By Mary DeLorey, DVM, Kettle Falls, Washington
It is common these days for horses to live into their thirties and beyond. Their teeth, however, were really only developed to last into their twenties under optimum conditions. Unfortunately, the majority of our domestic horses do not live under those optimum natural conditions in which they evolved. Everything we, as equine veterinarians, can do to prevent the premature attrition of the horse's teeth will stand them in better stead to live better, longer lives.
For instance, most major malocclusions start as small discrepancies when the horse is young, often when the permanent teeth are just erupting between the ages of 2 1/2; and 5 years of age. Small problems recognized and corrected at this age never turn into the large problems we currently see in the older horse population. A veterinarian well-trained in equine dentistry has the skills to prevent most, if not all, major dental problems that have previously been accepted as an inevitable part of equine aging. Did you know that all horses should receive a comprehensive dental examination before the age of 2 1/2; and at least yearly thereafter? Did you know that by the time most owners recognize that their horse is having difficulty eating or weight loss is apparent, that horse's dental condition is likely to be severely abnormal? Did you know that many parrot-mouthed (over bite) or sow-mouthed (under bite) foals can have near-normal bites without surgery or orthodontics if the condition is recognized early? Did you know that periodontal disease is the number one cause of tooth loss in the horse? Did you know a qualified veterinarian can diagnose, treat and- in many cases- PREVENTperiodontal disease?
It makes little difference if you are new to horse ownership or a seasoned professional. Chances are, you may not be intimately familiar with the expanding field of equine dentistry. Horse owners of various experience levels have many questions about proper dental care for their equine charges. "My horse is only 3 years old. He doesn't need his teeth looked at..... does he?" "How often should my broodmares be examined?" What about my daughter's 4-H mount?" "My dressage horse is suddenly hanging on his right rein, but my vet just floated his teeth six months ago. What's wrong?" "My 25-year-old Appy is having trouble eating. She slobbers and drops wads of hay. Could it be her teeth?"
The answers to the above questions will vary with each individual horse and each individual circumstance. There are, however, some general tendencies based on a horse's age, gender, career, overall health and dental health that provide guidelines from which to make recommendations.
First though, a basic understanding of how a horse chews and some rudimentary knowledge of the anatomy is necessary to comprehend the need for thorough dental care on a routine basis. The most basic differences between a horse's teeth (an herbivore or plant eater) and the teeth of humans or dogs or cats (omnivores and carnivores) is that a horse's teeth are not completely covered in enamel, and what is visible in the mouth is not meant to last the horse's entire life. Omnivores (creatures that eat all types of food from vegetables to meat) and carnivores (predominantly meat eaters) have teeth that are completely covered in hard enamel, which allows their teeth to withstand the forces necessary to chew their diet without wearing away the tooth surface. Horse's teeth are made up of vertical "columns" of three different materials, only one of which is enamel. The other two materials, dentin and cementum, are not as hard. This configuration is actually designed to allow the horse's teeth to slowly wear away as they grind their coarse diet of plant roughage. It's okay that their teeth slowly wear away since as a given amount of tooth is used up, new tooth crown will erupt into the mouth to take its place at a rate of about 3-4 mm per year. A horse's permanent teeth are about four inches long!
As you can imagine, most of that length is hidden from view in the jaw and skull bones. And if you do the math, that's enough tooth to last an average of 25 years under ideal circumstances. That "ideal circumstance" is the hitch in this picture. Ideal circumstances for the horse include the following: reproduction according to the forces of natural selection, exposure to a varied diet (including grasses from fine to coarse, wild grains, broad leaf plants and the fine sand-like silicates that accompany these plants, herbs, twigs, leaves and even bark) and, most importantly, exposure to these forages 24 hours a day, every day of their lives. Does this environment resemble your horse's lifestyle? Not mine, and not likely yours. Add two other factors- domestic horses are usually ridden or driven, requiring communication through their mouths, and we humans expect our equine partners to be with us a long, long time- and you have a situation that expects and presumes a lot of the horse's dentition. Without a fairly regular program of correction and maintenance beginning early in life and periodically as they age, most domestic horse's teeth will not wear properly and will not function into old age, effectively reducing his or her life span.
A mature horse has from 36 to 44 teeth. Front to back, he has six upper and six lower incisors (front teeth, the ones you can see readily when you part his lips) used for nipping and tearing forage. Geldings and stallions usually have four canine teeth (two upper and two lower; these are the teeth that you can see in the bars of the mouth.) Most horses will have two wolf teeth as youngsters (small, shallow rooted teeth located just in front of the first cheek tooth on the upper jaw, occasionally also appearing on the lower jaw), which are typically removed at about a year of age. Then there are 12 premolars and 12 molars comprising the cheek teeth, the bulk of the grinding apparatus. These are arranged six cheek teeth to an arcade or row of teeth (two upper and two lower arcades). The cheek teeth are packed so closely together that they appear as one long chewing surface. All together, the horse's mouth is (or should be) a highly specialized and finely tuned grinding machine, uniquely and perfectly suited for its intended purpose.
The biomechanics of mastication plays a major role in how a horse wears his teeth. There are two or three important concepts here. One is that the horse's lower jaw is narrower than his upper jaw. This means that the two upper arcades overhang the two lower arcades by 1/4 to 1/2 inch. The teeth in the two lower arcades also sit slightly to the inside of the upper arcades.
The second concept is that a horse moves his jaw in a roughly elliptical pattern when he chews. He drops the lower jaw down, moves it over to the right or left, brings it up into contact with the upper teeth on that side, then moves the lower jaw back toward center, grinding the lower teeth across the chewing surface of the upper teeth on that side. There is also a small front to back motion component during the chewing cycle. Abnormally opposed teeth can impede this motion. Due to the above outlined anatomy and movements, it is possible for the horse to chew on only one side at a time. The third concept is that each individual horse's preferences, habits, genetics, conformation, diet and dental health determine whether or not he will wear all his teeth in a normal and uniform manner.
Since most domestic horses are not bred for proper dental conformation, are not housed in such a way that allows them to browse on varied forage for at least 18 hours per day, are expected to begin work very early in life, and are expected to remain active very late in life, it makes sense that we, as their caretakers, should conscientiously address their dental health.
When does dental care first need to be addressed? That one has an easy answer: at birth! At least a cursory visual and digital inspection of the foal's mouth should be performed by your veterinarian during the "well-baby" examination the day of or the day after birth. In addition to the rest of the physical examination, your veterinarian will check to make sure that the foal does not have a severe over- or under-bite that could make nursing difficult and predispose to other dental abnormalities as the foal matures. It's also important to make sure that the foal's palate is normal so that it can swallow without difficulty. In the first two weeks of life, your foal will erupt 16 deciduous (baby) teeth!
A foal's deciduous premolars (see equine dental glossary) are all in use within the first few weeks of life and can soon start to wear abnormally if they do not meet up properly. If there's an overbite, for example, not only are the incisors misaligned, often the baby's premolars don't match up either since the entire lower jaw is too short. The portion of the tooth that overhangs will not have a tooth surface to grind against as the rest of the tooth wears. The hook-shaped overgrowths that result can prevent the lower jaw from growing to the length of the upper jaw. While there are orthodontic devices and surgical remedies to correct truly severe over- and under-bites, they are expensive, difficult to maintain and have variable rates of success. Whenever appropriate, it is far easier to let Mother Nature do the best job she can by periodically removing the hooks, ramps, ridges, etc. that inhibit normal jaw growth. In many cases, this is all that is necessary to correct a mild to moderate over- or under bite.
During the first year of life, in addition to 12 deciduous premolars, the youngster also erupts two more sets of deciduous incisors, for a total of 12. All 24 baby teeth are in place by the age of about nine months. At this age, most horses will also erupt two wolf teeth and the first permanent molar set erupts behind the baby premolars. By the time the foal is a yearling, he has erupted 24 to 30 teeth! If there have been no problems detected previously, it is strongly recommended that a skilled veterinary professional perform a complete dental exam on every horse no later than 12 to 18 months of age. At this age, all of the deciduous teeth have been "in wear" long enough that their edges are likely very sharp (remember how the chewing pattern wears the teeth). Many owners do not realize that even very young horses need comprehensive dental attention. Deciduous teeth are softer than permanent teeth and wear sharp edges much faster. It is not uncommon for yearlings to have ulcers or lacerations on their cheeks and tongues from these razor sharp points. The wolf teeth, which become sharp and can cause pain when the horse is bitted, are best removed as a yearling. This is a good time to make the young horse comfortable and ensure that the stage is set for the next phase of dental development.
Your horse's mouth undergoes the largest turnover of deciduous to permanent teeth between the ages of 2 and 3 1/2 years. He will lose two sets of deciduous incisors and shed two sets of premolars, all to be replaced by permanent teeth. He will have already erupted his second set of permanent molars, and the third set may be getting ready to erupt by 3 1/2 years of age. That's up to 24 permanent teeth in 1 1/2 years! If certain baby teeth wait too long to fall out, they are termed "retained." The longer the baby teeth take to "shed," the longer it takes for the permanent ones to replace them and become useful for mastication. While it is detrimental to remove deciduous teeth before the permanent ones are ready to move into place, it is also potentially troublesome to leave old baby teeth in place too long. If pairs of deciduous teeth shed asynchronously, the corresponding permanent teeth erupt asynchronously also. This situation is undesirable since it sets up uneven chewing surfaces in the mouth that the horse will have difficulty overcoming on his own. Incisors can also be affected by imbalances caused by pairs of teeth that erupt too early or too late. Therefore, the attention of a skilled veterinary professional can be very important in promptly correcting imbalances and preparing the mouth for normal adult development.
By the age of 4 1/2 to 5 years of age, a young horse should have shed or be very close to shedding the last deciduous teeth, and all permanent teeth should be erupted. It's very possible that a horse may have retained a set of baby incisors or even a set of baby premolars at this age. These should most likely be removed. Brand new permanent teeth get very sharp very quickly as the horse begins to use them in earnest, and should be smoothed. Geldings and stallions may have four canine teeth that are breaking through the gum line at the age of 5 years. These are the teeth easily visible in the space between the incisors and the cheek teeth. Some horses experience discomfort associated with the eruption of these teeth, which may explain fussy behavior that appears suddenly during this time. This is the time to make any small adjustments to keep the mouth in balance as the last permanent teeth come into wear.
A Note on Canine Teeth
By 6 years of age, the only teeth not fully erupted may be the canines in geldings and stallions. As these teeth reach significant size, they can become like small daggers protruding from the gums. While they do not interfere directly with the bit or any chewing surfaces, their sharp edges can be quite painful as they contact the tongue and lips during eating and bitting. It is common practice to round the tops so that they are non-irritating. They serve no useful purpose in domestic horses, so shortening them is not detrimental. Also note that occasionally, a mare will have canine teeth. They are usually much smaller than their male counterparts', but they should be addressed similarly.
Once your horse has reached the age of 6 years, all his permanent teeth are in position and in use. If your horse has had periodic, comprehensive dental care up to this time and has no severe malocclusions or dental disease, he's well-poised for lifelong dental health. He should receive maintenance care, including smoothing of sharp edges, minor rebalancing and troubleshooting every 8 to 12 months. Horses that are in demanding competition, have heightened sensitivity or pre-existing dental abnormalities may need routine attention more frequently, perhaps every six months, to maintain dental health and comfort. Each horse is an individual with unique needs. A veterinarian skilled in equine dentistry can work with you to determine a schedule most appropriate for your horse.
Horses over the age of 16 to 18 that have had regular, skilled dental maintenance may require little more than a younger horse with similar care. In general, however, there are some things that need periodic monitoring. In the older horse, the crown that has been slowly erupting out of the jaw over his entire life is running out. This progression brings with it the tendency toward periodontal (gum) disease, the increased possibility of fractured teeth, diseased roots and loose teeth. There are many different ways to approach these problems, and more work is being done to understand the best management options. Often, early periodontal disease can be successfully treated with focused cleaning and local use of special antibiotics and protective materials. Sometimes more aggressive techniques are necessary to arrest the disease. Loose teeth recognized early can be shortened and rested so that the opposing tooth is not continuously grinding against it. Some of these may reestablish their firm connections. Other loose, damaged or diseased teeth are best removed. But, then regular maintenance is still important since the surrounding teeth may migrate into the space created by tooth extraction. Again, a horse that has had regular, skilled dental care during his youth and middle age is much less likely to develop significant problems in his golden years.
Perhaps the most compelling argument for the value of comprehensive equine dental care is the comfort factor. Equine veterinarians skilled in dentistry are constantly amazed at how much discomfort horses will endure without any overt signals to their owners. Horses are eating "machines." They are designed to eat at least 18 hours a day. This is a survival instinct deeply ingrained in their very cells. Most horses will continue to eat and will adapt to the difficulty or the discomfort until the pain is so severe or until mechanical forces make it physically impossible to do so. It is not uncommon for otherwise very conscientious owners to be surprised, appalled and then embarrassed that their equine friend has endured such pain or difficulty for so long without complaint. By the time the average owner notices a "problem," the abnormalities inside the mouth are likely to be severe.
One of the most important concepts that horse owners can embrace from all this is thatprevention is the absolute key to good equine dental health. The idea that a horse doesn't need dental attention until he is in his or her middle age must disappear. The tendency to abnormally wear the teeth is usually present very early in life. Minor abnormalities detected at the age of 1 to 5 years can usually be easily corrected and need never become an issue. If the same problems are left undiagnosed until that horse is older, much more aggressive techniques are required to correct the situation. In certain circumstances, the problem may become so severe that it is not correctable at all. Even in such severe cases, there is much the veterinarian, experienced in equine dentistry, can do to make that horse comfortable and as healthy as possible.
What if you've just purchased a 5-year-old dressage prospect, a 10-year-old barrel horse or a 15-year-old pony hunter and you don't know what level of dental attention this new horse has received throughout his life? The sooner you arrange for a veterinary professional skilled in equine dentistry to perform a comprehensive examination, the better. Many, many horses have never had their teeth examined at all by the age of 5 or 10, or even 15! Just because the horse has been "floated" before does not necessarily mean that he has ever had a comprehensive exam and equilibration. There is an entire jungle of abnormalities that can develop even by the age of 5 or 6 that "floating" will not address. "Waves," "steps" and "ramps" develop when some of the teeth in an arcade remain too tall and cause the opposing teeth to become over-worn, giving a roller coaster appearance to the line of teeth as you sight from front to back. "Hooks" on the upper first cheek tooth or lower last cheek tooth can overhang the opposing tooth and impede jaw movement or can even dig into the opposing gums.
Incisors can develop abnormalities of wear and meet at a diagonal or curve instead of a straight line, making balanced function of the jaws impossible.
Periodontal disease is common in middle-aged horses that have not received regular comprehensive dental care. Of course, the longer these types of abnormalities go unaddressed, the more severe and the more difficult to correct they become. A veterinary professional experienced in equine dentistry is also acutely aware of the importance of more subtle issues. There are integral concepts such as incisor length and angle, interocclusal space, occlusal angles, lateral excursion and quality and degree of premolar and molar contact that should be addressed in each and every horse.
The recent advances in veterinary dental health care are impressive, and more research is underway in veterinary schools and clinics. Horses and their owners are benefiting from this wealth of knowledge so that horses are living longer and more active lives. It is no longer uncommon for horses to live into their late thirties. If we want our equine partners to remain healthy and happy, it is important that we do everything we can to ensure that they are able to eat (and work) comfortably and effectively. A skilled veterinarian can prevent most abnormalities from ever becoming a problem, thereby maximizing the useful life of each tooth in your horse's head. Modern equine dentistry combines thorough knowledge of anatomy and biomechanics, current research and clinical findings with the most advanced equipment and the safest drugs to optimize your horse's dental health for a lifetime. Comprehensive dental care delivered regularly by an experienced veterinary professional may be one of the most beneficial health care services you can provide your horse.