GOALS AND PRINCIPLES
Open apex endodontics is a treatment modality that allows treatment of roots that cannot be treated successfully with a standard endodontic treatment. The goal of surgical endodontics is to remove the causal elements of the persisting periapical infection, as well as the associated periapical lesions. To remove the cause of the periapical infection, the apical end of the root(s) is surgically removed and the new apical end is cleaned, shaped, and filled three-dimensionally to seal the canal from the periapical tissue. The surgical exposure of the root apex allows the curettage of the periapical lesions, which are submitted for histopathologic evaluation.
Surgical endodontics is indicated for roots that cannot be treated with a standard normograde endodontic treatment, and those which have been unsuccessfully treated and whose prognosis is better with a surgical treatment than with retreatment. However, most studies have shown that the long-term prognosis is better with retreatment than with surgical endodontics. There have been cases where retreatment has been successful, even after surgical endodontic treatment has failed.
The choice between the two options, retreatment or surgical endodontics, should be based on the perceived cause of the failure. Cases where there are questions about the quality of the instrumentation, obturation, or restoration are definite candidates for retreatment. Indeed, faulty access or fracture site restorations have often been overlooked as a main cause of endodontic treatment failure. Vertical root fracture should also be considered a possibility with endodontic treatment failure. In this case, neither modality of treatment would work and the tooth, or its root if a root resection is considered, should be extracted.
The main indications for surgical endodontics are cases with inaccessibility to the root apex through the canal (pulpal stones, canal obliteration), cases where the cause of the lesion is not in the canal (extruded material, foreign bodies) or where, despite elimination of its cause, a periapical lesion self-perpetuates (periapical cysts). The medical contraindications for surgical endodontics are uncontrolled diabetes, end-stage renal disease, and immunodeficiency.
The dental contraindications are the cases where a retreatment has a better prognosis, where the apex of the root cannot be accessed surgically (palatal root of an upper fourth premolar), and where the tooth cannot be saved. A tooth, or its root, can’t be saved when it is not restorable, is compromised because of its periodontal status, or has a vertical root fracture.
The patient’s medical and dental history should first be reviewed. The patient’s database should include hematological evaluation and blood chemistry. Any systemic disease should be assessed to determine if the patient is a suitable candidate for anesthesia and endodontic treatment. If needed, the patient’s health status should be stabilized before the procedure. A blood clotting deficiency would be a serious problem during surgical endodontic treatment. If suspected from a review of the patient’s medical story, blood-clotting functions should be evaluated (bleeding time, activated coagulation time).
If not already done, or if the quality of the root canal treatment is questionable, a normograde endodontic treatment should be done or redone. Surgical endodontics is not a substitute for proper cleaning, shaping, and three-dimensional obturation of the radicular system.
The teeth most often treated with surgical endodontics in veterinary dentistry are the canine teeth and the carnassials. They are considered strategic teeth because of their greater importance with respect to their size and function. The roots of the carnassials and upper canine teeth are approached via a buccal mucoperiosteal flap. The semi-lunar incision is centered over the middle of the root to be treated. Palpation of the juga helps localize the root. The incision is continued apically over the far line angle of the next mesial and distal tooth. Its length should allow exposure of the apical area with passive retraction of the flap after its elevation with a periosteal elevator.
The roots of the lower canine teeth are approached via a skin incision centered over the apical third of the root on the ventral aspect of the mandible. The subcutaneous tissue and periosteum are elevated to expose the ventral cortex of the mandible.
The osteotomy is centered over the apical third of the root. The location of the apex can be estimated from the dental radiographs or by using the working length measurement made during the normograde root canal treatment. The osteotomy is performed with a high-speed hand piece and a round bur, or preferably a surgical bur (Lindman). The bur is cooled with sterile saline. A surgical hand piece has the advantage of not sending pressurized air, thereby preventing subcutaneous emphysema and air embolism.
The bone is removed circumferentially using an etching motion until the apex is found. The dentin is more yellow and softer in texture than bone. The apex is exposed enough to allow for its curettage, section, retro-instrumentation and filling. The pathological tissue is removed from the crypt with a bone curette and saved for histopathological examination. The most important part of the procedure is the removal of the infected material in the root canal. The apical end of the root is resected with a tapered fissure bur. It is recommended to remove at least 3 mm, but this has to be weighted with the size of the patient.
If the instrumentation of the canal is to be done with a bur, the cut is made with a bevel (bucco-lingual) of around 45SYMBOL 176 \f "Symbol" \s 10° to the long axis of the tooth. The bevel for the lower canine is mesio-distal. With ultrasonic or sonic root-end preparation, the bevel can be less than 45SYMBOL 176 \f "Symbol" \s 10°. The cut can even be perpendicular to the root’s long axis. There are less dentinal tubules exposed and fewer possibilities that a secondary canal is left untreated on the lingual aspect of the root.
Once the apicoectomy is completed, the crypt is rinsed and kept dry with collagen, bone wax, or similar product. Magnification and a good light source are essential for a thorough examination of the exposed surface of the root. It is important to look for the presence of secondary roots, secondary canals, an isthmus between principals and secondary canals, and any aberration of the radicular system that need to be instrumented and sealed.
By far the best way to instrument the canal and its ramification is to do an ultrasonic or sonic root-end preparation. The advantages are tremendous: better debridement, the walls of the preparation are parallel and centered with the canal, sterility is maintained during the preparation, there is no thinning of the lingual wall and less chance of perforation, and more retention of the filling cement. There is no need for a bevel when the apical part is cut off the root—more of the apical part can be removed with still more of the root intact. When the canal is cut perpendicular to its long axis, there is less inter-face with the retro-filling material where leakage could occur. Before ultrasonic or sonic root-end preparation was available, preparation was done with a miniature contra-angle on a low-speed hand piece or a straight hand piece. An inverse cone bur was used to create retention with an undercut.
Once the preparation is complete, the root-end is rinsed with sterile saline or a citric acid etchant and dried. It might be necessary to replace the material walling the crypt to keep it dry during retro filling. The preparation is inspected for its thoroughness.
The filling materials that give the best results are Super EBA and IRM. These ZOE cements are mixed to a clay consistency, introduced, and condensed in the canal until they form a slight overfill. Zinc amalgam, the previous standard material, is used less often as it causes more leakage than Super EBA or IRM. MTA is a new material that yields even better results than the ZOE cements during in-vitro studies. If it proves better in long-term in-vivo studies, its use might improve the quality of the seal at the apical end of the root.
After the cement is set, it is carved with a cold blade instrument. The filled apical end of the root can then be smoothed with a 30-blade composite finishing bur. A radiograph is taken to evaluate the quality of the filling.
The material walling the crypt is removed and the surgical site and underside of the mucoperiosteal flap are rinsed thoroughly to clear any debris. The bony crypt is then filled with osteo-promotive material (optional). The flap is sutured in placed with absorbable suture material on a swaged-on needle using a simple discontinuous suture pattern. Pressure is applied on the flap for two minutes with wet gauze to reduce the blood clot thickness underneath the flap, thereby favoring primary healing.
AFTER CARE AND FOLLOW-UP
Antibiotics are prescribed for seven days and analgesics (NSAID) for four days. During the first two weeks, the patient is fed only soft food and is not given anything to chew on (e.g., toys). During this period, it is recommended to rinse the mouth once or twice daily with a 0.12% solution of chlorhexidine. The healing of the mucoperiosteal flap is checked two weeks after the surgery and the regular oral hygiene procedures can usually be resumed at that time. A follow-up radiograph is taken four to six months post-operatively, and repeated every 12 months thereafter.
There have been very exciting improvements in dental technology during the last decade. These improvements do not mean necessarily that more endodontic treatments will be done surgically, as the new technology also improves the ability to treat root canals non-surgically. The new technology has had a tremendous effect on the quality of the dental work achievable today, and that means a better prognosis for treatment of endodontic disease in man and animal.
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