Endodontics. Lec.7 د. حسن الرماحي 5 th class. Obturation techniques

Transcription

1 Endodontics Lec.7 د. حسن الرماحي 5 th class Obturation techniques Broadly speaking, techniques of filling canals with gutta-percha can be divided into three main groups: 1- Use of cold gutta-percha. 2- Use of heat-softened gutta-percha. 3- Use of solvent-softened gutta-percha. Cold gutta-percha techniques Cold gutta-percha techniques are generally simple to master as they are not complicated by needing to soften the material with heat or solvents; neither do they require expensive and often complicated devices or equipment. However, it should be clear that cold gutta-percha cannot be compacted into irregularities within the canal system, with the result that this role must be fulfilled entirely by sealer. Cold gutta-percha can be used in a number of techniques: 1- Full-length single point. 2- Apical (sectional) single point. 3- Lateral condensation. 1_Full-length single point: With the advent of the standardized preparation technique, the method of filling canals with a single full-length gutta-percha point and sealer became popular. The theory behind the technique was simple and attractive; the canal was prepared to a round cross-sectional shape of standard size by use of reamers and then obturated by a gutta-percha point of matching diameter

2 However, it soon became apparent that a round canal shape was rarely a chivied, especially in curbed canals, and that single point obturation was less likely to be used, it would rely inevitably on substantial amounts of sealer to fill the gaps, resulting in increase leakage. It was also clear that discrepancies in size and taper between points and equivalent numbered instruments were prevalent. Current canal preparation techniques which aim to flare canal to produce a flowing conical funnel shape cannot be filled adequately with a single-point technique using zinc oxide or calcium hydroxide-based sealers, and therefore should not be attempted. 2_Apical (sectional) single point: In a tooth scheduled for restoration with a post crown, substantial part of the canal must be available to accommodate the post. The apical 4-5 mm of a point was cut off and then mounted on the end of a file before being introduced into the canal. Once the gutta-percha point seated at the end point of preparation the file was rotated, detached from the gutta-percha and removed. The technique was unpredictable and suffered from the same problems as the full-length point technique in terms of lack of fit. Therefore, use of an apical (sectional) single point is not recommended. 3_Lateral condensation: Lateral condensation of cold gutta-percha is taught and practiced throughout the world and is the technique of choice for many clinicians. It is simple and rapid to carry out, can be used in virtually all cases and is the standard against which many new techniques are compared

3 Lateral condensation involves the placement of a master (primary) point at the end-point of preparation followed by the insertion of additional (accessory) points alongside. The use of a standardized master point provides a predictable apical fit, whereas the accessory points obturated the space produced as a result of the flared canal shape. The resultant filling consists of numerous points cemented together and to the canal wall by sealer; it does not result in a merging of the points into a homogeneous mass of gutta-percha. A spreader is interested alongside the master point to improve the adaptation of the master point at the end-point of preparation and to create the space for accessory points. When inserted to within 1mm of the end-point of preparation, the spreader compacts effectively the master point apically and laterally, resulting in considerably less leakage than if the spreader had only entered part-way into the canal. In fact, the necessity to advance the spreader well into the canal is the only reason why canals are flared; a narrow, parallel canal shape would not allow a spreader to advance sufficiently to influence the adaptation of the apical region of the master point. Narrow preparations also predispose to the unwanted removal of the master point upon withdrawal of the spreader as it tends to pierce the master point rather than lie alongside it. The requirements for successful lateral condensation are therefore: 1- A flared canal preparation with a definite apical stop. 2- A well-fitting master gutta-percha point of standard size and taper. 3- A series of spreaders of the appropriate size and shape. 4- An assortment of accessory points which match the size and taper of spreaders. 5- An appropriate sealer. Well-fitting master point. The master cone must fit to the full length of the preparation, be tight at the end-point of preparation, and it must be impossible to force it through the foramen

4 The size of the master cone is guided by the master apical file used in the final preparation of the apical stop or matrix. The selected gp point is held with tweezers at a length equivalent to the working distance and then inserted into the canal. Ideally, the point should: 1- Pass down to the full working distance so that the beaks of the tweezers touch the reference point. 2- Be impossible to push beyond this position, i.e. through the foramen. 3- Fit tightly at the end-point of preparation, giving some resistance to withdrawal (tug back). The tweezers are squeezed slightly so as to notch the point and are then released leaving the point in situ. A radiograph is then exposed to confirm its position in relation to the end-point of preparation and the radiographic apex. Theoretically, if the original estimate of the working distance was corrected, the point should be in the appropriate position and canal obturation can proceed. Some authorities condense the master point with a spreader prior to taking the radiograph in order to ensure that it reaches the end-point of preparation. *Point reaches working distance but is loose. This may occur for a number of reasons. 1) The gutta-percha point was smaller than expected. During the manufacture of points - a tolerance of mm is allowed at d 1 so that it is possible for the point with correct nominal size to be smaller than the equivalent file size and prepared canal width. The solution is to try-in a selection of other points of the same size in the hope that one of the correct size will be found; to remove 1mm increments off the tip of the point with a sharp blade to increase the tip diameter; or to try-in a point of larger nominal diameter. If points are reduced in length, care should be taken to ensure that the tip has not been flattened before it is re-inserted into the canal. 2) The end point of preparation was wider than expected. Just as the size of points may vary, so can the size of files. The tolerance of files can be mm at d 1 so that it is possible for the canal to be wider than anticipated. The solution is the same as described above

5 The canal can become wider than expected through inappropriate choice of instruments and/or preparation technique, leading to the removal of excess dentine from the outer wall of the canal apically. Should this problem be identified, and then either a selection of points can be tried-in until one is found to fit, or an alternative filling method chosen. *Point passes beyond working distance through foramen. This can occur when the apical stop is inadequate or when the point is too small. If the stop is not sufficiently definite, then the point will pass more deeply into the canal and through the foramen. The solution is either to reprepare the canal with larger instruments until a distinct stop is created at the end-point of preparation or to remove 1 mm increments from the point until its diameter is sufficient to bind in the canal at the working distance. In general terms the creation of a definite apical stop is the solution of choice. *Point does not reach working distance. This is the most common problem which occurs with the positioning of the master point, and there are a number of reasons: 1- Straightening of curved canals. During the preparation of curved canals it is likely that some Straightening of the curve will occur as the instruments tend to remove more dentine from the outer curve apically and from the inner curve in the mid-root. Clearly, a straighter canal will become shorter as the files will pass along its length in a more direct manner to the end-point of preparation. During the selection and try-in of a master apical point in a curved canal an adjustment should be made to the length in order to take account of this phenomenon and a radiographic check on position completed before any attempt is made to achieve the original working length through further canal preparation. 2- The point was larger than expected. points can be larger and not seat fully. Thus, if a point is a short distance (> 2mm) away from the end-point of preparation it may be possible to try a selection of points of the same nominal diameter in the hope of finding one that fits. 3- The canal was not widened sufficiently at the end-point of preparation. This is a common problem and occurs when the master apical file is either smaller than its nominal size or, more likely, that it was not used sufficiently to widen the canal fully. It is essential that the master apical file is manipulated until it can pass down freely to the - 5 -

6 end-point of preparation without any undue force being applied. With insufficient preparation it may be possible to force the master apical file to the working distance; however, if the same technique is adopted with a gutta-percha point then it will bind and buckle short of the expected length. The solution to this problem is to select a new file and reinstrument the canal to the working length until the file is loose. 4- Dentine debris is blocking the apical region of the canal. This is another common problem which occurs as a result of insufficient irrigation. Prevention is better than cure as many blockages are difficult to eliminate. Thus, during canal preparation copious volumes of irrigant should be used and canal preparation should include frequent and effective recapitulation at the end-point of preparation. The solution to this problem is to irrigate the canal thoroughly and then to manipulate gently small files deep within the canal in an attempt to disrupt the compact dentine and float out the debris in the irrigant. Selection of spreaders and accessory gutta-percha points: Once the master apical point has been selected, it is important to select and try-in the spreader in order to insure that it can pass down the canal to within 1 mm of the end-point of preparation. Spreaders should be precurved in curved canals and a rubber stop used to identify the length of insertion. To eliminate the risk of root fracture, excessive condensation pressure should be avoided by the use of finger spreaders. Spreaders are either manipulated with fingers (like files) or have long handles. The working part can have a non-standardized taper or standardized international organization for standardization (ISO) 0.02 taper, the same as most files. Non-standardized spreaders have relatively small diameters at the tip but a range of tapers from extra-fine through fine, medium to large; some - 6 -

7 manufactures use letters rather than words to denote the degree of taper, e.g. A-D. Spreaders with a standardized taper are manufactured with ISO diameters such as size 20 up to size 40.The choice of spreader design, that is, with non-standardized taper, is determined by operator preference and the type of accessory points to be used. When nonstandardized spreaders are used the points should be non-standardized; however, standardized spreaders require standardized accessory guttapercha points. In this way the space created by the spreader will be filled by the point. It is important to realize that space created by standardized spreader cannot be filled adequately with a non-standardized point. It is sound clinical practice to use spreaders and points from the same manufacture to ensure compatibility. Completion of lateral condensation The initial phases of lateral condensation have already been described. After these preliminary stages, the filling procedure is relatively straightforward: 1- The master point, spreader, accessory points and sealer should be carefully arranged to ensure that they can be handled efficiently. 2- The canal should be dried thoroughly with paper points. Use of alcohol to promote effective drying is not recommended for inexperienced operators. 3- The sealer should mix, carried into the canal and smeared (buttered) onto the canal wall. Sealer application can be achieved using a hand file rotated anti-clockwise, by coating a paper point and inserting into the canal, or by coating the master point itself. There is no need to apply a large volume of sealer with spiral filler

8 4- The master point should be buttered lightly with sealer and then inserted immediately to the full distance so that to notch made by the tweezers lies at the reference point. 5- The spreader is then placed alongside the point and pushed apically with controlled force until it reached the appropriate depth, 1 mm from the end-point of preparation. The direction of force should be apical with no lateral rocking of the spreader to prevent root fracture. In straight canals the spreader can be rotated at the same time as being pushed apically; however, this is contraindicated in curved canals. Apical pressure should be applied in a constant manner for approximately 10 s to achieve the appropriate compaction of the gutta-percha in an apical and lateral direction. In curved canals the spreader should be applied either lateral to or on the outer aspect of the master point; it should not be applied along the inner aspect of the curve or the spreader is likely to pierce the point and drag it out subsequently. 6- The first accessory point should be inserted into the space created by the spreader and seated fully. 7- The spreader is then cleaned and reinserted immediately into the canal as described above. On this occasion the spreader will not enter the canal to the same length. 8- The second accessory point is inserted into the space. 9- The sequence of spreader application and point insertion continuous until the canal is full. The number of additional points required will vary from case to case

9 10- If the final restoration is not post-retained, the excess gutta-percha emerging from the canal should be removed with a hot instrument and condensed vertically at the orifice with a plugger that fits the canal tightly to ensure a satisfactory coronal seal. In anterior teeth the guttapercha should be reduced to below the gingival level in order to maintain the translucency of the crown and to prevent the possibility of sealer staining the dentin; in posterior teeth the gutta-percha should be seared off at the canal orifice. Lateral condensation is relatively simple to carry out, rapid, and has been used for many years with considerable success. However, since it is impossible for cold gutta-percha to flow into irregularities within the canal system, parts of the canal must either remain unfilled or be filled only with sealer which has been forced into these regions by the pressure exerted through the insertion of spreaders and points