This series on oral care and dental disease is provided by Eric M. Davis, DVM, a Diplomate of the American Veterinary Dental College.  Dr. Davis is the former Director of the Dental Referral Service at the Cornell University Hospital for Animals, and is currently the Director of Animal Dental Specialists of Upstate New York, a referral clinic for veterinary dentistry and oral surgery located in Fayetteville, New York. Dr. Davis can be contacted at emdavisdvm@gmail.com or at 315-445-5640.

Endodontics is the discipline of dentistry that deals with diagnosis and treatment of diseases of the pulp and the consequences of infection and/or necrosis of pulp tissue. Crown fractures can be described by their severity:

1. A "chip fracture" implies a small piece of enamel has broken off the crown, resulting in exposure of the dentin only.
2. A "near exposure" implies a more substantial piece of enamel and dentin has fractured, and only a very thin layer of dentin covers the pulp tissue.
3. A "complicated crown fracture" implies that the pulp tissue has been exposed by the fracture.

Regardless of the severity of the fracture, a radiograph should be taken to be sure that the tooth has not already been irrevocably damaged.  Recall that the pulp chamber in an immature tooth is very large, while the pulp chamber of a mature tooth becomes thinner with age, as the dentinal walls become thicker.  Therefore even a minor appearing chip fracture in an immature tooth may actually result in a near-exposure of the pulp.  With a "chip fracture", where only the dentin is exposed, as long as there remains 2mm or more of dentin to protect the pulp (determined radiographically), no treatment may be necessary. In such cases, I will usually contour the rough edges and apply a dentinal bonding agent and/or sealant over the fracture, to prevent bacteria from percolating through the dentinal tubules to invade the pulp tissue.

In the case of a "near exposure", usually a pulpal "blush" may be visible as a pink dot on the surface of the fractured dentin, signifying that the pulp tissue is separated from the external environment by just a scant amount of dentin, (which is porous anyway).  This tooth requires either endodontic treatment or extraction, since pulpitis is inevitable.  Remember that in this scenario, the cellular extensions of the odontoblastic processes as well as nerve endings are now exposed.  Exposed dentin is sensitive to heat, cold, touch and osmotic gradients.  The hydrodynamic theory suggests that due to blood pressure within the pulp cavity, there is a net OUTWARD FLUID FLOW of fluids from the pulp toward the enamel.  Pain from dentin exposure is due to fluid movement pulling on the odontoblastic processes and the associated nerve fibers.  Thus sweet drinks (osmotic difference) or air movement across exposed dentin draws more fluid out of the tubules causing pain. Left untreated, a near exposure will usually result in a non-vital tooth.

Any tooth with a crown fracture that has obviously resulted in exposure of the pulp, requires that something be done about it IT SHOULD NOT BE IGNORED.  Remember the "3 R's" when looking at a fractured tooth in a patient: the tooth should either be REMOVED (extracted), REPAIRED (endodontic therapy), or the patient should be REFERRED but the tooth should NEVER be left to continue to ROT!!!  A tooth with exposed pulp subjects the patient to PAIN and INFECTION - the two most important reasons why we should provide dental care.  When the pulp is exposed, it quickly becomes contaminated, inflamed and necrotic.  However, irreversible pulpitis may also occur following blunt trauma, with swelling and ultimately ischemic necrosis and extravasation of blood breakdown components into the more porous dentinal tubules.  As the pulp tissue is dying, it is very painful (as related by humans), but once the pulp is dead, the intense pain subsides.  Bacteria, necrotic debris, inflammatory mediators etc. ultimately leak out of the apical delta and into the periapical periodontal ligament space and adjacent vascular bone. Contamination of bone by bacteria and inflammatory mediators is referred to as osteomyelitis.  We all learned very early during our veterinary education, that osteomyelitis is a BAD disease.  With time, several scenarios may occur.  A periapical abscess may form, which again is very painful until a fistula develops, whereby the pressure can be relieved and the pain will subside.  (Often, practitioners unfamiliar with dental care may confuse such a fistula with deep pyoderma or surmise that a foreign body is present.  Antimicrobial therapy is usually prescribed, but is often only temporarily effective in treating the infection.)  Another possible sequela to endodontic disease is the formation of a periapical granuloma or cysthistology is necessary to differentiate these two conditions.  Another possibility would be the extravasation of inflammatory exudate resulting in external root resorption.  Regardless of what occurs, pain and infection persist until a treatment is performed. Remove, Repair, or Refer but don't ignore. 

Endodontic treatment (repair) offers the following advantages over extraction:

1. Removal of only the diseased pulp from within the tooth is less traumatic to the patient than is removal of the entire tooth.
2. Endodontic treatment avoids complications of extraction such as oronasal fistula, dry socket, jaw fracture, hemorrhage, tongue protrusion and/or lip entrapment.
3. In some cases, endodontic treatment can take less time to perform than extraction and flap surgery, thus is better for the patient.
4. The patient retains the use of the tooth.
5. A high success rate often occurs following endodontic ("root canal") therapy if done properly.

Three commonly performed endodontic treatments include:

Total pulpectomy (a.k.a. conventional endodontic therapy, a "root canal")
Partial coronal pulpectomy (a.k.a. vital pulpotomy, vital pulp therapy)
Apicoectomy (a.k.a. surgical endodontic therapy or retrograde filling)

I do not like to refer to the procedure of total pulpectomy as a "root canal" since the latter is so often thought of as such a painful and horrible treatment.  Why would anyone subject his or her beloved pet to a root canal? "Why I'd rather put her to sleep than make her have a root canal". On the other hand, if I ask the owner "we either remove the tooth or we can repair the tooth, which would you prefer?"   By far, most pet owners respond, that they would prefer that the tooth be saved rather than be removed.

What is the purpose of performing a "root canal"?  If we can completely sanitize and debride the pulp cavity of its necrotic and/or infected contents, and if we can pack the cleaned canal with an impervious seal, then the body will successfully eliminate any residual periapical infection that may have leaked out of the apical delta into adjacent vascularized tissues. Thus, this treatment is indicated when pulp exposure has occurred or the tooth is non-vital (concussion injury with totally discolored crown).  This procedure is contraindicated any time the tooth can not be completely sealed, such as if the tooth is immature and the root apex has not completely formed, or if the periapical infection has resulted in external root resorption.  Endodontic therapy should only be considered for periodontally healthy teeth.  If the tooth is loose or otherwise compromised by periodontal disease, root canal therapy would be of little benefit.  And of course, if the patient has severe systemic illness, extraction would probably be recommended over endodontic therapy. The main advantage of root canal therapy is that the patient gets to keep the tooth and there is a relatively high success rate.  In a recently published (2002) retrospective study of 127 root canals, 69% showed radiographic improvement  (mean follow-up, 13 months post-op) following endodontic treatment, and an additional 26% showed no radiographic evidence of failure.  Thus a positive outcome occurred in 95% of treated teeth. Endodontic treatment failed in only seven of the 127 treated teeth. 

Partial vital pulpectomy, also called vital pulp therapy (previously referred to as a "vital pulpotomy") is a procedure performed on an immature tooth that has suffered a pulp exposure, either traumatically or iatrogenically (such as during crown reduction therapy for orthodontic abnormalities). The purpose of this procedure is to keep the pulp tissue alive so that production of secondary dentin can continue, resulting in a stronger, mature tooth. Using strict aseptic technique, a small amount of coronal pulp tissue is removed (partial coronal pulpectomy).  Then, layers of dental materials are placed onto the remaining pulp tissue after hemorrhage has been controlled (direct pulp capping).  An impervious seal must be placed onto the remaining tooth (coronal restoration) to prevent microleakage from contaminating and killing the pulp tissue.  With this procedure, yearly radiographic follow-up (three-year minimum) is critical to assess treatment outcome.  Although vital pulp therapy can sometimes be used to treat VERY ACUTE pulp exposures in mature teeth, the more time that passes the poorer the outcome.  A recently published, retrospective study showed that when vital pulp therapy was performed less than 48 hours following traumatic pulp exposure, the success rate was 88%.  However those teeth that received vital pulp therapy two to seven days following traumatic pulp exposure, the success rate was 41% and if the tooth was treated one to three weeks after exposure, successful outcome was 23.5%.2 Therefore, most veterinary dentists recommend root canal therapy even for acute pulp exposures in mature teeth, since the results are more predicable and the requisite follow-up is not as strict.

1 Vaattovaara HK, Verstraete FJM, Kass PH: Results of root canal treatment in dogs: 127 cases (1995-2000).  J Am Vet Med Assoc 220 (6); 775-780, 2002.

2 Clarke DE: Vital therapy for complicated crown fracture of permanent canine teeth in dogs: a three-year retrospective study.  J Vet Dent 18 (3); 117-121, 2001.