Current Equine Dentistry

The following information was given at a Seminar on Equine Nutrition and Health sponsored in part by the Virginia Horse Industry. It was held on October 17, 2008 at The Middleburg Agricultural Research and Extension (MARE) Center, Middleburg, Virginia. The following is being posted on HorseHints with the permission of the lecturer. This Seminar was beyond outstanding. My husband, Bill and I, feel so fortunate to have been able to attend.

Overview

Equine dentistry is not new: horses have had their teeth worked on for hundreds of years. However with increased research in the field, more horses are benefiting from complete dental care well beyond the "basic float."

Dental Anatomy and Function

In order to understand why equine dentistry is important to the horse, it is helpful to understand a little about its oral cavity and how it functions.

Adult horses have twelve incisors that are used to shear off grass. These teeth (unless a severe overbite or underbite is present) are in contact when the horse's jaw is at rest. Male horses have four canines; the two lower ones are found closer to the incisors than the upper canines. These canines sit in the bars of the mouth (interdental space). If present in females, the canines are usually small and often have not erupted.

The first premolars are more commonly known as wolf teeth and are often found on the upper jaw (the maxilla) in front of the first cheek tooth. Wolf teeth are only infrequently found on the lower jaw (the mandible). These teeth, both upper and lower, occasionally do not erupt and are known as "blind" wolf teeth. Wolf teeth are rudimentary and serve little purpose. They, like the canines, are known as brachydont and, once erupted, do not continue to "grow."

The rest of the premolars and molars are collectively known as cheek teeth. In each row or dental arcade there are three premolars and three molars, making six teeth in each arcade. The cheek teeth, like incisors, are known as hypsodont teeth. Unlike our own teeth, hypsodont teeth are mostly crown with very little root. This crown keeps erupting until the tooth has worn out (expired). The premolars and incisors erupt as "baby" (deciduous) teeth. The approximate times of eruption are listed in figure l, below:

Figure l

Approximate Shedding Times of Deciduous Teeth

• Incisor 01---------2 1/2 years
• Incisor 02---------3 1/2 years
• Incisor 03---------4 1/2 years
• 2nd Premolar (06)--2 1/2 years
• 3rd Premolar (07)--3 years
• 4th Premolar (08)--3 1/2 to 4 years

For ease of record keeping and discussing horses' teeth, veterinarians number all teeth using the Triadan system. Numbering starts with the upper right middle incisor (101) and continues to the last upper right molar (111). As you face the horse, the middle upper incisor on your left would start the 100 quadrant, then, in a clockwise fashion the rest of the quadrants are numbered. Therefore, the horse's last lower right molar will be the 411. A few more points are important to understand how a horse's mouth functions. Their upper jaw is 25-30% wider than their lower jaw. This is why sharp points tend to develop on the outer aspect on the upper cheek teeth and the inner aspect of their lower cheek teeth. When their jaw is at rest, a horse's cheek teeth are not in contact. In order for a horse to chew its food, the incisors must slide across one another for contact to occur on the cheek teeth. Interestingly, horses chew in a wider pattern (hence utilizing their teeth more efficiently) when eating grass. When fed grain, they chew in a very short pattern (known as degree of lateral excursion). Hay causes them to chew somewhere between the two. The mandible not only moves from side to side but also front to back. This becomes important when a horse is collected; its mandible needs to slide forward. As the horse's head is lifted, the mandible slides back. On a dental headstand this sometimes makes it appear as though the horse has an overbite when it really doesn't.

In the past many owners were taught horses did not need routine dental care. Floating was sought for older horses who were losing weight, dropping feed or perhaps those that "chewed funny"or tossed their heads excessively when ridden. Often wolf teeth were extracted before a horse was bitted, but this was usually done blindly, often with a modified screwdriver and without sedation. A normal exam was not included. Luckily for the horse, times have changed. Dental problems are now being identified and treated, sometimes in horses as young as a few months old.

In order for dental abnormalities to be addressed they must first be identified. An oral examination should be performed on all horses at least once a year; young horses and horses where problems have been identified need to be checked at least every six months. An examination should include at least a cursory physical on the horse. Some older horses with metabolic disease or horses with other health problems should have their medical conditions addressed before dentistry is performed. It may be easiest to have an explanation of how the dental work is to be approached.

If the owner is present, Dr. True begins by asking if they notice anything they think may be a dental problem. All information is recorded on a dental chart; she reviews this chart before subsequent visits so she knows what was done in the past and what amount of sedation was needed. Her dental exam starts with a check of the whole head; she wants to know if there is pain in the face. This part of the exam is either performed before or just after the horse is sedated. Next, she examines the horse on a headrest; which can either hang or be supported by a stand. She wants to inspect the horse's incisors (and canines if present) for approximate age, tarter, damage, abnormal growth or wear. Then she moves the mandible while holding the head to check lateral excursion. While the majority of horses do not need their incisors reduced, this technique determines which ones do.

After inspecting the horse's mouth while closed, she then uses a full mouth speculum to examine the rest of the mouth. Checking the mouth with her gloved hands as well as a light and dental mirror ensures a thorough job.

Horses less than five are dealing with shedding deciduous teeth and the addition of molars. These young cheek teeth can be quite sharp and can cause painful ulcerations to both cheeks and tongue. With new teeth erupting, sharp points appear quickly and should be checked and filed every six months, if necessary. Crowding of teeth can also occur. Removal of these deciduous teeth (caps) is sometimes necessary. Yearlings should be checked for wolf teeth. If deemed necessary, extraction of these teeth is easiest in this age horse. The only time an overbite or an underbite can be helped is in a very young horse. If severe enough, a type of orthodontics can be used.

In addition to sharp enamel points, horses over six can begin to develop overgrowths of certain teeth. Hooks and ramps develop on the first and last cheek teeth. Waves involve more than one tooth and a step is usually due to a missing tooth that opposes the step. These overgrowths (especially upper hooks) can cause the mandible to become locked in place, which prevents the horse from bending at the poll. All of these overgrowths need to be filed down; if overgrown more than 3-4 mm, this process should be staged in 3-6 month increments.

If these horses did not receive proper dental care when young, their cheek teeth may resemble the New York skyline. Unfortunately, these older horses cannot be "fixed," only helped by taking small amounts of tooth down. This is because the older the horse, the closer the teeth are to completely expiring. Older horses also deal with loose teeth, increased amounts of periodontal disease and tumors. Sharp enamel points will need to be addressed as well.

Take Home Message from Dr. True: As research advances on equine dentistry, our horses certainly benefit. Treating periodontal disease, virtually unheard of ten years ago, is now routine. Root canals are possible to save damaged incisors. All of this knowledge translates to horses that are keeping their teeth longer and having more comfortable mouths through their lives.

That, indeed, means much more than just a pretty float.

Dr. True graduated from Virginia-Maryland Regional College of Veterinary Medicine in 1986. After completing a large animal medicine and surgery internship at Texas A&M in 1987, she joined Woodside Equine Clinic in Ashland, VA. Since joining Woodside, the practice has grown from two veterinarians to ten. Dr. True has a special interest in dentistry, and has lectured and taught labs on the subject. In the past, she has served on the AAEP dental committee as well as the board of the VVMA. As part of Woodside, Dr. True also enjoys the preventive health aspect of veterinary medicine. Dr. True currently lives in Ashland with her husband and her six-year-old daughter. In her spare time, she enjoys running, cooking, gardening, riding and spending time with family and friends.