Common disorders of the mouth

Bit related problems

      By far most oral injuries are caused by pressure from the riding equipment, the bridle, bit and noseband.  Many of them are painful and likely to affect animal welfare.

Pressure wounds in the cheeks and corners of the mouth 


 Mild pressure wounds in the corners of the mouth. Too long bit increases the risk                                          


The soft tissue adjacent to the first cheek teeth is frequently affected by the equipment. Continuous and/or repeated pressure on the same spot, induced by the bit and noseband, results in reduced blood flow and development of pressure wounds. They tend to reach deep into the soft tissue and take long to heal. Serious pressure wounds in the corner of the lip can take several months to heal. 


Serious pressure wound adjacent to the first cheek teeth. Those are often mistaken to be caused by sharp edges of the teeth. The typical appearance of the lesions reveals a chronic history as they are characterized by hyperkeratosis surrounding an ulcerated centre.

To reduce the risk of bit-induced lacerations in the mouth it is imperative that the pressure is not always on the same spot. This can be avoided by varying the training methods and by frequent change of equipment. Fitting of the bit is of great importance. Preferably it should be stable in the teeth-less part of the mouth. Too long bits tend to be drawn above the teeth where they pinch the soft tissue between the hard metal and the hard teeth.


Injuries of the bars (interdental space)


The bars are covered with a very thin layer of soft tissue that can’t resist any pressure from the bit. Pressure on this area will result in pressure wounds and inflammation of the soft tissue. In more serious cases the periost and the bone are affected. Bits with a port increase the risk of those injuries prohibiting the tongue in lifting the bit and protecting the bars.  


Bit related injuries of the teeth


Abnormal wear of the first cheek tooth (long,open arrow). Wolf tooth (short, open arrow). Caries resulting from abnormal wear of the first cheek tooth (black arrow)

“Chewing on the bit” is quite a common behaviour that unfortunately incurs the risk of damaging the first cheek teeth. Abnormal wear of their surfaces can result in development of caries which may end up with toothache. The pressure from the bit may also cause drifting of individual teeth. 

The rider has the responsibility to stop this behaviour as it will sooner or later harm the horse.

The wolf tooth

A small rudimentary developed tooth close to the first upper cheek tooth can be seen in more than 50% of horses. The anatomic position makes the wolf tooth easy to come into interference with the bit, causing discomfort for the horse. It makes it harder for the horse to accept the bit and increases the risk of chewing on the bit. This is why the wolf teeth are recommended to be extracted.


Age related problems

The young horse


Shedding the milk teeth can cause temporary problems in the mouth. The horse can have some difficulties chewing and may have problems with the digestion and get fever.  Approximately 15% of the young horses have some deviations in the shedding process which most often normalizes by itself. Trainers and keepers of young horses must be aware of this physiology to avoid a development into problems.


The permanent cheek tooth (black arrow) is not fully developed until very close to the time of eruption. Any manipulation /damage to the milk tooth (white arrow) can potentially create livelong problem to the permanent tooth. Floating of milk teeth can interrupt this sensitive process. Short black arrow shows the permanent incisors erupting.


The old horse


In the old horse the teeth become very short and eventually loose their attachment to the alveolar bone. It is a normal feature that the older horse needs longer chewing time due to lack of enamel. Excessive strain can lead to loosening of individual teeth and thus cause temporary pain and chewing problems.

Teeth will wear down by age, and eventually become loose as a normal development.


Congenital disorders

Overbite and underbite


Over- or underbite of the cheek teeth are common disorders of the equine mouth. It causes uneven wear of the teeth as parts of it are not touching their counterpart. Consequently those parts will not wear down at the same rate as the rest of the teeth and thus lead to the formation of points or hooks.


It results in abnormal chewing and development of unworn tooth surfaces.


The result of an overbite                           The result of an underbite

"Parrot mouth" and "monkey mouth"

Occasionally, malformations develop during the foetal stage.  The most common congenital defects in horses are “Parrot Mouth” and “monkey mouth”.


"Parrot mouth"                                    "Monkey mouth"


Other disorders of the mouth

Stomatitis, food impactions and fracture

Infections of the oral cavity are quite common and can be due to various other health disorders. It can develop into infections in the mucosa of the mouth (stomatitis).  Food impactions (e.g. accumulation of feed inside the cheeks), which can be caused by various reasons, frequently leads to gingival infections and even the loosening of teeth.


Fractured teeth are common and can cause infections of the pulp or, in severe cases, lead to bone infections.  


Caries and root infection




Most common tomors found in the oral cavity of the horse proof to be benign.




Abnormal behaviour such as cribbing can lead to abnormal wear of the fron teeth.



Metabolic disorders can cause oral symptoms in horses. Loose teeth, of no obvious reason, could be a symptom of Cushing Disease (malfunction of the adrenal glands).







The young horse will inevitably change its teeth. Shedding the deciduous teeth can sometimes cause temporary problems in the mouth. The horse will have some difficulties feeding and may show some gastro-intestinal symptoms or even fever.  This happens with around 15 % of the young horses and even if it is a temporary problem which normally will pass by without any interference, trainers and keepers of young horses must be aware of this and avoid pressing them too hard during this period.