May 6, 2019
In my previous two columns, we looked at conventional (orthograde) root canal therapy, along with vital pulp therapy. This time, we will discuss surgical (retrograde) endodontics.
In instances where orthograde root canal therapy has failed, a decision needs to be made to either perform a second orthograde root canal therapy or to proceed to the next step: surgical endodontics. Extraction would be a third option for a failed root canal procedure if the owner no longer chooses to salvage the endodontically diseased tooth.
Besides its use as a treatment when orthograde root canal therapy fails, retrograde root canal therapy may be the chosen course of action when an instrument breaks off while performing an orthograde procedure. Instruments most likely to break off in the canal include Lentulo spiral paste fillers, barbed broaches, and rotary files. Sometimes the detached instrument portion can be entombed in endodontic filling material during orthograde obturation, but if not, a retrograde procedure may be warranted.
What is surgical root canal therapy? A surgical approach is made over the apical portion of the root, and bone is carefully removed to expose the root area (Figure 1). The apical 4 mm of the root is surgically removed, and the apex is sealed with a biocompatible restorative material that will act like a cork in a wine bottle to seal the apex and help prevent percolation of inflammatory and infectious components into the surrounding bone.
Though the success rate of root canal therapy is high, there are cases occasionally where a root canal procedure can fail. A retrospective study evaluated 127 roots treated with orthograde endodontic therapy in 64 dogs. Radiographs obtained before surgery, immediately after surgery, and during follow-up examinations were evaluated by two independent evaluators. Success was defined as 1) a periodontal ligament space that was radiographically normal and 2) radiographic evidence of possible preoperative root resorption, if present, had not progressed. Treatment was considered to show no evidence of failure if possible preoperative root resorption had ceased, but a preexisting periapical lesion had remained the same or only decreased in size and not completely resolved.
In this study, treatment was considered a failure if:
Follow-up time varied, with a mean of 13 months. Sixty-nine percent of roots showed success as defined above, whereas 26 percent of roots showed no evidence of failure. Six percent of roots showed radiographic evidence of failure. The success rate was lower for canine teeth than for maxillary carnassial teeth. Roots with preexisting periapical pathology had a lower success rate. Interestingly, the radiographic quality of the obturation was not associated with outcome. Results of this particular study suggested root canal treatment offers a viable option for salvage of periodontally sound but endodontically diseased teeth in dogs.1
When designing studies to assess success of endodontic procedures, it is important to define what is meant by “success.” In his manuscript in the Journal of Veterinary Dentistry (JOVD), Robert Menzies, BVSc, DAVDC, states, “The patient’s view of success may be the maintenance of an asymptomatic tooth, the clinician’s view [of success] may be an asymptomatic tooth with resolve of radiographic abnormalities, and the scientist may look for histological evidence of resolve of periapical inflammation.”2
Although intraoral dental radiography is considered in many ways to be the clinical gold standard of evaluating a treated tooth in a patient’s mouth, even dental radiography has limitations and variations depending on technique and positioning.2 Coupled with normal anatomic variations that can mimic periapical evidence of endodontic disease (so-called “chevron” lucencies), this challenge makes diagnosis of success or failure more abstract in some patients, even when dental radiographs are performed. Cone beam computed tomography (CBCT) appears to be a more sensitive and accurate test to diagnose lesions in endodontically diseased teeth in humans.3 For this reason, CBCT is becoming a more common tool in the armamentarium of the veterinary dentist.
Next month, we’ll further discuss the new technology of CBCT.
John Lewis, VMD, FAVD, DAVDC, practices dentistry and oral surgery at Veterinary Dentistry Specialists and is the founder of Silo Academy Education Center, both located in Chadds Ford, Pa.
1 Kuntsi-Vaattovaara H, Verstraete FJ, Kass PH. Results of root canal treatment in dogs: 127 cases (1995-2000). J Am Vet Med Assoc. 2002; 220(6): 775-780.
2 Menzies RA, Reiter AM, Lewis JR. Assessment of apical periodontitis in dogs and humans: a review. J Vet Dent. 2014; 31(1): 8-21.
3 Venskutonis T, Daugela P, Strazdas M, Juodzbalys G. Accuracy of digital radiography and cone beam computed tomography on periapical radiolucency detection in endodontically treated teeth. J Oral Maxillofac Res. 2014; 5(2): e1. doi: 10.5037/jomr.2014.5201.
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