This photo is of a 6 year old Thoroughbred mare that did not shed her baby incisor teeth correctly. The tooth in the center of the photo should have been lost at around 2.5 years of age when the adult tooth erupted. The baby tooth on the left side of the photo should have been shed at around 4.5 years of age. Retained baby teeth can cause periodontal disease and other issues that affect the adult teeth and should be removed. In this case, the baby teeth were extracted and the teeth underneath were not damaged but the adult tooth on the left side is slightly out of alignment.
David Warren, D.V.M.