Livestock Update, June 1998
Bayard A. Rucker, DVM
The importance of regular oral examinations and floating is difficult to overstate. Minor problems which could evolve into significant dental abnormalities can be detected and corrected. Additionally, performance problems caused by soft tissue paid from contact with sharp teeth can be eliminated.
The horse has evolved from the eocene period as a three toed 26 inch tall mammal with low crowned brachyodont teeth (similar to humans), into a 60 to 72 inch 1100 lb. animal with greatly increased demands on the digestive system. A doubling of the height requires an eight-fold increase in food intake. The teeth have lengthened and have reserve crowns that continually erupt throughout the life of the horse. The head has lengthened and deepened to accommodate these changes. The teeth are worn off at the chewing (occllusal) surface by the grit, silica, and coarseness of the material being chewed.
Horses select food with their sensitive upper and lower lips. The lips are drawn back as the incisors (front teeth) grasp food. The tongue moves food into the mouth where the molars grind food into small particles. The free ranging horse prefers grasses and legumes but will eat shrubs, woody plants and even roots. Unlike the cow, the horse cannot regurgitate food and chew it again. If mastication of food is incomplete, incomplete digestion and absorption of nutrients can occur as well as the occasional case of colic. The 24 cheek teeth (molars) are arranged in four rows or arcades of six teeth. The first cheek teeth begin just behind the commissure (corner) of the mouth and continue rearwards to the front corner of the eye. The maxillary or upper molar arcades are wider apart than the mandibular or lower arcades of molars. The anisognathic (unequal) arrangement couples with side to side chewing causes the occlusal or chewing surface to become tilted with the inner edge of the lower teeth taller that the outer edge. The inner edge of the upper teeth is shorter than the outer edge. The taller edges of the teeth (inner on lower arcades, outer on upper arcades) develop sharp tooth points that are removed when the teeth are floated.
Horses confined to stalls with free access to hay will exhibit feeding patterns similar to free ranging horses and usually eat 10 to 12 hours per day in sessions lasting 30 to 180 minutes. In contrast, confined horses with limited access to hay will eat their grain and spend the rest of their time in boredom, i.e. standing, lying down, searching for food, chewing wood, etc.
The horse chews by moving the mandible (jaw) in a side to side oval pattern. The jaw is opened, moved to the side then closed. The extent of the lateral movement or range of motion of the mandible is influenced by the consistency and nature of the food being eaten. Horses eating grain or pellets have limited lateral movement of the jaw compared to horses eating forage. The decreased motion influences molar wear resulting in more problems with sharp points on the molars.
Signs of dental disease
Included with these notes is a sheet listing signs associated with dental disorders. The tendency of a horse to show signs of oral pain is highly variable. Horses with major abnormalities may act normally, while minor problems may cause persistent training difficulties. Signs are usually related to soft tissue pain from contact with sharp edges or points on teeth. Performance problems include head tilt, inflexibility, protruding tongue and nosing out to name a few.
A complete oral examination is a vital part of routine dentistry as well as a part of lameness, insurance or prepurchase examination. Identification of dental, ocular, neurological or musculo-skeletal abnormalities can be detected early.
Historically, floating or removal of sharp enamel points was performed to facilitate mastication of food. In recent years, floating has evolved to accommodate the demands of performance. Although technique varies with each practitioner, the goal is to remove sharp points and edges from molars preventing soft tissue damage. Floating should also prevent soft tissue damage when soft tissue is trapped between teeth and bit or bridle.
Proper shaping of the upper first and second cheek teeth prevents cheek injury between the bit and attached leather and these teeth. Shaping the lower first cheek teeth stops soft tissue pinching as the bit moves back and forth in the mouth.
The last upper and lower molars frequently cause performance problems. The inside of the lower molars presses against the side of the tongue. Smoothing last two lower molars is essential in preventing tongue irritation and aiding in keeping the tongue quiet in the mouth. The last two upper molars are covered by the large masseter muscle. The muscle traps the cheek and maintains a constant pressure pushing the mucosa into the points creating the ulcers. Smoothing these teeth aids frequently results in smoother transitions and turns.
A simple way to check if the cheek is sore is to gently push with the heel of the hand into the masseter muscle about three inches below and just in front of the eye. The horse will flinch and jerk the head upward if this area is tender or inflamed.
Occlusion simply means contact. Proper incisor and molar contact are necessary for grinding of forage. At rest, the mandible is directly below the maxilla. To observe this, raise the horse's nose to eye level and open the lips; the lower incisors should be directly under the upper incisors. The contact surface between these teeth should appear as a straight line, parallel to the ground. When the mandible is pushed to the side, the incisors remain touching until the upper and lower molar arcades touch each other. Because the molars are angled, when the molar arcades meet, the incisors separate. The drawing represents the relationship between the incisors and molars. If the incisors have an abnormal shape or are too long (from lack of wear during several years) the molars cannot grind food properly. An oral examination will identify incisor abnormalities and treatment needed.
How far the mandible moves before the molars touch is determined how molar contact is maintained when grinding food. Remember the horse chews backward from the manner that a practitioner checks occlusion. The horse moves the mandible to the side, closes the mouth, the molars touch and grind food and as the mandible returns to the resting position when the incisors touch and the molars separate.
An oral examination will assess the occlusion of both the incisors and molars. Molars are checked to determine if occlusion is uniform end to end and there is no interference from bumps, ramped up or tall teeth or hook formation on either end of the arcades.
Age related dental problems
Foals are born with the first three (deciduous or temporary) premolars erupted. (Premolars are molars that have temporary or deciduous teeth, three molars erupt into wear by age four, and all are called "cheek" teeth.) The temporary incisors are all erupted into position by 9 months of age. Foals are checked at or close to birth to determine if any congenital abnormalities exist. Deciduous teeth are soft and can develop sharp edges quickly. From age 2 to 4 months to about 18 months, these teeth should be checked every 4 to 6 months and floated if needed. Floating can be done without a speculum, requiring only three to four strokes of a float per molar arcade to correct.
Permanent premolars begin and are in wear from age two years and six months to age four years. An eruption timetable is included with these notes. The eruption of permanent teeth and deciduous teeth (cap) removal can vary two to three months. The permanent molars (last three check teeth) are also developing and erupting. The first molar erupts at one year of age. The last molar erupts into position at age three. Eruption "bumps" begin forming on the bottom of the mandible about age two. These bumps are the developing roots of the permanent third and fourth premolars. The bone of the mandible is remodeling and expanding to allow for the tooth elongation. The bone over these roots is quite thin and the roots can be damaged easily.
Check two-year old horses every six months or more frequently during eruption to remove caps. Loose caps cause pain with mastication. Caps can be retained and may need to be removed to prevent uneven eruption of permanent teeth. Examination and floating every six months after premolar cap removal will identify abnormal incisor or molar wear abnormal occlusion and maintain a pain-free mouth.
Horses with a mature mouth (over five years of age) should be examined at least every year. See the sheet listing abnormalities. Performance horses may need floating every six months, depending upon how sensitive they are to oral problems. Some horses become quite reactive to just one sharp point after they have been pain free for several months.
Horses over 15 years need yearly examinations to evaluate occlusion and the development of other age-related problems. These problems include worn out teeth, gingivitis and subsequent periodontal disease, wave and step mouth. Identification of these problems will enable your veterinarian to maintain your horse's teeth and health for many years.
Questions? Service? Dr. Rucker may be reached at Rt. 1, Box 2, Lebanon, VA 24266, (540) 889-5515 or firstname.lastname@example.org
(Contributed by Dr. Larry A. Lawrence, Department of Animal and Poultry Sciences)