Discussion

Endodontic treatment of human teeth has a long history and is today a well-established academic specialty. Endodontic treatment in humans as in horses has the potential to save teeth and thereby maintain oral function. Typical indications in the horse are periapical infections (including those resulting in sinusitis), and traumatic pulp exposure. An important advantage of doing endodontic therapy in hypsodont teeth is to minimise the risk for dental drift, a common, and in most cases unavoidable post extraction sequelae.
The differences between brachyodont teeth and hypsodont teeth are important. However the endodontic cases published have been performed using a retrograde technique. At the Animal Dental Clinic in Sweden and the University of Agriculture Sweden an orthograde technique has been developed with good long- term results.
The orthograde approach has some important advantages compared to the retrograde technique. Root canal preparation, obturation and sealing demands a very clean and proper working area and this is more achievable at the occlusal aspect. An orthograde approach takes advantage of the occlusal forces present each time the animal chews. The occlusal forces compress and force the sealant in an apical direction optimising their function. One of the advantages of the apical movement of sealant/intra-canal medicant is that it provides room at the occlusal aspect for additional sealant to be placed over time. Importantly, an orthograde approach easily allows for the endodontic treatment to be performed over multiple visits. Multiple visits are essential to ensure appropriate sterilisation of the root canal, monitoring of the biological response to the endodontic treatment, and breaking the procedure into working times well tolerated by most animals under sedation.
There is one crucial question to be answered before making the decision to perform endodontic treatment. The question is; Is it possible to access the affected parts of the tooth? If not, do not try endodontic treatment.
The orthograde technique is similar to the technique used in brachyodont teeth. In the first step access to the pulp cavity is created using a low speed round shaped low speed carbide burr. Before going further into the pulp horn the occlusal aspect is widened with a Lindeman burr (low-speed). Next step is to clean out the pulp cavity thoroughly using endodontic files (Hedstrom) of different length and diameter depending on the anatomy of the tooth. Indicator radiographs are taken during the procedure for guidance. The pulp cavity is irrigated with high volume of saline solution using an electric pump to facilitate removal of bacteria, debris and tooth material. Once the pulp cavity is clean and appropriately shaped it is dried using a suction system and small cotton pellets. Before the pulp cavity is sealed off, it is obturated with an emulsion of Ca(OH)2. The Ca(OH)2 must be thoroughly condensed so the water part of the emulsion is minimised. Finally the access sites are sealed with dental cement in at least 2 different layers that are not chemically attached to each other. This is for safety reasons if the outer layer is lost it will not interfere with the second layer.
On the initial visit 'temporary' fillings are used to allow easy access to the pulp cavity at the second visit. The second visit is recommended after one month. If the pulp cavity is clean and dry on investigation at the one month follow-up a more resistant seal is applied in at least 2 different layers. If there is liquid in the pulp cavity or other signs of failure the choice of therapy needs to be reconsidered. The whole procedure may need to be repeated. In cases where the initial treatment appears to be successful, follow- up is recommended at least once a year to make sure the restorative is complete. Follow-up radiographs are recommended no earlier than in one years time. At the yearly examination the normal tooth eruption should be noted provided that the endodontic therapy is still successful.
The described orthograde technique has been used in Sweden for more than 10 years. The long-term follow-up shows a high frequency of success. Treatment failures, when registered, are most often close in time to when the primary treatment was performed. The most common causes of failure are new dental fractures, and persistence of the endodontic infection resulting in fistula formation.
It is proposed that the cause of subsequent dental fracture of treated teeth is largely due to a combination of analgesia administered as part of the initial endodontic treatment and undetected microscopic fractures/infractions. The analgesia results in normal occlusal loading by the horse when chewing, which then causes nondisplaced crown fractures to progress and ultimately become displaced. Most new fractures are seen within the first 3 month after primary treatment. Fistula formation is explained by failure to eradicate the endodontic infection as part of the initial endodontic therapy. When fistula develops subsequent to initial endodontic therapy, repeat endodontic treatment often includes both orthograde and retrograde approaches in the same session.
In this author's opinion endodontic treatment is a good alternative in many cases to the more common treatment of extraction. There are many advantages to being able to save a tooth. One advantage of endodontic therapy is that initial failure still allows retreatment and the possibility of successful outcome. Tooth extraction is final and cannot be reversed. Endodontic therapy performed at a level which results in successful outcomes is technically challenging. Endodontic therapy and case management should only be performed by appropriately trained and equipped professionals.