied 4 to 5 times a day containing: Gabapentin, Lidocaine and Capsacian.
I take Percocet as needed for breakthrough pain.

I tried many other meds first, but this has helped me by far the most and I thank God daily.

Keep the faith!