The Anatomy of the Mouth

The different roles of the mouth of the horse 

 

 

The mouth of the horse is developed for effective intake, sorting and chewing of grass.

Under normal conditions a horse will spend 15 – 18 hours a day foraging.

 

The skull

A horse’s mouth has three major sectors with separate rôle in the feed intake.  The incisors cut the forage (1), which is then moved into the middle sector, the interdental space (2). This is where any indigestible or foreign bodies are supposedly discharged, before moving the fodder into the hind cavity for chewing (3).

 

The interdental space

 

Without a bit                                                                          With a bit

The interdental space between the incisors and the cheek teeth makes it possible to place a bit in the horse’s mouth.

It´s natural role is however to separate any foreign parts from the fodder which is of vital importance for the horse’s health. Therefore the interdental space is well supplied by nervous functions and extremely sensitive.  This should always be borne in mind when bridling a horse.

The oral cavity is filled with the soft tissue of the gum and the tongue. The bit has to “make itself a place” by reshaping the tongue.

 

The horse’s tooth (The equine tooth is hypsodont. Human tooth is brachyodont).

The major difference between the human and the equine teeth lies in the development of their roots. In humans the roots are fully developed as soon as the tooth has erupted, whereas in horses the roots are growing and developing for a number of years. The tooth’s crown or enamel on the other hand is fully developed by the time the young horse starts using it. Part of the crown is however, embedded in the alveolar bone (in the jaw) and called the reserve crown. It should be borne in mind that no more enamel will be generated after the time of eruption of the permanent tooth.

Equine teeth will wear down by chewing but at the same time they continue to emerge from the jaw (erupt). While the roots are still developing it will fill in the cavity that forms in the jaw (alveolar bone) but later on it becomes filled with bone tissue. From then on the teeth will keep shortening with wear, eventually loosening and falling out.

 

Deciduous teeth – milk teeth

 

Foals and young horses have deciduous teeth that are shed and replaced with permanent teeth during the age of 2.5 to 4-5 years. The first permanent jaw (M1) erupts when the horse is one year old. At the age of 5years, horses have got all their permanent teeth except for the canine teeth that may be hidden until the age of 7 or 8.

 

The skull with teeth  

The adult horse has normally got six upper and six lower incisors. Just behind the incisors are the canine teeth which may be lacing in the mares in many breeds. In the interdental space the jaw bones are covered by a thin mucous tissue. Further back there are 6 cheek teeth on each quadrant, 3 premolars and 3 molars. The premolars and molars have the same anatomy and the same function. 

A horse may have a rudimentary premolar, in front of the upper cheek teeth known as a wolf tooth.  About 50 % of horses have wolf teeth. The bit is likely to interfere with the wolf teeth while pulling the reins which may cause the horse discomfort. 

 

 

Overview of the oral cavity, the tongue and the cheek teeth

The arrangement of the check teeth with wider upper jaw and sloping surface of occlusion is designed for the efficient chewing. The outlining of the tooth arcs supports the soft tissue of the cheek and tongue and prevents injuries. The rough edges of the check teeth are of great importance for grinding.

The tongue is a strong muscle moving the feed between the different departments of the mouth. It is very sensitive although covered by a thick mucosa.  A groove is apparent between the inner part of the tongue which is connected to the underlying tissue and the free part of the tongue in the front.