A horse's adult teeth continue to erupt throughout their life as the grinding surface is worn down through chewing. A young adult horse's teeth are typically 4.5–5 inches long with the majority of the crown remaining below the gumline in the dental socket. The rest of the tooth slowly emerges from the jaw, erupting about 1/8" each year, as the horse ages. When the animal reaches old age, the crowns of the teeth are very short and the teeth are often lost altogether. Very old horses, if lacking molars to chew, may need soft feeds to maintain adequate levels of nutrition.
Young horses have a total 24 deciduous or milk teeth - 12 incisors and 12 premolars or grinders. Mature male horses have 40-42 permanent teeth and mares have 36-40 depending on the number of canine teeth present. Canine or bridle teeth erupt in the inter dental space at 4-5 years of age in male horses. They will only appear 20-25% of the time in mares and are usually smaller than those found in males. The first premolar (wolf-tooth) may be absent or rudimentary. In most horses it is only present in the maxillary (upper) jaw. Click link to see table for average eruption times.