Endodontics is the treatment of the pulp of the tooth (Endo- = inside; -dontic = tooth). Endodontic therapy is a specialist procedure and should not be undertaken without adequate training and supervised experience. The following outlines the more common endodontic treatments that are required in small animal dentistry.
Types of Endodontic Treatment
There are four main types of endodontic treatment, each of which has specific indications. They are:
1. Pulp capping
2. Partial pulpectomy with direct pulp capping
3. Root canal therapy
4. Surgical endodontics
Conventional (Standard) root canal therapy is the most commonly indicated type of endodontic treatment. It involves total removal of pulp tissue, i.e., total pulpectomy, cleaning and filling of the root canal, followed by tooth restoration.
Root canal therapy is indicated when there is or may be irreversible pulp pathology, (e.g., generalized pulpitis or pulp necrosis, often in combination with periapical involvement) in the mature permanent tooth. Immature permanent teeth are a special consideration and are dealt with separately.
The objectives of conventional root canal therapy are:
1. To clean and disinfect the pulp chamber and root canals
2. To fill the root canal(s) with a non-irritant, antibacterial material thus sealing the apex
3. To close the access and exposure sites with a suitable restorative material
Many different methods are employed in the preparation and filling of root canals. In simple terms, root canal therapy involves removing the pulp, replacing it with an inert material and restoring the tooth. The inflamed or dead pulp is removed using special files. Once the pulp has been removed, the root canal is cleaned, both mechanically with files but also chemically with a disinfectant. The clean and disinfected root canal is then filled with inert material and the crown is restored with a suitable restorative material. The tooth is not restored to its original shape and size as the biting forces in the dog are much greater than those in man and the restoration would be likely to fail if this was attempted.
The whole procedure is performed under general anaesthesia with strict radiographic control. It is time consuming, as each step needs to be performed with meticulous detail to ensure a successful outcome.
The outcome of conventional root canal therapy should be monitored radiographically 6-12 months post-operatively. This will also require general anaesthesia. Evidence of disease around the tip of the root at this time indicates the need for further endodontic therapy or extraction of the tooth. Further endodontic treatment usually consists of re-doing the root canal therapy, often in conjunction with surgical endodontics (usually removing the tip of the root and sealing the root canal from this direction as well).
Special Considerations with Immature Teeth
A partial pulpectomy and direct pulp capping procedure is indicated for recent tooth crown fractures with pulp exposure in immature teeth. An immature tooth has a thin dentine wall and an open apex, allowing a good blood supply to the pulp. Treatment is aimed at maintaining a viable pulp, as this is needed for continued root development.
Necrotic immature teeth require endodontic treatment if they are to be retained. The procedure is an adaptation of conventional root canal therapy as already described for the mature permanent tooth. The necrotic pulp tissue is gently removed and the pulp chamber and root canal thoroughly cleaned. It is important to remove all the necrotic tissue, which usually extends slightly beyond the radiographically verifiable open apex. Sterile calcium hydroxide powder or paste is packed into the root canal, extending just beyond the apex. A degree of apexogenesis (normal root length and apex development) or apexification (treatment stimulated root closure) can be stimulated if this procedure is performed. The exposure site is sealed with a restorative material. The tooth is monitored closely and the calcium hydroxide dressing is changed approximately every six months, as a fresh dressing is more effective in stimulating apexogenesis and apexification. When no further root development can be seen radiographically and if the apex is closed, a conventional root canal treatment should be performed. A conventional root canal treatment can only be carried out if the apex is closed. If the apex is still open and closure cannot be stimulated by repeated calcium hydroxide dressings, it may be possible to obtain an apical seal using a surgical approach and placing a root filling in a retrograde manner.
It must be noted that multiple general anaesthesia episodes are required and thus in most cases extraction of an immature tooth with a necrotic pulp is the best course of action. Salvage procedure as described above is really only indicated for the strategic permanent teeth that have undergone some degree of maturation.
It should be noted that immature teeth might well be present in the mature animal if trauma caused pulp necrosis during the developmental period. Treatment of such teeth is the same as for any immature permanent teeth, regardless of the actual age of the animal.
New Trends in Endodontics
Root Canal Preparation
Root canal preparation using hand files and irrigation is meticulous and time consuming. Ultrasonic instrumentation to debride and shape a root canal is quicker. Such instrumentation is available and works well for short roots with closed apices.
Root Canal Obturation
A variety of methods for filling the debrided and shaped root canal are available. All techniques are operator sensitive and have a learning curve. The methods can be divided into two broad groups, namely sealer and gutta percha or sealer only.
The traditional and most commonly used method is sealer and cold compaction of gutta percha. Modifications to this include compaction of gutta-percha that has been softened in the canal and cold compacted; compaction of gutta-percha that has been thermoplasticized, injected into the system and cold compacted or compaction of gutta-percha that has been placed in the canal and softened by mechanical means.
In recent years, both in man and dog/cat obturation has been achieved using sealer only (usually a calcium hydroxide based material). The procedure is quicker than the sealer and gutta percha methods and long term evaluations are promising.
The root canal should be filled with sealer or sealer and gutta percha, but the crown should be filled with a suitable restorative material. The importance of a tight marginal seal cannot be over-emphasized. If the restoration is leaking, the endodontic treatment is likely to fail. Restorative materials such as combinations of glass ionomers and composite allow for technically simpler restorations of access preparations.
Surgical endodontics involves apicectomy and retrograde filling. This procedure is indicated when anatomical abnormalities do not allow for conventional orthograde access to the root canal system. It can also be used when conventional endodontic therapy has failed and it is deemed essential to maintain the tooth. This latter use was very popular in the 1980's, but has fallen out of favour as good results can be achieved by simply redoing the conventional treatment. In this context, surgical endodontics should be viewed as salvage and only performed if redoing conventional endodontics does not result in healing of the periapical lesion.