Introduction

Over millions of years rabbits have evolved to gain all the nutrients they need from an herbivorous diet and so their teeth have adapted too, to best fit their requirements for biting off and chewing of long, fibrous food such as grass.

Because the constant chewing of tough, fibrous matter wears down their teeth, the teeth continue to grow throughout life. The upper and lower incisors (front teeth) of rabbits grow 4 and 5 inches a year respectively (1).

Rabbits have 6 incisors (2 upper sets and one lower set) and no canine teeth. Their cheek teeth are made up of 3 upper premolars and 3 upper molars and 2 lower premolars and 3 lower molars on each side (2).

The normal structure of their jaw at rest allows the incisors to touch but not the cheek teeth; in this way a rabbit can use its incisors to cut food material without interference from the cheek teeth. Food can then be taken into the mouth with the prehensile lips and incisors and then moved via the tongue to the cheek teeth. When ready to chew, the rabbit changes the position of the jaw and brings the cheek teeth into contact (2). Because of this method of action a normal jaw shape is vital for proper wear of the teeth as well as constant access to fibrous matter to keep the teeth worn down.

Common Teeth Problems

Malocclusion

Symptoms:
In the case of incisor malocclusion the symptoms are easy to spot. The rabbit will be having difficulty eating, possibly leading to weight loss and the mouth will be forced open by the elongated teeth, the start of an abnormal tooth wear pattern can be spotted by carefully lifting up the rabbit’s upper lips to examine the upper and lower incisors (best performed whilst the rabbit is on its back). The rabbit may also have weepy or tearing eyes and will generally appear off colour.

Cause:
Malocclusion occurs when the upper and lower teeth do not meet properly whilst chewing, preventing them wearing down and leading to overgrowth; this can become quite serious if not treated, with the upper incisors growing into the lower jaw or the lower incisors growing into the nasal passage. See picture below:


Pictures from: (3)

It may become hard for the rabbit to close its mouth and when the rabbit tries to chew the long teeth can stick into the fleshy parts of the rabbit’s mouth and cause it pain. They also make it hard for the rabbit to pick up its food.
There are several causes of malocclusion with the majority of cases being caused by a genetic defect or poor diet (other reasons such as injury or calcium problems may also lead to malocclusion (2)).
The main genetic defect (mandibular prognathism, or MP) that leads to malocclusion of incisors is well documented in rabbits. In this recessive disorder, both the doe and buck rabbit must carry and pass the trait to their offspring, 81% of those who get the trait will have a problem with their teeth. Rabbits with this trait typically show signs by 8-10 weeks of age- at or just after the time of weaning-starting with incisors that just meet (1). Genetic defects are the main cause of malocclusion in pet rabbits and are (obviously) irreversible. The teeth can either be maintained at the correct length through trimming for the rest of the rabbit’s life or in extreme cases be entirely removed.

A poor diet is also implicated in cases of malocclusion as insufficient access to hay or grass can lead to the improper or abnormal wear of the incisors (where the rabbit may resort to gnawing at the hutch to wear the incisors down or through boredom, this can lead to a slanted wear pattern as the rabbit turns its head to chew on the side). If the incisors are not being worn down through constant chewing action on tough, fibrous matter they will start to overgrow and remedial action may need to be taken to restore the teeth to the correct length. In the case of poor diet being the cause, if the diet is corrected soon enough, the rabbit’s teeth should resume a normal wear pattern.

Treatment:
Clipping used to be the only method for keeping overgrown incisors in check; they were cut every 2 to 3 weeks using side cutters or dog nail trimmers. Although there are individuals who have employed these methods for years with success it only takes one occurrence of breaking off an incisor below the gum line that leads to a lifetime of dental problems (2).

David Crossley (dental specialist) states that: this barbaric practice results in a great deal of pain and suffering. Not only are the teeth left with sharp fractured surfaces that irritate the oral soft tissues, longitudinal cracks are also common involving sensitive dentine and often allowing infection into the pulp even if there is no direct pulp exposure. The forces applied to the teeth during clipping far exceed physiological limits and there is tearing resulting in ongoing pain and exacerbation of tooth growth abnormalities. The use of tooth rasps (coarse surfaced instruments as opposed to files) is just as bad as again the forces required exceed physiological limits and rock the teeth in their sockets causing further periodontal and apical damage. Even the use of fine diamond files can loosen teeth (4).

Burring is now the recommended method for trimming overgrown incisors using either a thin cutting bur or a thin cross cut fissure tungsten carbide bur, often powered by a Dremel tool or hobby drill. The incisor teeth are cut with the bur by repeated gentle strokes across the tooth surface. Only a light force is used to avoid applying too great a pressure to the teeth and to minimise heat build up (4). This can be performed whilst the animal is awake and is relatively quick and painless.

Sometimes in extreme cases tooth removal is necessary as it effectively removes the problem of malocclusion (see tooth removal section). The rabbit can then go onto lead a relatively normal life free from discomfort and the stress of constant vet trips for burring.

Cheek-Tooth Spurs

Symptoms:
Constant drooling (wet chin), refusal of food or eagerly takes food but seems unable to eat it (drops back out the mouth), constant tooth grinding (indicating pain), generally appears off colour and weight loss are possible symptoms. An otoscope cone or speculum with a light source can be used for an initial examination but if severe spurs are suspected an x-ray may need to be taken for confirmation.

Causes:
Rabbits with incisor malocclusion often have problems with malocclusion of their cheek teeth. The cheek-tooth malocclusion in these cases is most likely caused by the overgrown incisors preventing normal wear of the cheek teeth, and resulting in overgrowth. Rabbits that show just cheek-tooth malocclusion at a young age could have a genetic problem affecting the angle of cheek-tooth growth. (1).

Diet and nutrition may also be involved; again a lack of fibrous material in the diet may lead to reduced wear, causing the cheek teeth to overgrow. Excessively high levels of fluoride (chronic fluorosis) and a diet deficient in folic acid have been shown to cause similar problems (1).

Age is also a factor in developing molar spurs; older rabbits may develop elongated tooth-enamel points even though the length and angle of tooth growth may be normal. And also loss or damage of a tooth may lead to the overgrowth of the opposing tooth (1).
These spurs can overgrow if not treated and may puncture the cheeks or tongue of the rabbit leading to abscesses.


Pictures from: (5)

Athena had molar spurs when I adopted her and it wasn’t obvious as she had none of the common symptoms but they were discovered at her bunny MOT when the vet used an otoscope to check her molars so she was booked in to have them filed down under anaesthetic. So far with the correct diet they have not needed to be filed down again (a year later).

Treatment:
There are several methods of treating molar spurs and the most common is simply having them filed down by your veterinarian, who may use anything from a Dremel tool to a blunt-tipped diamond nail file. The rabbit is usually put under light anaesthesia (e.g., isofluane gas) and the procedure rarely takes longer than a few minutes (6). Sometimes these spurs may have to be removed every few weeks, as some members here are only too aware, and this can become costly (11).

David Crossley however believes that the practice of filing off spurs is largely a waste of time as it does nothing for the underlying problems such as tooth elongation and increased tooth curvature that develops when there is a reduced eruption rate due to inadequate tooth wear, so recommends complete coronal reduction of the cheek teeth. This would be performed using power equipment as it allows rapid removal of tooth substance without risking the damage to the tissues caused by use of a rasp (or worse, clippers). The end of a flat fissure bur is used, advancing it along the dental arcade one tooth at a time, to remove the bulk of the exposed crown, the end of the bur guard being placed on the coronal surface of the tooth and used to guide the bur. Work progresses one tooth at a time to both prevent heat buildup and to allow powdered tooth to be wiped away at intervals using a damp cotton bud. Once the teeth have been brought to the correct height the side of the bur can then be used to smooth the surfaces and restore the normal angulation as necessary (4).

Extraction is not recommended (see tooth removal section).

Tooth Root Infection and Overgrowth

Symptoms:
Watering/teary eyes is the main indicator of an incisor root infection along with scoring of incisors (they look ridged not smooth where they erupt), nasal discharge (may be white or clear), possibly accompanied by sneezing, symptoms of stress e.g. mites and a reduced interest in food. Overgrowth of the molar roots also results in teary eyes and may be felt as bumps or ridges underneath the rabbit’s jaw (if they have become very extended). Root problems can only be truly diagnosed via x-ray.


Picture author's own

Causes:
In younger rabbits it is mainly unknown why tooth roots elongate. David Crossley believes that it is due to a change in pressure when the teeth are not being worn down properly by constant chewing (7). But it has also been linked to calcium problems, where weakening of the bone structure of the jaw allows the tooth roots to grow into the bone. Tooth root elongation in younger rabbits has also been linked to a lack of sunlight and is apparently more common in house rabbits.

Older rabbits sometimes suffer gradual bone loss and when this happens, the molars may become a bit looser in their sockets, inviting uneven wear and other problems, sometimes extending to the roots. In some cases, molar roots in older rabbits can begin to extend farther into the maxilla (upper jaw) or mandible (lower jaw) than normal, and may impinge on the tear ducts, causing runny eyes. In other cases, overgrown molar roots may even puncture the sinuses or the eye orbit, allowing intrusion of mouth bacteria into areas meant to remain sterile. This, of course, could be the beginning of an abscess (6).

Treatment:
Zeus had been on penicillin injections for a month (one a week) for his incisor root infection, as a prior course of Baytril had no affect. The penicillin appeared to have cleared his infection as the teeth were coming through unscored and his eyes were dry however after a month the symptoms reappeared so he is being put on a longer course to try and clear the infection completely if at all possible (started 06/05/04) (12). Septrin is also recommended for treatment of tooth root infections.

Twiggy’s Fudge had his teeth removed due to the tooth root infection (by the same vet who is treating Zeus). The roots were then packed with an antibiotic impregnated gel to try and clear the infection. This has partially worked and there has been some improvement however the infection is not completely cleared and there is some tearing still.

Each rabbit is separately assessed and the treatment tailored to the rabbit’s needs. Unfortunately no one treatment works for all rabbits.

Tear-duct flushing may also be necessary to clear any blockage caused by the infection and to help flush out any bacteria present.

There is no treatment for molar root elongation, except a correction in the diet if there has been insufficient grass/hay fed previously. Increased access to direct sunlight (not through windows) has also been suggested to help.

Abscesses

Symptoms:
The obvious symptom is lumps or bumps forming along the jaw or side of the head (not matched by similar lumps on the other side). The rabbit may refuse food, generally not seem itself and grind its teeth in pain, however often the rabbit appears clinically unaffected (8).

The abscess may in unusual cases become pointed with a head similar to human spots and then burst. If they burst externally then cleaning is necessary (preferably by a vet), bursting internally is more serious as it can lead to blood poisoning (13).

Rather more unusual were the symptoms presented by my first rabbit, Fudge. At 10 weeks old he developed a persistent wheeze, which antibiotics didn’t seem to treat. This progressively got worse and was accompanied by sneezing after drinking, reluctance to eat and a general apathy. He was grinding his teeth, his incisors were wearing down at an odd angle and he was having real trouble breathing. Eventually an x-ray when he was 15 weeks old, by a specialist, determined an abscess at the base of his nasopharynx was constricting his airway and also making it difficult to swallow. Unfortunately due to the location under his brain it was inoperable and he had to be put to sleep. The specialist said this was an extremely unusual case and he had never seen anything like it in such a young rabbit.

Causes:
Abscesses of the head may be secondary to dental disease and can be caused by food packed between the tooth and gingiva, tooth fractures, tooth root infections developing into abscesses or a foreign body. They occur in rabbits of all ages and frequently develop rapidly (in a matter of a few days). The abscess may be soft or firm but frequently they have a soft center. They are usually not moveable and when bone is involved there may be bony swelling as well. The wall of the abscess is very thick and usually contains bacteria. The pus is thick, and creamy white in appearance (8).

Several different types of bacteria have been cultured from rabbit abscesses and these all respond to different antibiotics. If an abscess is reoccurring it may be necessary to swap antibiotics to try and treat the infection (9).

Treatment (8):

Regardless of the treatment method selected, it is important to remove any teeth that are involved either from tooth root infection or as a result of osteomyelitis (bone infection).

Two weeks of antibiotics is usually inadequate because of the great potential for recurrence and many recommend low dose, life-long antibiotic therapy to prevent recurrence. The traditional treatment of abscesses in mammals (lancing and draining) is not effective in rabbits. The pus is too thick to drain adequately and recurrence is common.

A technique used to treat rabbit abscesses involves lancing the abscess, scraping the wall, and leaving it open to heal along with wound irrigation. The wound is irrigated with an antiseptic solution such as dilute chlorhexidine or dilute povidone iodine. Irrigation is performed 2-3 times daily until a healthy bed of tissue is present. Once the wound bed appears healthy, topical treatment with an antibiotic cream or ointment is continued until the wound is well healed.

Recently, packing the abscess cavity with calcium hydroxide has been recommended. Once the pus is removed from the abscess and it is scraped out, the cavity is filled with dental calcium hydroxide. This material has a pH of 12.0, which kills bacteria but is supposed to be non-toxic to tissue. The material is left in place for 1 week then removed and the wound evaluated and if necessary new calcium hydroxide is used. This procedure is repeated until there is no evidence of infection and then the wound is allowed to close.

The most effective method in the majority of cases for treating abscesses of the head of rabbits involves complete (or as nearly complete as possible) removal of the abscess and filling the cavity with antibiotic impregnated beads. The release of the antibiotic is bimodal with a rapid release in the first few days followed by a slow, long-term release of antibiotic over weeks to months. The beads become surrounded with fibrous tissue within a few weeks and then only tissues within about 3 mm receive the high concentration of antibiotic. Because of this it is essential to remove the abscess as completely as possible before placing the beads.

Unfortunately abscesses don’t always have a good prognosis and rapid and effective treatment is the key to survival. However in some cases the abscess may be too deep to cure or may spread and steps will need to be taken to ensure the rabbit doesn’t suffer (13).

Tooth Removal

Causes:
Sometimes it becomes necessary to remove a tooth either due to malocclusion or a root infection or abscess. Both the upper and lower teeth need to be extracted, as the opposing tooth will overgrow if its partner is removed.

Mechanics:
In the case of continuously growing teeth such as those of rabbits it is not just a matter of loosening and removing the hard tooth substance as this may leave the growing tooth germ in situ. It is important that this germinal tissue is removed or destroyed at the time of extraction as remnants continue forming dental tissue following extractions (4).

Cheek tooth extraction is possible, but unlike incisor extraction it is not a practical solution for cheek tooth problems. Cheek tooth extraction tends to be quite traumatic as the teeth become elongated and deformed preventing simple removal by elevation. Removal of more than one or two teeth in one session is likely to result in peri-operative fatality due to the level of stress (4).

Use of antibiotic impregnated beads or gel may be necessary after extraction if a tooth root infection or abscess was present (10).

After Care (15):
- mash up pellets with water if their mouth is too sore to eat hard food immediately after extraction or use supreme recovery mixture (try Bunnyhugger’s Balls (14)) vegetarian baby food can also be used if desperate
- cut/chop up hay to make it easier to manage (2” strands)
- tear up grass so they can eat it
- chop up veggies into manageable sized chunks they can manipulate with their lips
- grooming may become more difficult especially around their rear so check to see there are no uneaten caecals sticking to their fur

Prevention of Tooth Problems

Many teeth problems, once started, will continue for the rest of the rabbit’s life so prevention is the most important factor.

Good breeding

With lops being bred for “cuter” more rounded faces and Netherland Dwarfs being bred for smaller heads and jaws (16) this has led to an increase in rabbits with malocclusion as their teeth no longer fit into their blunter or smaller jaw-line. When breeding it is possible to exclude rabbits with genetic teeth problems and prevent this trait being passed on, by breeding only from stock with the required characteristics and no malocclusion you should be able to produce good quality, healthy kits.

Unfortunately with the pet-shop demand for large volumes of cheap rabbits to sell there will be many who attempt to breed purely for profit so don’t research into the genetic make-up of the rabbits they breed from. This means that traits like malocclusion are not screened from the breeding pool and sadly more and more rabbits being sold in pet shops already have signs of serious teeth problems to come. I personally saw a rabbit with really teary eyes in my local shop so asked to examine him. Upon inspection he had severely overgrown front incisors, which were growing down onto his bottom teeth and where they hit the bottom teeth the upper incisors were moving out sideways apart from each other. The poor thing could barely eat and must have been in constant pain. I complained every time I saw him that he didn’t appear to have received veterinary attention until one day he disappeared. I was told a member of staff had adopted him and I hope for his sake that was true.

Diet

This is the factor you can have the most influence over!

Monocotyledons cause more wear on teeth so the majority of the diet should consist of fresh growing grass, hay and dried grass with small quantities of unimproved herbage (i.e. wild type, not commercially grown herbs and vegetables). This is the most effective diet to keep the teeth worn down because it requires prolonged chewing using the full surfaces of the cheek teeth (4).

Encourage your rabbit to eat the correct diet
- Try cutting down on pellets and commercial vegetables to increase hay consumption
- Try a few different hay sources (e.g. from local farms) as some rabbits prefer certain types of hay
- Try dried grass such as Ready Grass if they really won’t eat hay
- Chop the hay up and blend with grass or herbs to encourage eating
- Put it in their litter tray as they tend to graze whilst defecating
- Use toys such as boxes stuffed with hay or hay balls from online shops to add interest.
- Try and allow a period of grazing on fresh grass outside in the sun everyday, if possible.

Caroline Hyden (Caz)
18/05/05

References:
http://www.rabbit.org/chapters/san-d...lk/dental.html
http://www.veterinarypartner.com/Con...=5&SourceID=43
http://www.islandgems.net/malocclusion.html
http://www.dacross1.demon.co.uk/down...ooth-elong.pdf
http://www.peteducation.com/article....articleid=3078
http://www.bio.miami.edu/hare/dental.html
http://idisk.mac.com/waynestewart/Pu...4_Aug_2000.pdf
http://www.vspn.org/VSPNSearch/VINLi...it_abscess.htm
http://jcm.asm.org/cgi/content/full/...&pmid=11880435
http://www.therabbitcharity.freeserve.co.uk/vet-anti.html
http://forums.rabbitrehome.org.uk/viewtopic.php?t=4497
http://forums.rabbitrehome.org.uk/viewtopic.php?t=2842
http://forums.rabbitrehome.org.uk/viewtopic.php?t=1540
http://forums.rabbitrehome.org.uk/viewtopic.php?t=3571
http://forums.rabbitrehome.org.uk/viewtopic.php?t=2831
http://forums.rabbitrehome.org.uk/viewtopic.php?t=671