Root Canal Obturation with Gutta-Percha Points
Gutta-percha points are used to fill the root canal in various ways and with different techniques. The most important techniques are the dipping technique, the thermoplasticized guttapercha techniques, the lateral condensation technique, and the standardized technique. In addition, a combination of two or more of these techniques is used advantageously in many clinical situations.
The Dipping Technique
The dipping technique is based on gutta-percha’s property of becoming soft when dipped in chloroform, eucalyptol, or other organic solvents. When softened and forced into the root canal, a guttapercha point may be given the exact three-dimensional form of the root canal space. Unfortunately, the dipping technique has been advocated by some for use without a sealer. This is a misconception, probably due to the fact that the surface of a gutta-percha point has a certain stickiness in the softened condition. However, as stressed above, gutta-percha alone cannot seal the root canal. When the solvent has evaporated, the point loses its stickiness and gaps will develop between the point and the root canal wall. Thus, the use of a sealer is mandatory with all gutta-percha techniques. Traditionally, the dipping technique has been used with resin-based chloropercha-like sealers like Kloroperka N-0 or simply resin chloroform. However, all types of sealers may be used.
With the dipping technique the root canal should be prepared so that it either has a continuous tapered preparation or it should have a definite apical shelf in the root canal wall (apical box preparation). A master point is then selected which is two to three sizes larger in diameter than the final apical instrument, and the point should stop in the canal 2-3 mm short of the working length. This is checked radiographically and the master point is marked in this position at the level of an occlusal or incisal reference point. A second mark is used to indicate the distance the point has to be introduced further into the canal to reach the apical level of instrumentation.
The master point is then removed and a sealer is applied sparingly to the walls of the root canal. Subsequently, the master point is dipped in chloroform for about 5-10 seconds, depending on the size of the point. It is quickly reintroduced into the canal and firmly pushed in an apical direction until the second mark is at the occlusal point of reference, indicating that the guttapercha point has reached the correct apical level. Since the gutta-percha is soft, the master point will now have taken on the three-dimensional shape of the root canal apically, and this part of the canal will be sealed. In the wider coronal parts of the canal, accessory points dipped in sealer are inserted next to the master point, and by lateral condensation the canal is filled completely with gutta-percha. If the condensation is successful, a homogenous and bacteria-tight obturation of the root canal is achieved. The dipping technique is basically simple and straightforward. However, as with all soft gutta-percha techniques, overfilling of the canal will occur, especially if the master point is softened too much. In addition, there may be problems with shrinkage of gutta-percha when the material has been softened in chloroform. However, with experience, good long-term results can be expected with the dipping technique.
Thermoplasticized Gutta-Percha Techniques
These techniques use heat-softened gutta-percha and, as with the dipping technique, the goal is to achieve a bacteria-tight, three-dimensional filling of the root canal by softening the guttapercha.
The warm gutta-percha technique
With this technique, the gutta-percha is heated inside the root canal by means of hot hand instruments, so-called heat carriers. The root canal is given a continuous tapered shape, although the coronal parts of the canal are widened somewhat more than is the case with most techniques in order to facilitate the use of the rather large and rigid instruments required for the heating and condensation of the gutta-percha. Because of its greater flare, a nonstandardized (accessory) point is used as the master point. The pointed tip is cut off so that the point stops in the canal about 2-3 mm short of the working length. The master point is removed and a sealer is applied to the root canal wall. The use of a zinc oxide-eugenol-based sealer is recommended. The master point is then reintroduced into the canal and seared off at the canal orifice with a hot plastic instrument, and a cold root canal plugger is used to condense the warm guttapercha at the orifice of the canal in an apical direction. A heat carrier is then heated with a gas flame until it is red hot and is introduced 3-4 mm into the gutta-percha in the canal and quickly withdrawn. The warm gutta-percha is again condensed in an apical direction by means of cold root canal pluggers. This procedure is repeated to a level 5-6 mm short of the working length when it is assumed that the apical part of the canal is filled three-dimensionally with gutta-percha.
Since the root canal is sealed coronally during the vertical condensation of the gutta-percha, considerable apical and lateral hydraulic forces are generated. As a result, the root canal sealer is often seen to be forced into lateral and accessory root canals when this technique is used. If a root canal post is required, the obturation of the canal is considered completed when the apical 5-6 mm are filled. If not, additional sealer is applied to the wall of the coronal part of the canal and pieces of gutta-percha, 3-4 mm long, are heated and condensed vertically in the canal until the entire space is filled.
The warm gutta-percha technique is an ambitious technique. Its advantage is meant to be that the root canal system with lateral and accessory canals is more completely obturated when using this technique than with other more traditional techniques. Since the technique requires vertical condensation of softened guttapercha, it is rather difficult to control and, as with the dipping technique, overfillings of the root canal are commonly seen. No long-term follow-up studies of the results obtained with the warm gutta-percha technique have been published.
The injection-molded gutta-percha technique
With this technique, the gutta-percha is heated outside the mouth until it flows (about 160 °C) and by means of a pressure syringe is injected into the root canal after a sealer has been applied to the root canal wall. The injection needle has to be brought as close to the apical level of instrumentation as possible, and at least to the apical third of the canal. By slowly pulling the needle back while the gutta-percha is being injected, the entire root canal can be filled virtually in seconds.
Obviously, shrinkage of the gutta-percha occurs when the material is heated to such temperatures. To counteract the shrinkage as much as possible, only 2-3 mm of the canal should be filled at a time. A continuous condensation force is then exerted on the gutta-percha during the cooling of the material, which takes about 2 minutes. A new portion of soft gutta-percha is then added and again it is held under pressure until cooled. In this way the entire root canal is filled step by step.
This is, again, a method dealing with softened gutta-percha being vertically condensed in the root canal. The method is difficult to control and both overfilled and incompletely filled canals occur regularly. For this reason, the method is also used with an unsoftened master gutta-percha point, which, when placed in the root canal, will block the apical opening of the canal. Injection-molded gutta-percha is then used to fill those parts of the canal that are traditionally filled by accessory points and lateral condensation. Moreover, the injection technique has shown some promise in the obturation of blunderbuss canals of immature teeth after an apical mineralized barrier has been created by means of long-term calcium hydroxide treatment (see p. 120). On the whole, the suitability of the injection-molded gutta-percha technique greatly depends on whether the foraminal area of the root canal is plugged or not prior to the actual filling of the canal. No data on long-term results with this technique are available.
Thermomechanical condensation techniques
Efforts have been made to soften guttapercha inside the root canal by friction heat from rotary or vibratory instruments. Functioning systems have been developed and are commercially available. However, these systems are all technique-sensitive and difficult to control. In addition, frequent fractures of the instruments in the canal appear to be a problem. At this time it is difficult to foresee a breakthrough in obturation technique in this area.
Lateral Condensation Technique
The purpose of the lateral condensation technique is to fill the root canal three-dimension-ally and bacteria-tight with gutta-percha and a sealer without softening the gutta-percha with chemicals or heat. In this way, the conceivable problems with shrinkage of softened guttapercha are prevented, as are many of the difficulties of controlling the apical level of the root canal filling. The root canal is prepared with a continuous taper. A master gutta-percha point of the same size as the master apical file is selected and placed in the canal to the working length. The placement of the master point is controlled radiographically, and necessary adjustments are made. The master point is then marked at the level of an occlusal or incisal reference point and is removed from the canal. A sealer is applied sparingly to the canal wall or the master point is coated with the sealer before being reinserted into the canal to the correct apical level without being softened. A spreader, for example, a finger spreader no. B, is then introduced into the canal, ideally to the level of or near the apical end of the master point. The spreader is carefully moved back and forth to create space for an accessory gutta-percha point. In the process, the master point is forced laterally against the root canal wall and is deformed to match the shape of the root canal, hence the term “lateral condensation” of gutta-percha. An accessory point is selected to fit into the space made by the spreader. The spreader is then removed, the accessory point is dipped in sealer and quickly introduced into the canal to the level of the tip of the spreader, and importantly, without being softened. The spreader is used again in the same fashion, this time to the same level or to a level slightly coronally to the tip of the first accessory point, and a second point is coated with sealer and inserted. This sequence is repeated until the apical part of the root canal is filled three-dimensionally with gutta-percha. In the coronal flared part of the canal, larger spreaders and larger accessory points may be used to speed up the obturation procedure until the canal is completely filled with gutta-percha. And importantly, since the material was not softened, the root canal filling will be dimensionally stable.
This is an excellent technique when mastered. However, lateral condensation of gutta-percha in the apical part of the root canal is far from an easy procedure. In order to obtain a three-dimensional filling of the apical area of the canal with gutta-percha, the unsoftened points have to be deformed and given the shape of the canal by effective use of the spreader. This is difficult and the apical part of the canal may be filled mostly with sealer if the technique of lateral condensation is not fully mastered. Then, gradually as the sealer dissolves under the influence of tissue fluids, the obturation of the canal may be incomplete. Because of this, attempts have been made to improve upon the technique by using electrically heated spreaders during the lateral condensation. The gutta-percha is then softened by the heat and the immediate fill of the canal may be improved. However, as discussed above, heated and softened gutta-percha is bound to shrink and the long-term seal of the canal may be affected by the shrinkage.
Standardized Endodontic Technique
The standardized technique was made possible through the development of the standardized root canal instruments and the standardized gutta-percha points. It is based on morphomet-ric studies of the roots and root canals of human teeth and the findings that a cylindrical apical box may be prepared in the canal of most teeth in all groups of teeth. An unsoftened gutta-percha master point of the same size as the diameter of the apical box will then fit in the apical part of the canal, in principle like a cork in a bottle.
In developing this technique, the fact has been taken into account that other possibly more ambitious techniques may suffer from shrinkage of the gutta-percha or will often be single-point techniques without an optimal matching of the gutta-percha point to the shape and size of the apical part of the root canal. With the standardized technique, the principle of a single point plus sealer obturating the apical part of the root canal has been accepted, and the challenge of the technique then is to prepare the canal so that this becomes feasible and will give long-term results that are at least as good as or better than other accepted techniques.
The root canal is prepared according to the apical box technique. A standardized gutta-percha master point is then selected which is of the same size as the final instrument used with a rotary cutting action in the preparation of the apical box of the root canal. It should be remembered that the standardization of the gutta-percha points is less accurate than the standardization of the metallic instruments so that a few points may have to be tried before one is found that can be seated at the correct apical level of instrumentation, giving the desired resistance to dislodgment which is commonly referred to as tug back. The final placement of the master point is controlled radio-graphically, and necessary adjustments based on the radiographic findings may be made at this point. When the fit and placement are found to be right, the master point is marked at an occlusal or incisal point of reference and is removed. A sealer is then placed sparingly on the root canal wall or the master point is coated with the sealer. The master point is then reinserted into the canal to the working length without being softened. If the point does not reach the desired apical level, it is removed from the canal and a K-type instrument of the same size as the master point is used to clear the root canal, most often from dentin chips that may have become dislogded during application of the sealer. Please note that when appliyng this technique the final position of the master point in the root canal should not be affected by subsequent vertical or lateral condensation. It must, therefore, be placed exactly in its correct position before accessory points are inserted and condensed in the flared part of the canal.
When satisfied that the master point is optimally placed, a spreader is introduced alongside the master point to determine the apical level to which the first accessory point should reach. The flared part of the canal is then filled with accessory gutta-percha points dipped in sealer, and since the apical seal is provided by the master point a much less agressive lateral condensation than described for the lateral condensation technique is required.
An important advantage of the standardized technique is the systematization offered by a standardized instrumentation and obturation system. The technique is easy to comprehend and especially the obturation phase is simple compared to most other methods. Overfilling rarely occurs and long-term follow-up studies show that the root canal fillings remain dimen-sionally stable.
Possible drawbacl<s of the standardized technique are related to the instrumentation phase of the treatment in that the apical part of the root canal is prepared wider than is commonly seen with other techniques in order to ensure a clean canal and to obtain the desired cylindrical apical box. Canals which may create problems
for the standardized technique are especially found in mandibular incisors, maxillary first premolars, and maxillary lateral incisors. Still, with a proper understanding of root canal anatomy, the standardized technique will be an effective and safe method even in these teeth. Excellent long-term results in all groups of teeth are reported with the standardized technique.
Two-Step and Other Techniques
Occasionally during endodontic treatment there will be teeth with special problems where the routine methods have to be modified. In some instances, such as in teeth where the root canal divides into two canals in the middle or apical third of the root or in teeth with internal resorption, a technique in which the tooth is filled in two steps may be practical.
In teeth where the canal divides, both canals are prepared according to the technique used. Thereafter one of the canals is obturated. When this is completed, a heated root canal instrument is brought to the level where the root canal divides and the gutta-percha is removed coronally to this level. The second apical canal and the main canal are then filled in the customary way.
Similarly, in teeth with internal resorption the root canal apical to the resorption defect is filled first with the routine technique used. The gutta-percha points are then seared off at the apical level of the resorption lacuna. Thereafter, the resorption defect and the coronal part of the canal are filled by vertical condensation of softened gutta-percha without risk of overfilling the canal.
In teeth with incomplete root formation, the diameter of the root canal may be wider than the largest size gutta-percha point available. In such teeth it may be a good alternative to customize a master point to fit the root canal. This is done by heating several gutta-percha points in warm water and rolling them between two glass slabs until they become one point with a diameter slightly larger than that of the canal to be filled. The surface of the customized point is then again carefully softened in warm water and the point is inserted into the root canal to the working length. The point is moved slightly up and down in the canal, and after hardening is removed. Sealer is then applied to the canal and the customized point is reinserted to seal the apical part of the canal. Coronally, necessary accessory points are added under lateral condensation in the normal way. If the canal is blunderbuss-shaped, the apical end of the customized point is softened over an alcohol flame. It is then introduced into the canal and carefully but firmly forced toward the apical hard-tissue barrier so that the gutta-percha fills the apical undercuts in three dimensions. To minimize the shrinkage of the softened gutta-percha, a continuous force is exerted on the gutta-percha point during the material’s cooling period (2 minutes)