Definition

A malposition of the teeth that prevents the alignment of the teeth or jaw.

Clinical Signs

The most obvious sign is visible overgrowth or uneven growth of incisors.

A rat with malocclusion may salivate, rub at its mouth with its feet, or exude a foul odor from the mouth. Other signs include inability to chew hard food, weight loss, or sores developing in or near the mouth. Broken upper or lower incisor(s) is a sign that malocclusion may be an issue.

*Note: for additional information on recognizing various signs of pain or discomfort refer to: Signs of Pain in Rats.

Etiology

Rats are monophyodont, having only one set of teeth during their lifetime. Under normal circumstances rats have teeth that consist of 4 opposing incisors, two smaller on top and two longer curved ones on the bottom, as well as, a total of 12 molars towards the back of the mouth, three on each side of the jaw, both upper and lower. The incisors have an open root, unlike its 12 molars, which causes the teeth to grow continuously at approximately 4 to 5 inches per year. They are covered by a hard yellow enamel on the outside surface of one side, the color of which is due to the presence of an iron-containing pigment. This orange pigment is normal and deepens with age.

A rat’s incisors get their chisel like shape through the back and forth movement of the jaw during teeth grinding, which allows the rat to be able to gnaw effectively. The bottom incisors normally appear to have a small gap; this is due to having a hemi-mandibular joint which allows the lower incisors to slightly spread apart to aid in opening seeds and nuts.

In healthy rats the incisors are properly aligned and able to be maintained at a certain length through the process of natural teeth grinding without requiring something hard to chew on.

In a rat with malocclusion, the teeth are not aligned properly, and natural grinding cannot take place. The incisor(s) continue to grow and curve, and if not kept trimmed results in trauma to the soft palate, infection, and abscesses, which in turn will eventually lead to the rat starving. Malocclusion may be due to injury (such as loss of a tooth due to root damage or trauma), dental disease, genetics, tumors, or other noninfectious reasons.

It is important to check and do a visual exam of your rat’s teeth and mouth on a regular basis to access his oral health. Teeth that are misaligned should be trimmed on an average of every 2 weeks to 2 months (depending on the rate of growth). Infected molars can cause oral abscesses that can go undetected until they actually make their way to the rat’s epidermis. Abscesses are a concern if a foul odor is present in the rat’s mouth. In such cases the veterinarian may elect to open and debride the abscess and remove the infected tooth.

In cases of oral abscesses, or infections due to malocclusion, it is wise to institute a soft diet during the healing process.

Figures

Photos Showing Both Properly Aligned Teeth and Malocclusion

• Fig. 1: Comparing alignment and malocclusion of incisors in male rat (Murphy)
• See Figures:2, 3, and 4 in the section on Treatment below.
• Fig. 5: Teeth damage secondary to trauma in male rat (Ari)
• Fig. 6: Dental burring procedure due to malocclusion in 14-week-old male rat (George)
• Fig. 7: Malocclusion, Dental extraction in a 1-year-old male rat (Isaiah)
• Example 1: (From Abscess article) Fig. 2e: Oral Abscess

Diagnostics

Based on observation of teeth and mouth.

Obtain history.

Assess for underlying etiology.

Treatment

In the past, vets would simply clip the overgrown teeth with guillotine clippers or cat claw nail trimmers, and possibly instruct owners in how to safely do so at home.

• Fig. 2: Gathering supplies to trim teeth
• Fig. 3: Trimming teeth
• Fig. 4: Additional photos of how to trim teeth

While it is not unreasonable to trim a rat’s incisors with guillotine clippers or cat claw nail trimmers due to the narrow size of their incisors, serious complications can arise particularly if the underlying cause is neither understood nor properly evaluated. Subsequently, both British (BSAVA) and exotics specialty (AEMV) organizations currently recommend the use of a high-speed dental burr, ideally while sedated. Sedation and/or anesthesia reduces stress of the procedure in our prey animals while also preventing potential soft tissue injury from the burr in a conscious pet. However, depending on the vet’s technique, and the calmness of the animal, anesthesia may not be required.

The use of a high-speed dental burr prevents the potential tooth and jaw fractures that may result from the unnatural shear forces exerted by the use of nail trimmers. Additionally, while trimming incisors is considered palliative as overgrown teeth are typically due to permanent abnormal changes to underlying bone or root structure, correction, if possible, would be best accomplished by correction of the underlying issue combined with frequent atraumatic shortening of the incisors to a normal length using a dental burr that forms the smooth tooth tips that contribute to the painless normal chewing and bruxing behaviors that may ultimately create a functional wear pattern.

Depending upon the growth rate the affected teeth may need to be trimmed every two weeks to every 2 months. Where a misaligned tooth is the result of trauma, the opposing tooth can either be trimmed till the damaged tooth has reached its proper length or removed if the overgrowth is caused by a missing tooth.

In the event of infection, treat aggressively with an antibiotic such a clavamox, and by flushing the infected area several times a day with saline.

For pain management an analgesic such as infant Tylenol or an anti-inflammatory analgesic agent such as: Metacam (meloxicam) or Banamine (flunixin meglumine) may be given.

Refer to the Rat Medication Guide for information pertaining to medications.

*Note: malocclusion caused by cancer has a poor prognosis and surgery is usually not an option. Euthanasia should be considered, and discussed with the veterinarian, where such a condition precludes quality and comfort of life.

Nursing Care

• Assess teeth for proper alignment. In rats where malocclusion exists, assess for alignment once a week.
• Caution is advised with use of guillotine clippers if clipping both upper incisors in the event a high-speed dental burr is not available. Objective is to prevent brittle teeth from splitting.
• Use care not to twist teeth when clipping in order to prevent any additional damage to teeth or jaw.
• Take care to avoid soft tissue of mouth or tongue when trimming teeth. In the event the vet has instructed in how to trim teeth at home it is advised to have two people involved, one to hold the rat and one to do the trimming.
• If the rat is unwilling to stay still in hands have partner use a towel (like a mummy wrap) to restrain the rat.
• Teeth kept trimmed to ensure nutritional needs are met and that overgrown teeth don’t pierce the soft oral tissue causing infections.
• If pain involved medicate with a pain reliever as necessary to encourage food intake and prevent weight loss.
• Provide soft foods, if oral sores are present and not able to chew recommended diet, to ensure that the rat with malocclusion gets the proper nourishment. Oral area should be checked regularly.
• Weigh rat regularly to monitor for any weight loss. If present, increase caloric content of diet with supplements (e.g., Boost, Ensure, or Nutra-Paste).

Outcome

• Teeth aligned without splitting
• Integrity of jaw maintained
• Able to chew food without difficulty
• Maintains weight
• No mouth sores or abscesses present
• Infections resulting from malocclusion alleviated, or resolved

Prevention

• With genetic malocclusion there is no prevention, but rats with this disorder should not be bred.
• Keeping your rat from areas where he will fall will help to prevent injury-related malocclusion. This is especially important when dealing with elderly rats or rats that have disorders that affect balance.
• Checking your rat’s mouth regularly will help you to notice any infection, cysts, or tumors. Look for gum redness, swelling, pus, trouble eating hard food, or a foul odor coming from your rat’s mouth.

Consultants

• Nathalie Baldwin, DVM, Village Gate Animal Hospital and Pet Resort
• Adele Wharton BVSc, MRCVS, CertGP (F&L) Locum Veterinary Surgeon

Co-author

• Joanne “Bella” Hodges

References

1. Mancinelli, E., & Capello, V. (2016, August 29). Anatomy and Disorders of the Oral Cavity of Rat-like and Squirrel-like Rodents. Retrieved October 2, 2020, from https://www.vetexotic.theclinics.com/article/S1094-9194(16)30012-3/fulltext
   https://doi.org/10.1016/j.cvex.2016.04.008