What is a tooth root abscess?
Fig. 1: X-ray of a cat's jaw showing an abscessed lower canine root (shadow below tooth on the right shows bone infection).A tooth root abscess is a severe infection that develops around the root of a tooth. It usually occurs because of bacteria entering through a broken or traumatized tooth.
What causes a tooth root abscess?
A tooth root abscess forms when bacteria enter the exposed root canal of the tooth. The crown of a healthy tooth is covered by enamel, which is essentially impervious, preventing bacteria from entering the tooth. Under the enamel is a different dental hard tissue known as dentin. Dentin contains 300 to 400,000 small openings (tubules) that communicate with the center of the tooth.
In the center of the tooth is the pulp cavity, which contains soft tissue (blood vessels, nerves, and lymphatic tissue). The tissue in the pulp cavity is collectively referred to as the pulp. The pulp nurtures the normal tooth.
If the protective tooth enamel is chipped, thereby exposing the underlying dentin, or if the tooth is fractured more deeply, exposing the pulp, bacteria can gain access to the center of the tooth. In cats, this most often occurs when the tooth breaks and exposes the tissues under the enamel.
Once infected with bacteria, the pulp tissue becomes inflamed (pulpitis), and eventually the tooth dies (pulp necrosis). Inflammatory products produced by the bacteria and dying pulp tissue leak out of the bottom of the root (root apex) and infection now contaminates the bone surrounding the root, resulting in apical periodontitis.
"A tooth root abscess forms when bacteria enter the exposed root canal of the tooth."
A persistent infection can result in an abscess (an accumulation of pus) that may leak directly into the oral cavity or may leak out onto the skin (beneath the chin if the affected root is in the lower jaw or onto the face if the affected root is in the upper jaw). Pulpitis, apical periodontitis, and tooth root abscesses can be very painful.
A tooth root abscess may also occur secondary to periodontal disease. In this scenario, the infection does not travel down to the bone through the center of the tooth, but rather tracks along the outside of the tooth, through the supportive tissues that surround the root.
What is the most common location for a tooth root abscess in cats?
Fig. 2: Cat's upper fourth molar, showing a slab fracture.Any tooth can fracture, but the most commonly fractured teeth are the large upper and lower canine teeth, followed by the upper fourth premolars. As a result, these teeth are most likely to develop a tooth root abscess.
The maxillary (upper) fourth premolars in conjunction with the lower (mandibular) first molars are known as the carnassial teeth. When one of these teeth becomes infected, it is referred to as a carnassial tooth abscess.
What is a slab fracture?
A slab fracture develops when a cat's cheek teeth bite down onto a hard object at just the right angle and a portion of the tooth surface breaks off, exposing the underlying sensitive dentin and possibly even the pulp. The slab that breaks off may be a small chip or a large piece of the tooth and the fractured portion may extend below the gum (gingiva) onto the root surface.
Are there any obvious symptoms when a cat has a tooth root abscess?
Abscessed teeth are very painful, but cats may not show obvious signs of pain. Instead, your cat may be reluctant to chew on toys or might pull away when their head is touched. An observant owner may notice that their cat is only eating or chewing on one side of their mouth or is dropping food when eating. Some cats will have bad breath, while others may paw at the affected side of their face or rub their face on the ground. Cat owners may erroneously assume their pet simply has an itch, but the behavior may be an indication of an abscessed tooth.
"Cat owners may erroneously assume their pet simply has an itch, but the behavior may be an indication of an abscessed tooth."
If the abscessed tooth is the upper fourth premolar, the outward signs are often mistaken for some other problem, such as an eye infection or a puncture wound. This happens because these tooth roots lie just below the eye, and when they become abscessed, the infection quickly spreads to the surrounding tissues. The tissue below the eye usually becomes swollen and inflamed just before the abscess bursts. If you look inside the cat's mouth, there may be swelling and redness in the gums around the affected tooth.
How is a tooth root abscess diagnosed?
In some cases, the diagnosis of a tooth root abscess is simple, such as when there is an obvious slab fracture or damage to a tooth that is accompanied by discharge. However, intraoral dental X-rays (radiographs) are required to definitively diagnose a tooth root abscess.
What is the treatment for a tooth root abscess?
Fig. 3: Cat's lower canine is fractured, with nerve exposed.A tooth root abscess is a very painful condition and needs to be treated as soon as possible. Antibiotics will be prescribed to control the infection and anti-inflammatory and/or pain relief medication will be prescribed as well. Although this medical treatment will deal with the symptoms, it will not treat the underlying tooth injury and antibiotics alone will not cure a tooth root abscess.
There are only two options for treatment of the abscessed tooth. One option is root canal treatment (standard endodontic therapy), which can preserve the structure of the tooth. The other option is extraction.
The tooth root in question must be assessed clinically and via X-rays to determine if your cat is a good candidate for root canal treatment. The extent of trauma to the crown of the tooth, pre-existing infection (bone destruction around the root), along with the overall periodontal health of the tooth will impact whether a recommendation is made for root canal treatment or extraction.
Root canal therapy should be rechecked with intraoral X-rays (requiring a brief, general anesthetic) three to six months after the initial treatment, and annually for the next couple of years.
If the abscessed tooth has extensive bone loss around its socket, or if there is significant damage to the crown of the tooth, your veterinarian may recommend extraction as the best treatment. Your veterinarian is in the best position to recommend the appropriate option for your cat, depending on the severity of the abscess and the degree of damage to the tooth and surrounding structures.
Post-operatively, regardless of which treatment option is followed, antibiotics may be prescribed. Treatment for pain (anti-inflammatory and/or pain medication) will be prescribed. Your cat may require a change in diet during the post-operative recovery period. Once the surgical extraction site has healed, most cats can resume their regular diet and activity level.
All cats should have a dental examination performed by their veterinarian at least every six months. For a cat that has previously developed a tooth root abscess, your veterinarian may recommend more frequent dental examinations.
Fig. 4: X-ray of cat's lower canine after root canal therapy saves the tooth. 
Fig. 5: Cat's restored lower canine tooth after root canal therapy.
