Adult dogs have four different kinds of teeth -- incisors, canines, molars and premolars. Puppies have all of these except for premolars. The first set of teeth is called deciduous; the dog's permanent set will replace the dedicuous one between ages 3 months and 7 months, the rate depending on the kind of tooth. A healthy dog with all his teeth has four canines, same with a puppy. But a retained puppy tooth could skew the number of canines in a dog's mouth.
Most dogs have four canine teeth, two on the bottom and two on the top, one at each corner of the mouth. Usually, the permanent canine will grow right below the baby canine, directly replacing the deciduous tooth when it falls out. However, when the adult canine grows in a slightly different location -- such as just ahead of the baby tooth -- the adult canine will grow in and the baby tooth will stay in place. A dog in that case might have more than four canine teeth. The baby tooth will often be extracted upon recommendation of a veterinarian, as "double teeth" usually causes dental issues.