Overview of Dentistry in Large Animals
Most large animals are herbivores, and efficient dental function is the key to food intake and to the maintenance of normal body condition. The variations in anatomic structure, dental formula, and eruption schedule for deciduous and permanent teeth is fundamental veterinary knowledge and should be reviewed before performing dentistry on any species (see Table: Dental Formulas).
The deciduous and permanent dental formula of cows, sheep, and goats are similar. All ruminants lack upper incisor teeth, with the mandibular brachydont (short-crowned) incisors meeting with a maxillary cornified dental pad. In many herbivore species, the forces of almost continuous grazing or rumination leads to dental attrition. Dental crown wear has been matched by the development of hypsodont (long-crowned) teeth with the continuous eruption of the reserve crown. The dental arcades in the horse consist of at least nine teeth (three incisors separated by a diastema [the interdental space], three premolars, and three molars) in each quadrant of the mouth. These hypsodont teeth have regular serrations that expose sharp enamel edges for shredding and crushing cellulose material. At the same time, the brittle nature of the enamel of the tooth is protected by the surrounding dentin and peripheral cementum. In the normal course of masticating forage, the rate of tooth eruption is matched by the rate of occlusal crown wear. Adult male horses have large permanent canine teeth situated in the interdental space. These are absent or very small in mares (sexual dimorphism).
Of the common domestic large animals, horses generally require the most dental care. In the swine industry, removal or amputation of deciduous canine teeth in piglets and tusk amputation in breeding boars may be part of routine management. In New World camelids (llamas, etc), blunting the fighting teeth (ie, the upper single incisor and canine and the lower canine teeth) is done to reduce the danger and consequences of fighting. (Also see Llamas and Alpacas for additional information on dental care.) Exotic species may also have various dental conditions, eg, impacted tusks in young elephants or maxillary dental periostitis and actinomycosis in wallabies and kangaroos.
Dental disease (eg, broken teeth, periodontal disease, irregular dental arcade wear) is a common underlying cause of unthriftiness, loss of condition, or poor breeding or nursing performance. The classic signs of dental disease in horses include difficulty or slowness in feeding and a reluctance to drink cold water. During the chewing process, the horse may stop for a few moments and then start again. Sometimes, the head is held to one side as if the horse were in pain. Occasionally, the horse may quid, ie, it may pick up its food, form it into a bolus but drop the bolus from the mouth after it has been partially chewed. Occasionally, the semi-chewed mass of feed may become packed between the teeth and the cheek or become lodged in the esophagus, leading to choke. To avoid using a painful tooth or a sore mouth, the horse may bolt its food and subsequently suffer indigestion, choke, or colic. There may be a lack of desire to eat hard grain accompanied by uncrushed grain in the feces. Other signs of dental disease in horses include excessive salivation and blood-tinged mucus in the mouth, accompanied by the fetid breath of dental decay. Extensive dental decay and accompanying periostitis and root abscessation may lead to empyema of the paranasal sinuses and intermittent unilateral nasal discharge. There may be facial or mandibular swelling and development of mandibular fistulas from apical infections of the lower cheek teeth.
Horses may be reluctant to take the bit, shake their head when being ridden, or resist training techniques because of irregularly worn cheek teeth and sharp edges on the maxillary cheek teeth and accompanying buccal mucosa laceration. The presence of small upper first premolar “wolf” teeth in horses may or may not be associated with resistance to the bit.
In most cases, history, age, and clinical signs are correlated. A thorough physical examination should always be performed, followed by a detailed and thorough oral and dental examination. In most large animals, including horses, this may involve the use of sedation; certain animals may require general anesthesia. A thorough oral examination is facilitated by rinsing the mouth with warm water and illuminating the oral cavity with a bright headlamp while using an oral speculum. Most mouth speculums designed for horses or ponies can be modified by replacing the upper incisor plate with a flat padded gum plate for use in ruminants. A dental mirror or endoscopic camera greatly increases the quality of oral examination. The oral dental examination is often aided by radiography or other advanced imaging such as CT, scintigraphy, or MRI.
Routine dental prophylaxis consisting of a complete oral dental examination and odontoplasty of sharp enamel points is important in the health care of horses. Enamel edges should be removed twice yearly during the establishment of the permanent dentition and thereafter as frequently as needed, depending on the management of the horse. Horses that graze on free range or grass usually require a yearly dental prophylaxis; horses that are stall confined and essentially fed hay and grain may require twice yearly oral examinations and dental prophylaxis.
The objective of dental prophylaxis is to remove sharp enamel edges of cheek teeth that might be causing soft-tissue irritation and any occlusal surface elongations. This odontoplasty procedure is often referred to as "floating" the teeth. By maintaining the normal occlusal surface, development of irregularities of wear on the dental arcades is inhibited. Dental prophylaxis can usually be done with simple restraint and/or the use of sedatives and analgesics. Power equipment is now being used more frequently than handheld rasps to grind, balance, and realign the occlusal surfaces of the incisors and cheek teeth. Motorized dental instruments should be used carefully to avoid thermal and pressure trauma to dentin and pulp. This means using low-speed grinders (6,000–12,000 rpm) with short contact times, light pressure, and intermittent water irrigation, while removing no more than 3–5 mm of occlusal surface every 3–6 mo.
Sharp edges on wolf teeth have been incriminated as a cause of bit resistance in horses. These small teeth, located just rostral to the upper cheek tooth row, are often extracted in performance horses. This procedure can be done in the standing, sedated horse with the aid of local infiltration anesthesia. The gingival attachment to the tooth is elevated, and a dental luxator or elevator is used to loosen the tooth. A small extraction forceps can grasp the crown and pull the tooth from its socket. Minimal aftercare or diet and work restriction are required for socket healing.
Most dental procedures can be performed on the standing, sedated horse with or without regional anesthesia, but some major dental procedures (eg, repulsions and fracture repairs) usually require general anesthesia. Radiographic evaluation and protection of the airway from debris are necessary in most cases. Some decayed teeth can be extracted per os using molar separators, extraction forceps, and elevators. However, in some cases, surgical exposure and tooth repulsion or sectioning and elevation is preferred. Tooth preservation by root end resection and endodontic therapy has demonstrated that extraction is not required in all cases of dental decay in horses.