Originally published in the November 2014 issue of Veterinary Practice News
Tasha, an 18- month-old female Labrador retriever, recently was presented to me for a discolored right maxillary canine tooth (Figure 1). The discoloration was intrinsic, imparting a gray color to the entire crown. The enamel of the crown was devoid of any defects, cracks or fractures.
A tooth may be discolored due to abnormal formation of enamel, such as enamel hypoplasia or hypomineralization.
However, this tooth’s enamel was normal in thickness and texture. Exposure to the tetracycline family of antibiotics early in life can result in generalized discoloration of the teeth, but since only one tooth was discolored, a non-vital tooth secondary to pulpitis was most likely in Tasha’s case.
What Causes Pulpitis?
Pulpitis is inflammation of the pulp, which occurs most commonly due to blunt trauma to a tooth. This trauma may be caused by the patient bumping the tooth on something or biting down hard on something in a way that traumatizes the tooth without causing a fracture of the crown or root.
The colors seen with pulpitis—pink, purple, gray, brown—are due to trauma to blood vessels within the tooth, which results in leakage of red blood cells into the pulp chamber. The breakdown products of hemoglobin from lysed red blood cells diffuse from the pulp into dentinal tubules to just beneath the enamel, imparting a pink discoloration to the crown. Over time the discoloration progresses to a gray-brown color.
Pulpitis can be a painful condition because that inflammation in the tooth is similar to inflammation in the brain. Swelling within an enclosed structure results in damage to the remaining soft tissue within that structure.
Depending on the stage of the disease, the nerve fibers within the pulp may transmit sharp pain stimuli, or once the pulp within the tooth is dead, pain may subside until periapical disease develops.
JOHN R. LEWIS, NORTHSTAR VETS
Figure 2: Access sites are made through the cusp of the unfractured tooth to debride and clean the pulp chamber, and near the gingival margin to allow for straight line access to the root canal.
What to Do?
Tasha, like many dogs with dental problems, showed no clinical signs of discomfort. Should we monitor this tooth with frequent dental radiographs or should we recommend treatment? Electric pulp testing has been described in veterinary patients,1 but this technology is rarely available and false positives and false negatives make interpretation sometimes challenging.
I recommend treating the intrinsically discolored tooth, based on the fact that dogs just won’t tell us when they have a painful pulpitis.
JOHN R. LEWIS, NORTHSTAR VETS
Figure 3: Exploratory pulpectomy shows a partially necrotic pulp with an abnormal brown color to a portion of the pulp and lack of bleeding.
A landmark study2 published in 2001 showed that, of 64 discolored teeth that were explored via pulpotomy, 59 had gross evidence of partial or complete pulp necrosis (92 percent). Forty-two percent of discolored teeth evaluated radiographically in the study had no radiographic evidence of endodontic disease, suggesting that radiographic signs lag behind pulp inflammation and necrosis.
This study focused on teeth with crowns entirely discolored. Occasionally, I will see a canine tooth where only the tip of the tooth is discolored. This is an exception that I feel is reasonable to monitor rather than treat, since it is possible that the pulpitis was minimal enough to be reversible and isolated to only a portion of the pulp chamber; the remaining pulp may still be vital.
If monitoring shows that eventually the entire crown becomes discolored, treatment is warranted. If only the tip remains discolored, close radiographic monitoring is still warranted.
JOHN R. LEWIS, NORTHSTAR VETS
Figure 4: Radiograph of completed root canal therapy and restoration of access sites of the right maxillary canine tooth.
Two options exist for the pulpitis tooth: extraction or endodontic therapy. These teeth are often great candidates for endodontic therapy because they are often functionally important teeth—canine teeth are most commonly affected—and the crowns are intact.
Endodontic therapy is accomplished after taking dental radiographs to ensure there are no occult fractures of the crown or root. For the canine tooth, access sites are created near the gingival margin for a straight line access to the apical root canal. I also make a second access site into the tip of the tooth (the cusp) to allow for adequate cleaning of the coronal portion (Figure 2).
The root canal commences with removal of the pulp (Figure 3), irrigation, mechanical cleaning and disinfection, shaping of the canal, and filling of the canal.
The filling material in the root canal acts as a cork in a wine bottle, preventing percolation of fluids and bacteria into the periapical bone surrounding the root.
The final critical step of root canal therapy is placement of restorations that will seal the access sites to prevent microleakage. Whether to place a prosthetic crown over the endodontically treated tooth is decided case by case, depending on chewing habits and suspected likelihood of future tooth fracture.
Left untreated, periapical bone loss and root resorption can occur even in a closed system, either due to inflammation or infection. Although a tooth with pulp exposure provides a direct highway for oral bacteria to migrate to the periapical bone, a process called anachoresis (hematogenous spread of bacteria and colonization of a compromised site) may result in periapical infection even in non-vital teeth without pulp exposure.
1. Remeeus P, Verbeek M. Use of the dental pulp tester in veterinary dentistry. J Vet Dent. 1997 Mar;14(1):23-8.
2. Hale FA. Localized intrinsic staining of teeth due to pulpitis and pulp necrosis in dogs. J Vet Dent. 2001;18(1):14-20.