Dental stars are marks that appear in the central pulp cavity of the teeth as the horse ages. After some wear has occurred on the teeth, the central pulp cavity is exposed and the tooth is marked by the dental star. These begin as a dark line in front of the dental cup, which grows in size and becomes more oval in shape as the cups are worn away. Dental stars are usually first visible at age 6, on the animal's lower central incisors, and are very visible by age 8. They appear on the lower intermediates by age 9 and on the other incisors between the ages of 10 to 12 years.