Download Causes and Clinical Manifestations of Dental Disease in Pets

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In: 50° Congresso Nazionale Multisala SCIVAC, 2005 – Rimini, Italia
CAUSES AND CLINICAL MANIFESTATIONS OF DENTAL DISEASE IN PET RABBITS
Frances Harcourt-Brown BVSc MRCVS
Harrogate, UK
Rabbits teeth erupt and grow continually through life. The incisor teeth are used for cutting through vegetation,
gnawing and biting. Canine teeth are absent. The premolars and molars form a row of cheek teeth that grind food.
Deep grooves in the cheek teeth fit into corresponding grooves in the alveolar wall. A vertical longitudinal fold of
enamel runs down the centre of each cheek tooth. At the occlusal surface, the soft cementum and dentine wear
away before this enamel fold so that it forms a sharp ridge across the centre of each tooth that interlocks with the
interdental space between the two opposing teeth. This gives a characteristic zigzag pattern on lateral skull
radiographs. Tooth shape is maintained by wear against opposing teeth during periodic jaw movements that grind
the teeth into shape. An abrasive diet helps to maintain tooth shape. Rabbit's teeth grow rapidly. The incisors
grow at a rate of 2-2.4mm per week. The speed at which crowns grow is determined by the rate of eruption and
the rate of attrition. Taking teeth out of occlusion hastens their rate of eruption.
Progressive syndrome of acquired dental disease (PSADD)
In UK, most cases of dental disease in pet rabbits follow a progressive pattern of changes to the structure,
position and shape of the teeth. This progressive syndrome of acquired dental disease (PSADD) can be staged.
At the outset, the occlusion, shape and structure of the teeth is normal. The first change to take place is loss of
supporting alveolar bone and root elongation, followed by malocclusion caused by changes in the shape,
structure and position of the teeth. Increased curvature of the cheek teeth leads to the development of sharp
spurs that can penetrate or lacerate surrounding soft tissues. Lingually directed spurs on the lower third or fourth
cheek teeth are the most common although laterally directed spurs on the upper first and second cheek teeth also
occur. As PSADD progresses, the shape of the teeth becomes increasingly abnormal with crowns curling or
growing in any direction. Laterally or horizontally directed spurs can occur on the lower cheek teeth, which are
difficult to see through an auriscope in a conscious rabbit. Cessation of tooth growth is the next stage. The crowns
of the diseased teeth may break off altogether, usually just below the gingival margin. There may be an
improvement in the rabbit's condition at this stage. The gums heal over the site where the crowns should be. This
is most frequently found on the lower arcade of cheek teeth and can occur in rabbits that have never received any
dental treatment. PSADD culminates in crown loss and root resorption or calcification.
Changes in dent al structure are seen as part of PSADD. A common clinical finding in pet rabbits is horizontal
ridges on the upper incisors giving the teeth a ribbed appearance. These ridges may be found on incisors of
normal shape and length. In the later stages, diseased incisors may be beige or slightly brown. Areas of eroded
enamel are sometimes seen at the gingival margin. There may be areas of periodontal inflammation.
Clinical manifestations of dental problems
An early sign of dental problems may be a change in the rabbit's eating habits. Root elongation is an early feature
of PSADD and elongated roots press on the nerve supply causing discomfort when eating hard foods. Affected
rabbits may stop eating hay or leave favourite vegetables uneaten. As PSADD progresses, sharp spurs, absent
crowns or abnormal occlusion can impair prehension and mastication of food. These rabbits may drop food or
take a long time to eat. They lose weight.
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Palpable, hard bony swellings along the ventral border of the mandible indicate elongated roots of the lower
cheek teeth. Elongation of the roots of the upper first incisors can block the nasolacrimal duct and cause
epiphora. Inflammation of the lacrimal sac (dacryocystitis) can follow blockage of the nasolacrimal duct. This is
manifested by conjunctivitis and a purulent ocular discharge.
Spurs on the teeth can lacerate the tongue or oral mucosa. Ulcers can form on mucosal flaps that catch on the
teeth. Soft tissue injury within the mouth stimulates salivation and makes swallowing painful. Affected rabbits may
drool saliva continuously. Occasionally, the drooling is so severe that dehydration and electrolyte imbalances
occur. Soft tissue damage within the mouth is acutely painful. Pain slows gut motility, which, if left untreated, can
eventually result in hepatic lipidosis and death.
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Dental disease can interfere with caecotroph ingestion. To the owner, uningested caecotrophs have the
appearance of diarrhoea. They are soft and pasty with a characteristic strong odour and may stick to the fur under
the tail. Dental problems interfere with grooming, either by impairing the rabbit's ability to grasp dead hair between
the incisors or by making the tongue sore so the rabbit is reluctant to lick its skin and fur. Large numbers of
parasites such as Leporacus gibbus or Cheyletiella parasitovorax can build ip. Impaired grooming and uneaten
caecotrophs also increases the risk of flystrike.
Facial abscesses are commonly associated with dental abnormalities. They are found at sites where the
elongated roots have penetrated the bone.
Cause s of PSADD
The cause of PSADD is controversial. For her FRCVS thesis, the author conducted a comparative study of 175
prepared rabbit skulls and radiographs of 315 rabbits that demonstrate the progression of the changes that take
place in PSADD. Prepared skulls from pet rabbits affected by this syndrome are osteopaenic, suggesting
underlying metabolic bone disease. This is logical as animals, such as rabbits, with continually erupting teeth,
have a high demand for calcium for the continual formation of dentine and enamel. Investigation of the diet and
feeding habits of pet rabbits showed that selection of cereals and legumes from mixed rations can result in a
calcium deficient diet. Further studies showed that pet rabbits may have undetectable vitamin D levels and rabbits
with advanced dental disease have lower blood calcium and higher PTH concentrations than rabbits with healthy
teeth that are kept outside in conditions similar to wild rabbits.
Other proposed causes of acquired dental disease include temporomandibular joint disease, inflammation of the
molar roots and aging. Lack of abrasive food and abnormal chewing patterns is often cited as a cause of
malocclusion.
Causes of other dental problems
Genetic predisposition can cause mandibular prognathism and incisor malocclusion. This hereditary condition is
more common in Dwarf breeds. In mild cases, the incisor teeth occlude edge to edge rather that the normal
occlusal position of the incisors with the cutting edges of the lower incisor teeth resting against the peg teeth just
caudal to the upper first incisors. If the disparity between the upper and lower jaw length is great, the incisors
never occlude and become very long. Some authors cite genetic predisposition and skull shape as a cause of
acquired cheek teeth malocclusion but a study by the author of 1254 case records showed no significant
relationship between breed and treatment for dental disease.
Traumatic injury to the jaws and teeth can result in abnormal dentition. Fractured jaws or broken teeth can be the
result of a fall on to a hard surface. Some rabbits break their incisors by pulling on cage bars. Foreign bodies,
such as blades of hay, splinters or seeds in the oral cavity can become wedged between the teeth and set up a
chronic periodontal infection this displaces teeth or sets up periodontal infection. Neoplasms of the teeth, jaw or
surrounding soft tissue can result in dental problems, either directly or indirectly by pushing some teeth out of
position and causing malocclusion. Examples include fibrosarcomas, osteosarcomas and odontomas.
References
Crossley, D.A. (2003). Oral biology and disorders of lagomorphs. The Veterinary Clinics of North America. Exotic
Animal Practice. Ed. D.A. Crossley. Saunders, Philadelphia, pp.629-660
Harcourt -Brown, F.M. (2001). Textbook of Rabbit Medicine. Butterworth Heinemann, Oxford.
Harcourt -Brown, F.M. (2005). Metabolic bone disease as a cause of dental disease in pet rabbits. FRCVS Thesis
(in press).