DISEASE SUMMARY PAGE

Acquired Molar Abnormalities in Rabbits

Normal cheek teeth. Click here for full page view with caption Lingual spur on a lower cheek tooth of a rabbit.. Click here for full page view with caption Molar overgrowth. Click here for full page view with caption Rabbit with an elongated molar. Click here for full page view with caption Molar and incisor deviation. Click here for full page view with caption Cheek tooth spurs. Click here for full page view with caption Cheek teeth after burring off of spurs. Click here for full page view with caption Radiograph - rabbit with an elongated molar. Click here for full page view with caption Close-up elongated molar. Click here for full page view with caption Radiograph of normal teeth. Click here for full page view with caption Radiograph Stage 2 dental disease. Click here for full page view with caption Radiograph Stage 4 dental disease. Click here for full page view with caption Radiograph Stage 5 (endstage) dental disease. Click here for full page view with caption Prepared skull with endstage dental disease. Click here for full page view with caption

Summary Information
Diseases / List of Miscellaneous / Metabolic / Multifactorial Diseases / Disease summary
Alternative Names
  • Acquired dental disease
  • Progressive syndrome of acquired dental disease (PSADD)
Disease Agents "Any process interfering with normal eruption of or wearing of continuously growing teeth will result in dental disease." (J29.17.w2)
  • Trauma. (J29.17.w2)
  • Elongation of incisors preventing proper occlusion and wear of molars. (J29.17.w2)
  • Periodontal disease (Periodontal Disease in Rabbits), periapical abscesses and bone tumours, all of which can cause loosening or distortion of the teeth, and thereby malocclusion. (B600.7.w7)
  • Improper diet 
    • NOTE: It is generally agreed that incorrect diet plays a large part in the development of acquired dental disease (both acquired incisor abnormalities and acquired molar abnormalities) of rabbits, and that providing a correct diet (grass and other growing plants to graze, or hay and other green foods) can prevent development of most tooth abnormalities. However, there are a variety of different ways in which incorrect diets might affect tooth eruption. The following are the main suggestions: 

    1) Metabolic bone disease, due to inadequate dietary calcium, inappropriate dietary calcium:prosphorus ratio and vitamin D deficiency. (Th16.1.w1, J3.137.w8, J3.139.w7, J3.145.w8, J15.19.w3)

    • It has been observed that skull bone quality of pet rabbits with dental disease is much poorer than that of wild rabbits. (J3.137.w8)
    • Laboratory and commercial rabbits are fed a complete pelleted diet which is nutritionally adequate (they also generally have shorter life spans than pet rabbits which may live for 10 years); acquired dental disease is rare in these rabbits. (J3.137.w8)
    • Rabbit teeth grow constantly and rabbits need a constant supply of calcium. The minimum dietary calcium level required has been determined as 0.22% of feed for growth and 0.35 - 4.0% for maximal bone calcification (J284.26.w1); a level of 0.4% is the recommended minimum from the U.S. National Research Council (Nutrient Requirements of Rabbits, 1977). Another study of rabbits found a 10% increase in peak bone mineral density in the lumbar spine, as well as lower parathyroid hormone concentration and lower levels of biochemical markers of bone resorption and formation, when rabbits were fed a diet containing 1% rather than 0.5% calcium. (J519.29.w1)
    • Some pet rabbits are fed solely or mainly on feed mixes with various components including whole rolled grains, whole pulses, biscuit pieces and rabbit pellets. Rabbits may demonstrate food choice and fail to eat the pellets or grains. Many owners top up or replace the food, rather than waiting until all parts have been eaten. (J3.139.w7, J3.145.w8)
    • The vitamin and mineral supplement is usually contained in the pellets. An analysis of rabbit mixes from pet shops [published 1996] showed that, when the pellets and grains were removed (to mimic the diet as eaten), some of these diets had very low calcium levels (below recommended levels and even below the calculated minimum requirement); also, calcium:phosphorus ratios were reversed, e.g. 1:3 compared with the recommended 2:1. (J3.139.w7)
    • Additionally, many pet rabbits are kept solely or mainly indoors, particularly in winter, and do not have access to grass and other natural green foods, nor to sunlight, therefore cannot synthesise their own vitamin D (which would help with calcium absorption). While sun-dried hay does contain vitamin D, not all pet rabbits are given hay, and not all hay contains good levels of vitamin D. (J3.139.w7) Some pet rabbits, particularly those kept in hutches, have very low (even undetectable) plasma concentrations of 1,25-dihydroxycalciferol (vitamin D3). (J3.145.w8)
    • The low calcium, low vitamin D and reversed calcium: phosphorus ratio in the diet of some pet rabbits, could lead to metabolic bone disease. (J3.139.w7)
    • Loss of supporting alveolar bone may allow teeth to loosen in their sockets, allowing distorted growth. (J3.137.w8)
    • Secondary periodontal infection may allow further loosening of the teeth. (J3.137.w8)
  • 2) Reduced tooth abrasion and/or abnormal chewing movements due to physical form of the diet. 
    • The form of the food, such as pellets of preground material, reduces the amount of chewing and changes the chewing pattern. (J29.17.w1) Concentrate foods, providing nutrition in a lower volume and with less abrasive characteristics, reduces tooth wear compared to a diet of natural plant materials. (J29.17.w1, J60.6.w3)
    • a) The diet fed to pet rabbits is more concentrated and less abrasive than the diet eaten by wild rabbits, leading to the rate of wear being less than the rate of eruption. (B601.18.w18)
    • The cheek teeth elongate, forcing the mandible away from the maxilla, stretching the masseter muscles and increasing forces on the teeth. Force directed apically results in tooth intrusion into the alveolar bone. Forces directed slightly to the sides (tipping forces) result in altered occlusal contact between the opposing teeth, with the lingual side of the lower cheek teeth and the buccal side of the upper cheek teeth no longer coming into occlusion and therefore not being worn down; these elongate and form spikes and spurs. (B601.18.w18)
      • Molar elongation causes malocclusion of the incisors, which then elongate. (B601.18.w18)
    • Increased forces (both lateral and occlusally directed) impede eruption and affect the germinal tissue at the tooth apex, causing increased curvature and even tipping of the teeth. (B601.18.w18)
    • Spikes at the occlusal surface interfere with chewing, attrition decreases even further, the increased occlusal contact forces reduces tooth eruption from the gingiva, but due to continued tooth growth, the tooth elongates at the apical end and intrudes through the alveolus and surrounding tissues. 

    (B601.18.w18)

    • b) Amount of wear is decreased and chewing pattern is abnormal due to physical form of the diet.
    • Feeding of high-energy, compounded foods leads to inadequate wear of teeth and therefore elongation. (B602.34.w34a)
    • High calcium and vitamin D levels in commercial diets may increase tooth mineralisation, increasing wear resistance and decreasing attrition rate. (J213.6.w2)
    • When chewing foods such as pellets or grains, force on the teeth starts while the jaw is still closing, before it has moved as far laterally as it would when chewing normal vegetation, and is at a more vertical angle than normal (rather than being mainly lateral). (J213.6.w2)
    • The altered chewing results in alteration of wear, with greater force on, and wear of, the medial side of the upper cheek teeth and the lateral side of the lower cheek teeth. (J213.6.w2)
    • Elongation plus the normal curvature of the teeth causes formation of spikes on the edges of the occlusal surfaces of the teeth. (B602.34.w34a)
    • Elongation forces the jaw open at rest, until muscle tone increases sufficiently to prevent further eruption, and slows but does not stop tooth growth, therefore the teeth elongate at the apices. (B602.34.w34a, J213.6.w2)
      • The changed jaw angle causes malocclusion of the incisors and resultant incisor overgrowth. (B602.34.w34a, J213.6.w2)
    • Dysplastic changes occur in the newly-formed dental tissues due to proximity to the supporting bone or to abnormal environment where the apices have penetrated the bone and tissues. An early, mild dysplastic change is increased tooth curvature. (B602.34.w34a)
    • Increased curvature results in increased formation of spikes. (B602.34.w34a)
Infectious Agent(s) --
Non-infectious Agent(s) --
Physical Agent(s) --
General Description
Clinical signs
  • Anorexia, weight loss.
  • Salivation, staining of the sides of the mouth, throat and front legs with saliva. (J4.155.w7)
  • Listlessness, dehydration, failure to groom. 
  • Reluctance or inability to eat caecotrophs, leading to Caecotroph Accumulation in Rabbits and fly strike (Myiasis).
  • Matting of the forepaws (caused by pawing at the mouth).
  • Failure to groom.
  • Failure to eat hay, or only eating small amounts of hay. (J29.16.w5)
    • Elongating tooth roots place pressure on the tooth nerves at the tooth apex, therefore biting on hard foods may be painful. (J29.16.w5)
  • Recurrent gastro-intestinal problems, due to inability to eat sufficient fibrous food.
  • Facial abscesses.
  • Signs of pain.
(B600.7.w7, B601.18.w18, J3.139.w7, J4.155.w7, J15.19.w3, J29.16.w5, J60.6.w3)
Diagnosis
  • Visual inspection. This can be carried out in the conscious rabbit using an auroscope (or an illuminated nasal speculum which gives a wider field of view, and more thoroughly with the rabbit under sedation or anaesthesia. (B601.18.w18, J3.137.w8, J15.19.w3, J213.6.w2, J213.9.w1)
    • The conscious rabbit should be wrapped in a towel and held firmly during the examination. See: Physical Examination of Mammals - Handling for Physical Examination
    • Slide the auroscope down one side of the rabbit's mouth, then the other side. Assess:
      • The length and shape of the molars.
        • Normal molars have short visible crowns, arranged symmetrically. These should be light cream (or may be brown stained). The lingual aspect should be sharp but without any spikes. (J15.19.w3)
      • The presence of spurs digging into the tongue (lower cheek teeth) or gums (upper cheek teeth).
        • Spurs as short as 1 mm in length may cause significant discomfort. (B601.18.w18)
      • Defects in the enamel, dental caries. 
      • Damage to the soft tissues.
      • Any blood, discoloured saliva or pus.
      • Broken molars.
      • Absent teeth.

      (J15.19.w3)

    • Palpation of the head to detect swellings (e.g. hard swellings along the ventral border of the mandible, associated with elongated roots of cheek teeth). (J15.19.w3, J29.16.w5)
  • Radiological assessment. (J15.19.w3)
    • This provides information about the tooth roots and the bones. (J15.19.w3)
    • A lateral view is usually the most informative. In a true lateral the mandibles are superimposed on one another; more information may be available if a slightly oblique view is obtained. (J15.19.w3)
    • Superimposition of the mandible over the maxillae makes interpretation of the dorsoventral view harder; it is important to get good, straight positioning for this view. (J15.19.w3)
    • A dorsoventral view may show "blurring" (loss of definition) and a loss of normal root structure. It may be possible to see the root of the second upper premolar (if elongated) penetrating the lacrimal bone.
    • A lateral view may show:
      • Normal (Grade 1): Ventral border of the mandible smooth, without elongated tooth roots penetrating the periosteum. Occlusal surfaces of the cheek teeth present a regular zigzag pattern. The roots of the upper and lower cheek teeth have a parallel, smooth, vertical linear pattern.
      • Grade 2 (early dental disease): Ventral border of the mandible thin, with elongated cheek teeth roots and bony swellings where these penetrate the periosteum. 
      • Grade 3 (tooth crown growth abnormalities, occlusal defects): Loss of the normal zigzag pattern of occlusion of the cheek teeth. Elongated tooth roots. Distortions of the teeth.
      • Grade 4 (major crown abnormalities, cessation of tooth growth): Broken crowns, tooth growth ceases. Teeth may appear more radiodense and have lost their linear pattern. Some roots may resorb. Loss of enamel leads to a blurred outline of the teeth.
      • Grade 5 (steomyelitis and abscesses): pathological changes to the roots and surrounding bone; it may be difficult to determine the limits of adjacent teeth.

      (J15.19.w3)

    • Spurs often develop first on the second or third lower cheek teeth, and next on the first and second upper cheek teeth, which curl into the cheek. Later, the fourth and fifth lower cheek teeth may curve outward. Sometimes the fifth lower cheek tooth grows rostrally, along the occlusal surfaces of the other cheek teeth. (J29.16.w5)
Further Information
Treatment
It is generally agreed that, whatever else is or is not done, sharp hooks/spikes/spurs on the molars need to be removed. The extent to which reduction of molar crowns should be carried out, and whether or not this can alter the progression of acquired molar abnormalities, is debated. 
  • Removal of sharp hooks and spurs
    • Hooks, spurs or spikes can be cut using long-handled molar clippers. (B600.7.w7, J15.19.w3) or bone forceps. (J4.155.w7)
      • A flat fissure bar in a straight, low-speed dental handpiece, with a bur guard, is recommended. (J213.6.w2)
    • It has been noted that "simply removing "spikes" from the edged of the occlusal surfaces of the teeth does nothing to correct the underlying problem." (J213.6.w2)
      • Spikes should be removed as part of general molar reshaping and reduction. (J213.6.w2)
    • Note: 
      • Hooks often regrow after about six to 12 weeks if the teeth are distorted, since the regrowing teeth will not occlude properly. (J15.19.w3)
      • When dental disease is advanced, tooth growth may cease and trimming may no longer be needed; inspection for hook development should be continued at this stage. (J15.19.w3)
  • Reduction of elongated crowns
    • Equipment required
      • Molars can be shortened and smoothed with an appropriate instrument such as long-handled molar cutters (B601.18.w18) a diamond rasp. (B601.18.w18, J15.19.w3) or dental burrs. (B600.7.w7, B601.18.w18)
        • A flat fissure bar in a straight, low-speed dental handpiece, with a bur guard, is recommended. (J213.6.w2)
        • "Clipping and rasping are unacceptable because thy result in tooth fracture, and the energy transmistted into the teeth damages the periodontal and periapical tissues." (B602.34.w34a)
      • Care must be taken, whether using powered or unpowered instruments, not to injure the soft tissues of the mouth. Severe haemorrhage can occur. (B600.7.w7)
      • Burr covers should be used, although these can also cause soft tissue damage, and care is required that they do not give an excessive sense of security. (B601.18.w18)
      • Thermal damage can occur if prolonged burring is carried out without appropriate cooling of the teeth. (B600.7.w7)
      • Soft tissues can be retracted out of the way using a cheek dilator with wide blades, wooden spatulas, tongue depressors or scalpel handles. (B601.18.w18)
      • Moistened cotton buds can be used to moisten the tooth surface, reducing the risk of a burr "walking" off the tooth, and for removal of debris. (B601.18.w18)
      • With hand equipment (cutters for gross reduction, diamond rasp for smoothing), the procedure takes longer and reshaping is less accurate than with powered burrs. (B601.18.w18)
    • Reduction of molar length (coronal reduction) to allow return to normal wear
      • It has been suggested that in the early stages of dental disease, before significant structural changes have developed, repeated shortening of the molars at intervals of four to eight weeks, together with by provision of an appropriate diet, will allow redevelopment of a normal occlusive surface. (J213.6.w2)
        • If there is a mild alteration in tooth curvature, some correction may occur following repeated treatment. (J213.6.w2)
        • Once disease has progressed further, changes are irreversible and shaping every six to ten weeks will be needed for the rest of the rabbit's life. (J213.6.w2)
      • Radiographic assessment (lateral view) indicates the degree of elongation of the teeth, which can be used to determine amount of reduction needed. (J213.6.w2)
      • For each tooth in turn, the bur is used starting on the lateral aspect of the front tooth of the row and moving caudally along the tooth, then repeating on the medial aspect. Powdered tooth is removed using a damp swab and the next tooth in the row is shortened in the same way. Once all the teeth in the arcade have been shortened, the flat side of the bur is used to restore the correct occlusal angle.
      • If a total of 2 mm or more (mandibular plus maxillary) of tooth length has been removed, normal chewing may not be possible for several days while the masticatory muscles adapt. Assisted feeding may be needed during this time. (J213.6.w2)
      • Reducing the crown length will also remove spikes and most caries lesions. (J213.6.w2)
      • The extent to which molars should be shortened is debated. (B600.7.w7)
    • Reduction of molar length (coronal reduction) to allow normal eruption
      • Some practitioners suggest shortening molars down nearly to gum level, taking them temporarily out of occlusion to allow them to erupt normally. (B601.18.w18)
        • This is repeated at intervals of four to six weeks; several treatments may be needed. (B601.18.w18)
        • This is only useful in the early stages, not in the later stages of dental disease when treatment is only palliative.
        • Coronal reduction is contraindicated once eruption of the teeth has stopped. (B601.18.w18)
        • Radical reduction may expose sensitive dentine. An unbonded resin can be applied to fill and block the dentine tubules and prevent discomfort. (B601.18.w18)
        • Following radical coronal reduction, normal chewing will not be possible initially, therefore a postoperative recovery diet which does not need to be chewed should be fed. (B601.18.w18)
        • Return to a normal, abrasive diet including grass and hay as soon as possible. (B601.18.w18)
          • This is important not only for normal tooth wear but also for normal gut function. (B601.18.w18)
    • Reshaping following removal of spurs and removal of loose crowns only
      • "Corrective dentistry cannot restore normal occlusion to maloccluded cheek teeth because of the altered position, shape and structure of the teeth." (B600.7.w7)
      • Excessive shortening and smoothing should be avoided, as this may expose sensitive dentine, making it painful for the rabbit to eat. (J29.16.w5)
      • Once the molars show malocclusion and overgrowth, and the rabbit is presenter for treatment, the tooth roots have already elongated and the teeth are curved, therefore shortening of the teeth will not restore normal occlusion. (B600.7.w7, J29.16.w5)
    • Reduction of incisors
      • Once the cheek teeth have been shortened, the incisors are checked and shortened if necessary. (J213.6.w2)
      • It may be necessary to shorten the incisors also, since elongated incisors may prevent occlusion of the molars until the molars have grown. (B600.7.w7)
  • Removal of cheek teeth
  • Analgesia
    • This should always be given after trimming of the cheek teeth. (B600.7.w7)
  • Topical treatment of ulcerated and necrotic areas of the tongue. (J4.155.w7) See: Oral Soft Tissue Trauma in Rabbits
  • Improve the diet and if necessary add calcium supplements, to correct calcium deficiency leading to metabolic bone disease and dental abnormalities. (J15.19.w3) See details under prevention (below)
  • Antibiotics for early osteomyelitis or periapical infection.
    • Choice of antibiotic should be based on bacterial culture and sensitivity testing. (B601.18.w18) This is particularly important for fast-growing abscesses since unusual organisms may be involved. (B600.8.w8)
    • A study published in 2002 found that the bacteria involved in rabbit tooth-associated mandibular and maxillary abscesses included anaerobic gram-negative rods (particularly Fusobacterium nucleatum), anaerobic gram-positive spore-forming rods (especially Actinomyces spp.) and aerobic cocci, particularly from the Streptococcus milleri group. Pasteurella multocida was not isolated. All of the isolates tested were susceptible to chloramphenicol and to clindamycin, and most (96%) to penicillin, ceftriaxone and cefazolin, with 86% susceptible to azithromycin and tetracycline. However only 54% were susceptible to metronidazole and ciprofloxacin and only 7% to trimethoprim-sulfamethoxole. Clinically, 97 of 104 such abscesses (97%) had not recurred following treatment involving AIPMMA (antibiotic-impregnated polymethyl methacrolate) beads of clindamycin and/or ceftiofur. (J93.40.w5)
Prevention
  • Correct diet. (B600.7.w7, B601.18.w18, J15.19.w3, J213.6.w2)
    • While the exact mechanism(s) behind development of aquired dental disease may be debated, it is generally agreed that providing an appropriate diet can prevent most cases arising and may reduce disease progression. A diet more like that of the wild rabbit, based on grass and other green foods (or hay and supplementary greenstuffs) is considered to be ideal as the whole or major part of the diet.
    • Provide hay (and preferably grass in summer). This is an important part of the diet for pet rabbits. It provides (variable) vitamin D, fibre (essential for normal GIT function) and dental exercise which may encourage normal wear of the constantly-growing teeth.
    • Provide a balanced concentrate diet.
      • If using a mix (which allows the rabbit to eat selectively), give a smaller amount to encourage the rabbit to eat all its ration (and to eat hay). Once the food has been given, it should not be topped up or replaced until all components have been eaten.
      • A complete pelleted diet may be given. Some rabbits will not eat these, but acceptance is much higher with modern pelleted feeds. (V.w125)
    • Reduce feeding of energy-rich diets. (B601.18.w18)
    • Offer palatable green food daily.
      • Dandelion and clover are high in calcium. (J3.139.w7)
    • Alfalfa can be given (not all rabbits will eat this); this is high in calcium.
    • Provide a natural diet of unimproved pasture, or if this is not possible, hay plus some other green food. (J213.6.w2)
  • A vitamin and mineral supplement can be given for fussy eaters in which calcium deficiency has been diagnosed.
    • Nutrobal (VetArk) contains 208 mg calcium per gram and may be used for rabbits with severe nutritional osteodystrophy.
    • Vionate (Shirleys) contains calcium at 94.5 mg/g.
    • Arkvits (VetArk) contains calcium at 142 mg/g.
    • The supplement can be sprinkled onto preferred, easy-to eat soft foods such as bread or lettuce.
    • Note: Excessive supplementation may lead to development of urolithiasis. (J3.139.w7) See: Urolithiasis in Lagomorphs

    (J15.19.w3)

  • Provide access to the outside where the rabbit will have the option of basking in sun, particularly in summer, but preferably year-round. (B601.18.w18, J3.139.w7, J15.19.w3)
Associated Techniques
Host taxa groups /species
Disease Author Debra Bourne MA VetMB PhD MRCVS (V.w5)
Referees Molly Varga BVetMed DZooMed MRCVS (V.w125)

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