Medications, powered instruments, and other advances enable veterinary dentists to do a better job

by R. Clay Stubbs, D.V.M.

WHEN the use of horses was so important and prevalent in our culture, the lack of effective drugs and dental instruments prevented veterinarians from doing proper dental examinations and procedures. The tremendous advancements in drugs, tools, and techniques during the past 20 years have made us realize just how far in the dark ages equine dental care has been.

Even with the tools we have today, comprehensive dentistry is complicated and difficult. So it is easy to understand why so many horsemen and veterinarians have had little confidence in equine dentistry in the past. Even the best hands using the best tools previously available achieved small and short-lived benefits in most cases.

Development of superior drugs for sedation, pain relief, and chemical restraint and reversal have made tremendous progress in the field of equine dentistry possible. These drugs in competent hands allow modern practitioners to perform a thorough examination, which is the foundation of any successful medical procedure. Through more thorough examination, we now realize the extent of the clinical and subclinical problems that have been occurring simply because of mouth pain caused by the horse's teeth. We did not recognize these problems as dental problems until they disappeared after modern, comprehensive dentistry emerged.

Modern drugs have made it possible for us to use power tools with solid-carbide blades to produce rapid, safe, comprehensive dentistry that could not have been imagined before. They also allow us to perform these advanced and almost painless procedures in the standing horse, leaving an animal with no memory of a traumatic experience. This is especially beneficial in very impressionable, young horses in training.

We now commonly perform corrective procedures in the standing horse that a few years ago required general anesthesia, which meant more expense and more inherent risk. Consequently, these procedures often were done inadequately, or not at all. In my 41-year career in veterinary medicine, I have seen routine dentistry progress from an almost worthless procedure to one that is practical, safe, and extremely beneficial to almost every horse.

Tooth function

Horses' teeth are made up of enamel, dentin, and cementum. The enamel is equal in hardness to glass. Dentin and cementum are much softer. The unerupted portions of the teeth lie within their sockets in the jawbone. As the soft tissue attachments of the teeth to the bone push the erupting tooth past the gum tissue and into the oral cavity, the cementum is deposited on the tooth surface. This outer layer of cementum obliterates the space between the teeth and yields a row of teeth that is tightly packed together so that feed materials cannot be pressed between the teeth. This prevents the development of gum infection and the resulting consequences of periodontal disease, such as pain and tooth loss.

The cheek tooth's grinding surface reminds us of a gristmill, with transverse grooves and ridges running side to side. The uneven grinding surface occurs when the extremely hard, infolded, enamel ridges project above the cupped-out, concave areas of the softer dentin and cementum. This dentin between the infolded enamel ridges wears away much faster because of the abrasive effects of the feeds that the animal eats.

The outer covering of cementum wears away not only from the diet but also from the constant action of the cheeks and tongue. The loss of cementum on the edges of the rows of teeth exposes the folded enamel ridges, which resemble the edge of a corrugated metal roof. The exposed enamel forms the points that make up the serrated blade that we can see and feel so readily. The transverse grooves and ridges occur as a function of wear as the teeth move side to side across each other. All this roughness adds efficiency to the grinding of diet.

Another interesting and essential quality of equine teeth is that the parts of the teeth that wear away have no nerve supply or feeling. The only nerve supply is in the deeper pulp chambers, so the horse has no pain as the teeth wear away. If there is soreness after floating or dental procedures, it either comes from damage to the surrounding tissues or the deeply located pulp chambers.

Only overzealous dentistry opens the pulp chambers and exposes the nerves of the normal teeth.

Bite problems

Bite abnormalities occur when opposing teeth do not line up correctly or when abnormally short or missing teeth are present. Bite problems are due to abnormal eruption, abnormal wear, or deformed anatomy.

Because horses' teeth erupt (grow) and wear away at approximately an eighth-inch per year, by some form of grinding we can make changes to the long teeth, which then allow the short teeth to erupt into normal position. Probably the main reason for correcting bite problems is to increase the longevity of the teeth that are wearing prematurely.

Many bite problems produce opposing teeth with abnormal amounts of exposed crown. That means one tooth is abnormally short while the other is abnormally long. If teeth are too short, they usually degenerate prematurely, causing periodontal disease and the problems associated with it.

Obviously, these bite corrections are only possible if teeth are continually erupting. Because the rate of eruption slows down and eventually stops in the horse's 20s, we must proceed with caution in the older horse. Often the bite abnormalities are simply not correctable in the geriatric animal. Heroic attempts can leave the old campaigner with a permanently decreased ability to chew his food, especially forage.

It has been my observation that the most clinical response occurs when painful points are removed, even if bite problems go uncorrected. It is extremely easy and tempting for us to attribute some improvement in performance or eating ability to a particular bite correction. This is because we invariably diminish the painful points in the process of our corrective procedures.

Thoroughbred mouths

Significant differences exist in mouth anatomy from breed to breed and even in groups within breeds. Unfortunately, the Thoroughbred has some of the very worst and therefore painful mouth anatomy. In my experience, most Thoroughbreds have oversized tongues, huge points on their teeth, and very little room between the last three upper cheek teeth and the massive cheek muscles of mastication.

Tongue size is probably the most critical factor. Many Thoroughbreds have a tongue so large that it appears somewhat like a giant mushroom that looks as though it has a narrow stalk between the lower cheek teeth and then fans out laterally in both directions protruding over the teeth. It so totally fills the oral cavity that it seems as though the mouth could not close. In these horses, even the smallest points can cause signs of mouth pain.

The bottom rows of cheek teeth are much closer together than the upper rows. Therefore, as the horse chews in basically a circular motion, the lower rows of teeth pass up and slightly in between the wider, upper rows. This motion wears the grinding surface at a slight angle downward from inside to outside, when looking into the horse's mouth. This explains why the points are more prominent and painful on the outside of the upper teeth and the inside of the lower teeth. This also explains why most tongue damage is caused by the inside edge of the lower teeth.

Tongue wounds occur primarily during chewing or in response to bit pressure. The horse's response to bit pressure is to move the tongue. When the bit applies pressure to the tongue near the front of the mouth, the horse's tongue moves not only under the bit, but all the way back to the throat. Because the back part of the tongue is where the most crowding occurs, this is where most bitting difficulties arise. The most severe reactions usually occur when severe points cause tongue damage over the last teeth in the bottom rows.

Some horses with this problem will rear up and fall over backward when asked to flex at the poll. Unfortunately, the teeth at the rear of the oral cavity are the most difficult to address and, therefore, are responsible for a huge percentage of the failures of routine dentistry.

Being "on the bit" is desirable for most Thoroughbred racehorses. This translates to constant bit pressure, constant tongue movement, and, unfortunately in many cases, constant discomfort and agitation. A racehorse's mouth may be extremely painful without affecting its racing ability, so need for dental care may go unnoticed.

R. Clay Stubbs, D.V.M., has practiced equine dentistry for 17 years at his Stubbs Equine Dental Clinic in Johnson City, Texas. He holds six United States patents on equine dental equipment.