Managing dental abscesses in rabbits (Proceedings)
Anatomy and Physiology
Rabbits have 6 incisors (4 upper and 2 lower). The 2 first incisors are large and oppose the lower incisors. The 2 second upper incisors are called 'peg teeth' and are located just caudal to the first incisors. The incisors are relatively long compared with the cheek teeth. The incisors have a beveled cutting edge with both the upper and lower incisors being sharp on the rostral aspect. When the mouth is closed, the lower incisors rest on the peg teeth caudal to the upper incisors. Rabbits use the sharp edges of the incisors to cut off grasses. The roots of the incisors are dramatically curved and very long. They are deep to the roots of the cheek teeth and extend very caudally in the mandible and maxilla.
The cheek teeth consist of the molars and premolars. Rabbits have 3 upper premolars and 3 upper molars and 2 lower premolars and 3 lower molars. There is a lot of action during chewing between the upper and lower cheek teeth grinding fibrous grasses. They move in a rotary manner going both side-to-side and cranial to caudal. This crushes the grasses that the rabbit has cut off with the incisor.All of the teeth of rabbits grow continuously and do not overgrow because they are worn down by the opposing teeth. They depend on mastication to wear the crowns. New crown is produced below the gingival surface and continually pushed up into the oral cavity. Wild rabbits spend most of the day eating dry grasses, providing the necessary wear on the teeth crowns. Dental crown reduction is not necessary in normal rabbits. Overgrowth occurs if the rabbit does not wear the crowns sufficiently. Additionally, if the crowns are not worn adequately, root ankylosis occurs. The crown is stopped from moving and the root begins to grow into bone.
It seems likely that most rabbit dental problems are related to inadequate amounts of long fiber in the diet. Many rabbits are fed a pelleted diet composed of finely ground alfalfa easily crushed by rabbits. Dry grasses must be ground up before they are swallowed and this grinds the crowns allowing the root to push new crown up keeping the teeth and roots healthy.
Anorexia is a common presenting complaint and dental disease should be considered in any rabbit that presents for anorexia. Rabbits with dental disease are considered to be in pain and do not swallow as much as they normally would. They often have wet fur around the muzzle and ventral cervical fur. Ocular discharge is a presenting complaint that should make the clinician think of dental disease. The upper cheek teeth roots are close to the nasolacrimal duct. If ankylosis occurs, the roots grow away from the mouth and compresses or invades the nasolacrimal duct. Tears no longer drain properly and epiphora results. The discharge may be clear or may contain white, flocculent material. It seems that if the root tip is infected and breaks into the nasolacrimal duct, it causes the discharge to be more purulent in nature. Some rabbits will present for overt malocclusion of the incisor teeth. Many rabbits with primary cheek teeth disease present for incisor malocclusion which is actually secondary to abnormal cheek teeth. Do not just trim the incisors without investigating the cheek teeth. If the cheek teeth crowns overgrow, the mouth no longer closes properly which affects the occlusion of the incisors.
The incisors are relatively easy to evaluate. It is important to have a general idea of how long rabbit incisors should be so you do not trim teeth that are actually a proper length. The upper lip is split (harelip) but the lower is not. The lips are lifted and the length of the incisors assessed. The lower incisors should oppose the peg teeth and the four main incisors should have a beveled cutting edge. Put pressure on the bone at the base of the incisor crowns and try to express purulent material. There should not be any and if there is it indicates there is a tooth root infection.
Cheek teeth are more difficult to evaluate without general anesthesia. Externally, palpate the ventral line of the mandible. It should be smooth. Any lumps or bumps indicate root disease. Some rabbits' mandible will have a scalloped surface along the entire length indicating that most of the teeth are affected. One method used to visually check the crowns of the cheek teeth is to use an otoscope or vaginoscope inserted into the mouth of the conscious patient. Most rabbits react negatively to this procedure, chew constantly, and try to spit out the scope. This makes it difficult to assess the teeth properly and the clinician usually only gets a brief glimpse of the crowns.
In most patients to be able to adequately evaluate the cheek teeth, general anesthesia is required. Skull radiographs are also vital in assessing rabbit teeth and are best taken with the rabbit under general anesthesia. The mouth of the rabbit does not open very far making it difficult to visualize the cheek teeth crowns. Teeth specula and cheek dilators developed by Dr. David are very helpful in getting a good look at rabbit cheek teeth crowns. A cotton-tipped applicator is used to manipulate the tongue to allow the teeth to be assessed for overgrowth and the presence of spurs. The occlusal surfaces of both upper and lower cheek teeth are concaved. In most cases the upper teeth develop spurs on their lateral aspect while the lower teeth develop spurs medially. These can cut into the cheek or the tongue.
A rigid endoscope can also be used to assess the cheek teeth in an anesthetized rabbit. A conscious rabbit will bite the scope and cause expensive damage. The advantage to using a scope is that it magnifies the image allowing better visualization of subtle changes.