ReviewA review of equine dental disorders
Introduction
Dental disease is the main oral disorder of horses and is of major importance in equine veterinary practice, with up to 10% of practice time involving dental-related work (BEVA, 1965). Dental problems are the third most common medical problem in large animal practice in the USA (Traub-Dargatz et al., 1991). In addition, many postmortem studies have shown high levels of clinically significant, non-diagnosed dental disorders in horses (Wafa, 1988; Kirkland et al., 1994; Brigham and Duncanson, 2000a).
Section snippets
Clinical anatomy
The Modified Triadan system for equine dental nomenclature (Fig. 1) is used in this paper (Floyd, 1991).
Equine teeth have evolved to be hypsodont (long crowned) to cope with the high level of attrition associated with the prolonged (i.e., up to 18 h/day) mastication of their tough, silicate-containing, fibrous diet (Bennett, 1992; Capper, 1992).
The Triadan 05s (first premolar or “wolf tooth”) are vestigial if present, and Triadan 06s–08s (second–fourth premolars) are similar to the Triadan
Clinical signs of dental disease
The most common equine dental (and oral) disease is the development of sharp dental overgrowths, often termed `enamel points,' although these overgrowths will also include cement(um) and dentine if they become large. These overgrowths develop on the lateral (buccal) edges of the maxillary and the medial (lingual) edges of the mandibular CT and may cause lacerations of the cheeks and tongue during chewing (Becker, 1962). Likewise, soft tissue injuries from more focal dental overgrowths
Examination of equine teeth
Palpation through the cheeks may reveal food pocketing or detect major dental irregularities (such as a missing tooth or a large overgrowth) of the rostral three to four upper CT. Even if no such abnormality is palpated, the presence of pain (i.e., the horse pulling away or flinching) during this procedure may indicate the presence of sharp overgrowths on the buccal aspect of the upper CT (Scrutchfield and Schumacher, 1993; Easley, 1999a).
Observation of horses during mastication may reveal
Disorders of the incisor teeth
Compared to the CT, significant disorders of the equine incisors are relatively uncommon (Dixon et al., 1999a). However, as owners can easily visualise these teeth (without a gag), even minor incisor problems are apparent, in great contrast to CT disorders.
Disorders of the canine teeth (04s)
The canine teeth (04s, “tushes”) are usually only present in male horses, with vestigial 04s present in a small proportion of female horses. These teeth do not anatomically oppose each other, and this may be the reason why calculus, often extensive, accumulates on the more rostrally positioned lower canines. Unlike brachydont teeth, dental calculus is not a major predisposing factor to periodontal disease in horses, although extensive calculus formation at this site will cause gingivitis, local
Disorders of the 1st premolar (“wolf teeth”, 05s)
Wolf teeth are small (usually 10–20 mm long) brachydont teeth with variable sized (5–30 long mm) roots. They erupt at between 6 and 12 months of age and may be lost when the adjacent temporary 06s are shed at ca. 30 months of age. Remnants of the first deciduous CT (506/606) may resemble “wolf teeth” (Fig. 14). The presence of “wolf teeth” is blamed for many behavioural problems in horses and for interfering with the bit, and therefore, these teeth are frequently extracted. Some use the
Retained deciduous cheek teeth
Abnormal retention of the remnants of the deciduous CT (termed “caps”) can occur in horses between two and 4.5 years of age. These deciduous teeth are normally shed at 2.5, three and four years of age, respectively, for the 06s, 07s and 08s (Sisson and Grossman, 1971), but there can be much individual variation in the timing of deciduous cheek tooth shedding. If the deciduous teeth are very loose or just partially retained by gingival attachment, they can cause short-term oral discomfort.
Disorders of wear of cheek teeth
Due to the differential wear between the harder enamel and softer cementum and dentine, some enamel folds normally protrude on the CT occlusal surface, including medially on the mandibular and laterally on the maxillary CT (Fig. 24). There is subjectivity in determining what size of enamel protrusion constitutes an overgrowth. The development of large enamel overgrowths are claimed to be largely due to domestication with the associated feeding of concentrates, which markedly reduces the time a
Periodontal disease
Unlike brachydont animals, primary periodontal disease (i.e., inflammation of the gingiva, periodontal ligaments, cementum and alveoli) does not appear to be a significant problem in the horse (Dixon et al., 2000a), although historically it was claimed to be the major equine dental disease and was even termed “the scourge of the horse”(Colyer, 1906). It is likely that this previously recorded periodontal disease was in fact secondary to undiagnosed diastemata or CT displacements (Fig. 20, Fig.
Traumatic disorders of cheek teeth
Swellings of the maxillary and more so of the mandibular bones can be caused by external trauma, usually due to kicks. In the young horse, traumatic mandibular fractures will inevitably cause some damage to the CT reserve crowns that occupy much of this bone (Greet, 1999). In most cases of non-displaced fractures, conservative therapy (one to two weeks antibiotic therapy and feeding a soft diet for six to eight weeks) will be adequate, with the undamaged hemimandible acting as an effective
Idiopathic cheek teeth fractures
Fractures commonly occur in the CT, mainly the upper CT, in the absence of known trauma (Dacre, 2004). In most cases these are lateral saggital “slab” fractures through the two lateral pulp cavities (Fig. 28). The fracture site later becomes filled with food, thus laterally displacing the smaller portion, which may then cause buccal laceration. Removal of the smaller loose fragment with forceps, and rasping the sharp edges of the adjacent teeth will usually resolve the clinical signs.
Apical infections of cheek teeth
Apical infections of CT (in adult horses, such infections can also be accurately termed tooth root infections) are a significant problem, especially in younger horses, where the infections inevitably involve the supporting bones or paranasal sinuses. The cause(s) of these periapical infections in upper CT was previously believed to be a sequel to food accumulation and fermentation deep in the sites of the central vascular channel of the infundibular cement – the latter developmental disorder
Extraction and endodontic treatment of cheek teeth
Extraction of equine CT is a major surgical procedure with many possible immediate and delayed serious sequelae and consequently, this procedure should never be undertaken lightly (Dixon, 1997b; Easley, 1999c; Lowder, 2003). If any doubt remains concerning whether a cheek tooth is infected or not, conservative treatment should be undertaken rather than extraction; including antibiotic therapy (e.g., two weeks of oral trimethoprim and sulphonomide and/or metronidazole) for suspect mandibular or
Dental tumours
Dental tumours can include non-calcified epithelial tumours (which are derived from the epithelium that forms enamel) which are termed ameloblastomas, that may present as expansive soft tissue density lesions that can cause resorption of adjacent teeth and bone. Dental tumours also include a wide variety of calcified tumours from dentinal tissues (odontoma) or cement (cementoma) or combinations of all three dental components (compound odontoma or ameloblastic odontoma) (Head and Dixon, 1999).
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