Please get some recovery foods; you can mix them with mushed up pellets if your piggy doesn't like them.
Our syringe feeding guide has a section on dental care for guinea pigs:
Complete Syringe Feeding Guide
Here are our post-op care tips.
Tips For Post-operative Care
Dental guinea pigs won't eat straight after treatment as their mouths are very sore. They may not be able to eat normally for quite a while, depending on how good/bad your vet's knowledge and experience with guinea pig dentals is. Unfortunately, that means that teeth can overgrow rather quickly again when they are not ground down evenly.
Make sure that you ask your vet how soon and with how much painkiller you can step in as the mouth will be very sore.
The best way to get on top of dental issues are regular burring after-treatments every 2-3 weeks with increasing intervals to help rebalance the whole dental system, depending how severely affected it is. Unfortunately this is not possible with a full GA, which means that vets who insist on full GA have to wait until things are very bad and then start in square one again.
If you have problems with the recovery and ongoing dental issues, please contact furryfriends via her sanctuary. She is currently very busy and not able to come onto the forum, but as she looks specifically after guinea pigs with chronic severe dental problems, she has by far the most experience.
The vet she works in conjunction with is Simon Maddock at the Cat&Rabbit Care Clinic in Northampton, who sees dental piggies from all over the country and does about 15 guinea pig dentals each week - that is more than most vets do in their whole career!
The Excellent Adventure Sanctuary – Providing life-enhancing care for Guinea Pigs with extra needs
The Cat and Rabbit Care Clinic