This is a common observation by pet owners when problems are found in their pet’s mouth. Yes, the fractured tooth or inflamed gums hurt. It’s just that animals evolved masking their discomfort.
If an animal displayed weakness from an illness a predator would consume them for lunch. Our companion animals evolved as pack animals, which required them to mask any problems to ensure their position in the hierarchy. And lastly, evolution selected animals with these traits and protraction of disease.
Our pets reproduced every six months more or less. If a disease process caused the animal to die quickly their DNA was eliminated from the gene pool. If the animal survived several reproductive cycles their DNA was preserved. And that is why “it doesn’t seem to bother my pet” and why it takes a long time before the problem becomes obvious to the owner.