Dealing with diastemata

Diastemata, which is the pleural of diastema, are also being seen more frequently in equine practice.

While it was uncommon to diagnose a diastema 10 or so years ago, we now see at least one horse a week with the condition. This reflects better recognition of the condition by vets, largely through the efforts of Professor Paddy Dixon and colleagues at the University of Edinburgh, as well as advances in equine dental equipment.

But why do diastemata occur and cause such pain? How can we diagnose them promptly and accurately, and what is the best treatment?

Diastemata cause pain when food becomes trapped in the space between teeth, leading to packing of putrefying material, infection and tissue destruction. Inflammation then spreads to adjacent teeth, causing their erosion and eventual loss. These processes are intensely painful.

The cheek teeth of horses are normally kept close together by the way in which teeth erupt through life. The front and back teeth are aligned with their tops tilted towards one another, and it is this angle of eruption that compresses the surfaces of the teeth and prevents gaps forming. However, as horses age and progressively less tooth remains under the gum, their ability to maintain a tight grouping is lost. Also, with advancing age, loss of a tooth allows the other teeth to drift into the empty space resulting in gaps forming.

Diastemata can also develop when one of the cheek teeth fractures or becomes displaced, either towards the tongue or the cheek. Dental overgrowths add to the pressure put on these teeth during chewing, leading to their displacement. Diastemata can also occur in young horses as the result of abnormal conformation of their jaw and, or, cheek teeth alignment.

The fact that horses spend over 18 hours each day vigorously chewing means that some food fibres are inevitably forced into any spaces that form between teeth. If the gap is wide, then the food may simply fall out once it has decayed through the activity of saliva and bacteria in the mouth. But, if it is narrow, then food enters under the pressure of chewing but does not leave. It is these so-called closed or valve diastemata that result in oral discomfort and damage.

Progressive accumulation of food material in a diastema is followed by compression down into the gum at the margin of the teeth. This causes stretching of the structures around the teeth, inflammation, and destruction of soft and hard tissues. The pain is most apparent during chewing and this is why horses quid or drop food. Destruction of dental tissues may affect the eruption of the teeth, causing wavemouth, or infection of the tooth roots with the risk of sinusitis or infection of the underlying bone.

In addition to quidding, symptoms of diastemata include halitosis, with an often foetid odour to the breath, and packing of food resulting in an apparent swelling of the cheek. Some horses will appear to favour one side of the mouth when chewing, avoiding the affected side.

Such is the discomfort some horses will lose weight through not ingesting adequate food. Oesophageal obstruction ('choke') and pelvic flexure impaction may also occur because forage is inadequately chewed. Signs are usually more noticeable when long fibre feeds such as hay and haylage are fed, as opposed to short fibre chopped feeds like chaff and grass which is softer.

Diagnosis of diastemata requires careful and comprehensive examination of the mouth. This is achieved using a full mouth speculum or gag and an appropriate source of light, such as a head torch. Diastemata are more common on the lower jaw and can be difficult to visualise when they affect the rear most teeth. For this reason it is important to use a dental mirror, sometimes in combination with a special basket instrument to retract the tongue. Alternatively an endoscope can be used for direct inspection.

Diastemata are characterised by the presence of food fibres between teeth and there may well be a crater-like depression in the underlying gum. Touching or pressing the affected area is painful and deeply resented, even in a sedated horse. When food material is then washed out or removed with a long-handled dental pick, it is often blood-stained and rotten in both appearance and smell.

Diastemata frequently occur at multiple sites, making it essential to examine the entire mouth. Your vet may recommend taking x-rays to more accurately assess their location and severity, as well as to help identify any contributing factors and secondary complications such as sinusitis or bony infections.

Standard diastemata treatment is to widen the gaps so that food may move freely between teeth without becoming trapped. This is done using a special burr on a motorised dental rasp that grinds the edge of the two teeth lining the diastema. The gaps are widened progressively with thicker burrs.

Horses are sedated and, if the diastemata are particularly painful, the jaw injected with local anaesthetic to block the nerve. Care has to be taken not to grind into the sensitive part of a tooth and this is avoided by frequently checking the position of the burr with a dental mirror. It is also important to periodically cool the burr in water and spray the site with water, as excessive heat build-up can damage the structure of the teeth.

Treatment is invariably successful but, because teeth grow continuously during a horse's lifetime, eruption will result in gradual narrowing of the gap and necessitate further attention. Repeat oral examinations at 3-6 month intervals are advisable. Sometimes, in younger horses, only a single treatment is required as the teeth appear to 'grow back' in tighter alignment.

If a diastema is the result of a misplaced tooth or developmental problem, then extraction of the offending tooth may be considered. Also, in old horses where a diastema has caused the tooth to become loose, extraction is preferable. Sometimes, instead of or alongside diastema widening, the gap may be filled with plastic impression material.

Sometimes we encounter horses with food trapped in diastemata that are not painful, nor associated with recession or damage to the gum. These are probably not clinically significant and best left alone, with advice to re-check in six months' time.

In some cases, especially old horses with multiple diastemata, it may be necessary to modify the diet by excluding long fibre forages and replacing with finely chopped forages. Softening hay or haylage by soaking can also help prevent food packing.

Diastemata are arguably the most painful equine dental disease and should be considered in any horse that is quidding or experiencing difficulty eating. Careful inspection is required to assess their number and severity but, with proper treatment, even the most severely affected horses can make a full recovery.