Incisor Overgrowth – Rabbit

Introduction

Elodont teeth grow continually - rabbit incisors are reported to grow 12.5 cm per year so you can be prepared to saw off one centimetre a month! Genetic predisposition can occur, including anaesognathism (excessive narrowing of the already narrow mandible) and brachygnathism in rabbits. Dental disorders arise as a result of accentuation of the normal configuration - if the mandible is too narrow, molar malocclusion results; if too short, incisor malocclusion results; if both, all teeth are affected.

Brown (1992) states that there are five causes of incisor malocclusion in rabbits :

• congenital,
• infection of the roots of the incisor teeth,
• trauma to the teeth (caused by the use of nail clippers to trim the teeth, or by the rabbit pulling on the wire of the hutch),
• trauma to the head, and
• primary malocclusion of the molars.

Treatment

1. Saw the excess tooth away.
2. Extract the incisors, especially if molars are normal.

Extraction of incisors

Indications for incisor extraction:

• Intractable incisor pathology.
• Brachygnathism/Prognathism
• There must be no cheek tooth changes. Sometimes it is possible to get away with extraction of the incisors in the presence of cheek tooth abnormalities, but you and the client must be prepared for further attention (including coronal reduction) of the cheek teeth on several future occasions.

Procedure

1. Radiograph the teeth to assess the extent of dental tissue to be removed and to assess if infection is present at the apex.
2. Start with the lower jaw.
3. Gently cut the subgingival attachment with a #15c scalpel blade.
4. Gently cut the periodontal membrane with a 20G hypodermic needle bent to suit the socket (hence the previous radiograph), holding the socket as steady as you can. You’ll use several needles!) Arnolds and Veterinary Instrumentation market a special ligament cutter called the Crossley elevator for this, but it doesn’t suit the curvature of every tooth.
5. Keep cutting the ligament until the tooth is visibly and palpably loose. Concentrate on the inside curvature, the lateral and mesial surfaces of the teeth, as these are where the periodontal ligament is strongest. This takes quite a long time and is most difficult on the lingual/caudal aspect of the tooth. I usually work from tooth to tooth and back again, ie. I do not wait for the first tooth to be completely loosened before starting to cut the periodontal membrane of the second.
6. TAKE YOUR TIME! Do not attempt to extract the tooth until it is loose enough or you will break the root and there will be problems with infections or regrowth afterwards.
7. Remove the tooth carefully in the curved direction indicated on the radiograph, or follow your observation of the layout of the socket on clinical examination. Use your fingers – not a forceps. Do NOT twist the tooth in its socket as you would with a dog's or cat's incisors. You must not risk breaking the tooth.
8. If you do break the tooth, consider culture and antibiotic sensitivity of the socket. And prepare the client for the fact that the tooth may grow back and the whole procedure will have to be repeated especially as the “new” tooth probably won’t grow in a direction compatible with a comfortable mouth!
9. Repeat the procedure with the four maxillary incisors. In spite of their insignificant size, take the same care with the peg tooth as you did with the major incisors.
10. To prevent regrowth, push the extracted incisor back into its socket and traumatise the deep germinal tissue for about ten seconds. This includes the peg teeth.
11. In the event of infection, if you are sure you have removed all the tooth tissue (radiograph to confirm) the socket can be packed with doxycycline (Doxyrobe Gel®; Pharmacia – a lovely product but expensive!).
12. Postoperative care includes antibiosis and the provision of strips of vegetables and hay as prehension will now be undertaken solely with the lips.
13. Supportive nutrition may be offered post-operatively by stomach tube if necessary. This is probably part of your post-anaesthetic procedure any way.
14. Follow up diet should contain fibre as if the incisors were still present except that greens may have to cut in strips. Incisor-less rabbits can cope well with eating.

Prevention

Provision of grass or hay (Timothy) and edible branches (apple and pear twigs). (Trees that bear single-stoned fruits may have unacceptable amounts of cyanide in the bark so don’t offer peach, plum or cherry, for example)