I have 2 degus, one of them had tooth trouble a year ago.
She had her upper incisors clipped smaller, and they removed an infected molar.
It took a month for her to start eating properly.
What I did to help the process, was feeding her critical care (and also oat porridge) via syringe, and offering rolled oats, ryvita, and softened pellets, to give her some energy.
And because hay is the most important part in degus diet, I fed her some dried dandelion leaves, mint, basil and parsley to make her interested in hay again, and it worked, but took couple of weeks.
Now, after a year of all that, my goo is better than ever, eating and chewing normally, and we didn´t have to go to vet again