An abcessed tooth hurts when a human has it, but on a dog it is a little harder to detect. Your four-legged family member won't be able to say, "My tooth hurts." Keeping an eye on your dog's behavior can help you detect if it has an abscessed tooth. If you suspect that's the case, take your pet to a vet.
Smell your dog's breath. Bad breath indicates bacteria is growing in your dog's mouth.
Check your dog's teeth. The teeth should be white up to the gum line. Yellow or brown discoloration, especially near the gum, means calculus has formed. Also note if any teeth are cracked. A cracked tooth is a sign of an abscess.
Check your dog's gums. They should be pale red, with a knife-shaped pattern leading to the tooth. If the gums are bright red, especially near the teeth, or if the gums are rounded near the teeth, your dog has gum disease, which can lead to abscesses. Bleeding around the gums usually means an abscess has formed.
Note your dog's behavior. If it's eating less or lethargic, it could be a sign of an abscess or other problem. Consult your vet.