One word rodent and rabbit owners never wish to hear in association with their pet is malocclusion. Malocclusion means bad alignment of teeth. It is a term used to describe crooked teeth in any species, including us, but it is a more sinister concern for animals that have aradicular hypsodont (continuously growing) teeth. Proper alignment of the teeth is especially important for these animals. If the teeth do not line up correctly, they will not wear evenly. This can cause molar spurs that flare out into the cheek or tongue and ulcer painfully, incisors that grow into or outside of the mouth, or molar roots that will grow into the nasal cavity or jaw.
How do they get it?
Malocclusion or malo can have a number of factors. It can be genetic, occur after injury, or come from improper diet. Genetic malocclusions are usually present at birth.
A young rabbit skull displaying malocclusion. Thank you to Jana Miller for allowing us to use this photo.
In Netherland dwarf rabbits and other small dwarf breeds, mandibular prognathism is caused by a recessive gene with 81% incomplete penetrance. This is when the lower jaw is longer than the top. Even if the individual is homozygous for the recessive gene, about 19% will not display a longer jaw.
A rabbit’s top incisors should overlap the bottom. When they don’t, the teeth do not wear properly. Image Source
This makes it extremely difficult to completely eliminate in a breeding herd. In other animals, malo is assumed to be polygenic. There are likely several genes involved and it is much harder to predict and eradicate in breeding herds. Responsible breeders still monitor this in their breeding animals and remove affected individuals from the program.
Unfortunately, malo can also develop after an injury. Any facial injury that can cause a broken tooth, or swelling around the face can lead to uneven tooth wear that gets worse with time. Sometimes these can be managed on a case by case basis with your vet and may not lead to permanent damage.
Malocclusion can also come from improper diet. Whether you have a chinchilla, rabbit, guinea pig, prairie dog, or degu they need hay in their diet. Hay provides the necessary fiber to prevent GI stasis and assist in the recovery of any digestive upset. It also is an important source of grinding for the teeth, particularly the molars. As your pet eats the hay fibers, the molars in the the back of the jaw wear down. Without this wear, the molars begin to overgrow. This will cause a major issue with the molar roots invading the jaw or nasal cavity. Root elongation and the malocclusion resulting from it is usually preventable. Always provide your pet with hay. Give them access to safe woody material often and make sure they are getting their proper nutrition.
Malo is not always easy to detect until it is causing issues. The most obvious form of malo will show crooked front teeth (incisors).
A chinchilla displaying incisors with abnormal occlusion and color. Thank you to Brea Hake for allowing us to use this image. https://blschins.weebly.com/
This quickly leads to overgrown incisors that cause the animal to eat oddly. Pay attention to their eating habits. Their little quirks might be a sign that something is wrong. Pawing at the mouth, eating reluctantly, or sudden head movements can all be signs that your pets has something bothering them. If eating is painful or difficult for them, they will often only eat if they are very hungry. They can lose weight and even develop GI stasis as a result of mouth pain from malo. If the molars are too long, our pets will not be able to close their mouths. This can cause ‘slobbers’, or persistent drooling down the chin and chest of your pet. More advanced root elongation will cause jerky head movements every time the animal chews. The jaw will develop bony bumps along as the roots of the molars continue to force their way through the bone. The upper roots will invade the sinus and orbital cavity and may cause persistent sneezing or watery or bulging eyes. This is an advanced and painful condition and we feel it is best to put the sufferer to sleep.
Chinchilla skull with overgrown molars and incisors. Overgrowing molar roots cause ossified bumps on the jaw and in the nasal and orbital cavities. One of the top incisors in this individual had grown into the the roof of the mouth and molar spurs likely cause ulcers on the inside of the cheek. It would have been very painful for this chinchilla to eat. Thank you to Jana Miller for allowing us the use of her photos.
A radiogram of a rescue chinchilla displaying malocclusion.The molar spurs are present and roots are starting to grow into the jaw and nasal cavity. Thank you to Alicja Rosalowska for allowing us to use these images.
In most circumstances, the prognosis for malocclusion is not good. It depends on how early it is caught and what the cause might be. It is valuable to have annual checkups with your veterinarian. If your veterinarian is familiar with your pet it is much easier for them to detect an issue with their patient. Talk with your vet about annual radiograms to check the condition of the teeth. If early molar root elongation is found, you can take steps to correct it before it becomes painful and life threatening.
References and Further Reading
Crossley, David. (2010). Dental Disease in Rabbits and Rodents. LafeberVet. Retrieved from lafeber.com
Godfrey, R and D Godfrey. (2011). Genetic Welfare Problems of Companion Animals. UFAW. Retrieved from UFAW
Huang C, Mi M and Vogt D (1981) Mandibular prognathism in the rabbit: discrimination between single-locus and multifactoral models of inheritance. Journal of Heredity 72(4): 296-298
Legendre, Loic. (2002). Malocclusions in guinea pigs, chinchillas and rabbits. The Canadian veterinary journal. La revue vétérinaire canadienne. 43. 385-90. Retrieved from NCBI