Tooth root abscess in dogs: symptoms and treatment

Overview

The visible part of a tooth, the crown, is covered by hard enamel that protects the inner structures from bacteria. Beneath the enamel is dentine, whose tiny channels lead towards the dental pulp. Openings at the root tip allow infection to spread from the root canal into the surrounding jawbone. Inflammation of the dental pulp is called pulpitis.

An abscess may form a fistula: a tract through which pus drains into the mouth or onto the skin. If pus drains into the mouth, there may be no visible hole or scab on the skin. On the gum, the drainage opening may look like a small red pimple at the junction between the gum and other oral lining. Infection of the upper fourth premolar may appear externally as pus draining below the inner corner of the eye.

Causes

Fractures and periodontal disease

A deep fracture can expose the dental pulp to bacteria. Even a shallower chip can expose dentine, allowing bacteria to enter the tooth through it. A heavy impact can damage the pulp without a visible fracture. Bacterial infection can cause the pulp tissue to die. In periodontitis, infection can spread along the outer root surface into the tissues surrounding it.

A study of bacteria in fractured teeth sampled the root canals of 32 teeth with healthy periodontal tissues. Thirty different bacterial species were isolated from the canals examined. Of the bacteria isolated, 54% were Gram-negative. Anaerobic bacteria, which grow without oxygen, accounted for 42%. Of the bacteria isolated from the root canals, 53% could grow both with and without oxygen.

Risk factors

Chewing hard bones, antlers or nylon toys can fracture a tooth. Dogs often fracture canine teeth or large carnassial teeth used for gripping objects and chewing. A slab of a back tooth can break off when a dog bites a hard object at a particular angle.

Rotated teeth and older age increase the risk of periodontitis. Severe periodontitis can predispose a dog to a tooth root abscess. Small size and crowded teeth predispose dogs to periodontitis, which can then progress towards the root. Dogs weighing under 5 kg are susceptible to severe periodontitis. Plaque can also build up around a short-muzzled dog's crowded teeth, predisposing them to severe periodontitis.

Typical symptoms

Your dog may keep eating despite pain, but change how they handle food or toys.

• Your dog chews food on only one side of the mouth.
• Food drops from the mouth while eating.
• Your dog stops using chew toys they previously enjoyed.
• Your dog drools more than before.
• Your dog avoids having their head touched.
• Your dog rubs their muzzle against the ground.
• The gum around the painful tooth becomes red and swollen.
• Your dog's breath may smell worse than usual.

Swelling of the cheek or beneath the eye may develop before the abscess bursts. If the abscess drains into the nasal cavity, pus may discharge from a nostril. Opening the mouth can hurt, particularly when infection extends behind the eye.

Complications and consequences

Infection spreading behind the eye or beneath the jaw

Infection of the upper back premolars and molars can spread into the eye socket. Infection or an abscess behind the eye can threaten sight. In one series of dogs with soft tissue infection or abscesses behind the eye, a tooth root abscess was the underlying cause in 23.7%. In that group, 6 dogs had lost their sight by presentation (15.8%). In another study of 66 dogs with disease behind the eye assessed by CT, a dental infection was identified as the cause in only 1.

Rarely, infection around a lower tooth root can erode through the dense outer bone and drain beneath the jaw. In a small dog, the roots of the lower first molar occupy a large part of the jaw's supporting structure, so advanced periodontitis can weaken the jaw.

Diagnosis at the vet

Examining the mouth and taking dental X-rays

Your vet can assess the bite and look for visible fractures while your dog is awake. A thorough oral examination is performed under general anaesthesia. Measuring gum pockets helps assess the condition of the tissues supporting the tooth. Intraoral dental X-rays help identify the tooth causing the abscess and assess the area around its roots.

Bone loss around a root may appear on an X-ray as a dark area at its tip. A recent tooth root abscess can be painful even before clear X-ray changes appear. The root canal of a dead tooth may look wider than the canal of the corresponding healthy tooth in the same dog. Once the pulp stops functioning, the canal remains at its existing width, whereas a healthy tooth's canal narrows with age. In a study of superficial crown fractures of upper fourth premolars, X-ray changes were found in 27 of 111 teeth (24.3%). The same changes were absent from the 500 intact fourth premolars used for comparison (0%). The fracture study counted X-ray changes that may indicate disease around the root.

How is an abscess distinguished from other lumps?

A dark area at the root tip may be an abscess, an inflammatory tissue lesion called a granuloma, or a cyst around the root. In a series of 10 dogs with cysts, every cyst originated from a dead tooth. Nine of these 10 dogs had a soft, fluid-filled swelling beneath the oral lining or gum. Microscopic examination showed an epithelial layer lining the cavity in the cyst wall.

A lump beneath the jaw can resemble a salivary gland problem or an enlarged lymph node. In one 14-year-old dog, a lump measuring about 3 cm was initially suspected to arise from a salivary gland. Ultrasound found a cavity beneath the jaw, but the salivary gland looked normal. CT showed a tract from the root of the lower right first molar through the outer bone to beneath the jaw. A sample from this dog's abscess showed no aerobic bacterial growth after 48 hours.

Cone-beam CT can reveal a lesion at the root tip missed by conventional dental X-rays. The techniques were compared in a study examining 46 teeth in 16 dogs using both methods. Pulp tissue examination was available for 18 teeth. Cone-beam imaging reduces overlap of adjacent bones and teeth in the images.

Treatment

Extracting the infected tooth or treating its root canal

Extraction removes the source of infection from the jawbone. If infection is extensive, your vet may also remove infected tissue around the draining tract. The extraction socket can be closed with a flap of gum tissue. A broken root tip left in place can cause pain and infection later.

Root canal treatment can preserve a tooth important for function, such as a canine or carnassial tooth. An extensive fracture or poor attachment to the jawbone may make root canal treatment unsuitable. During treatment, infected or dead pulp tissue is removed, and the root canal is cleaned and filled. Finally, openings in the crown are sealed to prevent bacteria from re-entering the canal.

Pain is treated with pain relief prescribed by your vet. If facial swelling is acute and the procedure cannot be performed soon, your vet may use an antibiotic as temporary treatment. An antibiotic can settle symptoms while the infected tooth remains in place and still needs treatment.

Healing and follow-up X-rays

An extraction site check may be scheduled for 2 weeks later, allowing your vet to assess healing of the oral wound. After extraction of the lower molar and cleaning of the tract in the dog described above, the wounds looked clean at the 7-day check. The same dog's fistula had healed within 4 weeks. It had not recurred at the dog's 3-month follow-up.

The first X-ray check after root canal treatment is usually performed after 3–6 months, with annual monitoring thereafter. A treated tooth may be X-rayed as early as 3 months and again a year after the procedure. Enlargement of the dark area at the root tip during follow-up indicates root canal treatment failure.

A root canal treatment study involving different types of teeth followed 281 teeth in 204 dogs. Based on X-ray findings, treatment was fully successful in 199 teeth (71%). Lesions became smaller or remained unchanged without signs of failure in 71 teeth (25%). Treatment was classified as unsuccessful in 11 teeth (4%). In a study limited to fractured upper fourth premolars, 109 of 120 treated teeth healed according to X-ray criteria (90.83%).

During follow-up of the fractured premolars, 10 teeth showed no signs of failure (8.33%). Root canal treatment failed in 1 premolar (0.83%). In the same premolar study, a lesion at the root tip before treatment was associated with a poorer outcome.

Prevention

Daily toothbrushing removes plaque along the gumline. You can introduce it in puppyhood by gently wiping the teeth with gauze or a finger brush initially. The incisors and canine teeth are an easy place to begin because they are readily reached with a brush. A soft pet toothbrush is suitable for regular cleaning. A soft chew product should allow you to press a fingernail mark into its surface. Have a chipped tooth examined: even a fracture that leaves the pulp covered can be associated with a lesion around the root.

Important for dog owners

Tell your vet when the swelling or discharge began and whether your dog has changed how they chew. Previous dental injuries and procedures help your vet assess which tooth may be causing the symptoms. Do not force a painful dog's mouth open.

After extraction, give soft food according to your practice's instructions, often for about 7–14 days. Soaked dry food can provide a soft option during recovery. Keep chew toys and chew bones out of reach while your dog recovers. The mouth may be most painful 1–2 days after extraction. Mild swelling of the muzzle following extraction usually resolves within 3–5 days. Contact the vet who treated your dog if the wound has discharge, becomes red or smells unpleasant.

Contact your vet if marked swelling persists or first develops after 5 days. Get in touch sooner if swelling is severe and troubling your dog.

Frequently asked questions

Could a lump below the eye come from a tooth?

The roots of the upper fourth premolar and first molar lie below the eye. Infection around these roots can therefore cause cheek swelling, even if the problem initially looks like an eye condition or skin wound. Your vet uses intraoral X-rays to look for the infected tooth.

Could my dog have an abscess while still eating well?

Your dog may still approach the food bowl eagerly despite having a painful tooth. Pain may be more apparent in how they chew: they may move food to the other side of the mouth. Your dog may also prefer soft food to dry food.

Does a burst abscess still need treatment?

Pus may drain from an abscess onto the skin or into the mouth without intervention. CT can reveal a tract running from a tooth root to the skin. Your vet treats the source of infection by extracting the tooth or performing root canal treatment, even if the abscess has already emptied.

Why are antibiotics alone insufficient?

An antibiotic may temporarily ease symptoms if your dog's face is swollen and the tooth cannot be treated immediately. However, the infected tooth remains in place and needs a procedure even after symptoms improve. Root canal treatment removes infected pulp tissue from the canal.

Can a tooth be saved if there is an abscess around its root?

Root canal treatment may preserve the tooth if the remaining crown can withstand use and its attachment to the jawbone is adequate. Suitability is assessed by examining the tooth and taking images of its roots. Damage to the bone around the root affects the choice of treatment.