Dental Disease in Rabbits and Rodents

Key Points

  • Dental problems in rabbits and rodents are often related to either trauma or lack of normal wear and tooth elongation.
  • Unfortunately foods fed to many pet herbivores do not match their natural diet, providing too little tooth wear to compensate for normal tooth growth.
  • Uneven cheek tooth wear tends to result in formation of sharp enamel points or “spikes”.
  • Clinical signs of dental disease may include anorexia, weight loss, swelling of the jaw, hypersalivation, and an inability to fully close the mouth.
  • Epiphora, mild exophthalmos, and ocular proptosis may be seen as tooth “roots” invade the orbit.
  • Use an illuminated speculum or preferably an endoscope to examine the oral cavity. Deep sedation or general anesthesia is recommended for complete evaluation.
  • Full assessment of the dentition requires high definition skull radiographs.
  • Early tooth elongation can often be corrected by simply changing to a more natural diet, eg. grass and hay.
  • Significantly elongated teeth often require trimming. Never clip teeth. Instead use a bur in a dental handpiece. This permits rapid and precise reshaping of the teeth.
  • Chewing efficiency is noticeably reduced for a few days after trimming, and careful monitoring is recommended. Some patients require nutritional support; however discontinue supplemental feeding as soon as possible. Otherwise there will be insufficient tooth wear and dental problems will rapidly return or worsen.

Introduction

Rabbits and rodents may suffer from a wide range of dental problems from tooth fractures to tooth overgrowth, caries, and periodontitis, however the vast majority of cases are related to lack of wear and tooth elongation. Whilst an oral problem may sometimes be obvious, in most cases it must be presumed from non-specific signs such as weight loss and anorexia. Dental disease should be assumed to be present in herbivorous species such as rabbits, guinea pigs, and chinchillas, until proven otherwise as the incidence of dental abnormalities is extremely high. To obtain an accurate diagnosis it is necessary to understand dental anatomy and physiology as well as the range of potential pathology.

 

The natural diet of rabbits and caviomorph rodents

The European rabbit (Oryctolagus cuniculus), chinchilla (Chinchilla spp.), and guinea pig (Cavia porcellus) are true herbivores. The natural diet of the rabbit consists primarily of grasses, supplemented with other leafy vegetation. Chinchillas originate from mountainous areas in South America where vegetation tends to be particularly tough, fibrous and abrasive. Although guinea pigs and degus also come from South America, their natural habitats are different being respectively forest clearings and dry grassland.

Grasses and fibrous plants contain large numbers of phytoliths, highly abrasive silicate deposits which cause marked wear of the teeth. Fibrous diets also require prolonged chewing, which also promotes tooth wear. To maintain chewing efficiency, lost tooth substance is replaced constantly in these species, teeth continuing to grow and erupt throughout life.

 

Pathogenesis of dental disease

In the vast majority of cases, dental problems seen in rabbits and herbivorous rodents are related to lack of a suitable substrate for gnawing or lack of dietary abrasion. Pet herbivores may receive concentrates, in the form of grain or pellets, which are better suited to rats and mice. Even when herbivores are primarily fed hay or vegetation, these items are from lowland pasture where grasses are “soft” and much more nutritious, with much lower silicate content than the plants normally eaten by chinchillas and guinea pigs.

Genetics, metabolic deficiencies, and prolonged or extreme nutritional imbalances may also cause problems with tooth growth and eruption. Both vitamin C deficiency and excessive selenium intake interfere with collagen metabolism, potentially weakening periodontal ligaments in guinea pigs. This results in tooth instability and/or eruption problems. Vitamin A deficiency has also been shown to arrest incisor tooth growth in guinea pigs.

 

Early dental disease

Tooth growth normally keeps pace with the rate of attrition. When there is insufficient wear, exposed crowns begin to elongate subjecting teeth to increased occlusal stress. Although this stress reduces tooth eruption, growth continues. If eruption rate is reduced to less than about one-eighth of normal the newly formed tooth structure becomes deformed. In its early stages this deformity is seen as ridging of the enamel surface, but increased tooth curvature is another, more serious consequence. Unfortunately it is rare to see and recognize dental disease at an early stage when problems may be corrected relatively easily. Most herbivores have irreversible structural changes by the time they are presented, which can be as early as 3 months of age.

 

Clinical dental disease

Dental problems are common in rabbits and rodents such as chinchillas, guinea pigs, degus (Octodon degus) and prairie dogs (Cynomys spp.) and are frequently related to lack of wear and subsequent tooth elongation, intrusive growth or changes in tooth curvature. Since the curvature of maxillary and mandibular cheek teeth is in opposite directions, the occlusal surfaces of the dental arcades no longer meet effectively. This leads to the formation of sharp enamel points or “spikes”, typically on the buccal edges of the maxillary arcades and the lingual aspects of the mandibular arcades (Fig 1 and Fig 2). Dental spikes cause irritation and ulceration of mucosa resulting in reflex salivation and pain with chewing or swallowing. Excessive salivation is common in chinchillas, and wets the fur of the chin and forequarters, a condition called “slobbers”.

Chinchilla (Chinchilla lanigera) skull illustrating gross elongation and enamel point

Figure 1. Chinchilla (Chinchilla lanigera) skull illustrating gross elongation and enamel point or “spike” formation on cheek teeth. Photograph by David Crossley. Click image to enlarge.

 

The arrow indicates an enamel point or “spike in a rabbit

Figure 2. The arrow indicates an enamel point or “spike in a rabbit (Oryctolagus cuniculus); photograph by David Crossley. Click image to enlarge.

Although cheek tooth overgrowth is common in pet chinchillas and guinea pigs, the form of the problem varies between the species. In chinchillas, significant tooth root elongation can occur with or without visible coronal overgrowth.

Swellings may be palpable on the ventral surface of the mandible. The initial signs of maxillary tooth root elongation are dullness and depression. Epiphora, mild exophthalmos, and eventually proptosis of the eye may be seen as tooth roots invade the orbit.

Guinea pigs tend to have more severe intra-oral tooth overgrowth and less root extension. This is possibly related to the greater degree of root curvature in this species. Cheek tooth overgrowth in guinea pigs tends to force the mandible rostrally with secondary incisor malocclusion. As the mandible is forced into a more prognathic position, the last maxillary cheek teeth no longer occlude with the corresponding teeth in the opposite jaw and they elongate, as do the mandibular premolars. It is not uncommon to find that these premolar teeth have grown across and entrapped the tongue. The main signs of cheek tooth overgrowth in guinea pigs are weight loss and inability to fully close the mouth. In some cases the mouth is held so wide open that swallowing is almost impossible.

 

Diagnosing dental disease

Obtain a detailed history and carefully examine the patient for external visual and tactile clues suggestive of oral or dental disease. Drooling, tear overflow, oral-facial swellings, visibly abnormal incisor teeth, jaw chattering, or tooth grinding may all be observed. Jaw palpation may reveal swellings, muscle wasting, reduced jaw mobility, and oral discomfort based on the animal’s reaction to handling. Lack of normal repulsion of the eyes into the orbit under gentle pressure may also be seen.

Fully assess the patient prior to treatment and always assess the cheek teeth, which are almost always involved to some degree. Whenever possible, determine the underlying cause of crown elongation and malocclusion.

Oral examination

Visual intra-oral examination is challenging in rabbits and rodents due to the long, narrow oral cavity and the limited opening of the mouth. I have found the most useful tool in the conscious oral exam is the Welch Allyn illuminated bivalve nasal speculum. Insert the speculum into the oral cavity on one side of the incisor teeth, and separate the wings of the speculum to hold the cheek and tongue out of the way. A cursory oral exam may also be performed with an otoscope or a pediatric layrngoscope, although changes in the caudal oral cavity cannot be identified precisely.

When the patient is deeply sedated or anesthetized it is possible to use cheek dilators and a mouth gag. This permits a view of the oral cavity similar to that seen with the nasal speculum (Fig 3), but without the problem of patient movement. Complete examination of the back or occlusal surfaces of the cheek teeth requires use of a small, rigid endoscope with an angled view (Fig 4); they are readily available with viewing angles up to 120º.

Oral exam in a rabbit

Figure 3. Oral exam in a rabbit (Oryctolagus cuniculus) using a cheek dilator and a mouth gag. Photograph by David Crossley. Click image to enlarge.

 

Otoscopic view rabbit cheek teeth

Figure 4. Otoscopic view of cheek teeth in a rabbit (Oryctolagus cuniculus). Photography by David Crossley. Click image to enlarge.

In addition to visual examination of the dentition, tactile exploration of the teeth and probing of periodontal tissues should be performed. Deep pocketing is often present, but without the visible gingivitis that typically accompanies this condition in cats and dogs.

Radiology

Full assessment of the dentition and jaws requires radiography. The oral anatomy of most herbivores does not permit easy intra-oral dental film placement so obtain high definition anatomical view skull radiographs. Dental film gives excellent detail, but fine-detail single emulsion screen film or mammography film and higher end digital systems also provide sufficient detail. Obtain the three standard skull views:  lateral, dorsoventral, and rostro-caudal. The lateral view with the incisors slightly separated is most useful (Fig 5). It is more difficult to obtain a “perfect” lateral view in guinea pigs, when compared to rabbits and chinchillas, due to their head shape, the strong curvature of the cheek teeth, and the steeply angled occlusal planes. Evaluate films carefully:

  • What is the degree of mouth opening?
  • Do the cheek teeth arcades have a normal pattern?
  • What is the position the of tooth apices?
  • What is the degree of apical elongation or root extension, and are there any periapical changes?
  • Are there any missing teeth or evidence of bone loss associated with periodontitis?
Lateral radiograph of a normal rabbit

Figure 5. Lateral radiograph of a normal rabbit (Oryctolagus cuniculus) by David Crossley. Click image to enlarge.

Management of dental disease

The best method for learning rabbit dentistry is to routinely perform postmortem examinations following euthanasia of affected animals. Spending time practicing handling instruments and performing procedures on cadavers is always beneficial. When dealing with live patients, inform the client if you are not confident in your ability or if you do not have suitable equipment for the job, and advise referral to a specialist.

If early dental disease is recognized, institute a simple dietary change. Feed primarily grass and hay and less than 5% of other leafy vegetation, assuming the patient can be persuaded to eat these items. If the pet is “addicted” to unsuitable food, sudden withdrawal of these items may result in a refusal to eat with the risk of inducing hepatic lipidosis. Once grass and hay is consumed in significant quantities, gradually withdraw grains and pellets.

Coronal reduction or “tooth trims”

When there is significant tooth elongation but still only slight structural change, perform coronal reduction, or “tooth trims” and removal of enamel points or “spikes” in addition to instituting dietary correction.  Tooth trims may need repeating at frequent intervals throughout the patient’s life in order to prevent further progression of dental disease.

The only satisfactory way to shorten and reshape the teeth is with use of power equipment. Clipping is a barbaric, cruel procedure that results in pain and suffering, and should never be performed. Files or rasps may be used but the process is relatively slow, and the teeth may be loosened in their sockets. All modern small animal clinics should have dental equipment such as a polisher that takes interchangeable sterilizable handpieces. These units can be fitted with an inexpensive straight handpiece that will accept suitable burs and bur guards for tooth trimming.

High-speed dental turbine handpieces have the advantage for easily accessed incisor teeth of rapid and precise cutting without application of significant pressure, and can be used on conscious patients if they are accustomed to handling. Water spray is best turned off as few animals like being sprayed with water, but care is required to avoid the bur heating up. Incisor trims can also be performed using low speed equipment (i.e. DremelÒ hand held rotary equipment), though it takes longer to make each cut and a little pressure must be applied during cutting. This pressure should never exceed the normal physiological forces encountered during chewing. Also take care not to expose the pulp cavity, which elongates as eruption accelerates. When the teeth are very long trim them back by half the length of the exposed crown, then half the remainder, and by half again until the tooth is the correct length or pink coloration on the cut surface indicates that the pulp is being approached.

Access to the cheek teeth requires anesthesia and the use of a flat fissure bur. Use a bur guard or other form of soft tissue protection to avoid soft tissue injury (Fig 6). If using a bur guard, rapid height reductions are possible by positioning the tip on the occlusal surface and using it to guide advancement of the end of a cylinder bur through the crown of the tooth on first the lateral then the medial side. This removes about 2 mm of crown height at a time until it is judged from the radiographs that enough tooth height has been removed. Swabbing the teeth with damp cotton-bud at frequent intervals removed powdered tooth and helps lubricate the bur. When the first tooth has been reduced, then treat the next in line. Repeat the process until no further coronal reduction is needed. Then use the side of the cylinder bur or a round bur to smooth the occlusal surfaces and restore a normal 10º to 15º occlusal plane angle. Once the cheek teeth have been trimmed, ensure the incisors are short enough to permit cheek tooth occlusion so the patient can chew its food. If a bur guard is not available, then a large cylinder, round or tapered diamond bur is more suitable (safer) than a cylinder cutting bur.

Burring cheek teeth

Figure 6. Use of flat fissure bur with bur guard on cheek teeth; photograph provided by David Crossley. Click image to enlarge.

 

Management of structural changes

Carefully consider any major or complex treatment beforehand, since it is possible to add to the animal’s problems, rather than improving the situation.

Extraction is indicated when teeth become non-functional or tooth support has been compromised. It is essential to destroy growing tissue at its apex prior to removing incisor teeth, otherwise tooth regrowth will occur producing anything from a normal tooth to a diffuse mass of dentine embedded deep within the jaw. Cheek tooth extraction is only recommended for abscessed teeth, since this procedure creates secondary malocclusion due to irregular wear of opposing teeth and there is a risk of serious jaw damage. Extraction of one or two already loosening cheek teeth is practical, however extraction of a significant number at one time is very traumatic for the animal. Many fail to recover from such a surgery.

An alternative to extraction of mandibular cheek teeth or incisors is apical resection. Surgical removal of the growing dental tissue prevents further tooth growth. The remaining tooth structure either continues to erupt and eventually fall out, but possibly needing trimming before then if it is not wearing, or becomes anklyosed and resorbs. Both extraction and apical resection require surgical expertise and a thorough knowledge of anatomy. These techniques are only recommended for those working with rabbits and rodents on a regular basis.

Root elongation appears to be irreversible once it has developed. Gross abnormalities such as ankylosis, resorption, loss of cheek teeth, and/or severe, established root elongation suggest a poor prognosis. However always consider structural changes in relation to the animal’s demeanor and body condition. Some patients are able to cope with severe dental problems without any obvious signs of distress, needing only occasional trimming of the remaining teeth. When ongoing disease causes persistent distress despite attempted treatment then euthanasia is the kindest option.

Fractured teeth

Rodents, and to a lesser extent rabbits, are susceptible to tooth fractures, particularly incisor injury. Incisor fractures are best managed by repeated trimming and smoothing of affected and opposing teeth until the damaged dentition returns to normal function. In cases where there has been pulp exposure, aseptically create an access cavity and apply a calcium hydroxide cement dressing. This will act as a temporary filling that will not interfere with tooth wear and may permit continued normal tooth growth.

Recovery and monitoring

Follow-up and monitoring of progress is important after dentistry. Schedule reevaluation within 1 week and then again at one month post-procedure if all is well. Depending on the patient’s condition, further rechecks will be required anywhere from 3 to 6 week intervals to biannually.

During the first few days post-treatment, it is often necessary to provide nutritional support since chewing efficiency may be noticeably reduced. Shortening cheek teeth crowns leaves the stretched jaw muscles unable to fully contract at first. The jaw may even hang open at rest. The smoothed occlusal surfaces will also be inefficient at grinding food until enamel ridges have worn back, which requires several days of chewing an appropriate diet. Withdraw supplemental feedings as soon as possible otherwise there will be no tooth wear and dental problems will rapidly return or worsen.

For maximum benefit, repeat coronal reduction before the teeth become grossly elongated. When increased curvature results in “spike” formation it is even more important to perform the tooth trim promptly as any soft tissue injury delays recovery significantly.

Instruct owners to monitor the pet carefully. Changes in body weight and behavior are usually subtle indicators of problems well before gross elongation becomes evident. Slight weight loss (5% or less) is common during the first week or two in animals that have not previously eaten a grass-based diet. Rapid or more severe weight loss is significant and should be investigated.

 

Conclusion

Unfortunately for many of our domestic pets, the food they are given and the environment they are kept in do not match what they have in nature. When herbivores like rabbits, guinea pigs, and chinchillas receive concentrates, in the form of grain or pellets, with only limited access to hay and natural vegetation this diet provides too little tooth wear to compensate for the natural growth of the teeth. Until the message on prevention can be reliably transmitted to owners, we will continue to have oral and dental problems to manage.

Rabbit and rodent dentistry is still at an early stage of development. Nevertheless with an understanding of normal anatomy [link to article on dental anatomy] and the nature and extent of dental disease it is possible to devise an appropriate treatment regime for most dental problems. Although many of the dental problems seen in practice cannot be cured, most can be controlled or managed to allow the affected herbivore to maintain a good quality of life. Since the continuously growing nature of the teeth makes recurrence and progression of problems the norm, owner education and ongoing monitoring of animals is essential.

References