Despite the order of rodents is the largest mammalian order, this presentation will include only guinea pigs, chinchilla, degu, rats, hamsters and prairie dogs which represent three suborders: porcupine-like, rat-like and squirrel-like rodents. These representatives are kept as pets and may present in general practitioner's waiting room. Moreover in all these species, primary and secondary dental diseases are very often diagnosed. Dental diseases are accompanied by decreased food intake, weight loss, problems with appetite, drooling, digestive disturbances, facial deformities, exophthalmos and poor coat condition.
With their continuously growing teeth, these pets are predisposed to dental disorders every time when mistakes in nutrition occur. They suffer from periodontal disease, malocclusions, and fractured teeth that can all result in the formation of abscesses. Some dental problems, as in all edentulous creatures, can cause systemic complications.
Diagnosis of Dental Disease in Rodents
To make an accurate diagnosis it helps to have sufficient data regarding the patient, its history and the signs observed. In most cases, the history and an initial external examination of a sick animal will give indications as to any probable dental involvement.
Although it is possible to perform oral examination of awaken patient with the use of an auriscope as an oral endoscope in some species, the restricted field of view means that many lesions will be missed. Even when examining a patient under anaesthesia using mouth gags, cheek dilators, mouth mirrors and magnification, it is common for experienced clinicians to miss significant oral lesions.
Therefore, the complementary and very important part of examination is radiography. Positioning techniques vary from the ones used in dogs and cats: extra-oral instead of intra-oral techniques are employed. Four views are standard: lateral, dorso-ventral, diagonal, and rostro-caudal. The first three are similar to the ones used in horses; they allow a good look at the alignment of the teeth and at the anatomy of the radicular ends. The last position allows a good view of the sinuses and of the temporomandibular joints. In lateral and dorsoventral projection it is possible to use the reference lines. Using the reference lines, the extent of malocclusion in guinea pigs and chinchillas can be acquired more exactly and the results are reproducible by different examiners (staging). In addition to this, these special lines facilitate to accurately monitor the progress of dental changes and thus to predict a probable long-term prognosis. The reference lines are absolutely applicable for daily use in practice.
The most frequently recognised dental problem in rabbits and rodents is malocclusion of their easily examined elodont (aradicular hypsodont) incisor teeth. Without the normal regular wear from chewing or gnawing activity, these non-functional maloccluded teeth continue growing, further impeding function.
The second most common dental problem in these small herbivores is cheek tooth overgrowth. This often accompanies incisor malocclusion, either as a part of the primary condition, or as a purely secondary problem, but it is also seen as a primary problem in its own right. Cheek tooth overgrowth may result from lack of wear due to malocclusion or an insufficiently abrasive diet.
Whether a malocclusion is primary or secondary, abnormal tooth wear of the naturally curved cheek teeth tends to cause development of sharp enamel spikes/spurs which irritate the cheeks and tongue leading to wounds and ulcerations associated with pain.
The close proximity of the root apex of the mesial cheek teeth to the lacrimal duct accounts for the occurrence of epiphora and the frequent spread of periodontal infection from these teeth to the tear duct, producing the typical purulent ocular discharge.
Root extension of the mandibular cheek teeth leads to remodelling or thinning of the adjacent cortical bone with development of palpable swellings along the ventral surface of the mandible. Suspected mandibular or maxillary root extension is best confirmed radiographically.
Facial and mandibular abscesses are generally caused by dental problems, though infection of external wounds does also occur.
Pseudo-odontoma in prairie dogs. The constant, concussive force on the teeth of these prairie dogs causes the roots (or apices) to react, become irregular and thicken. As the roots increase in size, they begin to fill the nasal area. Since prairie dogs breathe only through their noses (called obligate nasal breathers), this increase in tooth size makes breathing difficult. The condition is worsened by obesity, which is very common in captive prairie dogs. The cause of this is theorized to be the unnatural materials (metal, wire, hard plastic) of which their enclosures are made. These materials are much harder than the grasses, clay, sand and stems on which they would normally chew in the wild. Prevention seems to be the best solution as surgical treatment brings relatively high risk and guarded prognosis.
Management
The incisor tooth overgrowth problem has traditionally been managed by repeated tooth shortening (preferably trimming using a diamond bur in a high-speed dental handpiece), without investigation of the underlying problem. In cases with recurrent overgrowth, extraction of the offending teeth has been suggested as a more permanent solution. In rodents, correction of incisor teeth by burring a reverse bevel on the mandibular incisors to create an incline plane like interlock with the maxillary first incisors, cannot be accomplished. In the majority of cases, occlusal equilibration of the cheek teeth is also required.
Treatment of the cheek teeth by removing enamel spikes and occlusal equilibration is sometimes possible, though the long-term results are poor in most cases. As with the correction of rabbit incisor malocclusion, the treatment is most successful if performed at an early stage, in mild cases. Dietary alteration (providing hay as the largest component of the diet) to increase the rate of attrition is highly beneficial in these cases. In more advanced cases, the provision of a more abrasive diet is helpful, but it is usually necessary to repeat occlusal equilibration at regular intervals.
For dental procedures in small herbivores, a series of dedicated tools is available: operating table with head and jaws positioners, examination instruments, dedicated low-speed handpicks and burs are necessary to perform safely and efficiently oral surgery. Nail clippers are not recommended, they are even viewed as detrimental as they can cause diagonal fractures causing pulp exposure, pulpitis, pulp necrosis, periapical granuloma, and even osteomyelitis and sepsis. Rasps are not on the list either, as they are inefficient and often cause trauma to the soft tissues of the oral cavity.
References
1. Capello V, Gracis M, Lennox AM. Rabbit and Rodent Dentistry Handbook. Lake Worth, FL: Zoological Education Network; 2005.
2. Jekl V. Rodents: dentistry. In: Keeble E, Meredith A, eds. BSAVA Manual of Rodents and Ferrets. 2nd ed. Gloucester, UK: BSAVA; 2009:86–95.
3. Boehmer E, Crossley D. Objective interpretation of dental disease in rabbits, guinea pigs and chinchillas. Use of anatomical reference lines. Tierärztliche Praxis Kleintiere/Heimtiere. 2009;37(4):250–260.