Dental malocclusion / overgrowth

Introduction

Significance

Commonest underlying cause of many seemingly unrelated clinical entities.
Easy to prevent, difficult to treat once clinical signs are evident.
Diet must always be discussed and corrected for all rabbits at consultation.
Oral cavity should always be examined with an auroscope regardless of presenting clinical signs. A bi-valve nasal speculum is also useful for conscious examination of the oral cavity.

Introduction

Common incidental finding during routine clinical examination.
Rabbit incisors grow 1.5-2 mm per week and depend on many hours per day of constant attrition on tough fibrous vegetation to maintain their normal working length; when fed on concentrates, attrition is minimal because the food is too soft and the calorific value so high that they only need to chew for a short time to satisfy their calorific needs (not their nutritional needs).
Calcium and vitamin D deficiency resulting in osteomalacia with insufficient bony strength to support the teeth.
Cause: mainly nutritional osteodystrophy and/or lack of attrition involving all the teeth; less commonly congenital malocclusion, especially in dwarf Dwarf Lop Netherland Dwarf breeds, traumatic fracture of maxilla, mandible, teeth from being dropped.
Signs: minimal until disease is severe, overgrown incisors damaging soft tissues of mouth, horizontal ribbing on upper incisors, palpable swellings along ventral border of mandible, dacryocystitis (NOT conjunctivitis), hypersalivation, dysphagia, anorexia, polydipsia, weight loss, fly strike, caked feces around anus (NOT diarrhea), abscesses.
Treatment: difficult once clinical signs have developed, rectify diet (especially hay and fresh greens), trim overgrown molars, premolars and incisors with dental burr (NOT nail clippers), calcium and vitamin D supplement with care and only if there is radiographic evidence of osteoporosis/osteodystrophy, teeth extractions, dissect out abscesses, antibiotics, euthanasia.
Prevention: natural raw diet rich in fibrous greens especially grass, hay, minimal concentrates (vitamin and mineral rich pellets, not bunny mix), management to reduce risk of osteodystrophy.

Print-off the Owner factsheets on Overgrown teeth, Feeding your rabbit, Caring for your rabbit before and after surgery and Health insurance for your rabbit to give to your clients.

Presentation

Normal rabbit incisors

Chisel-shaped.
'Peg teeth' are small secondary incisors immediately behind the upper incisors.
Lower incisors occlude between upper incisors and peg teeth.
Enamel of upper incisors is slightly yellow, smooth and shiny with one vertical groove running down each upper incisor.
Upper incisors on a much tighter curve than lower incisors.

Hereditary incisor malocclusion

Brachygnathism - particularly lop and dwarf breeds.
Incisors elongate along their natural curvature, growing through any structures they meet, most commonly lips, cheeks nasal cavity, hard palate.
If mouth closure is prevented by incisors, molars will become excessively long.

It is possible for a rabbit with overgrown molars to have normal looking incisors, so it is essential to look inside the mouth Dental examination.

Lack of attrition

Overgrowth of cheek teeth due to lack of attrition leads to altered jaw dynamics and can directly cause an incisor malocclusion as the jaws are forced further apart.
Altered forces on the dental tables can cause root overgrowth and protrusion in the absence of osteoporosis/osteodystrophy.

Osteodystrophic dental disease

Progression of this disease has been categorised into five stages, each of which carries a different prognosis. The range of clinical signs present at any one time will vary between individuals and during the progression of the disease.
Grade 1: normal.
Grade 2: subclinical dental disease:
- Horizontal grooves on maxillary (upper) incisors with or without slight deviation.
- Teeth may be a dull white (defective enamel) and lack the normal vertical groove.
- Palpable swellings along ventral border of mandible.
- Partial or complete obstruction of nasolacrimal duct with secondary infection (dacryocystitis Eye: dacryocystitis), often misdiagnosed as conjunctivitis.
- May be no clinical signs, hence importance of always examining rabbit mouths and correcting diet.
Grade 3: acquired crown abnormalities and occlusal defects:
- Aberrant growth, malocclusion, discoloration or fractures of incisors.
- Incisors may grow into adjacent soft tissues.
- Minor distortions of molars or premolars resulting in sharp spikes which may lacerate or penetrate tongue or buccal mucosa.
- Anorexia Anorexia and weight loss Weight loss.
- Caked feces around anus Sticky bottom syndrome, often misdiagnosed as diarrhea.
- Fly strike Fly strike.
- Salivation and wet chin and dewlap.

If molars/premolars not involved, there may be no clinical signs, unless incisors invade local soft tissues.

Grade 4: major abnormalities of tooth crowns and cessation of tooth growth:
- Periodontal disease - pus discharging around teeth especially incisors.
- Gross distortion of some or all teeth.
- Major pathological changes to tooth roots.
- Abscesses develop when periapical tissues and soft tissues penetrated by elongated tooth crowns become secondarily infected.
- Reluctance to eat hard food.
- Exacerbation of Grades 2 and 3 clinical signs.
- When teeth stop growing, crowns may break off and many clinical signs disappear.
- Some rabbits can eat and groom despite their oral ill health.
Grade 5: osteomyelitis Osteomyelitis and abscess formation Abscess:
- Mandibular, retrobulbar Eye: retrobulbar abscess and lacrimal bone abscesses form in association with periosteal penetration by premolar and molar tooth roots.

Incidence

Geographic

Developed countries where rabbits kept indoors as pets and fed inappropriately.
Rare in commercial rabbit farming as rabbits fed vitamin and mineral rich pellets and killed young.

Morbidity

Age

Congenital incisor malocclusion detectable at 3 weeks old.
Osteodystrophic dental disease not usually evident until 1 year old.

Cost

Grades 3-5 requiring oral/dental surgery becomes expensive as procedures often have to be repeated proving expensive.
Trimming incisors with dental burr in co-operative rabbit without anesthesia can be moderately expensive.
Prevention is inexpensive.

Special risks

Anesthesia

Poor body condition as a result of dental disease.
Aspiration of oral fluids, dental burr-cooling fluids, blood, pieces of tooth and other debris, and endotrachaeal tube in oral cavity causes great obstruction. Intranasal anesthesia is very helpful: block one nostril and insert the tube into the other; apply packing around the pharynx to protect it from aspiration - remember to attach a string to the packing to ensure its removal from the animal before recovery.
Use of injectable anesthetic agents to facilitate access to oral cavity (nasal anesthetic tube too narrow to allow fast enough flow rate, creates excessive resistance, too easily blocked by debris).
Injectable anesthetic agents perceived as dangerous because of inappropriate drug cocktails, overdosage often due to inaccurate weighing of ill rabbits, difficulty of reversing anesthetic agent.
Age.