Like people, dogs have two sets of teeth: what are known as deciduous or baby teeth which puppies are both with, and the permanent adult teeth. By 6 months of age, it is typical that all of the baby teeth have fallen out, and have been replaced by the permanent or adult teeth.
In certain breeds such as toy breeds like Yorkshire Terriers and Poodles, one or more of the deciduous teeth may be retained into adulthood, leading the presence of a double row of teeth, most commonly of the canine teeth, but also possibly of the thinner and sharper incisor teeth. In some cases, the roots of the permanent teeth may be affected and pushed out by the retained baby teeth. The best thing to do if the retained baby teeth do not fall out is to have them removed at the time of neuter or spay over 6 months of age. In that way, improper tooth and root alignment is avoided.