Cheek Teeth Malocclusion – Rabbit

Description

The pressure of opposing cheek teeth leads to stoppage of growth and alteration in the pulp cavity, germinal tissues accentuates the hitherto normal angulation of the teeth. The rabbit’s cheek teeth are normally tilted: uppers, laterally towards the cheeks; lowers, medially towards the tongue. This is accentuated once the growth (germinal) tissues are affected. This also means that growth may stop – a very unnatural state of affairs for the species. Sometimes these abnormal growing patterns result in the formation of discrete spurs with extremely sharp edges.

The spurs can also lead to loosening of the teeth – lever effect.

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.

Periodontal resorption leads to a loss of the tooth crowns.

Clinical Signs

1. Reduced number of droppings.
2. Epiphora from the migration of the roots of the molar teeth into the orbit of the eye.
3. Weight loss
4. Decreased food intake
5. Lethargy
6. Difficulty chewing
7. Ptyalism
8. Swelling around the head and neck, mandibular abscesses, maxillary abscesses
9. Ophthalmic conditions, lacrimal or nasal discharges
10. "Clagged vent" – ingestion of caecotrophs is painful when teeth cut the inside of the buccal cavity
11. Retrobulbar abscesses

Treatment

1. Restore normal malocclusion:
2. The aim is to preserve the tooth and to prevent overgrowth of the opposite one.
3. Address the underlying cause of the malocclusion.
4. Monthly or six-weekly prophylactic dentals.
5. Always warn the owner that there is a tendency for the condition to recur.
6. Over grown molars can be burred back to restore occlusion, at least temporarily

Procedure

• Keep the mouth open with a gag.
• Dilate the pouches.
• Hold the lip or tongue out of the way with a spatula. This protects the soft tissue.
• Burr back the excess tooth (or spur) with a medium speed burr (18,000 RPM).
• It should taken 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 (Veterinary Instrumentation http://www.vetinst.com)
• 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).
• Be extremely careful of the palatine vein. It will bleed badly if you hit it with the burr and may be very difficult to stop. From experience, I recommend to use the simple measure of pressing on the vein immediately with a dry cotton bud for five minutes, and not to try diathermy, radiosurgery or other means of coagulation.

Extraction of cheek teeth

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.

The main indication is facial abscess due to dental disease.

Procedure

• 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:
  • Used when there is no gross apical ankylosis
  • The procedure is essentially the same as that for incisor extraction (see above) except that a forceps is 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 tooth into the oral cavity
• remove via the surgical access.
• You may have to use luxators 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 (Life®; Kerr) 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 (procaine penicillin IM or SC q7days or oxytetracycline (SC q 72hrs). Often bone infections in the rabbit necessitate the use of antibiotics parenterally for life.

One must then address the matter of diet and impress on the owner that hard chewable food must be provided. A bolus of hard food held between diverging maloccluded teeth will not provide as much wear as normal, but it provides at least some wear and should be encouraged.

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.

References

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