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|Rabbit Teeth: How They Work|
By: Robin Ryšavy, DMA in consultation with Brock Exline, DVM
Before one can understand how a rabbit uses his teeth, one must first understand some basics of the dental anatomy of a rabbit.
An adult rabbit has 28 teeth. There are six incisors: two pairs of incisors on the "top" or maxilla (the second pair, often referred to as "peg teeth" are much smaller and are positioned behind the longer front incisors), and a pair of lower incisors on the jaw, or mandible. Rabbits do not have canine teeth, but do have three pairs of premolars on the maxilla, two pairs of premolars on the mandible, and three pairs of molars on the maxilla and also on the mandible. These premolars and molars are often referred to as "cheek teeth", and there are more "cheek teeth" on the maxilla than on the mandible, and the mandible is narrower than the maxilla. The cheek teeth are separated from the incisors by a fairly long space of cleft (diastema), which is extremely helpful when syringe feeding medicines to a rabbit. All rabbit teeth grow continuously throughout the rabbit's lifetime.
The four larger incisor teeth are used to grasp, tear, and slice, while the "cheek teeth" are used to grind and chomp. When at rest, the tips of the lower incisors are normally positioned between the maxillary first incisors and the peg teeth. The cheek teeth, however, should be slightly out of alignment in the "at rest" position. The cheek teeth are brought into alignment (occlusion) when the mandible (jaw) is slightly retracted and angled so that the jaw joint (temporomandibular joint) can reposition itself, allowing the cheek teeth to come together, while at the same time, separating the incisors. This allows the cheek teeth to move laterally while chewing, without interference from the incisors. The tongue, of course, plays an important role in moving food from the incisors back to the cheek teeth where it is ground.
According to Dr. David Crossley of the Animal Medical Centre Referral Services in Chorlton, Manchester, UK, "three to four millimeters of incisor tooth are worn away each week, with the cheek teeth wearing around this amount every month". Because a rabbit's teeth are made to wear down rapidly, an improper diet can affect the teeth in just a few days. Therefore, the type and form of food a rabbit eats is extremely important for maintaining healthy tooth wear.
Grass and other leafy vegetation is very abrasive and full of many different mineral particles. It takes a rabbit more time and requires more effort to eat grass and hay than it does to eat commercial pellets. Therefore, a diet high in this type of vegetation will cause more tooth wear than a diet where pellets are the main source of food. The grass and hay must be sliced into short sections by the incisors, and then ground by the cheek teeth which move laterally. Pelleted foods are usually quickly crushed by the cheek teeth. Grinding the lateral chewing motion is significantly reduced, which results in only partial tooth wear, and provides the potential for the development of painful spurs. It is also important to note that the mandible teeth grow up to one and a half times faster than the maxillary teeth, and as noted previously, there are more teeth on the maxilla than on the mandible, and the mandible is narrower than the maxilla. Because of these discrepancies, Dr. Crossley points out that "abnormalities of a tooth in one jaw may affect up to three teeth in the opposite jaw." To help prevent tooth problems, Dr. Crossley recommends that rabbits spend several hours a day chewing grasses and leafy vegetation.
Some breeds, such as dwarf and lop rabbits are more prone to having dental problems due to their shape and inbreeding. Once dental problems begin to affect how efficient the teeth can chew, most rabbits will change their eating habits. Often the rabbit caretaker will notice that their rabbit is more interested in eating higher energy foods such as commercial pellets instead of hay, grass, and other leafy vegetation. If the problem is not corrected right away by a rabbit savy veterinarian, it can lead to some serious medical consequences, which in some cases, are difficult, if not impossible, to reverse.
POTENTIAL DENTAL CONDITIONS
Elongation of cheek tooth crown
Spurs on the cheek teeth
Decay of bone or teeth (caries)
Soft tissue lesions, often located on the sides of the tongue, underneath the tongue, or on the cheeks
Root elongation of the cheek teeth
Swelling along the mandible (frequently mandible abscesses will develop which can lead to osteomyelitis)
Bulging of the eye (sometimes a retrobulbar abscess will develop as a result of dental problems)
Ocular discharge (sometimes caused by a tooth root obstructing the nasolacrimal duct)
Food impaction around cheek teeth which can lead to infection
Periodontal abscesses or infection
Temporomandibular joint problems (TMJ)
Fractures of incisor roots
SugarPatch, a little Holland lop, suddenly (literally overnight) developed an abscess just under her left eye in the middle of her cheek. She was taken to a rabbit savy veterinarian immediately, where surgery was performed to attempt to marsupialize the abscess via an incision in her cheek. Unfortunately, not as much was known about rabbit dental disease at the time, and the abscess quickly reformed because it was not the result of an infection in the cheek, but rather that of an infected cheek tooth. After removing the tooth (and later, several other cheek teeth), and a lengthy round of appropriate antibiotics, the infection cleared. Eventually though, all of SugarPatch's teeth became loose and infected, and all the cheek teeth were removed (not all at once, however). She had to have her vegetables chopped up, and unfortunately could not eat hay, but did enjoy American Pet Diner timothy pellets made into a soft mush. She lived for some time without any cheek teeth, and did not lose any weight, nor did she miss a meal. Her incisors were never problematic.
Buttercup, a dwarf Dutch rabbit, did not seem to have any dental problems until he was approximately five years of age. At that time, he began sneezing. Despite repeated attempts to get a nasal culture/sensitivity (all were negative), and a full course of several antibiotics, his condition continued to deteriorate. Although his eating habits had not changed, he veterinarian decided to examine his teeth to see if they could be contributing to his condition. Indeed, he had several molar spurs and two very loose molars which were removed. After this was done, he stopped sneezing. He continues to need to have his cheek teeth examined periodically and filed because the missing teeth make it impossible for the remaining teeth to be worn down properly.
Patty, a mini-lop/Holland lop mix, is another rabbit who has developed cheek teeth spurs now that she is older (Patty is currently 8 years old). She has had several cheek teeth removed because of infection, and has to visit her veterinarian every six weeks for filing of the remaining cheek teeth. She has never been particularly interested in eating grass or hay, but does enjoy her vegetables, and many leafy greens such as cabbage leaves, kale, bok choy, parsley, cilantro, and leaf lettuce. It is easy to tell when her teeth are becoming problematic as she will often refuse to eat part or all of her nightly salad, and will sometimes stop drinking from her water bowl.
Scooter, a Holland lop (God rest his litter soul), started drooling one day, although his food intake remained normal. Then, in addition to the drooling, his caretaker noticed that his breath smelled sour. He was on enrofloxacin (Baytril) for upper respiratory symptoms (sneezing and an ocular discharge), but the symptoms were not improving. His mouth was examined with the help of an otoscope (no anesthesia was required at this point) and a very long premolar spike was noticed sticking up at least a 1/2 inch into his cheek. No soft tissue abrasion had developed (yet), and after the spike was snipped off under anesthesia by his veterinarian, the drooling and sneezing stopped, and his eyes stopped running. He continued to need dental care every two to three months until his life ended as the result of liver disease, which his veterinarian believed to have been caused by chronic dental infections that were undetected throughout his life.
Fudge, a mini-rex, suddenly refused to eat. He had always been a good hay eater, along with fresh vegetables and leafy greens, and some pellets. Now, no matter what his human caretaker did, he would not eat on his own. He was syringe-fed canned plain pumpkin which he took readily. His veterinarian thoroughly examined him, but found no evidence of any dental problems when his mouth was examined with the help of an otoscope. There were no obvious gastrointestinal blockages either, although his GIT had slowed down due to his limited intake of food. Just prior to considering exploratory GIT surgery, his vet was asked to anesthetize Fudge and examine his tongue for lesions. Sure enough, some pretty substantial lesions and bruising was found on the underneath side of his tongue. After the crowns of his lower cheek teeth were filed and returned to a normal height (they were extremely long), he began eating. Fudge continues to be seen by his veterinarian for periodic molar floating (filing).
Murray, a Holland lop, showed no dental problems for the first 2.5 years of his life. Then suddenly he refused to eat, and went into a severe gastrointestinal stasis. After he was diagnosed with dental problems, and his teeth were filed, his GIT problems diminished, although his caretaker found he needed to have his molars filed every two weeks under anesthesia. Murray was also diagnosed with TMJ problems by his acupuncture vet, who treated him for this condition. It is not unusual for the facial muscles to become stretched and out of shape due to alteration in a rabbit's chewing method to avoid pain caused by dental problems. In Murray's case, it wasn't until his facial muscles, temporomandibular joint, and teeth spurs were treated simultaneously that his condition improved and he did not need to have his cheek teeth floated so often.
Majic, a dwarf rabbit who was a classroom pet was only fed commercial pellets. H enever received any fresh vegetables or leafy greens, and no hay. After being rescued and having access to grass hay and vegetation, Majic still refused to eat (except pellets). When his teeth were examined by his veterinarian, the bottom cheek teeth crowns were actually cupped and the upper cheek teeth fit into them. This malocclusion prevented him from chewing laterally with his cheek teeth. All he could do was chomp down on pellets. After the cheek teeth were filed down under anesthesia by his veterinarian, Majic could finally enjoy a diet of hay and greens.
Kermit, a polish dwarf always seemed to prefer his carrots grated, and did not eat a lot of hay or other vegetables. He did not seem to have any problems eating commercial pellets, until one day when he stopped eating everything. His caretaker took him to the vet for an examination. The only thing the vet found was a tiny spur on a premolar on the maxilla. Although one would think that one spur would not be enough to cause a hungry little rabbit to stop eating, after the spur was removed, Kermit began to eat again. Now he enjoys a variety of greens, some hay, and of course, his grated carrots (he trained his human well).
In closing, here are some key points to remember:
· Know your rabbit's eating habits and if changes occur, see your veterinarian immediately
· Structure your rabbit's diet to minimize dental problems and maximize their health
· Be sure to have your rabbit savy veterinarian check your rabbit's teeth periodically, even if there are no obvious problems.
· Remember, a diet which promotes healthy chewing for several hours a day means that not only will your rabbit be less likely to develop a malocclusion of other dental problems, it will also help satisfy their natural desire to chew (and possibly save your furniture from destruction).
Crossley DA (2001) Rabbit Dentistry: Basic Principles; in: TNAVC 2001 Small Animal and Exotics Proceedings,
Vol. 15 pp. 852-854.