Learning Objectives for Rabbit and Rodent Dentistry

This lecture will cover the pathophysiology, clinical presentation and approach to staging dental disease in rabbits and commonly seen herbivorous rodents such as guinea pigs and chinchillas. Diagnostic modalities include extraoral and intraoral radiographic techniques, endoscopy as well as computed tomography scans. Treatment of dental disease will be described but prognosis of patients varies greatly based on the stage in which the diagnosis is made. Prophylactic diet adjustments to a high fibre diet should be recommended for all pet rabbits and herbivorous species as dietary habits must be considered as one of the major potential factors resulting in acquired dental disease.

Introduction

Rabbits and herbivorous rodents such as guinea pigs and chinchillas have completely elodont dentition. The incisors, premolars and molars are continuously erupting and the clinical crown will gradually wear down and be replaced by the reserve crown. Dental disease in these species are caused by varying factors however emphasis should be placed at addressing inadequate dietary fibre as this is the leading cause of acquired dental disease. Treatment of affected animals consists of dental procedures such as occlusal adjustments, incisor height adjustments, extractions of severely affected incisor/cheek teeth and surgical treatment of any periapical abscessations. The goal of treatment for dental disease is restoration of elodont teeth to normal length and shape; therefore, improving function. Secondary control of inflammation and infection should also be initiated. Diet adjustment postoperatively is also necessary for the full recovery of patients.

Clinical Presentations

Rabbits affected by dental disease may present with poor body condition, anorexia, chewing disturbances, changes in food preferences (soft and palatable foods) and hypersalivation. Dental disease can also be accompanied by the development of facial abscesses, wet dermatitis, epiphora, exophthalmia and damage to the temporomandibular joint. Guinea pigs affected by dental disease most commonly present with anorexia and emaciation. They rarely show skin or ocular presentations. Chinchillas with dental disease usually present for weight loss, reduced appetite, poor fur quality, epiphora and hypersalivation. Signs of gastrointestinal disease signs should be closely monitored for all species. Dental disease may result in concurrent gastrointestinal stasis due to excessive fur chewing/self-grooming, poor appetite, pain and lack of dietary fibre.

Dental Disease in Rabbits

There are three main causes proposed for acquired dental disease (ADD) in rabbits:

1.  Congenital factors (mandibular prognathism, malocclusion)

2.  Nutritional (reduced fiber intake) or

3.  Metabolic bone disease (reduced sunlight exposure causing lower calcium levels and higher PTH)

These factors may result in improper or insufficient wearing of incisor and/or cheek teeth (CT) as well as formation of periapical abscessations and osteomyelitis. Staging of dental disease in rabbits is performed commonly by performing extraoral radiography and endoscopy. In early stages, mild or absent clinical signs may be seen. However radiographically, elongation of CT crowns is present with slight curving of first premolars. There is slight deformation in the ventral mandibular cortex and interproximal space of mandibular CT may begin to widen. The incisor teeth usually appear normal. In the later stages, the occlusal surface of the CT will be abnormal (“wave mouth”) and excessive CT crown elongation and differences in crown height is present (“step mouth”), curvature and deformation of the mandibular or maxillary CT roots may occur, ventral mandibular cortical deformity will become more obvious, eventual root perforation of CT1 and CT2 into cortical bone will occur, fractures of elongated CT frequently occur, abnormal curving and malocclusion of incisor teeth is present. In the late stages, an endoscopic oral exam will reveal excessive crown elongation, deviation of CT and spurs may be seen as well as resulting ulcerations. In the end stages, radiographically there is radiolucency of the mandible, compensatory bony calcifications of the mandible, general lack of normal CT anatomy and incisors and clinical crowns are non-growing/absent or fractured.

Other Diagnostic Modalities

Intraoral dental radiographic techniques have been described for rabbits and are advocated to allow early detection of lagomorph dental pathology. This technique can be performed in conjunction with extraoral views to aid in visualization and guide veterinarians in providing proper treatment and prognosis.

Computed tomography scans (CT scans) should be considered for advanced to late stages of dental disease to provide more details about the extent of the dental pathology, which is likely to be important for establishing a more precise prognosis and treatment plan for the patient.

Dental Disease in Guinea Pigs

Malocclusion of incisor teeth is less frequent but when seen is typically secondary to CT disease. Hence, they serve as excellent indicators of CT abnormalities. Excessive CT elongation and malocclusion is likely due to poor nutrition causing improper wear. Radiographically, malocclusion and elongation of the incisors may be apparent, deformities of the cortical bone may be seen but are subtler than in rabbits. These lesions are usually more painful in guinea pigs and may not be relieved by coronal reduction. On endoscopic exam, the occlusal angle is sloped more than the normal 45-degree angle from buccal to lingual in severe cases of malocclusion. There will be crown elongation and malocclusion of CT and one or both mandibular CT1 is commonly affected in early stages. This may cause entrapment and discomfort of the tongue. Food and hair impaction are very common. Buccal spurs of maxillary CT may also cause ulcerations.

Dental Disease in Chinchillas

Malocclusion of incisors are not frequently encountered and usually secondary to dental disease of the cheek teeth. Traumatic fractures of incisors may be encountered and may result in long term overgrowth and deviation. Crown elongation and malocclusion is caused by abnormal wear due to poor nutrition. Radiographically the occlusal surface is uneven, elongation of CT crowns with CT 1 being most commonly elongated in early stages, partial resorption and abnormal curvature of CT may occur and in later stages deformity of the ventral cortical bone is seen with wider interproximal spaces. Malocclusion and elongation of incisors and completely abnormal occlusal surfaces are also common in late stages. Endoscopic exam will reveal excessive elongation of crowns with increased alveolar crest and gingival margins and molar spurs. Proliferation of gingiva may also be present and are usually associated with pain and poorer prognosis. There is excessive wear and even absence of clinical CT crowns in end stage disease.

Dental Procedures

Specialised dental equipment such as cheek dilators, mouth gags, rodent table restrainer, periodontal probe, high speed dental handpiece or Dremel and appropriate burs, molar cutters, Crossley’s luxators for cheek teeth and incisors, small curved hemostat and extraction forceps are necessary for the successful dental procedures which may include coronal height reduction, dental extractions, and incisor trimmings. Surgical magnification and light sources are also highly recommended to allow better visualization of the inner oral cavity. The patient should be deeply anesthetized for all dental procedures to prevent accidental trauma due to head and tongue movements. The soft tissue such as the tongue or buccal mucosa should be shielded using an instrument such as a spatula. Moistened cotton tip applicators can be used to periodically clean the working surface of the teeth and remove tooth dust. Spikes and elongated crowns should be filed using abrasive burs on a low/high speed handpiece. Overgrown incisors are similarly filed back using an abrasive bur. After reduction in height, the teeth are then filed and shaped to restore normal chisel shaped appearance of the teeth. Extractions should be performed using the specialized Crossley’s luxators due to the long tooth roots and care should be taken to ensure entire tooth and its pulp tissue is removed. Extraoral extractions can be attempted when an intra oral extraction technique is not feasible. Indications of extraoral techniques may include retained dental tips, severe root deformities, abscessations and osteomyelitis especially of the mandibular cheek teeth.

Facial Abscesses and Osteomyelitis

A common sequala of ADD in rabbits and herbivorous rodents are the gradual formation of abscesses resulting from periapical infections. Abscesses are usually not painful, cool to touch, encapsulated in a thick wall and contain a very dense, white and creamy pus. Treatment of abscesses involve aggressive surgical debridement, marsupialization and long-term antibiotic therapy. Mandibular abscesses may develop under the masseter muscles (especially in guinea pigs) and even result in osteomyelitis and jaw deformities.

Dental disease in rabbits and rodents can be very rewarding to treat and most patients will have a good outcome if diagnosis is reached early and timely treatment performed. However, in chronic and advanced stages, treatment may also be performed periodically as a form for palliative care. Post-procedural supportive therapy would include analgesics such as opioids and nonsteroidal antiinflammatories, antibiotics, fluid therapy, and gastrointestinal motility drugs. Anorexic patients should also be supplemented with a commercial hand feeding formula such as Oxbow Critical Care (Oxbow Pet Products Murdock NE, www.oxbowanimalhealth.com).

Diet counselling should be performed for all owners of pet rabbits and herbivorous rodents to prevent ADD. Rabbits and herbivorous rodents should be fed a pelleted diet and ad libitum hay and grass. Commercial mixtures with seeds and other additives are not recommended due to their selective feeding behaviour which will favour ingredients which are high in energy, high in phosphorus, low in calcium and ultimately this does not support optimal chewing patterns. A rabbit’s optimal diet should be high in fibre (20–24%) and with optimal calcium and phosphorus ratio of 1.5–2:1. Therefore, only commercial pellets as well as hay and grass with balanced mineral content and ratio should be selected for feeding. Wellness exams and regular weight checks are recommended for all rabbit and herbivorous rodent patients.