Eliminating the Step Ledge in the Curved Root Canal in Cаse of Endodontic Retreatment of Teeth Previously Obturated with Resorcinol-formalin Method

Creating a step ledge during endodontic treatment is an iatrogenic complication. The step ledge is an artificially formed deviation from the natural trajectory of the root canal without communication with the periodontal ligament, as a result of excessive dissection of the dentinal wall (usually in the bend area), which does not allow the advancement of instruments to the apex, despite the passage of the canal itself. This complication is one of the most common during preparation of canals. There is little information on the prevalence of the discussed complications in the literature. According to Jafarzadeb H & Abbott, step ledges are found in 25-52% of cases of endodontic treatment. The most significant risk factor for creating a step ledge is the curvature of the canal: the stronger it is the higher is the risk of deviation during preparation. As a rule, a step is created in curved roots on the outer wall of the root canal, more often in molars. When trying to eliminate it, perforations of the root wall, straightening of the root canal, thinning of the root walls are possible. Such situations do not solve the problem, but on the contrary, aggravate it. If it is necessary to retreat a tooth, the possibility of a ledge increases, because in the root canal. There is an obstacle in the form of sealer and filler. The attempt of endodontic retreatment intervention cannot guarantee a positive outcome even with the use of modern effective methods of treatment. This is due both to the properties of the filling mass, which is very difficult to remove from the root canal, and to the formation of dentin and obliteration of the canals in the previously treated tooth. The creation of a step leads to the loss of the possibility of the root canal passage to the apical orifice and, consequently, the mechanical and medical treatment of the apical part of the canal. In its turn, this leads to the development and persistence of microflora in the untreated part of the root canal, resulting in periodontitis and tooth extraction. Thus, the elimination of steps in the root canal is a prerequisite for a successful endodontic retreatment of the tooth. When eliminating the step, it is necessary to find the true course of the root channel. This is not always possible even applying microscope, because sometimes the main course of the canal is located “around the bend” and it is simply impossible to see it. Thus, this manipulation is often performed, focusing only on tactile sensations. Since the use of machine rotary instruments will be ineffective in curved root canals to perform the manipulation, it is necessary to have an endodontic headpiece, performing reciprocal movements (± 30º), the collet of which can fix steel hand tools. Passing of steps is performed only by steel K-rimers or K-files, pre-bent in the direction of the root canal curvature. Here is the sequence of manipulations: Funnel enlargement of the root canal orifice. The enlargement of the root canal at the level of the step to approximately 40.02. If the channel is not sufficiently enlarged, the pre-curved instrument, when inserted into the narrow root canal, will straighten under the pressure of the walls, and the instrument tip cannot be directed towards the lesser curvature. Manipulations in the root canal, obturated with resorcinol-formalin resin, are carried out with a solvent or chelating agent. Using the reciprocating headpiece, the file is inputted into the canal and moved forward with pressure in the apical direction of the root canal. The use of a reciprocating headpiece ensures the direction of force of the steel instrument in a necessary direction. Periodically remove dentine scobs and filling material using ultrasonic and washing with sodium hypochlorite. When processing the instrument in the apex direction for 2-3 mm, a control radiograph should be made with contrast in the root canal, to control the direction of passage in order to prevent perforation.