Small mammal dental disease

Dental disease is a common condition of many of our small exotic mammal patients. The unique anatomy and dentition of exotic herbivorous species can pre­dispose them to developing dental disease for numerous reasons. Whilst omnivorous and carnivorous exotic mam­mals such as hedgehogs and ferrets can also develop dental disease similar to our companion species, this article focuses on the commonly presented small exotic mammals with elodont dentition.

Rabbits, guinea pigs, chinchillas and degus all have rostral incisors, used for gathering and breaking off food, separated from their grinding molar teeth by a diastema (Crossley, 2003). Rabbits have deciduous teeth that sometimes persist for a few weeks following birth that are then replaced with a total of 28 permanent elodont teeth (Crossley, 2003). Rabbits are unique from these other small herbivorous mammals in that they have six incisors, rather than four – four maxillary and two mandibular, with the smaller set known as the “peg teeth” sitting caudal to the larger first incisors (Harcourt-Brown, 2013).

Rabbits, guinea pigs, chinchillas and degus all have teeth that are arcadular, which means they have an open root, with germinal cells continually producing dental tissue at the apical end (Legendre, 2016) and are elodont, which means they continually erupt (Mans and Jekl, 2016). At rest, the mandibular incisors sit just caudal to the maxillary incisors in small herbivorous mammals (Harcourt-Brown, 2013). Dental attrition is achieved by the grinding of teeth against their opposing dental arcades, aided by the high-fibre diets of these animals. Rabbits have been demonstrated to chew unilaterally, lateral to medial in a crescent-shaped motion in order to effectively use the sharp enamel ridges on their molar teeth to break down fibrous food (Dantuma and Weijs, 1980). When less fibrous foods like nuggets or pellets are chewed, the chewing motion is more vertical than lateral and results in an altered pattern of tooth wear (Crossley, 2003).

Guinea pigs have 20 permanent elodont teeth and their premolars and molars, colloquially known as the cheek teeth, have a 30-degree angle from dorsobuccal to ventrolingual (Legendre, 2016), which is steeper than that found in rabbits and other rodent species. Chinchillas and degus have the same dental formula as guinea pigs (Mans and Jekl, 2016).

Although there are many different facets to dental disease in small exotic mammals, the most commonly encountered in clinical practice are malocclusion and elongation of teeth (Harcourt-Brown, 2013). Dental disease is often multifactorial in origin and predisposing causes include insufficient fibre in the diet, resulting in lack of dental wear, metabolic bone disease, from lack of dietary calcium and vitamin D, as well as lack of ultraviolet light and sometimes congenital deformities (Lennox, 2008). Incisor malocclusion can result in abnormal cheek teeth wear and vice versa (Figure 1).

Diagnosis

Common clinical signs of dental disease in small exotic mammals include dysphagia, anorexia, weight loss, hypersalivation and gastrointestinal stasis (Capello, 2008). However, there are less commonly known signs of dental disease that can easily be missed by the general practitioner. Dacryocystitis is seen in rabbits where the apex of the upper incisor roots compresses the nasolacrimal duct (Harcourt-Brown, 2013), and in chronic cases this can lead to infection of the duct. Reverse sneezing can be heard in chinchillas (Capello, 2008) and facial swelling can be a sign of dental abscessation in all species.

A thorough oral examination should be performed both during wellness and routine consultations to identify problems early, and when patients are presenting for clinical concerns. Examine the incisors by parting the lips and perform a molar examination with an otoscope. The clinical crown is short compared to the reserve crown (Mans and Jekl, 2016), and because not all patients are amenable to a conscious dental examination, if dental disease is suspected then an oral examination should be performed under sedation or general anaesthesia (Capello, 2006; Figure 2). In the author’s experience, pathology of the clinical crown can be missed on conscious oral examination alone, especially pathology of the caudal molar teeth.

This is an excellent time to perform dental imaging, if not yet acquired from the patient. Diagnostic imaging can provide vital information, such as tooth root lysis, evidence of abscessation, curving of tooth roots, spikes or spurs of the clinical crowns, and other dental pathology that cannot be viewed on an intra-oral examination (Figure 3). A full radiologic study of the skull must contain at least four views: a dorsoventral or ventrodorsal, a lateral and two oblique views (Capello, 2008). A rostrocaudal view is also very useful to assess the temporomandibular joint, mandibular symphysis and the occlusal plane of the cheek teeth (Mans and Jekl, 2016). Boehmer and Crossley (2009) developed a series of reference lines to evaluate radiographs for evidence of malocclusion in rabbits, chinchillas and guinea pigs; however, these must be interpreted with caution in radiographs that are not completely straight.

More recently, a move towards computed tomography (CT) has been seen in exotic dentistry (Figure 4). The main advantages of CT over radiographs are the lack of superimposition and the superior resolution, which is essential for small patients, and therefore allows the identification of much more subtle lesions (Capello, 2016).

Treatment

Treatment of dental disease depends on the abnormalities identified. A full examination of the mouth can be facilitated with a dental gag and cheek dilators, with a range of sizes available for different species. Spurs or sharp molar spikes should be burred with a mechanical hand piece, ideally with a protective guard to prevent iatrogenic trauma to the buccal and lingual soft tissues. Dental burring is about management of dental disease. Because the teeth of these species are elodont, it is likely that any patient that needs a dental burring will need another in the future with time between dental treatments varying between individuals (Lennox, 2008).

Treatment of dental abscesses requires extraction of the affected tooth, ideally identified with diagnostic imaging, and marsupialisation of the abscess externally. Molar extractions should be performed with a Crossley cheek tooth luxator in larger species, and care must be taken not to fracture the tooth on extraction, as any material left behind can act as a nidus for infection (Lennox, 2008). If the abscess is from an incisor root then all the incisor teeth should be removed, which can be achieved by a Crossley incisor luxator for rabbits, or with the use of a scalpel blade or hypodermic needle in smaller species (Lennox, 2008). Marsupialisation is performed by creating a stoma between the abscess capsule and the skin, allowing for daily flushing of the abscess capsule until full resolution of the abscess can occur. This is the ideal time for taking a swab for bacterial culture and sensitivity, and starting the appropriate antibiotic therapy based on these results.

Mouth gags used during dental procedures should be used with caution to prevent stress of the temporomandibular joint ligaments and masticatory muscles (Capello, 2006). During treatment and resolution of dental disease, analgesia is an absolute must. Dental disease is painful, and secondary sequelae such as mucosal ulceration (Figure 5), gastrointestinal stasis and tooth fractures or abscessation are also painful. At the very minimum, non-steroidal anti-inflammatories should be provided to the patient, although multimodal analgesia is often also required (Legendre, 2003).