Dentistry

Advances in Equine Dentistry

Above: Sharp points on a horses’ tooth. The figure to the left demonstrates a “Diagonal” Incisor Bite.

Proper care of your horse's teeth is a hot topic of discussion these days. Advances in understanding of anatomy and biomechanical function of the horse’s masticatory (chewing) apparatus are occurring in leaps and bounds. With this deeper understanding, the development of new, more precise instrumentation is enabling the experienced veterinarian to achieve a very high level of dental care for their equine patients. The difference between “just a float” and the expert dental equilibration available from specially skilled veterinary professionals is the difference between night and day. Many horse owners are wondering why all these advances are necessary; “After all,” some may wonder, “I’ve had horses all my life and they seemed to get along just fine with the old way.” This perfectly reasonable observation deserves a good explanation. 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, dogs or cats (omnivores and carnivores) is that a horses 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 chew their coarse diet of plant roughage. It’s ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○

o.k. that their teeth slowly wear away, since as a given amount of tooth is used up, the same amount of 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 4 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, grains, broad leaf plants and the fine sand-like silicates that accompany these plants, herbs, twigs, leaves, 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 6 upper and 6 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 they also appear on the lower jaw,) these are typically removed at about one year of age. Then there are 12 premolars and 12 molars comprising the cheek teeth, the bulk of the grinding apparatus. These are arranged 6 cheek teeth to an arcade (or row) of teeth

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An illustration of abnomally worn cheek teeth. (Illustration by Mary Delorey) (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 horses 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. Due to the above outlined anatomy, 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, conformation, diet, and dental health determine whether or not he will wear both sides evenly—or even if each tooth in each arcade wears evenly with its neighbors. 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 contentiously address their dental health. The adage “no hoof, no horse” can be applied equally well to dental health: “no teeth, no horse.” Most horse owners and many veterinarians use the term “floating” to describe routine equine dental maintenance. Floating is the process of removing the painfully sharp enamel points that develop on the outside edges of the upper cheek teeth and the inside edges of the lower cheek teeth. The term comes from the process of “floating” wet cement so that the surface is smooth. Proper equine dental equilibration involves much, much more than just floating. Even a basic “float” cannot be properly performed without a full mouth speculum to hold the AUGUST 2002

mouth open and special instruments to reach the less accessible teeth. Many razor-sharp points will be missed without proper equipment, adequate sedation and experience. But the sharp enamel points are only the tip of the iceberg. For years, interested and concerned veterinarians recognized that there were significant abnormalities of wear in most of their equine patient’s mouths: abnormalities like “waves” or “steps” where some of the teeth in an arcade remain too tall and cause the opposing teeth to become overworn, giving the arcade a rollercoaster appearance as you sight down the length of it; or “hooks” on the upper first cheek teeth and the lower back cheek teeth that overhang the opposing tooth and impede proper jaw movement or can even dig into the opposing gums; incisors that meet at a diagonal or curve instead of a straight line. But very few had any solid knowledge of how or whether to correct these abnormalities. Over the last 10 to 12 years, veterinarians have made great strides toward understanding the horse’s biomechanics of mastication. Greater understanding led to the development of superior instrumentation that allows nontraumatic, pin-point accuracy. The development of more effective sedatives and the realization that proper sedation is necessary to safely and properly complete the work has helped bring equine dentistry to the level it is today. The idea of simply smoothing sharp points off the edges is giving way to a much more enlightened approach that addresses the horses whole mouth, indeed the whole horse. Now veterinarians that have the interest and have made the effort to learn of the advances understand the subtle interrelationships of each element within the horse’s mouth. There are important concepts such as incisor length and angle, interocclusal space, occlusal angles, lateral excursion and quality of premolar and molar contact that a practitioner specially trained in equine dentistry can accurately evaluate and correct. There are advances in recognizing and dealing with diseased or damaged teeth and the surrounding tissues that were largely overlooked in the past. Proper equine dentistry will keep your horse’s mouth functioning at its peak potential. This will, in turn, help ensure that his or her teeth will be much more likely to remain healthy and effective into the geriatric years. A new

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study has demonstrated that horses with major abnormalities of where examination by a veterinarian skilled in equine dentistry wear have a decreased ability to extract nutritive value from their is of immeasurable benefit: between 12 and 18 months of age feed and that if these abnormalities are successfully corrected, when all the horses deciduous (baby) teeth are in wear and are those horses will improve their feed conversion values. Regular very sharp, the first permanent molar is erupting, and wolf teeth examination and correction by a practitioner skilled in equine should be removed; between two and three years when the first dentistry can make sure that your horse never develops these deciduous teeth are shedding (a process referred to as losing problems. He or she can make sure that your horse’s mouth caps), and remaining deciduous teeth are extremely sharp; becomes and remains a smoothly functioning “biomechanical between three and four years when more caps are shedding and machine”. Proper masticatory function not only ensures that remaining permanent cheek teeth are erupting; and finally at your horse will fully benefit from the five years when all permanent teeth expensive feed you provide for him, but should be erupted, and all caps should that his mouth will be comfortable and be shed. During this pivotal time a help him perform to his potential. young horse is losing 24 deciduous Perhaps the most compelling arguteeth and erupting at least 36 permament for the value of comprehensive nent ones. Young teeth tend to beequine dental care is the comfort faccome razor sharp very quickly, and tor. Equine veterinarians skilled in denproblems with asynchronous eruption tistry are constantly amazed at how of permanent teeth can set the stage for much discomfort horses will endure significant abnormalities of wear in without any overt signals to their ownlater life. This is the time to recognize ers. Horses are eating “machines”. They and head off such problems. Meticuare designed to eat at least 18 hours a lous attention at this stage will help day. This is a survival instinct deeply ensure that your horse will have a ingrained in their very cells. Most horses healthy and properly functioning will continue to eat, will adapt to the The chewing surfaces of a horses mouth showing mouth throughout his or her entire difficulty or the discomfort, until the sharp points, viewed from the front of the mouth. life. Prevention is the key to success. pain is so severe or until mechanical (Illustration by Mary Delorey) Most mature horses (those over the forces make it physically impossible to age of six) will do quite nicely with do so. It is not uncommon for otherwise very contentious periodic maintenance by a qualified veterinarian once yearly. owners to be surprised, appalled, then embarrassed that their Horses in competition or other type of work may require more equine friend has endured such pain or difficulty for so long frequent examinations to be sure that they stay free of sharp without complaint. By the time the average owner notices a enamel points and are not hindered in their athletic perfor“problem”, the abnormalities inside the mouth are likely to be mance by discomfort stemming from the mouth. Some horses severe. with significant abnormalities of wear or conformational flaws One of the most important concepts that horse owners can that lead to significant malocclusions may also need more embrace from all this is that prevention is the absolute key to frequent corrections to maintain optimum dental health. Each good equine dental health. The idea that a horse doesn’t need horse is an individual and an equine veterinarian experienced dental attention until he is in his or her middle age must change. with the advances in equine dentistry can develop a schedule The tendency to abnormally wear the teeth is usually present that best suits your and your horse’s needs. very early in life. Minor abnormalities detected at the age of one Just as there are advances in the human medical field occurto five years can usually be easily corrected and need never ring every day, so are the advances in knowledge and underbecome an issue. If the same problems are left undiagnosed until standing occurring in the field of equine veterinary medicine. that horse is older, much more aggressive techniques are re- The specialty area of equine dentistry is no exception. Equine quired to correct the situation. In certain circumstances, the veterinarians with specialized training and experience in the problem may become so severe that it is not correctable at all. field of equine dentistry have a mission to stay abreast of the Even in severe cases, there is much the veterinarian experienced latest information and to constantly improve their skills. Our in equine dentistry can do to make that horse comfortable and goal is to provide the very best service for you, the horse owner, as healthy as possible. and most importantly, to improve the lives and health of the Current recommendations for routine dental examination of horses with which we are so privileged to share our lives. horses starts during foalhood. Make sure your veterinarian makes an examination of the mouth part of the routine physical Dr. DeLorey’s practice is devoted exclusively to high quality examinations as the foal grows through nursing to weaning. equine dentistry. She serves horses and their owners throughout the Minor problems associated with poor conformation or develstate of Washington. She can be reached at (360) 895-0537 or opmental abnormalities can be headed off during this time. If www.nwequinedentistry.com you notice that your foal has an under- or overbite, make sure your veterinarian is aware of it! There are simple procedures that Recommended further reading: can be done to help encourage natural correction as the foal “Don’t Forget to Float”, Equus #87, Sept. 2001 grows or orthodontic procedures available for serious malocclu- “Does Your Horse Need A Dentist?”, The Horse, March 2000 sions. As the young horse matures, there are a few crucial ages “Baby Teeth”, The Horse, March 2001 18

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