Cheek Teeth Malocclusion – Rabbit

Introduction

Alterations in the position, shape and structure of the molars leads to malocclusion of the cheek teeth. Deterioration of tooth and bone quality can also contribute to the development of malocclusion.

The pressure of opposing cheek teeth leads to stoppage of growth and alteration in the pulp cavity and germinal tissues accentuates the hitherto normal angulation of the teeth. In normal rabbits, the cheek teeth are tilted: uppers, laterally towards the cheeks; lowers, medially towards the tongue. This is accentuated once the germinal tissues are affected. Initially the teeth tend to curl then become progressively distored. Sometimes these abnormal growing patterns result in the formation of discrete spurs with extremely sharp edges. This can lead to loosening of the teeth, thus increasing the risk of foreign material entering the socket.

Continuous growth and pressure against the crowns of the teeth in the opposing jaw stops the jaw closing and strains the masseter and temporalis muscles – a vicious cycle leading to atrophy of disuse of the jaw and a further reduction of bone density.

Malocclusion of the cheek teeth can lead to incisor overgrowth, and the observation of long protruding incisors might be the first sign of a cheek teeth problem the owner will notice.

Clinical Signs

Clinical signs relate to the pain experienced and the inability of the rabbits to eat normally:

Lack of grooming leads to a poor coat, build-up of skin debris and Cheyletiella mite infestations.

Digestive disorders are often seen: ileus, reduced number of droppings, intestinal obstruction from the ingestion of fur mats.

Uneaten caecotrophs due to a difficulty in reaching and ingesting the droppings. This leads to soiling of the perineal skin and can become a fly strike if severe enough.

Epiphora and dacryocystitis due to impingement on the nasolacrimal duct by the elongated roots and the upper incisors, often with secondary bacterial infection.

Abscesses seen as hard lumps along the ventral border of the mandible, or retrobulbar abscesses.

Incisor malocclusion and overgrowth due to the lack of correct chewing motion due to cheek teeth malocclusion.

Pain and anorexia due to the spurs on the cheek teeth. There is often profuse salivation and staining of the fur under the chin and on the forelegs.

Trimming Cheek Teeth

Corrective dentistry cannot restore normal occlusion to maloccluded cheek teeth because of the altered position, shape and structure of the teeth. Changes in the direction of growth mean that malocclusion recurs and the spurs regrown, often in a matter of weeks. However acquired, dental disease is progressive and eventually the germinal layer of the roots is destroyed and the teeth stop growing so trimming is no longer required.

The number of times that the teeth require trimming is variable, but is usually every 6 weeks initially.

Procedure

General anaesthesia is required and a mouth gag and cheek dilators are extremely useful. Hold the lip or tongue out of the way with a spatula. This protects the soft tissues. Dental burrs are the preferred instrument for removing spurs and reshaping cheek teeth, although molar clippers can be used if they are the only tool available.

Burring should not take more than a minute but, if it does, stop to cool the tooth frequently with a cotton bud soaked in cold water.

Helpful Hints

The nurse should hold the head (by the gag) and pull it forward extending the atlanto-axial joint or use a table-top gag. Rest your forearms on a sand bag, it makes your aim better! Keep the tongue pulled forward to prevent cyanosis.

Usual post-operative and post-anaesthetic procedures (fluids, analgesics, prokinetics) are useful.

Be extremely careful of the palatine vein. It will bleed badly if hit with the burr and may be very difficult to stop. If bleeding occurs, simple measure of pressing on the vein immediately with a dry cotton bud for five minutes may be more useful then trying diathermy, radiosurgery or other means of coagulation.

Extraction of cheek teeth

This is often requested by owners to prevent regrowth of spurs that require regular trimming. However the extraction of cheek teeth is inadvisable and often unnecessary, unless periapical abscesses due to the dental disease are present.

Extraction of cheek teeth follows the same principles as incisor extraction – special sharp elevators or bent hypodermic needles are used to cut the periodontal ligaments around these box-shaped structures.

It is not necessary to remove the opposing cheek tooth as an upper tooth occludes with two lower teeth and vice versa. Also, adjacent teeth tend to tip towards any gap that is left.

Procedure

Start with pre-operative radiography to assess root morphology. Follow-up must be maintained as the opposing teeth will need occasional occlusal adjustment to prevent overgrowth and interlocking into the space left after extraction.

Intra-oral approach:
This technique is used when there is no gross apical ankylosis. The procedure is essentially the same as that for incisor extraction except that forceps are used for the final extraction after the tooth has been fully mobilised in its “socket”.

Luxators are used to loosen the periodontal membrane especially on the mesial (palatal/lingual) and lateral (buccal) aspects of the tooth. Careful elevation with horizontal sectioning and removal of successive portions is generally effective when the root is too long to remove in one piece.

Extra-oral approach :
Buccotomy is advocated to approach maxillary teeth in some texts but is traumatic - avoid if possible.

Osteotomy is preferred via the ventral mandible or through the maxillary bone. Use a slow speed bur to cut away any bone (much may have been lost due to the original disease processes). “Transabscess” approach may be required but if so, flush copiously with povidone iodine solution. Elevate or repulse the tooth into the oral cavity and remove via the surgical access. Luxators may have to be used to sever the remains of the periodontal ligaments.

Postoperative care

Hillyer (1994) points out that after extraction the socket of a tooth should be cultured and appropriate antibiosis carried out.

Packing the socket with calcium hydroxide fills the dead space and has antiseptic properties – do not use calcium hydroxide powder or a paste made from the powder, the polymerised product is superior and doesn’t seem to cause thermal necrosis.

Suturing or gluing an empty socket is advised if several teeth have been extracted (prevents impaction with foodstuffs) but is not possible if only one tooth has been removed.

The animal is given prophylactic antibiotics: for rabbits, penicillin or oxytetracycline. Often bone infections in the rabbit necessitate the use of antibiotics parenterally for life.

Following extraction of one or more cheek teeth a careful watch must be maintained on the remaining (opposing) teeth in case coronal reduction is required. As rabbits have unequal numbers of teeth in upper and lower arcades there is no likelihood of the crown of a tooth growing into an opposing socket but coronal reduction may be required to allow proper masticatory excursion.

Prevention

Ensure breeding stock and growing rabbits have sufficient calcium and vitamin D, avoiding mixed cereal rations which enable selective feeding.

Provide ad lib fibrous food consisting of good quality grass and hay to encourage dental wear.

Feed a variety of weeds and wild plants which are balanced sources of calcium and good sources of indigestible fibre.

Feed fibrous vegetables such as broccoli, cabbage and spinach leaves.

Allow exercise outside each day which provides the opportunity to graze and prevents vitamin D deficiency.

Avoid muesli type mixes.

References

Hillyer, E. V. (1994) Pet Rabbits. Veterinary Clinics of North America: Small Animal Practice. 24 (1) 25-65

Harcourt-Brown, F. (2002) Textbook of Rabbit Medicine, Elsevier Health Sciences