Horse teeth refers to the dentition of equine species, including horses and donkeys. Equines are both heterodontous and diphyodontous, which means that they have teeth in more than one shape (there are up to five shapes of tooth in a horse's mouth), and have two successive sets of teeth, the deciduous ("baby teeth") and permanent sets. As grazing animals, good dentition is essential to survival. Continued grazing creates specific patterns of wear, which can be used along with patterns of eruption to estimate the age of the horse. Types of teeth A fully developed horse of around five years of age will have between 36 and 44 teeth. All equines are heterodontous, which means that they have different shaped teeth for different purposes. All horses have twelve incisors at the front of the mouth, used primarily for cutting food, most often grass, whilst grazing. They are also used as part of a horse's attack or defence against predators, or as part of establishing social hierarchy within the herd. Immediately behind the front incisors is the interdental space, where no teeth grow from the gums. This is where the bit is placed, if used, when horses are ridden. Behind the interdental space, all horses also have twelve premolars and twelve molars, also known as cheek teeth or jaw teeth. These teeth chew food bitten off by incisors, prior to swallowing. In addition to the incisors, premolars and molars, some, but not all, horses may also have canine teeth and wolf teeth. A horse can have between zero and four canine teeth, also known as tusks (tushes for the deciduous precursor), with a clear prevalence towards male horses (stallions and geldings) who normally have a full set of four. Fewer than 28% of female horses (mares) have any canine teeth. Those that do normally only have one or two, and these may be only partially erupted. Between 13 and 32% of horses, split equally between male and female, also have wolf teeth, which are not related to canine teeth, but are vestigial first premolars. Wolf teeth are more common on the upper jaw, and can present a problem for horses in work, as they can interfere with the bit. They may also make it difficult during equine dentistry work to rasp the second premolar, and are frequently removed. Tooth eruption Horses are diphyodontous, erupting a set of first deciduous teeth (also known