Introduction

Rabbits are the third most popular companion animals, after dogs and cats, and dental disease remains a common and frustrating presentation of captive lagomorphs.^1-4 The dental formula of the rabbit is I²/₁ C⁰/₀ PM ³/₂ M ³/₃

There are potentially six classes of malocclusion based upon etiology:

1.  Dietary-induced. Insufficient dental wear due to lack of fibrous grass hays in the diet has been strongly implicated as predisposing factors for dental overgrowth and malocclusion. Calcium and vitamin D₃ issues have also been suggested from the UK.

2.  Congenital malocclusion is also a very commonly cited cause of dental anomalies seen within the brachycephalic breeds, particularly the dwarf and lop-eared rabbits. The malocclusion becomes apparent within 6–12 months of age and is permanent.

3.  Tooth root infection (and osteomyelitis) is a common cause of malocclusion, which can occur at any age. In rabbits over a year of age, malocclusion due to infection must be considered the primary differential, although it can sometimes be difficult to determine whether infection caused the malocclusion, or vice versa. Physical evidence such as the presence of purulent material emanating from the gingival margin, and tooth discoloration should alert the clinician to the possibility of incisor root infection. Tooth root infection due to Pasteurella, Bacteroides, Fusobacterium and Staphylococcus are most common, and there may be involvement of both incisors and (pre)molars. Affected rabbits obviously experience tooth pain and become anorectic and debilitated. Where only the incisors are affected, the treatment of choice is complete incisor removal with appropriate antibiotic therapy for 4–6 weeks. In some cases radical debridement may be necessary where osteomyelitis is present. The prognosis must be considered poor to guarded depending upon the extensive nature of the infection.

4.  Dental trauma, as a cause of malocclusion, is primarily seen as a result of inappropriate clipping of the incisors. During the clipping procedure, the incisor(s) may fracture longitudinally down into the root causing the tooth to re-grow out of alignment. Dental trauma is also seen in solitary rabbits kept in hutches with large-gauge wire screens. These bored animals develop a habit of pulling on the wire screens of their hutch with their teeth, which over several months can result in a permanent incisor malocclusion. Husbandry improvements and incisor removal represent the best long-term solution for these animals.

5.  Head trauma is an uncommon cause of dental malocclusion, which is seen in cases involving interspecific aggression and falling injuries. Radiographic examination of the skull is often necessary to determine the extent of the damage to the teeth, mandible and maxilla. In general, fractures of the mandible or maxilla tend to cause most of the posttraumatic malocclusions, as individually damaged teeth can be removed. The main difficulty when dealing with traumatized rabbits is medical stabilization prior to anesthesia and surgery. Warm, stress-free surroundings are essential and nutritional/fluid support should be considered. Analgesia is of prime importance and the use of an opioid or nonsteroidal antiinflammatory drug should not be overlooked. Steroids are best avoided, but may be employed as part of the therapeutic regime for acute shock.

6.  Primary premolar and molar malocclusion is not an uncommon condition and may be either congenital or acquired due to trauma, (pre)molar root infection and inflammation. In cases of incisor malocclusion, (pre)molar involvement must be ruled out because, although incisor removal may be beneficial, it will certainly not be curative. In cases of (pre)molar malocclusion, repeat dental surgery will be required. It is therefore essential that all the teeth are thoroughly examined, both visually and radiographically, before dentistry is undertaken.

Diagnosis

History & Physical Exam

An accurate diagnosis is essential in order to provide the most appropriate treatment and accurate prognosis. A detailed history may indicate reduced food intake, ptyalism, selection of concentrates and cereals over fibrous hay, dropping food from the mouth, and weight loss. Every rabbit owner should be encouraged to keep an accurate log of their rabbit's weight, as 5% weight loss will often occur before the rabbit shows obvious clinical signs. The physical examination should be thorough. Palpation of the skull, particularly the maxilla and mandible, may indicate swellings or asymmetries associated with tooth elongation, periapical penetration and swelling of the jaw. Apical penetration often, but not always, leads to facial abscessation. General gastrointestinal complaints, including intermittent anorexia, abnormal palpation and auscultation of the intestinal tract, diarrhea, constipation, poor fecal production, ileus, etc., may all have their origins in the mouth. Poorly masticated and prepared food can cause problems for the intestinal processing and digestion of food.

For examination of the incisors, the rabbit can be restrained in a towel and the lips retracted to permit examination. The conscious examination of the premolars and molars is not as simple. Many feel that such an examination using an otoscope or similar device is helpful. However, such examination is often uncomfortable and stressful for a rabbit. When dealing with any rabbit showing any of the historical or physical signs of dental disease, conscious examination may or may not indicate a problem. It is impossible to examine all dental surfaces in the conscious rabbit. Therefore, no matter what the results of the physical examination, a complete examination under general anesthesia is warranted (and so the benefits of conscious examination become less obvious).

Dacryocystitis (due to elongation of upper premolar 2 impinging on the nasolacrimal duct) and facial abscesses (due to infected tooth root) are indicators of dental disease, and even if the rabbit is showing no other signs, a dental investigation constitutes an essential part of the case work-up.

Radiography

There can be little doubt that an accurate radiographic interpretation is probably the key to successful diagnosis, maximizing treatment success, and providing an accurate prognosis. Survey skull radiographs include left and right laterals, left and right open-mouth oblique views, and dorsoventral views. High-quality digital or slow speed, fine-detail film-cassette combinations are required (e.g., mammography).

Good quality radiographs can be used to stage the degree of dental disease:¹

Grade 1 - normal rabbit. The mandible has a smooth ventral border, tooth roots are of optimal length, normal skull and tooth structure and radiographic density, interdigitation (zigzag) of the occlusal surfaces of the premolars and molars, parallel smooth linear pattern of the premolar and molar teeth. Normal incisor occlusion.

Grade 2 - subclinical disease. Thinning of the bone along the ventral border of the mandible, root elongation and early root divergence from the usual parallel array, hard bony swellings at the site of periosteal reaction become palpable along the mandible, incisor malocclusion variable, infection unlikely. Prognosis good.

Grade 3 - weight loss, mild clinical signs. Further thinning of the bone along the ventral border of the mandible, continued root elongation causing increase in diastema diameter, further deviation of the teeth from the normal parallel array, hard bony swellings at the site of periosteal reaction easily palpable along the mandible, further deterioration of the normal occlusal zigzag pattern, variable incisor malocclusion, infection more likely. Prognosis guarded.

Grade 4 - weight loss, restricted food intake, obvious clinical signs. Further thinning and perforation of the bone along the ventral border of the mandible, pronounced deviation of the teeth from the normal parallel array, obvious bony swellings at the site of periosteal penetration, complete lack of occlusal zigzag pattern, cessation of root growth, broken crowns, dysplastic appearance of the teeth and loss of linear pattern, blurred dental outlines due to loss of enamel, variable incisor malocclusion, infection and abscessation likely. Prognosis poor.

Grade 5 - Pronounced weight loss, poor ingestion, ptyalism, severe clinical signs. Gross changes to the mandible and/or maxilla associated with osteomyelitis and facial abscessation, pronounced deviation of the teeth from the normal parallel array, complete lack of occlusal zigzag pattern, cessation of root growth, broken crowns and lost teeth, remaining teeth are obviously dysplastic with loss of linear structure and blurred outlines due to enamel loss, variable incisor malocclusion. Prognosis poor to grave.

Treatment

The decision to proceed with treatment should follow accurate diagnosis and discussion with the owner regarding prognosis. Most rabbits present with a history of anorexia and weight loss and require medical stabilization prior to prolonged anesthesia and surgery. When the patient's health status is questionable, it is often wise to temporarily improve the subject's condition by incisor burring and permitting a temporary return to normal feeding before incisor removal is attempted. Alternatively, anorexic rabbits can be fed Herbivore Critical Care Formula (Oxbow Pet Products) for a few days before surgery. A preoperative complete blood count, biochemistry panel, and urinalysis are also recommended prior to prolonged anesthesia and surgery.

Incisor Dentistry

Historically, incisor malocclusion has often been treated by clipping of the incisors with nail clippers. Clipping incisors is at the very least uncomfortable and probably a painful, stressful procedure for the rabbit. Moreover, the effects of clipping are invariably short-lived with the clipping procedure repeated at 3–6 weekly intervals, depending upon the degree of malocclusion and rate of tooth growth. In addition, there is a real danger of the incisors splitting, which often worsens the malocclusion and may lead to subsequent tooth root infection. A more effective approach is to use a dental burr or cutting disc to cut the teeth and shape the bite, and this can often be accomplished in the conscious patient, although sedation/anesthesia is often preferred. The rabbit is restrained in dorsal recumbency and a protective guard (e.g., plastic sheath of a hypodermic needle) is held behind the incisors and in front of the lips and tongue. The incisors are then cut back using a circular saw burr and shaped to permit a normal (or as normal as possible) bite. This method typically requires less frequent visits to the veterinary surgery, but again the effects are temporary with dental surgery required every 4–8 weeks.

The only permanent cure for chronic incisor malocclusion is surgical removal of all 6 incisors under general anesthesia. Rabbits with primary incisor disease tolerate this procedure well, which often results in significant improvement in both appetite and demeanor within a few days of surgery. It is important for both clinician and owner to appreciate preexisting premolar/molar disease, as incisor removal will not correct these problems and abnormal cheek teeth are likely to need repeated attention. Appropriate anesthesia is essential and in small rabbits naso-intubation may provide more room than an endotracheal tube. A small dental elevator (or bent 18–20-gauge hypodermic needle) is used to break down the periodontal ligaments around the lower incisors. The elevator is inserted down the medial surface of the incisor and gently rotated. This process of elevator advancement and rotation is continued, bearing in mind the orientation and position of the tooth root until the tough medial ligament is broken down along the entire length of the tooth. Once the medial ligament is completely broken, the tooth will become obviously loose. The weaker lateral ligament is then broken down in a similar manner and the soft tissues are separated from the tooth as deeply as possible. The incisor is then grasped using tooth extractors (or hemostats) and pulled in the direction of the natural curve of the tooth. The tooth root should be examined to ensure that the entire root has been removed (a completely removed incisor has a soft root) and that no infection is present. If there is any suspicion of tooth root infection, a root swab should be taken for culture and sensitivity. The curvature of the main upper incisors is much more pronounced than that of the lowers incisors, so it is important to extract the upper incisors with a more pronounced curve. The small secondary upper incisors (peg teeth) must also be removed. If an incisor breaks, it may be necessary to wait 6–8 weeks for regrowth before a second attempt can be made. There is usually little bleeding during the procedure. The tooth roots can be flushed with an oral antiseptic solution and, if possible, the gingival margins are sutured closed. Antibiotics are not usually required unless clinical concern warrants their use. If tooth root infection is suspected during surgery, antibiotic therapy (subsequently based upon culture and sensitivity) should be continued for 4–6 weeks. The rabbit should be placed in a warm environment until fully recovered, typically within 1–3 hours. Continued fluid therapy and nutritional support may be required. The use of post-operative analgesics, such as meloxicam, should be considered routine.

Premolar and Molar Dentistry

The anesthetized rabbit is positioned in sternal recumbency using a rabbit/rodent dentistry support device (www.SontecInstruments.com). Cheek pouches are held apart using pouch dilators. The surgeon, using a blunt metal probe to move the tongue and cheeks, can now examine all the teeth for spurs, overgrowth and looseness. Some means of focal illumination and magnification is recommended - either optical loupes, a table-mounted operating microscope or a rigid endoscope will provide much greater detail than the unaided eye. Using the metal probe to protect the soft tissues, a high-speed dental burr can be used to cut, size and reshape the premolars and molars, often down to the level of the gingival margins for the maxillary teeth. Loose teeth should be gently removed using forceps. Diseased, but firmly attached maxillary teeth will often require an extra-oral facial approach to aid removal, while mandibular teeth can be approached through the ventral mandible.

Cheek tooth infection and mandibular abscessation are not uncommon. To date the author's preferred method of treatment is radical surgical excision (including tooth removal) and marsupialization. Initially, with the rabbit orally intubated, an extra-oral approach is used to dissect the facial abscess free and identify and remove as much of the diseased tooth (or teeth) and bone as possible. The abscess cavity should be marsupialized to the skin. Systemic antibiotics may need to be continued for 6 weeks. The removal of one tooth does not require the removal of the opposite tooth, and rabbits can perform well following the removal of one or two teeth. However, as the number of cheek teeth removed increases, so do the chances of complications.

Postoperative Care

Rabbits will often start eating within a couple of hours of surgery. There are no special dietary considerations and all rabbits can be offered their usual pellets and ad lib hay. However, shredded, chopped or grated soft foods are often preferred for the first few days following surgery and should be offered in abundance. Rabbits that have had all their incisors removed cannot gnaw and so root vegetables will always need to be shredded; however, they can easily prehend hay and foliage using their lips. It is normal for the rabbit to quickly regain appetite. Owners typically report a major improvement in their rabbit's appetite, general activity and demeanor following successful surgery.

Incomplete tooth removal will usually result in tooth regrowth within 6–10 weeks of surgery. Repeat skull radiographs 6–8 weeks after surgery can be taken to confirm a lack of tooth regrowth. There will often be increased radiodensity in the region of the extracted teeth on radiographs taken 6–8 weeks after surgery. This is a surgically induced periosteal reaction within the tooth socket, which may be misinterpreted as tooth regrowth. Repeat radiographs taken 3–4 months after surgery will indicate a resolution of this reaction, and can again be used to confirm the absence of tooth regrowth.

References

1.  Capello V, Gracis M, Lennox AM. Rabbit and Rodent Dentistry Handbook. ed. Lake Worth, FL: Zoological Education Network; 2005.

2.  Capello V, Lennox AM. Small mammal dentistry. In: Quesenberry KE, Carpenter JW, eds. Ferrets, Rabbits and Rodents: Clinical Medicine and Surgery. 3rd ed. St. Louis, MO: Elsevier; 2012:452–471.

3.  Harcourt-Brown F. Diagnosis, treatment and prognosis of dental disease in pet rabbits. In Practice. 1997;19:407–421.

4.  Harcourt-Brown F. Textbook of Rabbit Medicine. ed. Oxford: Butterworth Heinemann; 2002.