Bad breath is a sign of gum disease. To check for gum disease, open your dog's mouth and look inside. If you see red and swollen gums, a yellow-brown crust of tartar at the gum line and pain or bleeding when you touch the gums, take your dog to the veterinarian to determine whether he needs to have his teeth cleaned.
Cleaning a dog's teeth may seem unnecessary, but gum disease can cause other serious problems. A painful abscess can result from gum disease when bacteria and then pus accumulate near the root of the tooth. An abscess needs to be treated immediately, since it can spread into the sinus cavity. When that happens you will see pus appear just below your dog's eye. The pain will cause your dog to stop eating, and eventually the bacteria will travel to other parts of his body and cause serious illness.
To prevent gum disease, clean your dog's teeth every day using a sterile cloth and water and a paste made out of baking soda and water or a commercial pet toothpaste and toothbrush. Never use human toothpaste to clean your dog's teeth; it can upset his stomach. If you are unsure about brushing your dog's teeth, your veterinarian can show you the proper way.
Also, offer your dog dry dog food every day and rawhide or synthetic bones several times a week.