In rabbits, as with other animals, optimal condition and wellbeing is closely linked to dental health. Maintaining dental health in most breeds of rabbit is closely linked with diet and when the rabbit has ample opportunities to chew on coarse fibrous grasses, its teeth are largely able to maintain efficiency and promote overall dental wellbeing. When dental health starts to decline, there are a number of problems that can occur, which are specific to the rabbit's unique anatomy and physiology. Continual growth of the teeth can lead to several conditions related to tooth overgrowth and occlusion; disease can progress quickly as the animal grows less able to close the mouth or chew effectively.
Dental disease is very common in rabbits but detection of disease can be challenging. It is vitally important that any abnormalities are identified as early as possible before serious problems occur with digestion. All rabbits should be routinely examined for signs of malocclusion and clients should be educated to detect early signs of disease and to support dental and digestive health with adequate opportunities to chew high-fibre vegetation.
The relationship of diet to dental anatomy
Rabbits are obligate herbivores and their cyclical digestive process requires high amounts of fibre to meet nutritional needs. In the wild, rabbits primarily consume tough fibrous grasses and leafy plants which wears down the teeth from prolonged mastication of coarse cellulose. Mature grasses contain naturally high silicate deposits which also exposes the teeth to significant abrasion and wear (Crossley, 1995; Harcourt-Brown 1996).
The extended chew time required for breakdown of fibrous vegetation results in significant wear of the tooth surface so, to maintain masticatory effectiveness, the rabbit requires constant replacement of the lost tooth surface throughout its lifetime. To meet this need, the rabbit's teeth erupt continuously.
Dental anatomy of rabbits
The rabbit has elodont, continually growing and open-rooted, dentition. Its teeth are aradicular, without an anatomical root, and hypsodont, meaning that the enamel crown extends past the gingival margin to allow for protection as the teeth are continually erupting past the gumline. The eruption of teeth is grouped, heterodont, so that the occlusal surface wears at an even rate; and, like most companion animals, rabbits are diphyodont, meaning they have two sets of teeth throughout their lifetime (Figures 1 and 2).
The deciduous teeth erupt in utero and consist of far fewer teeth than in the dentition of mature adults (Table 1). At or around the time of birth, the first deciduous incisors are lost and by about day 35 the final deciduous molars are replaced by larger permanent teeth.
| Incisors | Canines | Premolars | Molars | Total | |
|---|---|---|---|---|---|
| Deciduous | 2/1 | 0/0 | 3/2 | 0/0 | 16 |
| Permanent | 2/1 | 0/0 | 3/2 | 3/3 | 28 |
The molars and premolars are commonly referred to as cheek teeth. The mandibular and maxillary arcades work together as a functional unit grinding food and the rabbit moves these laterally and dorsoventrally against each other during mastication and this specific movement is called lateral excursion. The rabbit also has marked anisognathism whereby the mandibular arcade is narrower than the maxillary arcade. The consequences of this arrangement are that mastication uses the entire width of the occlusal surface (Hobson, 2006). The structure of each of the cheek teeth comprises parallel layers of dentine and enamel which appears as if it is folded on itself; these layers of dentine and enamel wear at different rates creating a serrated surface on the occlusal surface of the tooth (Lennox, 2010).
Causes of dental disease in rabbits
Pathogenesis of dental disease in rabbits can include a number of primary and secondary conditions such as genetics relating to size and shape of the skull, trauma from injury or illness, metabolic deficiencies or nutritional imbalance; however, the majority of dental disease in rabbits is related to inadequate wear and this can be seen in rabbits as young as 3 months of age (Harcourt-Brown, 1996).
The growth of a rabbit's teeth is continual, but it also fluctuates. Generally growth keeps pace with the rate of attrition so when the crowns are not worn down sufficiently, the elongated teeth put pressure on the opposing teeth producing occlusal stress that can slow tooth eruption. This process can delay eruption of tooth tissue, but it cannot stop it entirely and delayed eruption can cause detrimental consequences to developing tooth tissue including deformation of new tooth tissue, ridging of the enamel and, in severe cases, abnormal curvature and intrusive growth which can lead to significant ongoing health problems (Crossley, 2003). Additional problems can be related to maxillary and mandibular retrograde root growth such as: occlusion of the nasolacrimal duct leading to epiphora and maceration of tissues around the eyes; tooth roots protruding into the orbit and causing proptosed globes; and tooth roots erupting through the ventral mandibular border.
Common types of dental disease
Malocclusion
One of the most common dental problems occurring in rabbits is malocclusion whereby the teeth do not meet normally. Almost without exception, malocclusion is accompanied by coronal elongation whereby the growth rate exceeds wear on the opposing occlusal surface (Meredith, 2007). This can become a serious problem for the rabbit as its teeth can grow to abnormal lengths and shapes thereby preventing efficient mastication and causing an increased likelihood of health problems as the rabbit becomes increasingly unable to wear down the teeth evenly.
Malocclusion can be seen in young animals when it results from congenital or hereditary causes, such as jaw length deformities (Table 2). The consequences of these types of malocclusion are almost always insufficient attrition of the incisors. The natural curvature of the incisors causes curling with overgrowth back into the oral cavity. In some cases, the overgrown teeth can curve up and puncture the roof of the mouth leading to damage of the soft tissue and protrusion into the anterior nasal cavity. Incisor malocclusion also can lead to the rabbit being unable to close the mouth and this will lead to overgrowth of the cheek teeth.
| Common name | Clinical signs | Type(s) of jaw deformities that cause the condition |
|---|---|---|
| Underbite; cross-bite; tusk-teeth | The maxillary incisors curve dorsofacially into the mouth and the mandibular incisors project in an anterior/rostral direction out of the mouth and in front of the maxillary incisors. |
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| Overbite, parrot mouth | The maxillary incisors project in an anterior/rostral direction out of the mouth and in front of the maxillary incisors but as they have no opposition, their natural curvature causes them to curve dorsofacially into the mouth and the mandibular incisors tend to splay according to oppositional forces, but usually project out of the mouth. |
|
Malocclusion can also occur at any age as a result of trauma, nutritional deficiency, infection, or loss of a tooth which subsequently changes the occlusal surface and can result in lack of opposition to occlusal forces, and subsequent overgrowth or tooth deformities (Harcourt-Brown and Baker, 2001). However, the most common cause of malocclusion is coronal elongation as a result of insufficient wear from normal chewing activities and this is usually seen in mature animals (Table 3) (Verstraete and Osofsky, 2005).
| Type | Clinical signs | Causes | Consequences |
|---|---|---|---|
| Incisor overgrowth | Elongation of the crown; curled or grooved teeth; tusk-like teeth; uneven growth. | Caused by prognathism; insufficient wear; injury; uneven wear of the cheek-teeth; or occlusal stress resulting from insufficient dental attrition. | Can cause occlusal trauma and tooth root abscess. Can also lead to malocclusion and subsequent overgrowth of the cheek teeth. |
| Cheek teeth overgrowth | Uneven wear of occlusal surfaces of the cheek-teeth; formation of lingual spurs on the mandibular cheek teeth and buccal spurs on the maxillary cheek teeth. | Caused by incisor malocclusion; prognathism; retrognathism; marked (extreme) anisognathism; acquired decreased lateral excursion of the mandible; or occlusal stress resulting from insufficient dental attrition. | Sharp points of the spurs lead to trauma to the cheek and tongue dependent on the direction of spur growth; infection, salivation and reluctance to eat. Can also lead to malocclusion and subsequent overgrowth of the incisors. |
| Uneven wear due to tooth loss | Occlusal surfaces lack natural opposition from the missing teeth leading to lack of wear and overgrowth of the crown. | Trauma, infection extraction, hereditary or congenital causes. | Incisor overgrowth, formation of molar or premolar spurs, maxillofacial trauma, abcess. |
Incisor malocclusion in rabbits is often the result of brachygnathism where typically, the maxillary incisors overgrow and curve back and up into the oral cavity, and the mandibular incisors elongate rostrally protruding through the lips (Figure 3) (Crossley, 1995). Malocclusion of the incisors can be severe and have detrimental health effects. Without proper occlusal opposition, the incisors can grow at abnormal angles and cause significant damage to the oral cavity (Figure 4). This process frequently leads to infection, and progressive malocclusion of the cheek teeth so prompt treatment is required to prevent further problems.
Malocclusion may be isolated to the incisors but it more commonly affects the entire oral cavity. Once the incisors are unable to meet properly, it can cause inefficient mastication and uneven wear of the cheek teeth. Reduced lateral excursion during mastication can cause development of sharp enamel points, or spurs; the rabbit's natural anisognathism causes the mandibular cheek teeth to develop lingual spurs, whereas the maxillary teeth develop buccal spurs (Figure 5).
Spurs on the cheek teeth can seriously damage the mucosal tissue of the oral cavity resulting in pain and infection. The rabbit may have reluctance to swallow which can lead to evidence of salivation around the mouth, neck, and dewlap. This is usually accompanied by anorexia which can quickly lead to catastrophic gastrointestinal stasis.
Dental caries
Dental caries are points of decay and demineralization on a tooth caused by bacterial infection. The acid produced by pathogenic bacteria erodes the enamel and dentine causing destruction of tooth tissue and leads to holes in the surface of the tooth. This process can result in pain, root infection and tooth loss. It is an uncommon occurrence in rabbits due to the continual growth and replacement of tooth tissue, but high carbohydrate diets can factor into this process (Meredith, 2007).
Periodontal and endodontal disease
Serious dental disease like periapical infections, subsequent facial abscessation and osteomyelitis can occur for a number of reasons in the rabbit. Occlusal stress from misalignment can play a role by putting pressure on tooth roots and leading to tooth deformation thereby increasing susceptibility to periodontal disease (Fisher, 2012). Additionally, coronal elongation can lead to increased space between teeth, the relatively weak periodontal ligament can result in deeper periodontal pockets where pathogenic bacteria can invade (Meredith, 2007).
Other causes of periodontal disease include crowding of teeth, trauma, and trapped foreign bodies or ingesta. Submandibular, maxillofacial, or retrobulbar abscesses are common as the oral mucosa is damaged by sharp spurs on the teeth, or by misaligned incisors that have developed periapical infection. This set of conditions characterised by periodontal or endodontal disease accompanied by submandibular, maxillofacial, or retrobulbar abscesses is thought to be caused partly by elevated parathyroid hormone levels accompanied by vitamin D and calcium deficiency (Verstraete and Osofsky, 2005).
Clinical signs of dental disease in rabbits
Clinical signs in cases of mild dental disease may be minimal with the rabbit largely able to function normally and eat on a regular basis. As the severity of disease increases, the rabbit may have significant systemic illness and rapidly deteriorate (Box 1).
Rabbits presenting with anorexia or any of the moderate clinical signs should be considered urgent and provided with supportive care such as intravenous (IV) fluids, pain relief and assisted feeding until treatment can take place.
Clinical evaluation
Dental disease is not always apparent so basic dental examinations should be done routinely, whenever rabbits are seen in the veterinary clinic. The basic dental examination includes an external physical examination of the head and neck and an internal examination of the oral cavity using gentle restraint, and a speculum, as long as this is tolerated by the patient without causing too much stress. If further examination is warranted, or dental diseases is suspected, the rabbit can be assessed to determine if it is fit to undergo anaesthesia for further examination and treatment.
The external examination of the head and neck consists of several aspects:
Examination of the teeth can be challenging as the rabbit's mouth opening is small and it has fleshy tongue and cheeks. Inspecting the incisors involves pulling back the lips but examining the rest of the oral cavity requires a lighted speculum, good restraint, and frequently, mild sedation for the rabbit to prevent struggling.
Regardless of how healthy the incisors are, the rest of the oral cavity should also be examined to ensure good occlusion and overall health. Otoscopes and canine vaginal speculums can be used to visualize the molars but an oral endoscope is ideal. If an edoscope is not readily available, one of the best types of speculum is the Welch Allyn bivalve human nasal speculum which has a fiber optic light source and an adjustable bivalve speculum to aid in quick insertion into the mouth and easy cheek dilation (Figure 6 and 7).
Examination of the oral cavity consists of several aspects:
In the unconscious patient, gauze strips can be placed around the upper and lower incisors to aid in opening the mouth without compressing the cheek tissue or otherwise obscuring the view into the oral cavity. Oral wire speculums can also be used for longer term retraction of the jaws.
Thorough examination of the oral cavity often requires sedation or anaesthesia. Rabbits are obligate nose breathers so using a mask over the nose is one way to anaesthetise the rabbit using gas inhalant, however, with this method there is an increased risk of human exposure to anaesthetic vapors so care should be taken to reduce risks. Short acting injectable anaesththetics or intubation and gas anaesthetics can also be used although endotracheal tubes can make it even more difficult to work in the small oral cavity.
Dental radiography is very useful to determine the extent of dental disease especially in cases where there are signs of malocclusion. Typically views include lateral skull, V/D or D/V, left and right obliques, and a skyline view (Boehmer and Crossley, 2009). High resolution mammography film provides excellent contrast and should be used when possible to visualise the entire tooth from root to crown and to observe any signs of root elongation which can lead to abscesses (Verstraete and Osofsky, 2005). Normal non-screen size 4 dental (occlusal) films are another option for capturing an entire lateral rabbit skull and overall detail is good. In addition, non-screen size 1 dental films are small enough to be placed into the rabbit's oral cavity to image the incisor teeth using the bisecting angle techniques and again this provides good detail (Figure 8 and 9).
If abscesses are suspected, computed tomography is also very useful to visualise affected soft tissue and alveolar bone, and diagnostic bloodwork may also be indicated.
Treatment of dental disease
Treatment of dental disease varies with the condition. In severe cases, the patient will need to initially be stabilised prior to anaesthesia with supportive care including IV fluids, pain relief and adequate/assisted nutrition to support gut motility. If antibiotics are needed to control infection, culture and sensitivity are useful. It is important to be aware of the potential for suppression of normal enteric flora, so typically those antibiotics with selective Gram-positive spectrum are avoided, or used with care (Jenkins, 2004; Pollock, 2006).
For mild cases of malocclusion, treatment almost always involves occlusal adjustment. Trimming of the sharp edges or overgrown teeth will be needed and frequently the process needs to be repeated every few weeks to months to ensure efficient mastication is preserved. Every effort should be made to restore normal morphology of the teeth so that they are able to function as normally as possible between trimmings (Aiken, 2004).
Many rabbits are able to have the incisors trimmed without sedation but sedation is required to safely trim the cheek teeth without risking lacerations to the rabbit's oral tissues from the dental instruments. The process of trimming the incisors usually involves a long bur high speed dental drill. Another alternative is the use of acrylic burs in slow speed hand pieces as they do not cause trauma to soft oral tissues as high speed long burs can. It is important that the teeth are not trimmed using nail clippers, bone nippers or similar as these cause unnecessary force on the crown leading to a much higher risk of longitudinal splitting of the incisors, and subsequent root abscessation (Fisher, 2012).
In severe cases of incisor malocclusion, trimming often needs to be done every few weeks and this can be stressful for the rabbit so the veterinarian may elect that the teeth be extracted. This is a challenging procedure and care must be taken to destroy the germinal cells in the socket so that incisor re-growth does not occur. Most rabbits do well with extracted incisors as long as their food is cut into lengths that they can take into their mouth and chew with the cheek teeth so that these teeth do not develop overgrowth and malocclusion as well.
Root abscesses can be invasive extending into the soft tissue and salivary ducts. Treatment can be challenging and complete surgical excision cannot be assured in most cases so reoccurrence is common. Tooth extraction, surgical debridement and marsupialisation of the abscess are frequently the best solution in these cases although subsequent surgical follow up is often required to combat spread of the infection (Capello, 2004). Either way, radiographs must be taken before surgery to assess the extent of tooth root involvement and evaluate for osteomyelitis of the mandible or maxilla.
Nursing care
Many cases of dental disease is rabbits goes undetected at home and it is these cases that often present in critical condition once the owner determines there is a problem and brings them into the clinic. The worst case scenario is that the rabbit has stopped eating and producing faeces or is depressed, bloated and recum-bent. The first thing to consider when presented with these cases is to observe for evidence of gastrointestinal stasis and pain. Pain relief, fluids and assisted feeding may be required and only once the patient is stable should anaesthesia be attempted to treat any underlying dental disease.
Recovery after anaesthesia also should focus on controlling pain and maintaining gut motility. If a feeding tube has been placed, an assisted feeding plan should be developed using a high fibre herbivore recovery food to promote proliferation of normal gut microflora and assist in rapid recovery. The rabbit should be encouraged to eat on its own as soon as possible to begin wearing down the teeth. It can take several days after treatment of malocclusion for chewing efficiency to be back to normal so clients should be advised to keep a close eye on the rabbit to ensure adequate faecal output and observation of normal chewing behaviours. If coarse low-nutrient grasses are not initially tolerated, a very-high fibre pellet can be used such as Supreme Fibafirst with 30% coarse fibre. This will assist the rabbit in developing good habits of extended chewing and help to keep the teeth worn until it is happily eating coarse vegetation again (Hamlin, 2012).
Conclusion
Dental disease is a very serious condition for the rabbit. Continuously growing teeth require constant wear to maintain masticatory efficiency, and lack of attrition from insufficient abrasion can cause rapid disruption of dental occlusion leading to devastating health consequences including infection, anorexia, gastrointestinal stasis and even death. Early detection of dental disease is key to effective treatment. All pet rabbits should be checked routinely for dental abnormalities that could lead to dental disease even in cases where dental disease is not suspected.
When dental disease is detected, any alterations in function should be treated immediately and followed up with close observation to ensure that the rabbit's digestive process has not been compromised as a result of insufficient fibre.
Even for otherwise healthy rabbits, educating clients in detecting signs of gastrointestinal stasis and early dental disease are vitally important and they should be encouraged to bring the rabbit in for regular dental examinations. Preventative dental care should always include dietary advice with coarse low-nutrient hay being the cornerstone of a good nutritional plan to promote adequate dental wear and dental health.