Horses have evolved to survive by constantly grazing on whatever forages are available in their environment. This typically consisted of coarse grasses and other fibrous plant materials. The constant grinding motion of chewing and breaking down these materials to start the digestive process causes excessive wear and tear on the teeth, particularly the molars. In fact, if horses were born with teeth like ours, they would quickly wear them down to the gums with all that chewing, and ultimately starve. Instead, nature came up with an efficient system to continually replace the grinding surfaces on the teeth, ensuring that the horse could effectively break down plant material well into their twenties.
This is achieved by the evolution of teeth that continue to “grow,” or erupt, throughout the horse’s lifetime, until the root is effectively used up. Depending on how coarse the diet is, most horses have enough reserve crown to last at least into their twenties and often beyond.
Foals have a partial set of baby teeth, consisting of 12 molars (rear grinding teeth) and incisors (front nipping teeth) present at or shortly after birth. Behind those deciduous teeth are the roots of the full adult set, which start to come in around two years of age. Gradually, the adult teeth push the baby teeth, or “caps,” out and a full adult set of 24 molars and 12 incisors are present around five years of age. If you look at the skull x-ray in a horse under four years of age, it is easy to see the small rounded baby teeth sitting atop the long adult roots that are embedded deep in the jawbone. The adult molars in particular are so long that you can often see eruption bumps on the underside of the jaw and on the sides of the face because the underlying tooth roots barely fit inside the skull. On the other hand, if you were to observe the skull x-ray of a horse in its twenties, the molar roots are very short because most of the reserve crown has been used up through years of grinding.
COMMON DENTAL PROBLEMS
There are some dental problems that are unique to certain age groups while others will affect all horses from foalhood to senior years. While some problems can only be identified with a full dental exam using a speculum and possibly x-rays, depending on the issue, there are many clues that you can detect to help determine if your horse needs a veterinary dental exam.
Misalignment: Dental exams should begin shortly after birth because congenital malocclusions such as parrot mouth (overshot upper jaw), bulldog mouth (overshot lower jaw) and monkey/wry mouth (crooked jaws that don’t line up) can often be corrected with surgery and braces if caught in time, while the foal’s skull is still growing and they don’t rely on a lot of jaw movement when nursing from the mare. Many of these issues are easy to spot by simply parting the lips and observing the incisor alignment. Normally, the upper and lower incisors meet evenly without any over/underhang.
Although good incisor alignment is essential in wild horses because they must be able to nip off grass with them for efficient grazing, even fairly significant misalignments do not pose a large health risk to a domestic horse that is fed cut hay and concentrates.
It is still important to be aware of any malocclusions though, because poor alignment in the incisors indicates that a similar issue exists further back in the mouth, affecting the molars. Since the constantly erupting adult teeth rely on an opposing grinding surface to ensure level wearing of the dental table, an overshot jaw, for example, will result in the development of a large downward hook in the upper front molar, and a similar upward hook on the rear bottom molar. If left unaddressed, the rear molar hook can develop over time into a huge spike that digs into the opposite gum causing severe discomfort, infection and weight loss. Identification of this potential problem in the early stages followed by frequent dental check-ups and floating will easily prevent a major problem later in life. If you spot an obvious incisor misalignment when you part your horse’s lips, it is worth having a proper speculum exam to determine if similar issues are present deeper in the mouth.
Shedding Caps: Young horses normally shed baby teeth, called caps, without too much trouble, either spitting them out or swallowing them while eating. The front incisors tend to lift off the front of the gum as the adult teeth slide in from behind. Sometimes the baby teeth don’t get a direct push from the adult teeth and they shift off to one side without loosening up enough to fall out. While unsightly, this rarely bothers the horse and they are easily nipped off when the horse is sedated for some other procedure.
The molar caps can be more problematic if they refuse to let go, causing jaw pain, large tender lumps on the lower jaw and sinus pain and swelling with ocular discharge on the upper jaw. Affected horses are often suddenly difficult with a bit in their mouth and may pull hard on one rein or toss their heads to avoid contact. Impacted caps can be removed with special forceps, and the behavioural issues and painful swelling usually resolve on their own. More severe cases and those with sinusitis can benefit from nonsteroidal anti-inflammatory drugs and antibiotics.
Wolf Teeth: Wolf teeth can also cause problems if they interfere with the bit, and can be extracted with sedation and local anesthetic.
Not to be confused with canine teeth, which are much larger and appear closer to the front of the jaw, wolf teeth are often small and peg-like, with short roots (though their size and appearance can vary considerably). Some don’t even erupt fully from the gingivae (gums). When they appear, wolf teeth are found close to or right next to the molars. Canine teeth, on the other hand, typically erupt within a couple of inches from the incisors.
Wolf teeth, which can erupt anywhere from birth to 18 months, are usually visible by six months of age. They are permanent, without deciduous precursors.
Sharp Enamel Points: Even horses with perfect jaw alignment can develop sharp enamel points that irritate the gums and cheeks.
If you examine a normal horse’s molars when a speculum in place, you will see that the lower jaw is slightly narrower than the upper jaw, and the grinding surfaces have a slight slope to them resulting in the overgrowth of enamel ridges on the lingual (tongue) surface of the lower molars and similar sharp edges on the buccal (cheek) side of the upper molars. This occurs because normal grinding motion has a “figure 8” characteristic rather than a straight side-to-side action.
Over time, these points can cause lacerations to the cheek and tongue as well as preventing a full grinding cycle, which reduces feed efficiency, and can predispose a horse to colic as abnormally long fibre lengths and intact grains make it to the intestine. Sharp points can also cause pain-induced fussy behaviour when bridled, especially if the noseband is tight and forcing the cheeks against the teeth.
One way to check for grinding issues is to stand beside the horse and gently grasp the lower jaw with one hand while steadying the top of the nose with the other. Try to move the lower jaw back and forth relative to the upper jaw while the mouth is closed. Sharp points, especially asymmetrical ones, can create a generally reduced range of motion, or a normal lateral excursion to one side with a short excursion in the opposite direction. If you are able to watch the incisors move back and forth while doing this, you should be able to slide the lower jaw at least two incisor widths in either direction. You can also very carefully slide your finger between the cheek and the upper molars to feel for sharp edges, but a horse will often start chewing when you do this and it is very easy to get bitten. Grasping the tongue and pulling it out of the mouth to provide better access and prevent biting down should be left to professionals because injury to the tongue (and the handler) can occur.
Fractured Molar: Any horse can suffer from a fractured molar. Sometimes these are easily apparent during a pre-floating speculum exam, but others will require an x-ray to fully characterize the damage. While the crown may only appear to have one crack in it, the root may have fragmented into several pieces and this is important information because it allows the surgeon to decide the best approach for removal of the diseased tooth.
Signs of molar fracture can vary and many are discovered long after the initial incident because horses are stoic and will often carry on with molar and jaw fractures as if nothing is wrong. Sudden swelling over a tooth root, which may subsequently open and drain pus, is a common sign. Evidence of oral pain, dropping feed, bitting problems, unilateral purulent nasal discharge, and foul breath are all evidence of possible fracture. Any suspicion is worth investigating right away because cracked teeth allow feed material and bacteria into the tissues and can result in tooth root abscesses and eventually osteomyelitis, a serious bone infection.
Loose Teeth: As horses age, they literally run out of root, and, eventually, the molars will loosen and become ineffective for grinding. Sometimes these teeth need to be removed because as they wiggle around they cause pain, predispose the horse to tooth root abscess and reduce appetite and feed efficiency, which is critical in seniors. Older horses are likely to suffer from PPID (Cushings), which makes them more susceptible to infection and more likely to develop secondary bacterial issues such as sinusitis and root infections. These individuals require extra-careful monitoring.
Rotted Teeth: Another condition that develops in older horses is call Equine Odontoclastic Tooth Root Hypertrophy (EOTRH). In this condition, the incisor tooth root starts to deteriorate near the gumline and excessive mineralization develops around the tooth along with overgrowth of the gingiva. Draining infected tracts can form and the tooth may spontaneously fracture. This incredibly painful condition can affect all of the incisors and occasionally the canine teeth as well.
If identified early, we can slow the progression with antibiotics and oral rinses, but eventually extraction becomes the only way to keep the horse pain-free. While the surgery is difficult and prolonged, it can be performed in a standing sedated horse with lots of local nerve blocks. Extensive cases often undergo extraction in stages rather than removing all the teeth at one time. Most horses respond dramatically after removal of the diseased teeth and go back to eating heartily and bucking and playing in the paddock, something they have not done for years.
Early EOTRH can be hard to identify but as the situation progresses it is unmistakable. The gums bulge outward above and below the affected teeth, and abnormal mineralization (hypercementosis) is seen on the exposed tooth. The gums hypertrophy and bleed easily, and the degenerative tooth roots become infected and form draining tracts that erupt alongside the teeth. The affected tissue and infection can create a foul odor and the horses show signs of pain and are reluctant to eat. A hard candy or having the bit clanked against these teeth is excruciating for them.
Early and regular dental exams are key to preventing problems and treating small issues before they blow up into large problems. While a full exam with a dental speculum is necessary for proper evaluation of the equine mouth, there are many observations that any horse owner can make along the way to help you decide if your horse needs dental attention.