Rabbit and Rodent Dentistry
World Small Animal Veterinary Association World Congress Proceedings, 2007
Rod Salter, BVSc, MACVSc (Veterinary Dentistry)
Melbourne Veterinary Referral Centre
Glen Waverley, Australia

Biography

I have been involved with Veterinary Dentistry since the inception of the Australian Veterinary Dental Society in 1990. Along with three others I was one of the initial group to be admitted to ACVSc Membership, in 1993, by examination in veterinary Dentistry. I have attended and lectured at each AVA and American Veterinary Dental forum since 1994. In 2001 I was an invited lecturer at the WSAVA program in Vancouver. I wish to become both an American Diplomate and a Fellow of the Australian College. I would like to establish a Vet Dentistry training centre for vets and vet nurses.


The teeth of dogs and cats with their large roots and strong periodontal ligament require the extraction principles of breaking down support and tooth sectioning into individual root segments. Both rodents and lagomorphs have a heterodont dentition, with varying tooth shapes of incisors, premolars, and molars.

The rabbit's deciduous teeth start to exfoliate possibly even before birth, with the tips of the maxillary incisors present at that time; total replacement occurs by 3-5 weeks of age.

The dental formula of rats is 2 x (1 1/1, C 0/0, P 0/0, M 3/3) = 16. The lagomorph dentition has four maxillary incisors as compared with two in rodents, as well as additional premolars. The dental formula for rabbits is 2 x (12/1, C 0/0, P 3/2, M 3/3) = 28.

In lagomorphs, the location of the two smaller rudimentary maxillary incisors (peg teeth) directly caudal to the two large grooved incisors is a double-row dentition. The large incisors of both groups are continuously growing and considered to be aradicular hypsodonts, i.e., long-crowned without a true root structure. The exposed or clinical crown is the supragingival portion, while the reserved crown is subgingival.

All lagomorph cheek teeth and guinea pig molars are also aradicular hypsodonts. Rats, mice, hamsters, and gerbils have molars that are brachyodont (short-crowned, closed roots) that do not continuously grow or erupt.

The continuously growing teeth have some interesting characteristics that fit well with their form and function. The periodontal ligament has an intermediate group of collagen fibers that attach to either the alveolar bone or cementum, not both, with "splicing" in between. This intermediate plexus differs from the traditional view of ligament fibers running the entire distance from bone to tooth, and may provide a more suitable mechanism by which continually growing or erupting teeth can have extensive tooth movement using this middle zone.

Enamel on the incisors of both rodents and lagomorphs is thickest on the facial surfaces, thinning as it extends onto the distal and mesial surfaces; it is nearly nonexistent on the lingual aspect, which is covered with softer dentin and some cementum. This configuration of dental hard tissue promotes a wearing pattern that results in a sharp, chisel-like tooth.

In rabbits, the large maxillary incisors grow at a rate of 2.0 mm/wk, while the mandibular incisors grow 2.4 mm/wk anteromesially. There is a faster attrition rate, typically due to dietary influences alone, of the lower incisors to compensate for the difference.

The position of the most apical portion of incisors may vary depending on the animal. Rat maxillary incisors extend for two-thirds of the diastema, while the mandibular incisors reach distally to the last molar. Guinea pigs have maxillary incisors that end near the mesial aspect of the first cheek tooth, with their mandibular counterparts traveling lingually and to the level of the second cheek tooth. Lagomorph maxillary incisors extend for one-third of the diastema, and the mandibulars reach the mesial surface of the 1st premolar.

In rabbits, mastication is typically performed in a lateral, scissors-like fashion due to a horizontal oral mandibular fossa of the temporomandibular joint. The lower incisor cuts back and forth in between the peg teeth and the larger maxillary incisors. The lateral grinding movement is facilitated in the caudal teeth with a flat occlusal surface and deep transverse enamel folds.

Rabbits as young as 3 weeks may exhibit mandibular incisors that are level with or even extend labially to their maxillary counterparts.

The teeth continue to grow without proper occlusive wear, with the maxillary incisors starting to curl or twist in the mouth. Once the teeth are overgrown, the animal cannot eat properly, may drop its food (quidding), traumatize the tongue, and have excessive salivation (ptyalism or "slobbers") that can lead to wet dewlap (moist dermatitis) in rabbits. Excessive overgrowth may cause the maxillary incisors to penetrate into the sinuses or ocular sockets.

Malocclusion and overgrowth of the incisors with failure to properly close the mouth can further lead to molar overgrowth and malocclusion in rabbits and rodents with aradicular hypsodont cheek teeth. If the condition is left untreated, maxillary molars may flare outward, lacerating the buccal mucosa, while the mandibular molars overgrow lingually, potentially trapping the tongue either ventrally or dorsally.

Cheek teeth overgrowth is seldom recognized until signs are well advanced, due to the difficulty in routinely examining the teeth, and holds a poor prognosis.

Traumatic malocclusions are the result of overgrowth of a tooth after the loss or fracture of its opposing counterpart. Loss of proper attrition may lead to many of the same symptoms and problems as atraumatic malocclusion.

Crown trimming or reduction must be done, preferably with a diamond burr or disc on a regular basis every 3-8 weeks until normal occlusion is re established, or in some cases indefinitely. Owner must realise that, with a malocclusion or loss of a tooth causing overgrowth of the opposing tooth, treatment is an on-going, long-term commitment.

If a tooth is lost entirely to trauma or has extensive infection that is unresponsive to conservative therapy and antibiotics, extraction of the remaining structure and the opposing tooth may be chosen over the need for regular crown reduction.

The location of the tooth, type of tooth (hypsodont or brachyodont), and general patient health determine the advisability of extractions. Some individuals are in extremely poor condition at the time of presentation, and antibiotics, anti-inflammatory drugs, fluids, force-feeding, and nursing care may be in order to improve general health prior to anesthetic stress.

Location of the tooth becomes important to accessibility. Incisors have good accessibility, while many cheek teeth do not. Occasionally, buccotomies must be performed in some species for visibility and accessibility; however, food impactions, healing problems, and scars may result. Close attention to locations of vascular, neural, and other structures must also be considered.

Closed-rooted cheek teeth (brachyodont), such as those in the rat, can be extracted with some care with an intraoral approach using curved elevators. This technique involves care and practice. In the mouse, gerbil, and hamster, the brachyodont cheek teeth are extremely small and difficult to properly remove, unless highly mobile. Broken roots can seldom be addressed without inducing excessive oral trauma in very limited spaces.

With extraction, some migration of adjacent teeth and slight supereruption of opposing teeth no longer in occlusal contact may occur and require ongoing monitoring.

With open-rooted cheek teeth an intraoral approach is usually difficult and time-consuming, while buccotomies have their own associated problems.

With the mandible, an extraoral approach through the bone covering the apices is generally best. A simple incision is made over the bony enlargement or abscess site. The specific location is best determined by use of radiographs and a knowledge of the apical anatomy.

Guinea pigs commonly have three normal alveolar juga, or bone elevations, that may mimic an abnormality and can be palpated on the ventral surface of the mandible, representing the apical border of the first and last two cheek teeth.

The cortical plate can generally be curetted open with a periosteal elevator or a high-speed dental burr. The impacted or infected teeth can often be extracted through this access site. In some cases, teeth will need to be repelled into the mouth from the access site.

If a cystic lesion is encountered, it must be thoroughly curetted.

Good closure can be difficult, especially for the intraoral side of the defect. When possible, the attached gingiva should be loosened with a periosteal elevator on either side of the defect and should be sutured closed with absorbable suture material. The bony defect may be packed with an appropriate osteogenic material. The external access is sutured with absorbable suture material.

The oral cavity should be cleaned and disinfected with an oral chlorhexidine solution. Complicated or time-consuming extractions should have both pre- and postsurgical radiographs taken.

The next step in incisor extraction is the severing of the epithelial attachment. A surgical blade or a small, sharp periosteal or dental elevator can be used for this purpose. The blade is inserted into the gingival sulcus until it meets with the resistance of the alveolar crestal bone. The sulcal incision is extended around the entire tooth, thus releasing the epithelial attachment. Actual elevation and removal of the tooth can be performed using a periosteal elevator, a refined elevator, or an injection needle and a small pair of extracting forceps.

Elevators should be sharpened and shaped on a regular basis specifically for use in small herbivores.

The elevator is used to elevate between the tooth and alveolar crest to separate the periodontal ligament. The mesial ligament attachment is typically the most difficult to break down. The instrument is placed against the periodontal ligament and used in a sight twisting movement parallel to the reserved crown, while being pressed apically. The process is repeated around the circumference of the tooth, until the reserved crown becomes loose and can easily be removed with small extracting forceps. The extracting forceps should not be used to attempt forcible extractions, as this can result in fractures of the tooth or supporting bone.

An alternative method is the use of syringe needles in the place of elevators. In rabbits, 18- and 20-gauge needles work well for most teeth. In rodents, because of the greater size variability, the needle must be selected to fit the incisor.

Once the tooth is removed, the socket is cleaned and curetted of debris or granulation tissue. Bony prominences and spicules are reduced with a burr, curette, or rongeur. If infected, the sockets should be left open for drainage, unless hemorrhage is a problem. In these cases, clean the socket well, flush with saline, and suture closed with absorbable suture material.

Antibiotics are recommended if active infection is detected. The patient should be rechecked in approximately 10-14 days to inspect the healing process. Most patients quickly return to eating after surgery in a matter of hours, but occasionally some with sore mouths need encouragement or force- feeding.

Should reserved crown tips be broken off in the alveolus, regrowth of the tooth may occur in 4-8 weeks, necessitating a second attempt at extraction at that time. Periodically, the remaining portion may not regrow but become a focus of chronic infection requiring additional attention.

In chronically infected cheek teeth surgical intervention may be required. Radiographs should be used to pinpoint the location, as there is great variation as to the apical location within lagomorphs and rodents. An incision is made along the ventral border of the mandible and reflected facially and coronally.

Commonly, alterations in normal bone structure will be observed at the pathologic site, indicating appropriate access. If these are not observed, radiographs must be relied on for access selection. In many cases the bony structure will be soft from disease and can be carved away with a sharp periosteal elevator, or #2 or #4 round ball burr or a diamond burr.

Copious water flow should be used with burrs to prevent thermal damage to adjacent hard tissues.

Once the reserved crown is exposed, the No. 2 Molt ordinarily works well to remove the fragments and to thoroughly curette the lesion.

Fill the site with polymethacrylate bone wax impregnated with tobramycin, and suture it closed using a small-gauge absorbable suture material.

References

1.  Wiggs and Lobprise, Veterinary Dentistry Principles and Practice

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

Rod Salter, BVSc, MACVSc (Veterinary Dentistry)
Australia


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