Most pets are brave and do not show obvious signs of pain until it is excruciating. They will continue to eat despite significant discomfort.
When you think about it, they really have no other option. They may start to chew on one side or prefer softer foods, but in many cases the signs are quite subtle and easily missed, even by a diligent owner.
Pets with dental disease will not stop eating until the pain is so severe that starving slowly is an easier option. This can take months or years of disease to happen. Please don’t wait for this to happen.