Session #1003

Abstract

Diseases of the oral cavity, particularly syndromes of acquired dental disease, are the most common disorders in pet rabbits, guinea pigs, chinchillas and degus. In the most recent two decades, the number of articles and books describing dental disease and its therapy have increased. However, there are still oral cavity disorders which are not exactly described and therapeutic approaches which need to be verified by clinical practice. This lecture and paper describe oral cavity anatomy, clinical approach and therapy of selected oral cavity diseases.

Introduction

As a result of the increasing numbers of rabbits, guinea pigs, chinchillas and other small mammals being kept as private pets, dental disease is being observed more frequently in veterinary clinics. The incidence of oral cavity disease is approximately 30–80% and varies both between species and within a species with age, with older animals affected more frequently.^1-7 In the most recent two decades, the number of articles and books describing dental disease and its therapy have increased.^1-30 However, there are still oral cavity disorders which are not exactly described and therapeutic approaches which need to be verified by clinical practice. This article describes an approach to the dental patient and therapy of selected oral cavity disorders.

Oral Cavity Anatomy and Physiology

Rabbits, guinea pigs, chinchillas and degus have completely elodont dentition. The permanent rabbit dental formula is I(2/1), C(0/0), P(3/2) and M(3/3) for rabbits and I(1/1), C(0/0), P(1/1) and M(1/1) for other species listed above.^1,9-14 Dentition is diphyodont (deciduous and permanent teeth) and heterodont. Rabbits also belong to Duplicidentata due to the presence of a double set of maxillary incisors (incisors and peg teeth). Premolars and molars have similar structure, and in each quadrant of the oral cavity they form a uniform functional grinding unit. Enamel width is more prominent at the labial part of the cheek teeth and buccal part of the maxillary cheek teeth; it is why the larger enamel ridges are present at these locations, which could imitate spikes. The mandibular arcade is narrower than the maxillary arcade. Rabbit incisors, premolars and molars are continuously erupting through life at the rate of 2–5 mm per week for incisors and 3–4 mm per month for premolars and molars. However, recent studies showed that premolars and molars can erupt almost as quickly as incisors (3–4 mm a week).¹⁵

Guinea pigs, chinchillas and degus belong to Simplicidenta due to the presence of a single set of maxillary incisors. Premolars and molars have similar structure, and in each quadrant of the oral cavity they form a uniform functional grinding unit. Each mandibular cheek tooth is in occlusion with the corresponding maxillary cheek tooth. The occlusal plane is oblique (approximately 30°) in guinea pigs and almost horizontal in chinchillas and degus. The mandibular arcade is wider than the maxillary arcade.

Pathophysiology of Dental Disease

Diseases of the oral cavity, particularly syndromes of acquired dental disease, are the most common disorders in pet rabbits, guinea pigs, chinchillas and degus. Dental disease is multifactorial, and many local and systemic conditions that affect the mouth and oral cavity have been described, including hereditary, infectious, metabolic, traumatic conditions (including foreign bodies), electrical accidents and neoplasms.¹

If the cheek teeth are not worn adequately and elongate intraorally, the mouth is held more open, stretching the masseter muscles and increasing the resting occlusal pressure on the teeth. As a result, the incisors elongate and lose the normal chisel-like wear pattern and animals have problems with bolus formation. As a result of metabolic bone disease, even physiological chewing forces may cause apical intrusion (retrograde elongation) and loss of alveolar-supporting bone. Loss of supporting alveolar bone and forces generated during chewing and tooth growth affects the curvature of the cheek teeth. Widening of the interproximal coronal surfaces, presence of sharp spurs, coronal elongation and abnormal cheek teeth occlusal surfaces are common findings at this stage. In addition, occlusal pressure could prevent eruption of cheek teeth so that the apices intrude and induce bony remodeling of adjacent tissues. When this painful condition occurs in maxillary incisors, epiphora may be clinically evident as a result of nasolacrimal duct obstruction. In degus, retrograde elongation of maxillary premolars and molars can lead to partial nasal cavity obstruction. Mandibular cheek teeth apices also elongate and, in more severe cases, penetrate through the ventral mandibular cortex. As the condition progresses, mastication becomes more uncomfortable and only soft foods may be selectively eaten, resulting in further tooth growth due to lack of wear.¹⁶

Horizontal enamel ridges, which can be seen on the labial part of the incisors, are results of apical germinative tissue pathology. Such enamel dysplastic changes are commonly associated with calcium metabolism disorders.¹⁷

As all the teeth erupt continuously, many factors may have a negative effect on tooth substance (dentin, cementum, enamel) formation. This may lead to improper periodontal alignments, macrodont teeth development and presence of more than one tooth in the alveolar sockets, which is commonly seen in guinea pigs.^18-20

Periodontitis, dental caries and dental resorptive lesions are commonly present in chinchillas, guinea pigs and rabbits.^12,21

Clinical Signs

An accurate history should be obtained from the owner, and a routine clinical examination should be performed on all patients presented for dental procedures. Animals suffering from systemic disease require special attention, and life-threatening conditions should be addressed immediately. Clinical signs are associated with hypersalivation, anorexia, chewing disturbances, changes in food preferences (soft and palatable feed particles) and poor body condition. In some cases, dental disease can also be accompanied by the development of facial/odontogenic abscesses, wet dermatitis, epiphora, exophthalmia and damage to the temporomandibular joint.

Diagnostics

Diagnosis of incisor, premolar and molar pathology is based on clinical examination, intraoral examination under anaesthesia and radiography or computed tomography. Combination of oral cavity endoscopy and computed tomography is the most beneficial for optimal diagnostic and treatment planning.^7,17,22-25

Pathology can be identified only when the examiner is familiar with normal anatomy of teeth and skull of the individual species and pathological changes.

For basic oral examination, animals are restrained manually. Larger animals (rabbits) are wrapped in a towel or an assistant holds the animal’s thoracic limbs and supports its back; the practitioner holds the animal’s head and retracts its upper lips with one hand while examining the oral cavity with the laryngoscope in the other. Conscious oral cavity examination starts with an evaluation of facial symmetry and palpation of the jaws. Signs of heat, discharge, crepitus and presence of facial masses should be noted. Lateral and horizontal lower jaw excursion should be evaluated very gently. Discomfort and pain on manipulating the jaws may be due to a jaw fracture, disease of the temporomandibular joint or because of retrobulbar pathology. If pain is noted, the animal should be monitored closely since it may easily become stressed during examination, leading to possible collapse. Palpation of the ventral border of the mandible and zygomatic area can reveal bony swellings associated with apical teeth elongation.¹³

The oral cavity is long and narrow, making it technically more difficult to examine than the oral cavity of dogs and cats. An otoscope or a paediatric laryngoscope is recommended as a tool for oral examination of conscious animals. When a pathological process is found during conscious oral cavity examination, the animal should be anaesthetized for a more thorough oral cavity inspection.¹³

Radiography and/or computed tomography examination should be a part of standard examination protocol of all animals with suspected or clinical dental disease.^7,17,22-26

Anaesthetized rabbits should be closely monitored; injectable premedication and induction (midazolam, butorphanol/buprenorphine, medetomidine [low dose 0.01–0.02 mg/kg BW], ketamine) with isoflurane anaesthesia is the preferred combination of the author. In cases of mild or severe health impairment, urinalysis and blood haematology and plasma chemistry are used as a part of presurgical examination. Intubation is necessary in patients with cardiorespiratory disorders or during longer procedures in animals where it is possible (rabbits). Some clinicians recommend intubating a rabbit in any surgical procedure. In cases of intraoral clinical crown height trimming and occlusal surface adjustment, the author (VJ) prefers to not intubate the patient, as the tracheal tube interferes with further treatment. However, use of gauze as pharyngeal packing will prevent dust aspiration during dental procedures.

Care must be taken when adjusting the mouth cavity opening to prevent temporomandibular joint injury. Anaesthetic gas may be delivered via customised nasal mask or commercially available facial mask for small animals.

Therapy

All the procedures, treatment plan and prognosis should be explained precisely and consulted again with the client at any point of the therapy. The conservative approach is possible only in cases where no inflammation is present, or periodontitis or another inflammatory process does not affect the tooth to the level where surgical extraction is the best option for the treatment.

Analgesia

Perioperative analgesia (metamizole [dipyrone], NSAID such as meloxicam or carprofen, buprenorphine/methadone intramuscular; or lidocaine, fentanyl, ketamine in CRI) and long-term chronic pain management is commonly necessary as an adjunct therapy to the surgical treatment. Some of the general rules which prevent painful stimuli during clinical crown reduction and occlusal surface adjustment are 1) prevention of heating injury during teeth drilling (do not spend more than 3 seconds on one tooth at one time), 2) prevention of soft tissue (skin and gingiva) injury when using dental burr and 3) using a minimal pressure with the burr when reducing clinical crown.

Local analgesia using lidocaine and/or bupivacaine should be implemented as a part of multimodal analgesia, especially in cases of teeth extraction (infraorbital nerve block, mandibular nerve block).²⁷

Chronic pain management may be provided using nonsteroidal anti-inflammatory drugs (meloxicam 1 mg/kg PO q 24 h), gabapentin (5–30 mg/kg PO q 12 h), opioids (buprenorphine, long-acting buprenorphine) and their combinations.²⁸ Other drugs can also be used (e.g., tramadol, cannabinoids); however, their efficacy has not yet, in these species, been scientifically described.

Peri and Postoperative Care

Peri and postoperative care may include fluid therapy, thermal support, gastrointestinal motility drugs (e.g., metoclopramide, ranitidine, cisapride, itopride) and analgesics. The author may use the motility medications on a case by case basis. Animals should be closely monitored until uneventful recovery. If the animal refuses to eat, convalescent diets for herbivorous small mammals are offered, preferably orally via syringe (Supreme Science® Selective Recovery, Oxbow Critical Care, Emeraid Intensive Care Herbivore®).

Clinical Crown Reduction and Occlusal Surface Adjustment^7,17,29

The aim of intraoral incisor, premolar and molar clinical crown reduction and occlusal surface adjustments is to establish as much physiological occlusion as possible. In old rabbits, some teeth may erupt slowly and have arrested growth, so the aim of the therapy is to allow the rabbit to chew and not to correct all the teeth to the normal clinical crown height. The author uses carbide and steel drills for the clinical crown reduction and then finer diamond drills for occlusal surface adjustment and finalizing the procedure. In cases of guinea pigs, chinchillas and degus, occlusal plane and clinical crown reduction should be as physiological as possible, as chewing pattern is different from rabbits.

Apicoectomy in Guinea Pigs

Macrodontia in guinea pigs is, in comparison with other pet herbivorous rodents and with rabbits, a relatively common disorder. The aetiology is not yet exactly described, but structural changes of the continuously growing tooth seem to be responsible for chronic infection/irritation of the germinative tissue of the affected tooth. The macrodontia is commonly present with other disorders associated with dental disease syndrome such as apical and coronal elongation of the incisors and/or premolars and/or molars, changes in tooth curvature, occlusal surface changes, periodontitis, dental caries and other dental and soft tissue pathologies.

In guinea pigs, teeth in the mandibular arcade, based on the author’s experience, are the most commonly affected. Diagnostics are based on thorough oral cavity examination, radiography and/or computed tomography. Macrodont premolars and molars can be easily identified with the use of the radiographic technique described by Minarikova²¹ or by techniques described by Crossley and Böhmer²⁶. Nevertheless, computed tomography can show a more detailed picture of the overall tooth quality¹⁹ and is the author’s preferred imaging method.

Therapy includes treatment of the primary disorder and affected tooth extraction, which can be done intraorally, extraorally or by their combination. The author’s preferred method is apicoectomy, where the apical part of the tooth is removed by an extraoral approach using a dental burr. After the tooth substance is removed, the use of antibiotic-impregnated beads or marsupialization (used by the author) in cases of bacterial infection, with simple skin closure is recommended. The coronal part (the tooth remnant) acts as a natural plug and prevents feed impaction into the wound after the extraction. This remnant is then worn down by natural chewing and then released into the mouth cavity. In the meantime, the wound is healing from the apical part of the alveolus and preventing further complications.

Odontogenic Abscesses

Appropriate treatment of osteomyelitis includes surgical intervention in combination with antibiotic therapy, analgesia and supportive care. Marsupialization, thorough debridement, affected tooth extraction and affected bone removal are critical in the primary control of the source of infection. Other treatments include a combination of surgical debridement and tooth extraction with local use of AIPMMA beads, long-lasting doxycycline gel or manuka honey and wound closure. Systemic antibiotic treatment for a minimum of 2 weeks after surgery is also recommended.^30-32

Choice of anti-infective agents for the treatment of osteomyelitis is based on cytological and microbiological findings and antimicrobial susceptibilities.^33,34 Bacterial pathogens commonly involved in periapical lesions are Fusobacterium nucleatum, Prevotella heparinolytica, Prevotella spp., Peptostreptococcus micros, Streptococcus milleri group, Actinomyces israelii and Arcanobacterium haemolyticum. The thick consistency of rabbit pus makes aspiration and drainage of these abscesses very difficult and sole antibiotic therapy unsuccessful. Antimicrobial agents demonstrate variable penetration into bone. However, agents with poor bone penetration can achieve bone tissue concentration above minimum inhibitory concentration for target pathogens. Experimental studies performed in rabbits generally demonstrate excellent bone penetration by fluoroquinolones and satisfactory bone concentration achieved by beta-lactams. As an antibiotic of first choice, the author recommends parenteral administration of beta-lactams (penicillin G) or oral metronidazole.

In cases where surgical treatment of osteomyelitis is not feasible, suppressive oral antibiotic therapy has been described to control the disease. Potential benefit from chronic antibiotic suppressive therapy exists; however, it is not an effective alternative to surgical treatment of bone infection.

Acknowledgments

This article was supported by the grant of the University of Veterinary Sciences Brno 2021ITA15.

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