A tooth that no longer has a blood supply is a non-vital tooth (Fig. 1). Sometimes these teeth are discolored pink, grey, purple, yellow, or they are more opaque than surrounding teeth. Other times the teeth are fractured. However sometimes the crown appears normal and the diagnosis is based on a radiograph. The radiographic appearance of a non-vital tooth can be normal, or can show periapical lucency consistent with loss of periodontal ligament and bone lysis at the root apex. Some non-vital teeth show a wide pulp canal compared with other teeth. It can be especially useful to radiograph the contralateral tooth for comparison. The explanation for the wide canal requires an understanding of tooth maturation. When a tooth is young or immature, it has a wide canal. With aging the canal diameter becomes narrow, as the dentinal wall of the tooth becomes thicker. If a tooth dies when it is immature, the development of the tooth is arrested at this stage.
Why does a tooth become discolored and why does this cause the tooth to die? Trauma to pulp causes hemorrhage, which stains the dentin. Usually this is irreversible, but occasionally it is not. Trauma can be in the form of mechanical, thermal, chemical or inflammatory. The pulpitis sustained during trauma causes a pressure necrosis of the pulp, as it is trapped inside a closed space. 92% of discolored teeth are non-vital.
A dead or non-vital tooth (T/NV) may lead to pain and/or infection. Therefore treatment with extraction or root canal therapy should be performed to prevent pain or infection. Since our patients can’t talk to advocate for themselves, it is imperative that we understand this pathology and risk of pain and infection to our patients, and advocate for them to their pet owner. Unfortunately it is still common for veterinarians to recommend a “wait and see” approach, not realizing that subtle pathology can cause profound discomfort for months and years before an abscess is visible to the naked eye.
Abrasion and Fractured Teeth
It is not uncommon to discover fractured teeth (Fig. 2) on a good oral exam. It is important to determine if pulp exposure is present. If you are unsure, a closer evaluation using a dental explorer can help. If still unsure, then evaluate under anesthesia and with a dental radiograph, looking for evidence of endodontic disease. If pulp exposure is present, then advise treatment with either an extraction or root canal therapy to save the function of the tooth. It is not acceptable to take the “wait and see” approach. All teeth with pulp exposure are prone to pain and infection. I make the analogy that having a broken tooth with pulp exposure is like having a chronic open wound that never heals. If the abraded surface feels smooth like glass then most likely there is not pulp exposure. It is always good practice to radiograph teeth that are abraded to make sure there is no evidence of endodontic disease.
Abrasion (AB) is very common in dogs and does not necessarily need to be treated if it is a longstanding condition. Rapid abrasion can cause dentin sensitivity and should be treated with dentin bonding to eliminate sensitivity and protect the pulp. Severe abrasion can cause pulp exposure, necessitating extraction or root canal therapy. Counsel the client to remove abrasive toys from the pet’s environment. Items that are abrasive include tennis balls, and sometimes fleece toys and Frisbees if pets are obsessed with them.
Fractured teeth are categorized regarding whether they have pulp exposure or not. An uncomplicated crown fracture does not have pulp exposure. A complicated crown fracture does have pulp exposure. If the fracture extends below the gum line, then the root is also fractured. Sometimes just the root of the tooth is fractured.
- Uncomplicated = fracture limited to enamel or dentin (T/FX/UCF)
- Uncomplicated crown-root fracture (T/FX/UCRF)
- Complicated = causing pulp exposure (T/FX/CCF)
- Complicated crown-root fracture (T/FX/CCRF)
- Root fracture (T/FX/RF)
Endodontic disease is inflammation, infection or necrosis of the pulp tissues of a tooth. It can be insidiously painful. The pulp tissues include nerves, blood vessels, odontoblasts, connective tissue and lymphatic structures. Most endodontically diseased teeth progress to dead teeth. Most commonly endodontic disease is caused by a concussive trauma, with or without obvious pulp exposure. Other possible etiologies include hematogenous bacterial infection, ischemia (tooth avulsion or thromboembolism), or other causes of pulp exposure such as caries, resorptive lesions, severe periodontal disease that has caused bone loss to the apex of a tooth root.
An endodontically diseased tooth may appear normal externally, or it may be completely or partially discolored (yellow, brown, pink, purple or gray). It may be fractured. A radiograph may show periapical lucency consistent with a periapical abscess or granuloma. Widening of the periodontal ligament space near the root apex may be seen, as well as root resorption. With progression, an “apical blowout” may be seen clinically. Bone perforation and localized cellulitis can result in a facial abscess at the level of the tooth root apex.
Root canal therapy involves removal of the diseased pulp tissue, sterilization, debridement, shaping, and filling the canal to seal the tooth from bacterial penetration, and finally restoring the tooth.
Tooth Resorption (TR)
Tooth resorption (Fig. 3) is the progressive destruction of the calcified substance of permanent teeth by clastic cells. It can be extremely painful, and is one of the most common oral diseases seen in cats. It is also frequently found in dogs. Despite the high prevalence of this disease, there is confusion about nomenclature, classification, diagnosis and treatment in the veterinary profession, and much remains unknown in both veterinary dentistry and human dentistry about this condition.
For more information, read the Tooth Resorption in Dogs and Cats post on this site.
Missing teeth can be confounding. Are they problematic? Sometimes they are, and a radiograph of an area of the mouth where teeth are missing is vital to answering this question. Differential diagnoses include: retained tooth roots, impacted or unerupted teeth, unerupted teeth associated with a dentigerous cyst, advanced tooth resorption (stage 5), or a tooth that is truly not there. Retained tooth roots can cause pain or infection. In young animals an impacted or unerupted tooth can lead to formation of a dentigerous cyst. A dentigerous cyst is a benign cyst of the alveolar bone, but can be a serious source of pain and inflammation as the cyst expands and causes resorption of surrounding tissues including bone and tooth roots. These cysts can be quite destructive. They are fairly common in brachycephalic breeds including Boxers, Bull Mastiffs, Shih Tzu’s and many other breeds, and are common at the mandibular first premolar tooth. Always take dental radiographs of missing teeth.
- Cohen’s Pathways of the Pulp, Editors: Hargreaves KM, Cohen S, Berman LH, Mosby Elsevier 2011.
- Veterinary Endodontics, Niemiec B, Gawor J, Startup S, Thuen P, Moore J, Hiscox L, Coffman C. Practical Veterinary Publishing 2011.
- Veterinary Dentistry: Principles and Practice, Wiggs RB, Lobprise HB, Wiley 1997.