Introduction to Rabbit Dental Disease
World Small Animal Veterinary Association World Congress Proceedings, 2015
Marc H. Kramer, DVM
Avian & Exotic Relief Veterinary Services, Miami, FL, USA

Introduction

Rabbits, guinea pigs, chinchillas, and prairie dogs are herbivorous species.

They have a very specialized nutrition and nutritional requirements.

Complications due to dental disease are wider and more severe when compared to those of carnivores.

The "syndrome" that most rabbit/rodent dental diseases are referred to is called acquired dental disease (ADD).

Clinical exam: Symptoms of dental disease can be varied.

 Poor coat quality

 Weakness

 Painful posture

 Anorexia/dysphagia

 Dehydration

 Reduced or abnormal feces

 Soft or watery feces

 Epiphora

 Dacryocystitis

 Nasal discharge

 Exophthalmos

 Panophthalmitis

 Dewlap, facial, and inguinal dermatitis

 Mandibular and/or maxillary masses

Dentition of Rabbits

Dental formula: 2I 0C 3P 3M/1I 0C 2P 3M

Incisors

 4 upper incisors: 2 rows of 2 incisors per row; the caudal most upper incisors are much smaller and are called the "peg teeth".

 2 lower incisors: In a resting position, the lower incisors occlude with the peg teeth or in a small notch between the rostralmost upper incisors and the peg teeth.

Premolars and Molars

 Collectively referred to as the "cheek teeth"

 No functional difference between premolars and molars

 Each upper arcade has 6 cheek teeth.

 Each lower arcade has 5 cheek teeth.

 Roots of the upper cheek teeth lie extremely close to the orbit and the nasolacrimal duct.

All teeth in the rabbit are elodont (open-rooted). They continuously grow throughout the life of the rabbit.

In the rostrocaudal view of the skull, the upper and lower cheek teeth are out of occlusion; the upper cheek teeth lie in a more lateral position and the lower cheek teeth are medial.

Acquired Dental Disease of the Incisor Teeth

Commonly, the lower incisors will elongate and protrude rostrally, while the upper incisors will elongate and curl inwards.

Incisor teeth can appear out of occlusion, at abnormal angles, appearing in various states of deterioration.

Causes

 Congenital (not considered an acquired dental disease, since it is congenital)

 Mandibular/maxillary abnormalities (e.g., tumors, jaw fractures, etc., that disrupt incisor occlusion or growth)

 Secondary to ADD of the cheek teeth

 Traumatic (fractures of the incisor teeth)

 Metabolic (e.g., poor nutrition, lack of sunlight)

Acquired Dental Disease of the Cheek Teeth

Pathophysiology

Three main etiologies have been proposed for the pathophysiology of ADD:

 Congenital defects

 Mandibular prognathism

 Maxillary brachygnathism

 Nutrition

 Insufficient wearing of occlusal planes

 Fractures due to inappropriate food

 The diet of pet rabbits is not identical to that of free ranging rabbits

 Even rabbits allowed to graze freely likely do not consume grasses with the same types and amounts of silicates

 Nearly 100% of pet rabbits will develop ADD during their lifetime, and many cases will be mild or inapparent

 Nearly 100% of the owners feed rabbits improperly

 Insufficient wearing leads to excessive elongation of crowns and roots, with bending of the axis of the cheek teeth, deformation of apexes and development of spurs

 Physiology of chewing: 4 basic movements in the rabbit

 Rostrocaudal, caudorostral, lateral, and vertical

 The degree of lateral motion of the jaw is partially determined by the type of food consumed

 Hay or natural fibrous vegetable food produces wide lateral movements with reduced vertical motion

 Concentrated pelleted food or grains produces reduced lateral movements and more extensive vertical motion (more pressure on roots, less wearing)

 Metabolic

 Metabolic bone disease, a.k.a. nutritional secondary

 Hyperparathyroidism (NSHP)

 Frances Harcourt-Brown proposed this pathophysiologic hypothesis based on the following observations

 Many rabbits who live outdoors with exposure to natural sunlight do not develop ADD

 Most rabbits with metabolic bone disease demonstrate demineralization of the skull bones

 A study performed on more than 80 rabbits with ADD and MBD demonstrated parathyroid (PTH) level much higher than normal levels

History

The rabbit is prone to hide or minimize clinical symptoms. History is always incomplete, absent, or misleading.

 The rabbit is eating nothing or less than normal? How much less than normal?

 Complete review of diet offered and consumed

 Quantity/quality of stool

 Does the rabbit chew frequently without food present?

 Is the rabbit interested in food, but dysphagic?

 Is the rabbit drinking?

Physical Exam

Clinical Exam - Without Anesthesia

Thorough dental evaluation must always be performed in rabbits and rodents, even in the absence of significant history supporting dental disease.

It is mandatory to perform inspection of oral cavity always after the clinical exam without sedation.

Clinical Exam - With Anesthesia

In cases of suspected or confirmed acquired dental disease, it is mandatory to perform a complete clinical examination under anesthesia.

During clinical examination under anesthesia, additional diagnostic testing is very important.

Basic Principles of Anesthesia and Analgesia

Most dental procedures depend on the anesthetic protocol for induction.

Compare and contrast induction with injectable vs. inhalant drugs.

Induction with Injectable Anesthesia

 Option 1 (deep sedation)
Ketamine/butorphanol/dexmedetomidine

 Option 2 (mild-moderate sedation)
Midazolam/butorphanol

 Other injectable sedation options exist.

After 5–10 minutes, rabbit should be sufficiently sedated

From there, administer:

 Oxygen (when possible)

 Oxygen + isoflurane at 1%–3% if a greater depth of anesthesia is needed

Advantages/Disadvantages

 Quicker induction time (2–5 minutes)

 Less stressful for most patients

 Quicker achievement of surgical anesthetic plane

 Respiratory depth and frequency, cardiac activity, blood pressure: more depressed than inhalant agents alone

 Longer recovery time (although administering atipamezole at the end of the procedure can be used to reverse the dexmedetomidine and allow for a faster recovery)

Induction with Inhalant Anesthesia

Oxygen + isoflurane at 3%–5% (by face mask)

Advantages/Disadvantages

 Longer induction time

 Constant restraint of the patient needed during the induction phase

 More stressful

 Risk of apnea in rabbits

 After induction, the proper surgical anesthetic plane is still not achieved

 Respiratory depth and frequency, cardiac activity, blood pressure: less depressed than injectable agents

 Quicker recovery time

Patient Intubation for Anesthesia - Is It Always the Best Choice?

Intubation provides more direct delivery of anesthesia to the lungs, provides emergency respiratory access, and can prevent accidental aspiration.

Rabbits can usually be intubated, with some exceptions; special techniques are required for intubation.

The endotracheal tube may interfere with taking radiographs of the skull, and with certain dental procedures.

Nasal intubation, nasotracheal intubation, and orotracheal are all possible options depending on the procedure performed.

Author's preferred anesthetic regimen for diagnosis, initial evaluation, and treatment of dental disease:

 Induction of anesthesia with injectable agents

 Maintenance of anesthesia with supplemental isoflurane as needed

 Maintenance with oxygen alone, if anesthetic plane is deep enough

 Allow the patient to breathe room air only if the patient is well oxygenated (can monitor with pulse oximeter)

 Removal of the face mask at the instant collection of radiographs

 Maintenance of supplemental isoflurane (by face mask or orotracheal intubation) during oral endoscopy

 Maintenance of supplemental isoflurane (by face mask or orotracheal intubation) during intraoral dental procedure

 Maintenance of supplemental isoflurane (by face mask or orotracheal intubation) during the extraoral procedures

Radiology

Know your equipment, get accustomed to correct setting for rabbit skull views

 Mammography x-ray film provides much greater detail and high resolution

 Review different radiographic projections in class: lateral, ventrodorsal, left and right obliques, and rostrocaudal; and (optional) intraoral projection

 Normal radiographic appearance: lateral skull radiograph

 Lower incisors should occlude with peg teeth

 Lines drawn parallel to roof of maxilla and floor of mandible should converge if extended way past the film; parallel or diverging lines are abnormal

 Zig-zag line to represent occlusal surface of cheek teeth

 Strong uninterrupted line of cortical bone at base of mandible below tooth roots

 Normal radiographic appearance: VD radiograph

 First upper premolar teeth visible

 Evaluate symmetry and quality of tympanic bullae

 Evaluate zygomatic arches, orbit, etc.

 Normal radiographic appearance: oblique views

 Allows evaluation of a non-superimposed view of the cheek teeth

 Primarily evaluating the lower cheek teeth roots

 May also be able to view upper cheek teeth roots

 Normal radiographic appearance: rostrocaudal projection

 Evaluate another view of the occlusal surfaces and the resting position of the upper and lower cheek teeth

 Nasolacrimal duct can be evaluated radiographically with contrast media

 Specialty rabbit/rodent dental instrumentation

 Mouth gag cheek dilators spatula

 Dental rasp

 Table top mouth gag device (great investment!)

Oral Endoscopy

 Endoscopic equipment

 2.7-mm rigid 30-degree bevel endoscope

 Light cable, light source

 Videocamera for endoscope recording device

 TV monitor

Why Oral Endoscopy?

 Technically simple procedure

 Requires no special skill or specialization Allows a thorough inspection of the oral cavity offers a magnified perspective of dental disease Highly reduces risk of missing lesion

 Facilitates coronal reduction and other therapeutic procedures

 Can facilitate endotracheal intubation

 Allows recording of pictures for veterinarian's database and for demonstration to the owner

Additional Diagnostic Testing

 Culture and sensitivity

 Histopathology

 CT Scan

 Early stage of cheek teeth malocclusion

 "Wave mouth" and "step mouth"

 Spurs (lower cheek teeth usually get lingual spurs; upper cheek teeth get buccal spurs)

 Mid- to late-stage cheek teeth malocclusion

 Tongue lesions (ulcerations)

 Cheek soft tissue lesions (ulcerations)

 Root elongation

 Osteomyelitis

 Facial abscessation

Summary

 Rabbit dental disease is a complex subject

 This was just an introduction to the topic

 Practicing on rabbits requires familiarity with the complexity of dental disease and dental anatomy, since it is extremely common

 Continuing education is exotics is key to success!

Speaker Information
(click the speaker's name to view other papers and abstracts submitted by this speaker)

Marc H. Kramer, DVM
Avian & Exotic Relief Veterinary Services
Miami, FL, USA


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