My vet told me a lot of dogs have high pain thresholds and/or will hide their injuries, so they won't necessarily stop eating from mouth pain. He wasn't trying to upsell me, I was asking why my dog was avoiding food and wondering whether it could be a tooth problem (so unlikely to be the case).

That doesn't help much I know, just make sure you get advice from people you trust have a care about dog's quality of life.