These are also commonly called “carnassial abscesses” because they most often occur with
fractures of the maxillary fourth premolar. However, any infected tooth can result in a clinical
abscess, and so this is actually a misnomer. It is critical to note that these teeth have been dead
and infected for a long time (sometimes years) and have just recently showed outward clinical
signs. The patient has been subclinically infected for a long time.
Clinical Presentation:
Tooth root abscesses should be a differential diagnosis in any case of acute facial swelling
(Figure 1). They are most often associated with a complicated crown fracture (See fractured
teeth above). However, it is critical to note that uncomplicated crown fractures can often result
in clinical abscessation (Figure 2). In fact, the lack of an escape route for the gas created by the
anaerobic bacteria makes this a common scenario for abscessation.
Figure 1: Carnassial abscesses in 2 dogs.
The location of the swelling/fistula, ventral and rostral to the eye, is classic for a carnassial abscess.
This was confirmed by dental radiology in both cases.
Note the significant facial swelling and neck edema in (b)
Figure 2: Carnassial abscess from an uncomplicated crown fracture.
This tooth is clinically abscessed, as evidenced by the swelling (white arrows).
Note that there is minimal damage to the tooth (yellow arrows).
The infection was confirmed by dental radiology.
Intrinsically stained (discolored) teeth can also create clinical abscessation (Figure 3 a and b).
Additionally, teeth that appear outwardly normal can be dead and infected. Advanced
periodontal disease may result in a class II perio-endo involvement and leading to clinical
abscessation (Figure 3 c). Finally, abscesses can be created by retained roots from either a
fracture or a failed extraction attempt (Figure 4). Just because there is not a visible tooth, does
not mean that there are no roots. A recent study (submitted for publication) reported that 92% of
“extracted” carnassial teeth had retained roots, and that the majority of these had radiographic
signs of infection.
Figure 3: Additional teeth which can create abscessation.
This patient had draining tracts on both the maxilla and mandible for over three years (a),
and had received numerous rounds of antibiotics as well as several exploratory surgeries.
The teeth were never addressed as they looked “normal”.
However, the maxillary fourth premolar was intrinsically stained (b).
Dental radiographs confirmed periapical rarefaction to the maxillary fourth premolar as well as a class II
perio-endo lesion to the mandibular left first molar (c).
The infection destroyed the bone around the distal root and exposed the apex (red arrows).
It then spread through the pulp chamber creating infection on the mesial root (blue arrows).
The bone is weakened in the area, predisposing the patient to a pathologic mandibular fracture.
These teeth (as well as numerous others) were extracted and the patient went on to fully recover.
Figure 4
Recheck radiograph of a patient who had the maxillary fourth premolar (208) “extracted”.
There are two retained roots (white arrows).
The distal root has periapical rarefaction, indicating active infection.
The infected teeth harbor anaerobic bacteria which create a constant low grade infection through
the apex and into the surrounding bone. Oral infections may be spread by the bloodstream to the
vital organs (bacteremia). Veterinary patients tend to control the infection for a significant
amount of time. Eventually, however the infection can overwhelm the body’s defenses and
cause the abscess.
Diagnostic tests:
Dental radiographs are required to definitively diagnose an abscessed tooth. Skull films are
generally insufficient to diagnose this subtle pathology associated with most tooth root
The presence of a tooth fracture alone does not necessarily indicate that the tooth is the cause of
the infection/swelling. The presence of periapical rarefaction is the diagnostic key (Figure 5).
Furthermore, it is recommended that the entire arcade be radiographed to ensure that there are
not additional teeth involved (Figure 6).
Figure 5: Periapical rarefaction of the maxillary left fourth premolar in the patient in 3 (a).
The areas of periapical rarefaction (lucency) (red arrows) are diagnostic for a tooth infection.
Figure 6: Periapical disease to maxillary first molars.
Both of these patients were presented for “carnassial abscesses”.
(a) The maxillary fourth premolar is infected (green arrows), but so is the first molar (red arrows).
(b) This may have been missed without dental x-rays resulting in treatment failure.
(b) This patient had the maxillary P4 extracted a month ago for a suspected carnassial abscess.
The dental radiograph confirmed complete extraction of the tooth (blue arrows).
It also revealed that M1 is infected and is likely the cause of the swelling (red arrows).
No radiographs were made for the original surgery, so it is unknown if the P4 was a problem at all.
Finally, note that the first molar is infected due to periodontal loss (green arrow).
Emergency treatment:
Emergency treatment is directed at relieving the pain and decreasing the amount of infection. If
drainage has been established via fistualtion, the pain has decreased. The patient was likely
more painful in the days/weeks leading up to the swelling/draining tract. Pain medications
should be prescribed in addition to broad spectrum antibiotics. It must be stressed to the owner
that treatment should alleviate the acute issues, but it will not solve the problem. The tooth must
be definitively treated (see below), and treatment should be performed before the antibiotics are
finished to avoid developing resistance.
Definitive therapy:
Once the tooth becomes infected, there is no way to effectively medicate the root canal system.
Further therapy is therefore required, regardless of the resolution of the acute problem. The
infection will smoulder for a period of time and then recur, leaving the patient to suffer through
that entire intervening period.
Definitive treatment options include complete extraction or ideally root canal therapy (See
fractures above). Furthermore, the prognosis with root canal therapy of an abscessed tooth is
very similar to this procedure on a vital tooth (Figure 7).
Figure 7: Endodontic therapy on an abscessed canine.
(a) Pre-operative dental radiograph of a patient with a chronically infected maxillary left canine.
This is evidenced by the large area of periapical rarefaction (red arrows).
(b) One-year recheck revealing resolution of the rarefaction, indicating successful therapy.