Brook A. Niemiec, DVM, FAVD, Diplomate AVDC
This is the third article in a series on how to provide optimum dental care as well as increase dental compliance in veterinary practice. As such, it will present very common oral problems and their proper therapy. You can read the first two articles in the series, Dental Services: Good Medicine for Patients & Practices (September/October 2011) and The Importance of Dental Radiology (November/December 2011), at todaysveterinarypractice.com.
Several of the endodontic conditions discussed in this article may be well known to readers, but since veterinary dental education is quite variable, even these common conditions will be presented. Some of the pathologies presented are more subtle and warrant careful consideration, as they are no less painful or damaging than more obvious conditions, and should be afforded the same level of respect as classic endodontic disease. The consequences and treatments of many of these diseases are largely misunderstood by the general veterinary profession.
Beyond the information presented on diagnosis and care, this article will convey the deeper impact of specific dental pathologies in a way that allows you to communicate the significance of the conditions to your clients. This communication should help you increase the number of patients receiving dental prophylaxis and treatment per your recommendations, presenting an opportunity to improve the patient’s health as well as the practice’s financial health.
The crown of the tooth is made up of 3 layers (Figure 1):1,2
- Pulp Chamber: The innermost layer is the pulp chamber (or root canal), which is comprised of blood vessels, nerves, and connective tissue.
- Enamel: The outermost layer is the enamel, which is 96% inorganic material. Enamel has no sensory ability and no ability to regenerate if damaged or lost.
- Dentin: The middle layer, between the pulp chamber and enamel, is called dentin. Dentin makes up the majority of the tooth structure in mature animals and has a similar mineral density to bone. Dentin contains millions of dentinal tubules that radiate from the root canal to the periphery of the dentin, which is covered with enamel (Figure 2).
Each one of these dentinal tubules contains an odontoblastic process with nervous innervations, resulting in a dynamic living structure with sensory ability and the capability to respond to stresses.3
Canine dentin has 50,000 to 100,000 tubules/mm2, which is twice the number of tubules in human teeth.4 Therefore, dogs’ teeth are twice as sensitive as ours.
RESPONSE TO INFLAMMATION
Teeth are subject to many sources of inflammation; in veterinary medicine, the result is generally traumatic.5 Once the tooth undergoes trauma, it reacts with inflammation. This reaction is termed pulpitis, which can be reversible or irreversible:
- Reversible pulpitis indicates that the tooth will respond favorably to therapy and remain vital.
- Irreversible pulpitis eventually results in pulp death and necrosis.
Direct pulp exposure will invariably result in pulp death, necrosis, and subsequent infection, unless treated immediately with vital pulp therapy. This therapy protects the pulp with a medicant; then 2 layers of restorative material. The goal is to maintain long-term tooth vitality and in order to have a chance at success, this therapy must be performed properly and immediately.6 Even under ideal conditions, vital pulp therapy has a poorer prognosis than standard root canal therapy.7-10
Traumas, such as uncomplicated crown fractures, attrition, and abrasion, will result in inflammation that is reversible or irreversible depending on the degree of inflammation and treatment (if any). Over time, the tooth may respond to inflammation by increasing the distance between the injury and the pulp (tertiary dentin) or decreasing dentin permeability (dentinal sclerosis). This may be sufficient to protect the pulp; however, it is impossible to measure.
Hydrodynamic Theory of Dentin Sensitivity
The intimate association of nerve fibers with odontoblasts (cells that produce tooth dentin) is an area of active speculation. It is still unclear how odontoblasts and nerve endings interact. One theory regarding this interaction is the Hydrodynamic Theory of Dentin Sensitivity.
It states that the movement of fluid in dentinal tubules is the basic event that elicits dentinal pain (Figure 3). The direct exposure of the dentin allows for more rapid movement of fluid. Heat, cold, dessication, and dental probing can all displace fluid and therefore elicit pain. In this theory, it is A fibers (nerve fibers that have the fastest rate of transmission of nervous impulses) that are activated by fluid movement.
Broken teeth are a very common problem in veterinary patients.11,12 In fact, 1 out of 10 dogs has a broken tooth in their mouth with direct root canal (nerve) exposure,13 which is called a complicated crown fracture (Figure 4). This number does not include the numerous pets with uncomplicated crown fractures (Figure 5) or fractured teeth that do not directly involve the root canal system. Both types of tooth fractures require therapy, but the treatments are often different.
Complicated Crown Fractures
Complicated crown fractures are the most easily diagnosed form of endodontic disease, requiring only an oral examination for diagnosis.
Avoid “Wait & See”
While it may seem obvious that an exposed nerve hurts or a diseased tooth would be a source of infection, this knowledge is not universal. It is a common misconception among clients and even some veterinarians that these fractures don’t hurt because the pet is eating normally. Many clients are told to “Just keep an eye on it” or “Since it doesn’t bother him, wait until it abscesses.” The fact is, once the nerve is exposed, the tooth cannot heal itself and requires therapy.
Subtle Clinical Signs
Fractured and/or infected teeth affect animals by creating pain, infection, and even fatigue, but often these signs are subtle or hidden. In addition, signs of infection generally present gradually and are, therefore, less noticeable. Because animals are typically more stoic than humans, lack of obvious signs of oral pain should not be misinterpreted as a benign state. Veterinary dentists often see animals that continue to eat normally despite the presence of lesions that should be causing intense oral pain.
After a broken tooth eventually dies and much of the associated pain subsides, the root canal system acts as a bacterial pathway, allowing both local infection and systematic bacterial spread through the bloodstream. Spreading bacteria can negatively affect numerous vital organs, including the heart, liver, kidney, lungs, and brain, leading to serious systemic disorders.14-17
All teeth with direct pulp/nerve exposure must be treated with either root canal therapy or extraction.12,18 Ignoring these teeth is not an option, as prior to tooth death, the living nerve is excruciatingly painful, and subsequent infection follows. Most owners see a notable or even dramatic improvement in their pets’ attitudes and energy levels after therapy is provided.
Uncomplicated Crown Fractures
Uncomplicated crown fractures are also a very common finding on oral examination,19 particularly in large-breed dogs. These fractures result in direct dentinal exposure, and exposed dentinal tubules likely create significant pain (or sensitivity) for the patient (as discussed earlier). In addition, some of these teeth become nonvital due to the traumatic incident and/or associated inflammation.
Therefore, it is recommended that these teeth be radiographed to ensure vitality (Figure 6). If teeth are found to be nonvital, they must be treated with root canal therapy or extraction. If teeth appear vital, the application of a bonded sealant is recommended to decrease sensitivity (see More at Todaysveterinarypractice.com).
In addition to long-term, low-grade systemic infection, over time an infected tooth may eventually cause swelling or an abscess (Figure 7).12,20 This is also a very painful situation, demanding prompt therapy. Unfortunately, in many cases, abscessed teeth have existed for years prior to the appearance of clinical signs. Furthermore, tooth abscesses typically wax and wane until they are definitively treated.
For example, facial swelling may temporarily resolve (especially if treated with antibiotics), but will eventually recur. The animal’s immune system can often temporarily control the local infection, but ultimately the swelling/abscess cannot be cured until definitive therapy is performed. Definitive therapy is either root canal or extraction.
Discoloration is another clinical sign of tooth death and potential secondary infection (Figure 8). Affected teeth can appear pink, purple, yellow, or grey. A study showed that 92.7% of these teeth are nonvital, despite the lack of clinical or radiographic signs of disease.21
Nonvital teeth lose their natural defense ability and are often infected via the bloodstream, which is known as anachorisis. Therefore, most veterinary dentists do not rely on radiographic appearance to determine vitality of stained teeth. All intrinsically stained teeth should be treated the same way as a fractured tooth—with root canal therapy or extraction. Intrinsic staining differs from extrinsic staining (eg, coffee stains in humans) because it is caused by blood product breakdown from pulp hemorrhage.
Another case of camouflaged endodontic disease is a nonvital tooth that appears completely normal (Figure 9).12 The vast majority of these cases have some outward sign of disease and will show evidence of nonvitality if transilluminated.22 However, some cases can only be diagnosed with dental radiology. This highlights the importance of full-mouth dental radiology as part of all patients’ dental prophylaxis.23,24
As stated previously, all teeth with direct pulp exposure as well as stained and/or nonvital teeth must be treated.12,20 The treatment options for these teeth are root canal therapy or extraction. When properly performed, either treatment should result in resolution of pain and/or infection. There are advantages and disadvantages to each treatment, and recommendations vary depending on which tooth is involved and the level of disease.
Root Canal Therapy
Briefly described, root canal therapy involves removal of the nerve and associated structures, disinfection and filling of the canal, and restoration of the surface of the tooth (Figure 10).25,26
The advantages of root canal therapy compared to complete extraction include:
- Minimized pain and discomfort
- Retained function of the tooth
- Maintained strength of the jaw
- Decreased surgical complications.
Although almost any tooth can be treated with root canal therapy, it is specifically recommended for treating larger, strategic teeth, such as the canine or carnassial teeth. The lower canine teeth are specifically associated with jaw strength; avoiding extraction of these teeth, if possible, is optimal.
Extraction involves complete removal of the tooth and its root(s). This is an important point, as only complete extraction will resolve infection; retained roots are a very common complication with extractions (Figure 11).
The advantages of extraction include:
• Decreased surgical time and expense (for smaller teeth)
• No long-term follow-up.
Endodontic disease is a very common condition in small animal veterinary patients. Many of these conditions are easily diagnosed, such as complicated crown fractures and discoloration. Other conditions are less obvious (eg, uncomplicated crown fractures) and may require dental radiographs for definitive diagnosis.
Therefore, a complete oral examination should be performed on all patients and a thorough oral examination and radiographs completed during every dental procedure. Finally, teeth affected by endodontic disease should be treated. Root canal therapy (especially with strategic/large teeth) is ideal, but complete extraction is also acceptable.
- Figure 1: Reprinted from Small Animal Dental, Oral, and Maxillofacial Diseases—A Colour Handbook, Niemiec BA, London: Manson Publishing, 2010, with permission.
- Figures 2 and 3: Reprinted from Veterinary Endodontics, Niemiec BA, Tustin, CA: Practical Veterinary Publishing, 2011, with permission.
- Theuns P. Endodontic anatomy. In Niemiec BA (ed): Veterinary Endodontics. Tustin, CA: Practical Veterinary Publishing, 2011.
- Lewis JR, Reiter AM. Anatomy and physiology. In Niemiec BA (ed): Small Animal Dental, Oral and Maxillofacial Disease—A Colour Handbook, London: Manson Publishing Ltd, 2010.
- Hargreaves KM, Cohen S. Structure and function of the dentin-pulp complex. Pathways of the Pulp, 10th ed. St. Louis: Mosby, 2011.
- Hernandez SZ, Negro VB, Paulero RH, et al. Scanning electron microscopy of pulp cavity dentin in dogs. J Vet Dent 2010; 27:7-11, 2010.
- Startup S. Tooth response to injury. In Niemiec (ed): Veterinary Endodontics. Tustin, CA: Practical Veterinary Publishing, 2011.
- Moore J. Vital pulp therapy. In Niemiec BA (ed): Veterinary Endodontics. Tustin, CA: Practical Veterinary Publishing, 2011.
- Trope M, McDougal R, Levin L, et al. Capping the inflamed pulp under different conditions. J Esthet Restor Dent 2002; 14(6):349-357.
- Kuntsi-Vaattovaara H, Verstraete FJ, Kass PH. Results of root canal treatment in dogs: 127 cases (1995-2000). JAVMA 2002; 220(6):775-780.
- Niemiec BA. Assessment of vital pulp therapy for nine complicated fractures and fifty-four crown reductions in dogs and cats. J Vet Dent 2011; 18(3):122-125.
- Clarke D. Vital pulp therapy for complicated crown fracture of permanent canine teeth in dogs: a three-year retrospective study. J Vet Dent 2001; 18(3):117-121.
- Startup S. Tooth response to injury. In Niemiec BA (ed): Veterinary Endodontics. Tustin, CA: Practical Veterinary Publishing, 2011.
- Dupont G. Pathologies of the dental hard tissues. In Niemiec BA (ed): Small Animal Dental, Oral and Maxillofacial Disease—A Colour Handbook. London: Manson Publishing, 2010.
- Golden AL, Stoller NA, Harvey CE. A survey of oral and dental diseases in dogs anesthetized at a veterinary hospital. JAAHA 1982; 18:891-899.
- Mealey BL. Influence of periodontal infections on systemic health. Periodontol 2000; 21:197-209, 1999.
- Niemiec BA. Periodontal disease. Top Comp Anim Med 2008; 23(2):72-80.
- Pavlica Z, Petelin M, Juntes P, et al. Periodontal disease burden and pathological changes in the organs of dogs. J Vet Dent 2008; 25(2):97-108.
- Debowes LJ, Mosier D, Logan E, et al. Association of periodontal disease and histologic lesions in multiple organs from 45 dogs. J Vet Dent 1996; 13(2):57-60.
- Holmstrom SE, Frost P, Eisner ER. Endodontics. Veterinary Dental Techniques, 2nd ed. Philadelphia: WB Saunders, 1998.
- Theuns P, Niemiec BA. Bonded sealants for uncomplicated crown fractures. J Vet Dent 28(2):130-132, 2011.
- Niemiec BA. Oral pathology. Top Comp Anim Med 2008; 23(2):59-71.
- Hale FA. Localized intrinsic staining of teeth due to pulpitis and pulp necrosis in dogs. J Vet Dent 2001; 18(1):14-20.
- Huffman LJ. Oral examination. In Niemiec BA (ed): Small Animal Dental, Oral and Maxillofacial Disease—A Colour Handbook. London: Manson Publishing, 2010, pp 39-61.
- Verstraete FJ, Kass PH, Terpak CH. Diagnostic value of full-mouth radiography in cats. Am J Vet Res 1998; 59(6):692-695.
- Verstraete FJ, Kass PH, Terpak CH. Diagnostic value of full-mouth radiography in dogs. Am J Vet Res 1998; 59(6):686-691.
- Niemiec BA (ed). Veterinary Endodontics. Tustin, CA: Practical Veterinary Publishing, 2011.
- Holmstrom S, Frost P, Eisner E. Endodontics. In Niemiec BA (ed): Veterinary Dental Techniques, 2nd ed. Philadelphia: WB Saunders, 1998, pp 312-317.
For educational videos of the pathologies discussed in this article, please visit dogbeachdentistry.com.
Brook A. Niemiec, DVM, FAVD, Diplomate AVDC, is chief of staff of Southern California Veterinary Dental Specialties, with offices in San Diego and Murrieta, California, and Las Vegas, Nevada. He has authored many articles and chapters, including the recently published Small Animal Dental, Oral and Maxillofacial Disease: A Colour Handbook (Manson Publishing). Dr. Niemiec founded the veterinary dental telemedicine website vetdentalrad.com, which also offers instructional videos and educational posters. He lectures extensively at national and international conferences and is the coordinator and instructor of the San Diego Veterinary Dental Training Center (vetdentaltraining.com). Dr. Niemiec received his DVM from University of California–Davis.