Dental Malocclusion in Rabbits - A case report

 

Two terminologies that define rabbit dentition are Elodont and Hypsodont, i.e., they grow continuously with no anatomic root and have an elongated crown that protrudes from the gum line. The dental formula of the rabbit is 2(I 2/1, C 0/0, PM 3/2, M 3/3) =28. What stands out in their dentition is that they have two 2 ‘peg teeth’ that are placed behind the maxillary incisors, unlike most animals.

  

Images depicting the dentition in rabbits and the presence of peg teeth behind the maxillary incisors. Reproduced from https://www.theveterinarynurse.com/review/article/causes-examination-and-treatment-of-dental-disease-in-rabbits 

 

Rabbit mouths also exhibit anisognathism, which means that their lower jaw is naturally narrow when compared to the upper. The elongated crown is divided into a ‘clinical crown’ which is visible above the gum line and a ‘reserve crown’ which remains below the surface.

 The maxillary incisors are covered with hard enamel only on the labial/rostral side but is absent on the lingual side, hence the lingual surface wears off faster than the labia surface and results in a sharp edge. The mandibular incisors have enamel on both sides which suits for occlusion between the two rows of maxillary incisors. (i.e., rostral to the peg teeth)

    The mastication process can be divided into a cutting phase (caused by the vertical motion of incisors) and a grinding phase (caused by the horizontal motion of cheek teeth). The grinding phase of mastication ensures proper wear of both mandibular and maxillary cheek teeth, which is only achieved when coarse roughage such as hay is consumed. Any process that disturbs eruption or wear of the teeth can lead to dental disease.

Although dental disease can be due to a multitude of causes including congenital, traumatic, and metabolic bone disease, improper wear due to dietary indiscretion is the most commonly reported cause.

Without fiber and normal masticatory movements, the elodont teeth continue to grow and create pressure on the apex which will be further pushed into the socket. This results in the elongation of the reserve crown and bending of the apex which will change the direction of growth in the clinical crown.  Over time, this will hamper both horizontal and vertical movement of the teeth resulting in clinical signs of dental disease.

‘Millie’ was a 14-month-old Dutch rabbit who presented with a complaint of inappetence and a moist patch of skin with mild alopecia on the ventral surface of the lower jaw. Completely oblivious to the possibility of it being a sign of dental disease, I treated it for bacterial dermatitis with a Chlorhexidine spray. Upon re-presentation 2 days later, with signs of worsening, I briefly examined the oral cavity after realizing the wetness was due to ptyalism or drooling. A brief oral examination using an otoscope revealed mucosal abrasions on the tongue which warranted a complete oral examination under general anesthesia.  

            Ptyalism leading to moist and sensitive skin on the ventral aspect of the mandible

A makeshift oral speculum was designed atop the operating table using ESF connecting rods, 1.5 mm K-wire, and 22G orthopedic wire which were accessible in the Operating room.

               Improvised oral speculum made from orthopedic implants 

Anesthesia was induced with a Xylazine (5mg/kg) - Ketamine (30mg) combination which was sufficient for most parts of the procedure. Isoflurane (2-3%) was administered through a mask during the latter half of the procedure.

Detailed oral examination revealed lingual spurs on all mandibular cheek teeth and mucosal erosions on the tongue. It was a clear case of ‘sharp molars’ due to dental malocclusion. The spurs were roughened with a high-speed dental burr having a steel tip.

Intraoral images show the lingual spurs on the left mandibular cheek teeth impinging on the tongue which in the image is pushed aside with a No.3 BP handle.

Postoperative image showing the lingual spurs reduced using a dental burr

The anesthetic recovery was uneventful, and the rabbit started oral feeding soon after recovery. Although the condition is likely to recur in a matter of months, the rabbit resumed normal feeding after the surgery. The owner was advised to feed more roughage and reduce the quantity of roughage.

Rabbit resuming feeding during the recovery phase

Takeaways

·         A high-fiber diet that provides extended chewing opportunities is key for good dental health.

·         Ptyalism, inappetence, and weight loss are signs hinting at a possible dental disease,

·         An illuminated nasal speculum or an otoscope is essential for examining the oral cavity. Although General anesthesia and an oral speculum are a must for any procedures to be carried out.

 

References 

1) https://www.theveterinarynurse.com/review/article/causes-examination-and-treatment-of-dental-disease-in-rabbits. 

2) https://www.mspca.org/angell_services/dentition-and-disease-of-the-domestic-rabbit-oryctolagus-cuniculus/

3)             https://www.sciencedirect.com/science/article/pii/B9780123809209000080