Equine Dentistry

Equine Dentistry Charles T. McCauley, DVM, Diplomate ABVP and ACVS Assistant Professor, Equine Surgery Equine Health Studies Program, School of Veterinary Medicine Louisiana State University, Baton Rouge, LA 70803 (225)-578-9500 www.LSUEquine.com

Introduction Domestication has significantly improved the quality of life and prolonged the average life expectancy of horses. Improved nutrition, housing, preventive health care and parasite control programs have resulted in a large population of geriatric horses, sometimes living into their thirties and forties. Highly processed grain diets, confinement, minimal exposure to continuous grazing, feeding from elevated troughs, and minimizing exposure to environmental abrasive substances have as a consequence affected the way in which the horse’s teeth erupt and wear. With the increasing age of the horse population, comprehensive dental care is becoming more important. Up to 10% of equine veterinary practice time in the US involves dental related conditions. Horse’s teeth are long and primarily composed of reserve crown that is buried deep below the gum line (gingiva) within the upper (maxilla) and lower (mandible) bones of the jaw. Unlike humans, the crown erupts continuously as the horse ages until it is exhausted and only shallow roots remain to hold the tooth in the bone. Throughout the horse’s lifetime, the continuously erupting crown of each tooth is worn away at a rate of 2 – 4 mm per year by the opposing tooth. Once the reserve crown is exhausted, the horse is unable to chew properly and as it has been said, “horses do not die of old age, they simply run out of teeth”. Although we associate dental disease with obvious clinical signs, more often than not dental problems develop slowly without outward symptoms. Frequently there are no obvious external signs until the disease has progressed to complications such as infection of the gingiva, tooth roots, bone or sinus. When signs of dental disease are present it may be manifested by any of the following signs: • Quidding – dropping partially chewed, saliva soaked food • Halitosis – bad breath • Weight loss, poor body condition, or failure to gain weight • Head shaking, bitting problems, resistance to the bit, and abnormal head carriage • Excessive salivation • Reluctant or slow eating or chewing • Food pouching • Oral pain • Changes in fecal consistency – ranging form dry hard fecal balls to diarrhea and often comprised of undigested long fibrous material • Other behavioral/training issues Many times poor dentition is mistaken for behavioral or training problems that appear not to be correctable. Lack of appropriate dental care can lead to early attrition and tooth loss, making it difficult for older horses to maintain their body weight and can also lead to systemic manifestations of dental disease such as choke (esophageal obstruction) or colic.

Dental Anatomy Adult horses have 36 to 44 permanent teeth. These teeth include 6 upper and 6 lower incisors. There are normally 3 or 4 premolars and 3 molar teeth in the upper and lower jaw, which are collectively known as the cheek teeth (Figure 1). The first premolars, if present, are usually poorly developed or vestigial and are termed “wolf teeth”. These teeth are frequently removed by veterinarians due to the perception that failure to remove wolf teeth will result in problems with the bit. The remaining premolars and molars are used primarily for grinding the fibrous feed material typical of the horse’s diet. It is important to remember that the upper jaw is wider than the lower jaw. To accommodate this, the occlusive or grinding surface of the cheek teeth is slanted approximately 15-degrees.

Figure 1 – Equine skull demonstrating normal upper and lower canine, premolar and molar teeth. I = incisor, PM = premolar and M = molar.

Dental Examination The only way to accurately identify abnormalities in the dentition of a horse is by complete and thorough oral and dental examinations. A proper dental examination is performed with the horse adequately restrained in a stock and usually sedated. The dental examination typically begins with a discussion of any history of abnormal behaviors. This may give clues to an existing problem that needs to be addressed. In addition, it is important for the person performing the examination to have an understanding of the horse’s use. The number, position and alignment of the incisors are evaluated first. Supernumerary (too many) incisors and fracture or missing incisors are not uncommon and should be noted. Malocclusion of cheek teeth such as hooks or steps can prohibit normal front-to-back and side-to-side movement during eating and chewing. Side-to-side movement or lateral excursion of the lower jaw in relation to the upper jaw is necessary for the normal chewing and grinding motion of the horse and should be evaluated. While the upper jaw is held in a fixed position, the lower jaw is moved laterally. A normal lateral excursion is roughly the width of 1½ teeth. In addition, due to the normal angle of the cheek teeth, as lateral movement continues and the grinding surfaces of the cheek teeth come into contact, the incisors should separate approximately 2 – 6 mm. Also necessary for normal

chewing, the incisors must be flat and level from one side to the other. Locking of the jaw, decreased lateral excursion and failure of the incisors to separate are all indication of abnormalities of the cheek teeth. Examination of the cheek teeth is facilitated by use of a full mouth speculum, dental mirror and bright light source. This should include examination of the soft tissues including the inside of the cheek and tongue for the presence of ulcerations, lacerations or erosions. Each cheek tooth in both the upper and lower dental arcades should be examined for evidence of abnormal location, presence of sharp enamel points and abnormal overgrowths, fractures, spaces between the teeth (diastema) and areas of decay. Suspicious areas should be further investigated using a dental probe and the tooth should be assessed for looseness.

Dental Abnormalities Foals, Juveniles and Young Adults It is a misconception that young horses do not need regularly scheduled dental examination and care. Sharp enamel points begin to develop almost immediately after eruption of the cheek teeth. At a minimum, foals should be examined at birth and again at weaning for evidence of congenital abnormalities such as overbite or parrot mouth (Figure 2) and developmental abnormalities such as poor incisor alignment and errant cheek tooth eruption.

Figure 2 – Parrot mouth in a young foal. Tumors of dental origin and those affecting the bones of the jaw are also commonly diagnosed at this age. Eruption of the permanent teeth begins at approximately 1 year of age and continues until the horse is 4 – 5 years old. As the premolars erupt, they cause resorption of the deciduous root and push the remaining deciduous crown up above the gum line. This premolar cap is usually lost shortly after the molar tooth erupts through the gum. In some instances, this cap can

be retained and have sharp spicules of enamel that may penetrate the gum when pressure is applied by the opposing premolar resulting in pain. Affected horses are often presented to veterinarians for examination due to excessive dropping of feed or behavioral problems. Removal of retained caps results in almost immediate resolution of oral pain. In addition to retained premolar caps, asynchronous eruption of premolar and molar teeth can result in malocclusions that can affect the horse’s ability to adequately grind feed. This problem is easily recognized and corrected on a routine oral examination. Finally, there is evidence to suggest the enamel of horses up to 6 – 7 years of age is softer than that of older horses. Because of this, sharp enamel points may reform earlier after routine dental care in young horses. For these reasons, it is recommended that young horses form birth to 7 years of age undergo a dental examination approximately every 6 months. Adult Horses Mature horses between the ages of 7 – 15 years of age with normal dentition typically require only annual examinations and routine care. The most common abnormality observed in this group of horses is the development of sharp enamel points on the outer surface of the upper check teeth and the inner surface of the lower cheek teeth (Figure 3).

Figure 3 – Sharp enamel points affecting the outer margin of the upper cheek teeth. If left untreated, these enamel points may continue to lengthen, causing painful ulcers or lacerations of the cheek and tongue (Figure 4). Another common abnormality of the adult horse is the development of hooks on the first upper premolar and last lower molar. These hooks develop as a result of abnormal alignment of the mandibular and maxillary cheek teeth. Hooks may restrict the normal front to back movement of the lower incisors in relation to the upper incisors with change in head position. This is especially important when horses are expected to bend at the neck and poll. Hooks affecting the last lower molar are more difficult to treat due to

the depth of the teeth in the mouth, minimal working space and close proximity of the bone and surrounding soft tissues. Minor oral trauma frequently accompanies reduction of these hooks. Other malocclusions result in steps or waves. A wave is a series of overgrown teeth opposed by a corresponding series of over worn teeth. Although there are several techniques for the correction of steps or waves, these abnormalities may not be correctable in a single dental treatment due to the potential for invasion of the pulp chamber if excessive tooth is removed. Therefore, additional treatment at a more frequent interval (often every 4 – 6 months until the malocclusion is corrected) may be necessary.

Figure 4 – Traumatic ulcer (bold arrow) secondary to sharp enamel points and a large premolar hook (thin arrow). Geriatric Horses Although geriatric horses may suffer from any of the malocclusions previously described for adult horses, the most severe dental abnormality in these horses is periodontal disease. As the cheek teeth erupt, there is a natural tapering of the tooth from the occlusal surface to the root. In young horses, all 6 cheek teeth are packed tightly together with no normal space between the teeth. As the tooth erupts and the occlusal surface is worn, this tapering results in formation of spaces known as diastema between the teeth. Food and other debris can become trapped in these spaces and undergo fermentation. This food packing and bacterial fermentation has a negative effect on the natural defenses in the mouth and infection of the gingiva occurs. With time, this infection migrates along the tooth eventually affecting the surrounding bony and soft tissue attachments of the tooth to the jaw (Figure 5). Periodontal disease may eventually lead to infection of the tooth root, tooth root abscesses and premature tooth loss. Although there are usually no obvious outward clinical signs, this is a painful condition that eventually will lead to

difficulty chewing, weight loss and potentially other more serious health problems such as secondary infection of the sinuses and colic.

Figure 5 – Example of severe bone and tooth loss secondary to periodontal disease in a geriatric horse. Compare the bone surrounding the teeth of this specimen to that in Figure 1. Treatment of periodontal disease is much more difficult than prevention. Prevention involves routine dental examination and maintenance as previously discussed. Treatment involves removal of all packed feed material and debris, instillation of an antibiotic gel and covering the affected area with dental impression material to prevent further mechanical trauma. A more advanced treatment for periodontal disease is flushing and disinfection using the Equine Dental System by Pacific Equine Dental Institute (P.E.D.I.). This technique utilizes high pressure air abrasion and flushing with sodium bicarbonate (baking soda) and disinfection. If periodontal disease is severe enough, removal of the affected tooth may be the only viable treatment. As horses age, eruption begins to slow and the availability of reserve crown begins to decrease. Older horses with significant malocclusion must be treated carefully. Severe steps or waves may be present; however, aggressive treatment especially removing excess crown to bring the teeth into more normal occlusion may result in removal of too much remaining crown, thus permanently affecting the horse’s ability to grind feed. Essentially any sharp enamel structure(s) should be corrected by removal of a minimum of remaining crown. Because formation of these points is dependent on continued eruption and wear, they are usually slow to reform if they recur at all. Finally, older horses’ teeth will expire and either fall out or become cupped. This condition is not correctable and these horses must be managed through dietary modification.

Systemic Manifestations of Dental Disease Besides the obvious oral manifestations of dental disease in horse, there are several disease processes that can be directly related to disease of the teeth and surrounding structures. Because the last 4 maxillary cheek teeth are embedded in the sinus, infection that travels along the tooth may invade the sinus and surrounding bones. This condition is usually recognized by malodorous discharge draining from a single nostril on the side of the affected tooth. As fluid builds up in the sinus there can be swelling of the face directly over the involved tooth and distortion of the facial bones. Eventually a draining tract may open on the face. Radiographs of the head in these patients will often demonstrate fluid in the sinus and destruction of the bone supporting the tooth and its root. In these cases, surgery is often necessary to remove the affected tooth and drain the sinus. These diseased teeth can sometimes be removed in the standing, heavily sedated patient, but frequently require general anesthesia and opening of a bone flap into the sinus. On many occasions, a small enamel fragment or diseased bone that is not identified at the time of tooth removal may require additional surgery for complete removal. Abdominal distress or colic is another condition that is highly associated with preexisting dental abnormalities. Malocclusion of the cheek teeth will prohibit effective grinding of fibrous material. This, in addition to other environmental factors such as failure of the horse to drink adequate water and poor quality hay, may lead to impaction of the large colon, ileum, or cecum. In older horses, tooth loss commonly leads to esophageal obstruction (choke) because of inadequate mastication (chewing). This condition is also difficult to treat and can lead to esophageal damage and rupture. In addition, if the horse aspirates a large amount of saliva and feed material severe sometimes fatal pneumonia can develop. Although not completely, each of these conditions to a large degree is preventable by regular dental examination and care.

Conclusion The importance of comprehensive routine dental care cannot be overemphasized. Many painful and potentially debilitating dental conditions are preventable if appropriate dental care is provided. Not only can the horse be saved form painful conditions affecting the mouth, but the occurrence of potentially performance limiting and life threatening conditions that are expensive to treat and require extended periods of time off may be significantly decreased.

Does Your Horse Have a Dental Problem? The LSU Equine Clinic is now offering a regular comprehensive equine dental service for routine and advanced procedures. This service will be provided each Thursday. Please contact the LSU Equine Clinic (225-578-9500) for more information or to schedule an appointment.