When dealing with oral cavities in a typical small animal clinic, most practitioners handle dogs and cats with fairly similar problems. Add other small mammals to that mix, and the difference in the structure and function of the pocket pets' oral cavity and teeth brings new challenges.
Functions of Dentition
With dogs and cats, both modified carnivores, the oral cavity has a wide opening and the teeth are brachyodont, with short crowns, distinct roots that mature with root closure and a set length. In herbivores, including many small mammals, the oral cavity has a small oral opening, helpful in keeping the vegetation in the mouth during chewing and grinding. To compensate for the regular attrition of the teeth caused by chewing roughage, the teeth must continue to erupt, in order to maintain a constant height in the mouth.
In horses, the constant wear is offset by a continued eruption of the tooth. Since the roots of equine teeth close like those of dogs and cats, the remainder of the tooth is considered to be a long crown; some of it "submerged" under the gumline, and the rest is exposed crown. This radicular hypsodont structure results in a tooth that gradually gets shorter as it continues to wear down, though staying at a proper occlusal height caused by continued eruption.
Small herbivores, such as rodents and rabbits, have teeth (with the exception of some rodents' cheek teeth) that are continuously growing. In other words, there is no true root structure as the apex remains open, producing tooth structure throughout the life of the tooth (aradicular hypsodont–no root, long crown). This tooth growth pattern plays a very important role the entire life of the patient, because there must be a balance between attrition and growth. If that balance is ever compromised, even with one tooth, significant consequences can result.
Rabbits have continually growing incisors and cheek teeth (all aradicular hypsodont), and are distinguished from rodents in that they have a smaller pair of upper incisors (peg teeth) behind the large maxillary incisors.
Lagomorph dentition: 2 X (I 2/1; C 0/0; P 3/2; M 2 – 3/3) = 26 to 28
All rodents also have continually growing incisors, but only the one large maxillary pair, with no peg teeth. Some rodents (chinchillas and guinea pigs) also have continually growing cheek teeth, while others (hamsters, gerbils, mice and rats) have molars that resemble those of dogs, cats, or even humans (brachyodont).
Chinchillas/guinea pigs: 2 X (I 1/1; C 0/0; P 1 – 2/1; M 3/3) = 20-24
Rats/mice/hamsters: 2 X (I 1/1; C 0/0; P 0/0; M 2 – 3/ 2 – 3) = 12 to 16
Because of the small oral opening, complete evaluation is difficult even in an anesthetized animal, much less an alert one. Any external signs of slobbers (wet dewlap), swelling or drainage can alert you to possible oral problems, and most pets will allow you at least to look at the incisors, which are frequently part of the problem. Occasionally, in a quiet, larger animal, you might be able to visualize part of the caudal oral cavity with an otoscope, but that can vary from pet to pet.
Sedation or anesthesia in a compromised patient can be risky, so caution is advised. Many texts cover anesthesia in pocket pets and should be consulted if necessary. Intubation can be quite challenging, and the endotracheal tube is one more structure in a restricted area. Custom mouth gags or retractors can facilitate examination, and some form of lighting is also helpful. Using a No. 4 intraoral radiograph for survey skull films can provide additional information, but using smaller films inside the oral cavity can be difficult.
Evaluation of the caudal part of the oral cavity, particularly in those patients with continually growing cheek teeth, is essential to ascertain any evidence of cheek teeth overgrowth or involvement. Look for teeth or areas where teeth are not in a level occlusal plane; areas of inflammation or infection; and regions of tooth overgrowth—hooks or points.
The most common problem in rodents and lagomorphs is incisor overgrowth.This is commonly due to malocclusion of the incisors, but can also occur with inappropriate diet, injury to teeth or caudal teeth problems that keep the mouth open. Once there is any discrepancy in the occlusion of the incisors, no matter what the cause, the problems can worsen from there because the normal balance of attrition and tooth growth is disrupted. These malocclusions tend to be genetic (though occasionally traumatic or dietary in nature), so the owners must be advised to cull the individual (or relations) from breeding programs.
If left untreated, incisor overgrowth, can not only change eating habits, but also the cheek teeth cannot get adequate attrition if the mouth cannot close properly, and will start to overgrow. Unfortunately, even a small level of caudal cheek teeth overgrowth will then wedge the mouth open further, exacerbating the problem. >
In addition, any level of cheek teeth involvement can be difficult to manage, given the small mouth opening, so presence of problems warrants a more guarded prognosis. The occlusal planes, when viewed from the front, angles down at the lateral (labial aspect.) With this wear pattern, overgrowth will result in hooks on the lateral or labial aspect of the upper cheek teeth, often lacerating the cheeks, and in hooks on the medial or lingual aspect of the mandibular cheek teeth, which can even cause "tongue-tie" (trapping of the tongue either above or below the teeth edges). If there has been any tooth loss (periodontal abscess, fracture or extraction), not only can the adjacent teeth shift into the space and out of their normal occlusal pattern, but the opposing tooth can overgrow into the space. Any of the variations tend to compound problems, because returning the teeth to a normal, functional state can be challenging if not impossible.
Since the most common dental problem in pocket pets is incisor overgrowth, the most common treatment is odontoplasty, or trimming the teeth. With young pets that are already displaying a slight malocclusion, the owner must be informed regular trimming—every six to eight weeks—will be necessary to avoid complications of caudal teeth overgrowth. The optimal trimming will return the teeth to proper occlusion (difficult if the malocclusion is significant), with a chisel edge on the teeth (longer on the front surface because of the presence of enamel).
Often, trimming is done with guillotine-blade nail trimmers because these tools can be used on many pets without sedation, but the chance of fracturing the tooth is always a possibility. A more precise method uses a cutting bur on a slow or high-speed handpiece to more accurately trim the tooth back down to its normal architecture. Some patients will allow this without sedation, but use a tongue depressor behind the teeth for protection. It is easiest to contour the chisel shape on the teeth with a sedated or anesthetized pet, and sometimes full anesthesia is necessary anyway, depending on the patient. If there is any caudal teeth involvement that requires additional evaluation or therapy, full anesthesia is necessary, so more precise odontoplasty is possible.
Odontoplasy may also be necessary with the caudal teeth, but working with these teeth is much more challenging. Because access to these teeth is difficult, special mouth gags or retraction can help. Floating the cheek teeth can be done with small file or rasps, burs on a handpiece or ronguers. Protect the adjacent soft tissue from these instruments. Once you have reasonably reduced any areas of overgrowth, close the animal's mouth and move it in a lateral movement (lateral excursion) to help smooth the surfaces and evaluate for adequate motion.
With patients that experience occlusal problems, consider extracting the incisors to avoid or moderate continuing problems in the caudal portion of the mouth. Although the "root" structure is very long and curved, with proper equipment and lots of patience, extraction is possible. The key to extraction is carefully elevating the coronal portion of the tooth around its total circumference, because once this area of the periodontal ligament is loosened, the remaining periodontal ligament is structured to allow more movement than a typical tooth. Special elevators, including small winged elevators or even modified 18-gauge needles, are needed to work with these small teeth. Careful elevation of all surfaces will eventually result in significant loosening of the tooth, but before actual removal, press the tooth back into the alveolus with a slight rotational movement to remove the plug of pulp tissue with the tooth. Using small dental extraction forceps, remove the tooth following the arc of the "root". Even with good pulp removal (look at the apex to see if you got the soft tissue out or if the tooth is hollow), regrowth of the tooth is always possible, so the owners must be informed of the possibility. If the tooth breaks off and you're unable to retrieve the remainder, you'll always get another chance at extraction–it just might not re-grow in a typical manner. Once the incisors are extracted, regular monitoring is necessary, particularly if there is any level of cheek tooth involvement.
Dr. Lobprise is a past president of the American Veterinary Dental Society and is an associate at Dallas Dental Service Animal Clinic