I'm actually dealing with something similar myself right now, except mine has a joey in pouch on top of the dental issues.
The other day I noticed Cocoa's tooth gap that she has always had on her front teeth has gotten considerable bigger. Upon a closer inspection of her mouth she also has tarter or plaque built up on her teeth. I've been monitoring her teeth for a couple months now but in the last couple weeks the gap spread pretty quickly.
She is currently on clavamox to address possible infection/abscess for the next two weeks. Once the medicine course is done we will go back to the vet to see if she needs tooth extractions or not.
Once the joey comes out of pouch Cocoa will be getting a teeth cleaning at the vets but she will need put under anesthesia for that so the vet wants to want till the joey is out
I was also informed today to provide some live safe tree branches in Cocoa's cage, this will aid in tooth cleaning they strip the bark down with their teeth and kind of use it as floss to clean the teeth and in between them as well.
Dental issues and abscesses are not uncommon for gliders, especially older gliders.
Signs to look for include teeth spreading, loose teeth, swollen eyes, puffy face, belly fur turning tan or brown. These symptoms are NOT always present or visible but are clear indicators of dental issues if you do see them.
All these pics are of the same glider the last one shows the progression of the front tooth gap.