Rabbits belong to the order of lagomorphs along with hares. They have 6 incisor teeth and 22 cheek teeth (molars and premolars). The dental formula is 2 x (I 2/1, C 0/0, P 3/2, M 3/3) = 28. All teeth are hypsodont (constantly growing) and grow about 2 mm weekly. The whole tooth is also covered in enamel so rabbit teeth are 'aradicular' i.e., have no roots--the teeth embedded in bone are more correctly called reserve crown. There is a division of labour. The incisor teeth are sharp and chisel-like for slicing the food while the cheek teeth have a large occlusal surface with transverse folds of hard enamel for grinding down the food.
Causes of Dental Malocclusion
Congenital defects occur in dwarf and some lop breeds that have mandibular prognathism. This is where the jaw is abnormally long compared to the maxilla causing lack of wear of incisors. The mandibular incisors grow out straight while the maxillary incisors begin to spiral. It can start from as early as 8-10 weeks but often may go unnoticed until 9-12 months.
Trauma can lead to incisor teeth fractures that frequently cause apical damage so regrown teeth may become deformed. The other more common cause is lack of attrition caused by a low fibre diet. During normal chewing action the jaws appose one side at a time and rotate laterally at a rate to 120 times a minute. When a rabbit is fed a low fibre diet this normal chewing mechanism fails to occur causing less wear and molar malocclusion. Rabbits are also browsers and when fed cereal rations they will selectively eat the cereal portion leaving behind the pellets that contain the fibre and calcium needed for healthy dentition.
A rabbit with healthy dentition will eat a variety of foods and have no problems chewing large amounts of hay. The coat will be healthy and shiny and the perineal area spotless indicating normal grooming and caecotrophy. The mandibles will feel smooth underneath. The incisor teeth will have the normal chisel appearance with vertical enameling and the molar teeth will appear straight and regular when the mouth is viewed with a speculum.
Rabbits with Dental Disease: What Signs to Look For
The clinical signs may depend on which part of the dentition is mostly affected i.e., the incisors, the molar crowns or molar 'roots'. Obviously in many case all three areas can be affected.
Rabbits with congenital incisor malocclusion have the classical curved walrus teeth with often adjacent ulceration of the gums. These rabbit are usually young and appear quite well as there is rarely any deep pain. Mild weight loss and perineal soiling may be present due to the physical obstruction of the teeth hindering eating and grooming.
Rabbits do not use their incisor teeth for prehending food so rabbits with severe malocclusion can have these teeth extracted. Extraction in usually successful though in some cases the teeth can regrow. As this is invasive painful surgery the rabbit should be given assisted feeding for a day or two and given lots of analgesia.
As deep alveolar sockets are left after incisor extraction, antibiotics should be given for 7-10 days post operatively to prevent secondary Pasturella infections.
Molar Crown Problems
Lack of fibre in the diet causes irregular wear of the teeth leading to crown elongation and malocclusion. A typical pattern of soft tissue damage ensues. The upper molar crowns form spurs abrading the buccal surfaces while the lower molars form spurs protruding medially into the tongue. These cases initially avoid hay and favour foods like cereal ration which requires less chewing.
These rabbits are often in excruciating pain especially when spurs lacerate the tongue causing the graphically termed 'lingual kebab'. They become anorexic, withdrawn in behaviour and suffer rapid weight loss. They hypersalivate due to pain and get a secondary moist dermatitis of the chin. They adopt a hunched posture and have abnormal motions and gut disturbances. As they are unable to eat they often become polydipsic to compensate.
These patients are often very debilitated and need to be stabilised before anaesthesia. The surgery is relatively straightforward the aim being to burr down the elongated crowns and remove the sharp spurs. Great attention must be given to avoiding cutting or damaging the sensitive soft tissues of the mouth.
Molar 'Root' Problems
These can be secondary to longstanding molar crown problems so tend to commonly occur--but not always--in older rabbits. The chronic lack of abrasive diet leads to the root becoming initially elongated and flared. It then becomes deformed with osteomyelitis and abscesses forming around the base of the tooth. Large soft tissue swellings can be felt along the lower mandible or less commonly lateral to the maxillary arcades. Although these abscesses are often dramatically large they are usually non painful to touch. Pressure from the maxillary roots can also cause secondary dacryocystitis and epiphora. These rabbits may have pain on chewing due to the elongated roots pressing nerves but they are not normally as ill or debilitated as rabbits with molar spur problems.
As the dental abscess derives from the base of the tooth this is major sterile orthopaedic surgery necessitating curetting down to bone level. The abscess is then either packed with antibiotic impregnated beads or marsupialised to the exterior.
Rabbits should be kept in hospital for assisted feeding, antibiotics and analgesic until fully recovered. Rabbits with marsupialised abscesses will need to have the wound flushed twice daily with diluted Betadine.
Stabilisation of the Dental Patient
Treatment will depend on the category of dental problems. Rabbits with molar crown problems may often be very debilitated by the time they present. Longstanding anorexia may lead to secondary problems of snuffles and gut stasis problems. Paradoxically some rabbits with dental problems survive by eating high calorie treat foods only and often present as obese. A short period of anorexia puts these patients at risk of hepatic lipidosis.
Great attention should be given to stabilising the dental patient before attempting surgery. The rabbit must be given a full clinical examination and checked for any underlying respiratory infection or secondary gut stasis problems. All equipment needed like mouth gag, pouch dilators and dental burrs must be prepared and laid out in advance to minimise surgery time. Cotton buds and warm sterile saline for flushing should be available.
During the peri-operative period it is important to constantly monitor the rabbit in the following five categories--hypoxia, hypothermia, hydration problems, hypoglycaemia and 'hiding pain'.
Underweight patients need to be weighed and a target weight set. Assisted feeding needs to be instigated taking into account calorie intake and fibre. As rabbits do not tolerate nasogastric tubes well, assisted feeding is best achieved using a wide bore syringe and either pureed pellets or herbivore mix (liquid hay e.g., Oxbow Herbivore mix). This should be fed to the rabbit 3-4 times daily. Daily motions need to be monitored. A normal rabbit passes 150 faecal pellets per day so if there are less faecal pellets or they are smaller than normal, gut motility agents should also be given. Metoclopramide can be given either by injection or oral syrup to help stimulate gut motility.
Many rabbits are dehydrated on presentation so need to be given fluid intravenously prior and during surgery. Milder cases can be given daily sc fluids. If the rabbit is willing to drink, oral fluids should also be given 2-3 times daily to help prevent the extensive surface area of the gastrointestinal system from dehydrating.
Rabbits are prey animals so even if in severe pain they may not show overt signs. Signs of 'hiding pain' are withdrawn behaviour, hunched appearance, anorexia or eating only soft foods. Analgesics like carprofen and meloxicam are very useful for dental pain. Meloxicam oral syrup is honey flavoured and much enjoyed by sick rabbits!
Sick rabbits often have subnormal temperatures and must be kept in warm ambient surroundings. They should be kept at 35°C during surgery and not returned to 24°C until fully awake and mobile. The rabbit pinna represents 12% the surface area of the rabbit and is major source of heat loss. During surgery the ears should be kept warm and insulated (wrap in bubble wrap).
Many sick rabbits have underlying respiratory problems so pre-oxygenation may be necessary. During anaesthesia patients should either be intubated or given intra nasal oxygen to prevent hypoxia. The rabbit should positioned in sternal recumbency with the thorax raised higher than the abdomen to prevent the viscera pressing on the small thoracic cavity.
Discharging the Patient
It is very important that the owner is educated on aftercare for their pet rabbit at home. They should be advised to make sure the rabbit is eating and passing normal motions. In the event of the rabbit failing to eat they must be shown how to syringe feed the rabbit or else advised to return the rabbit back to the hospital for further nursing.
Long-term the owner must be made aware that rabbits teeth grow continuously so dental problems can recur. They must bring the rabbit in for a checkup at the first signs of anorexia, change in stool or withdrawn behaviour. Rabbits which have had their incisor teeth removed will need to have their food sliced in future and their coat brushed occasionally.