Incisor Overgrowth – Rabbit

Introduction

Rabbit incisors are elodont teeth, i.e. they grow continually. Incisor overgrowth is common in rabbits. It is either primary or secondary depending on the cause.

Primary overgrowth occurs early in life as a consequence of inherited skeletal malocclusion (maxillary brachygnathism resulting in a relative mandibular prognathism, anaesognathism - excessive narrowing of the already narrow mandible). 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.

Secondary overgrowth usually occurs in rabbits 1 year or older as a result of cheek tooth overgrowth. This is the most common cause of incisor malocclusion in the rabbit.

Trauma to the teeth or head can also result in incisor pathology.

Incisors have been shown to grown up to 5mm/week if not in contact, and disease progression can be rapid if no action is taken.

Clinical Signs

Signs are similar to those seen with cheek teeth malocclusion, including: ptyalism and wet fur around the chin, weight loss, poor hair coat, clagged vent, ileus, epiphora and visible overgrowth, twisting, splaying or slant of the incisors.

Diagnosis

Clinical signs are suggestive of a dental problem, along with a history of anorexia, weight loss and feeding concentrates.

The rabbit should be restrained in sternal recumbency by an assistant and the lips retracted to examine the incisors.

Cheek tooth examination should also be performed, as disease processes are usually linked. Sedation is usually a sufficient means of restraint and examination is facilitated by the use of a gag and a cheek pouch dilator.

Treatment

It must always be remembered that treatment of the cheek teeth is usually also required.

Incisors can be trimmed on a regular basis (every 3-4 weeks) or complete extraction can be performed.

Incisor trimming

This is best done using a dental drill but good clippers may have to be employed if a drill is not available (this leads to a much higher risk of iatrogenic damage to the teeth).

The teeth should be cut horizontally at the estimated desired length. The bur can be used to apply a bevel to the incisal edges and to remove sharp edges. The drill should be used at full speed with light contact pressure, and it should be kept moving on the tooth at all times to prevent excess heat build-up.

Care should be taken with the lower incisors, as their pulp may extend above the gumline when erupting quickly. Trans-illumination should reveal a pink triangle, and the tooth should be trimmed 1mm above that.

Trimming incisors can usually be done without sedation in co-operative rabbits.

Extraction of incisors

Indications for incisor extraction:

• Young animal, who would otherwise need incisor trimming every month for the rest of his life
• Intractable incisor pathology
• Brachygnathism/Prognathism

Procedure:

All 6 incisors (4 main and 2 upper peg teeth) are extracted.

General anasthesia and analgesia is required. Radiograph the teeth to assess the extent of dental tissue to be removed and to assess if infection is present at the apex.

Start with the lower jaw. Gently cut the subgingival attachment with a #15c scalpel blade. Gently cut the periodontal membrane with a 20G hypodermic needle bent to suit the socket (hence the previous radiograph), holding the socket steady. There are special ligament cutters available on the market for this, but they don't suit the curvature of every tooth. 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. It is a good idea to work from tooth to tooth and back again, loosening several teeth at once.

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.

When adequately loosened, push the extracted incisor back into its socket for about ten seconds to traumatise the deep germinal tissue and prevent regrowth. 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.

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!

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.

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.

Postoperative care includes antibiosis and the provision of strips of vegetables and hay as prehension will now be undertaken solely with the lips. Supportive nutrition may be offered post-operatively by stomach tube if necessary, following the practice post-anaesthetic protocol.

Follow-up diet should contain fibre as if the incisors were still present except that greens may have to be cut in strips. Incisor-less rabbits can cope well with eating.

Any teeth may re-grow even when removed entire. It is more likely when the pulp is not extracted with the tooth. If the pulp remains in the socket it is best left and a second extraction procedure performed at a later date.

Prevention

Provision of grass or hay (Timothy) and edible branches (apple and pear twigs) will provide adequate abrasion for the normal wear of incisors and cheek teeth. Supplemental foods such as concentrates or muesli-type food should not be necessary.

(Note: 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.)

References

Crossley, D (2010) Dacross Services Online Veterinary CPD

Gorrel, C (2004) Veterinary Dentistry for the General Practitioner, Elsevier Health Sciences