Not sure why the surgery for this horse is a week away - the tooth/teeth needs to come out, and the sooner the better. An upper molar’s roots go up into the sinus cavity, and the infection/snot coming out of the horse’s nose indicates that there is bacteria leaking up though your horse’s mouth into the sinuses. No amount of antibiotics are going to clear up the infection that has now lodged in the sinuses. And the longer this tooth stays in, the more damage the infection is causing - bone loss, sinus cavity deterioration, etc.
I have a horse that had a cracked upper molar, undiagnosed for over a year. He had discharge, but it didn’t smell. A college vet school x-rayed, found the cracked molar, and told me to give 3 months of antibiotics. The discharge went away, but came right back once the abx were gone. More antibiotics, rinse and repeat. And repeat, repeat.
Finally, I brought my horse back to the vet school - Had an MRI done because no one there could believe that this was ‘just’ a cracked molar problem (still no smell to the discharge) - and a large area in my horse’s sinuses looked to be a tumor (it was actually a huge sinus cyst encasing most of the infection). Scheduled to have the tooth pulled - and flaps (2) were cut in the side of my horse’s face - vet school couldn’t get the tooth out.They did try to clean up the massive infection which smelled petrid now that the cyst had been opened. Sewed my horse up and told me to call an equine dentist - thankfully, I have an excellent one in my state, and he was able to remove the tooth through my horse’s mouth in under 45 minutes.
However, since the infected tooth had been left in for so many months, my horse had significant bone loss and no (not kidding) sinus walls left. He also had a huge hole from mouth to sinuses where the tooth was, and 2 face flaps that were a bugger to get healed/stop leaking food. He had to have sinus flushes 2 x day for several days/months (through a tube sticking out the top of his forehead) - I just left him at the clinic for 6 months, until bringing him home with a ‘plug’ in the empty tooth socket. The plug was taken out after 6 months when he had finally grown membrane over the socket hole - and in time, his face flaps finally healed. Two years out now, and while he still has a ‘dent’ in his face where a chunk of bone had to be removed, it’s not that noticeable.
Sorry for the ‘book’ but wanted to share what can happen if a cracked tooth is left to the ‘wait and see’ approach. If your vet isn’t comfortable removing the tooth (and many aren’t, especially an upper molar), please please find an equine dentist! My costs were about 5 times more than they had to be, and I’m lucky that my horse healed.
I went back and reread your post - you’ve got 2 cracked teeth, while I only had the one. How do you know that both aren’t causing infection?
(Sounds like you well know that now. So sorry you’re in this spot, though.)