I'm a bit concerned--how did the vet know the roots are growing into the sinus cavities without taking an x-ray? Or did they take one, but you can't take it with you? Legally, you're allowed to have copies of everything in your rabbit's file, you just have to pay to make copies for it.
Also, simply grinding down the exposed part of the tooth, which sounds like what the vet did today, isn't going to fix the roots of the tooth growing into the sinuses. I'm pretty sure that if the teeth are growing into the sinuses the only option to fix that is extraction. I hope others who have "been there, done that" with their own rabbits will have more information.