The emphasis of this lecture will be on description of the pathophysiology of dental disease, indications for surgical treatment and proper postoperative care. Participants will gain knowledge about basic normal dental anatomy and chewing physiology plus up to date information about disease prevention and recurrence. Understanding of dental disease development is especially important for veterinary nurses, because they play a key role in preventative health care and in providing advice to owners. Dental treatment is generally a palliative treatment and owner education is necessary to understand the treatment and postoperative care and nursing.

Anatomy

Rabbits have completely elodont dentition (continuously erupting). The permanent rabbit dental formula is I (2/1), C (0/0), P (3/2) and M (3/3). Their incisors, premolars and molars are continuously erupting through the life at the rate of 0.2–0.3 cm per week for incisors and 0.3–0.4 cm per month for cheek teeth. Dentition is diphyodont (deciduous and permanent teeth) and heterodont. Rabbits also belong to Duplicidentata due to the presence of a double set of maxillary incisors (incisors and peg teeth). Premolars and molars have a similar structure and form in each quadrant of the oral cavity, a uniform functional grinding unit. Enamel width is more prominent at the labial part of the cheek teeth and buccal part of the maxillary cheek teeth, which is why the larger enamel ridges are present at these locations, which can imitate spikes. The mandibular arcade is narrower than the maxillary arcade.

Aetiology and Pathophysiology

Diseases of the oral cavity, particularly acquired dental disease, are the most common disorder in pet rabbits. Dental disease is multifactorial and many local and systemic conditions that affect the mouth and oral cavity have been described, including hereditary, infectious, metabolic and traumatic conditions (including foreign bodies), electrical accidents and neoplasms. It seems that both metabolic bone disease and improper wear are the main causes of dental disease in pet rabbits.

If the cheek teeth are not worn adequately and elongate intraorally, the mouth is held more open, stretching the masseter muscles and increasing the resting occlusal pressure on the teeth. As a result, the incisors elongate and lose the normal chisel-like wear pattern and animals have problems with bolus formation. As a result of metabolic bone disease, even physiological chewing forces may cause apical intrusion ('root elongation') and loss of alveolar supporting bone. Loss of supporting alveolar bone, along with pathological forces generated during chewing and tooth growth affect the curvature of the cheek teeth. Widening of the interproximal coronal surfaces, presence of sharp spurs, coronal elongation and abnormal cheek teeth occlusal surfaces are common findings at this stage. In addition, occlusal pressure could prevent eruption of cheek teeth, so that the apices intrude and induce bony remodelling of adjacent tissues. When this painful condition occurs in maxillary incisors, epiphora may be clinically evident as a result of nasolacrimal duct obstruction. Mandibular cheek teeth apices also elongate and, in more severe cases, penetrate through the ventral mandibular cortex. As the condition progresses, mastication becomes more uncomfortable and only soft foods may be selectively eaten, resulting in further tooth growth due to lack of wear.

Horizontal enamel ridges which can be seen on the labial part of the incisors are the result of apical germinative tissue pathology. Such enamel dysplastic changes are commonly associated with calcium metabolism. Primary incisor elongation/malocclusion is diagnosed in less than 10% of rabbits with dental problems, whereas the other 90% are secondary to premolar and molar teeth malocclusion.

Clinical Signs

An accurate history should be obtained from the owner and a routine clinical examination should be performed on all patients presented for dental procedures. Animals suffering from systemic disease require special attention and life-threatening conditions should be addressed immediately. Associated clinical signs are hypersalivation, anorexia, chewing disturbances, changes in food preferences (soft and palatable feed particles) and poor body condition. In some cases, dental disease can also be accompanied by the development of facial abscesses, wet dermatitis, epiphora, exophthalmia and damage to the temporomandibular joint.

Physical Examination and Treatment

For basic oral examination rabbits may be restrained manually. Rabbits are wrapped in a towel or an assistant holds the animal's thoracic limbs and supports its back; the practitioner holds the animal's head and retracts its upper lips with one hand, while examining the oral cavity with the laryngoscope in the other. Conscious oral cavity examination starts with an evaluation of facial symmetry and palpation of the jaws. Signs of heat, discharge, crepitus and presence of facial masses should be noted. Lateral and horizontal lower jaw excursion should also be evaluated. Discomfort and pain on manipulating the jaws may be due to a jaw fracture, disease of the temporomandibular joint or because of retrobulbar pathology. If pain is noted, the animal should be monitored closely since it may easily become stressed during examination, leading to possible collapse. Palpation of the ventral border of the mandible and zygomatic area can reveal bony swellings associated with apical teeth elongation.

The oral cavity of rabbits is long and narrow, making it technically more difficult to examine than the oral cavity of dogs and cats. An otoscope or a paediatric laryngoscope is recommended as a tool for oral examination of conscious animals. When a pathological process is found during conscious oral cavity examination, the animal should be anaesthetised for a more thorough oral cavity inspection.

Anaesthetised rabbits should be closely monitored; injectable premedication and induction (midazolam, butorphanol, medetomidine, ketamine) with isoflurane anaesthesia are the preferred combination of the author. In case of mild or severe health impairment, urinalysis, haematology and plasma biochemistry are used as a part of presurgical examination. Intubation is necessary in cardiorespiratory comprised patients or during longer procedures. Some clinicians recommend intubating a rabbit for any surgical procedure. Heating pads, warm fluids and oxygen supply are standard care throughout the procedure. An oral cavity examination is done with the rabbit in sternal recumbency and using horizontal and cheek teeth dilatators. Care must be taken when adjusting the mouth cavity opening to prevent temporomandibular joint injury. Anaesthetic gas is delivered via customised nasal mask. Peri- and postoperative care include rehydration, gastric motility drugs (metoclopramide, ranitidine, cisapride, itopride) and analgesia (non-steroidal anti-inflammatory drugs (NSAIDs), opioids). Rabbits should be closely monitored and in an oxygen-rich environment until uneventful recovery. Radiography, computed tomography and endoscopic examination are very important imaging methods leading to proper diagnosis and an optimal treatment plan.

Surgical treatment of incisor teeth and clinical crown adjustment of cheek teeth requires special instruments (burrs, diamond disc, dental rasp). In cases of severe incisor elongation, a complete set incisor extraction is necessary to prevent further soft tissue damage and problems with ingestion. Patients with periapical infections (osteomyelitis) need very intensive care and the approach is similar as to any other bone surgery.

Disease Prevention and Diet Recommendation

Rabbits should be fed a pelleted diet and ad libitum hay and grass. Commercial mixtures are not recommended due to rabbit selective feeding behaviour, where an animal picks up only some ingredients which are high in energy, high in phosphorus, low in calcium and which does not support optimal chewing patterns. An optimal diet should be high in fibre (20–24%) and with optimal calcium and phosphorus level with a ratio of 1.5–2:1. It means that not only commercial pellets, but also hay and grass should have a balanced mineral content and ratio. Regular weight checks and veterinary clinic visits are recommended for all rabbit patients.

References

1.  Capello V, Gracis M, et al. Rabbit and Rodent Dentistry Handbook. Lake Worth: Zoological Education Network, 2005.

2.  Capello V, Lennox A, eds. Dentistry of exotic companion mammals. Journal of Exotic Pet Medicine 2008;17:69–131.

3.  Harcourt-Brown F. Textbook of Rabbit Medicine. Oxford: Reed Educational and Professional Publishing, 2002.

4.  Jekl V, Knotek Z. Evaluation of a laryngoscope and a rigid endoscope for the examination of the oral cavity of small mammals. Veterinary Record 2007;160:9–13.