Obturation: Sealing the Root Canal System
Obturation of the root canal system represents the final phase of the root canal treatment process. The assessment and evaluation of root canal treatment is solely based on the appearance and placement of the obturation material. Obturation is a direct reflection of the efforts taken by the clinician during the biomechanical shaping and disinfection process. If the prior steps are not addressed appropriately, the outcome will always be questionable.
The purpose of obturation is to prevent the reinfection of a root canal system that has been properly shaped, cleaned and disinfected. Successful obturation requires the use of materials and techniques capable of densely filling the entire root canal system from the apical terminus
of the canal to the cavo-surface margin.1
There are three main objectives for creating a seal in the root canal space:2
- To prevent outward movement of bacteria or bacterial toxins from the canal space to the surrounding periapical tissues.
- To prevent the inward movement of tissue fluid from the periapical tissues into the canal space.
- To entomb residual bacteria that may have survived the treatment process.
Properties of ideal obturating material
In 1981, Dr. Louis I. Grossman described ten properties that an ideal obturation material should possess:3
- It should be easily introduced into the root canal system.
- It should seal the canal laterally as well as apically.
- It should not shrink after being inserted.
- It should be impervious to moisture.
- It should be bacteriostatic or at least not encourage bacterial growth.
- It should be radiopaque.
- It should not stain tooth structure.
- It should not irritate periapical tissue.
- It should be sterile or easily and quickly sterilized immediately before insertion.
- It should be easily removed from the root canal if necessary
Unfortunately, no obturation material in existence today completely satisfies all of Grossman's requirements. Although other obturation materials do exist, gutta-perch is a material that comes the closest to fulfilling these criteria. Gutta-percha is also the "gold standard" to which all other obturation materials are compared. Therefore, gutta-percha based obturation products remain the most popular obturation material among practitioners.
Many obturation techniques exist, most of which use a cement sealer in conjunction with a core material. There are several types of sealers and core materials available in the market place today. For the purpose of this article, specific sealer types will not be discussed and gutta-percha will be the primary core material of interest.
Currently there is very little evidence in the existing literature that supports the superiority of one obturation method over another.4 The literature also suggests that no obturation material or technique completely prevents leakage.5 This is most likely due to the porous tubular nature of dentin and canal irregularities.6 This being said, the technical nature of some obturation methods may lend to a more unpredictable outcome when compared to others.
cold lateral compaction
Cold lateral compaction is a common technique for obturating the root canal system and is the method taught in most dental school rograms.7 When examining the steps involved with cold lateral compaction, it is clear that this an extremely technique sensitive method of obturation.
The technique as described uses a standard size gutta-percha cone in a size corresponding to the prepared diameter of the canal. This is termed the "master cone." With sealer applied to the canal walls, the master cone is placed in the canal to the predetermined working length. A spreader is then placed into the canal between the lateral canal wall and the master cone until it reaches within 1-2mm of the working length. Accessory cones (corresponding to the size of the spreader) are placed in the space created by the spreader. This process is repeated until the spreader no longer advances beyond the coronal one third.
Taking a closer look at this method, it's inadequacies become clear. The lateral compaction process does not produce a homogenous mass of material, but rather relies heavily on the sealer to fill the voids between the gutta-percha cones. In essence this method relies more on the sealer to create the seal rather than the gutta-percha. In order for this method to have the best chance of success, it is imperative for the spreader to reach within 1-2mm of the working length. In this author's experience when observing clinicians performing this method, most are unable to achieve the proper depth penetration of the spreader. This may be due to inadequate flaring of the canal, improper spreader selection or fear that applying too
much apical pressure will cause and over-extension of obturation material. If the proper depth can not be achieved the predictability of the apical seal is compromised.
When the clinician is able to achieve adequate penetration of the spreader, a non-rigid, feather tipped accessory gutta-percha cone is now expected to follow the exact pathway created by the spreader. The small diameter and non-rigid nature of these accessory cones leave ample opportunity for buckling and/or bending of the guttapercha prior to achieving its desired length. It is difficult if not impossible to clinically determine whether or not all the accessory cones were able to reach the appropriate depth undamaged.
Due to the radioopaque nature of both the core material as well as the sealer, radiographically, the clinician may not see the inadequacies of cold lateral compaction (Figure 1). This gives the clinician a false sense of density. But when seen clinically the inadequacies of this technique are apparent (Figure 2).
The introduction of heat to gutta-percha
In 1967 an obturation method was described which applied heat to gutta-percha during the obturation process.8 The introduction of heat gave the gutta-percha thermoplastic properties which allowed for a better adaptation of the material to the canal walls as well as the ability of the material to better fill canal irregularities. This method was termed "warm vertical compaction." Although some clinicians still use the warm vertical compaction method as described in 1967, it was this landmark paper along with the introduction of greater tapered rotary instruments that spawned a more common variation of this technique called "continuous wave of condensation."
Continuous Wave of condensation
Continuous wave of condensation is an obturation technique that applies a heated "plugger" into a single custom fit greater tapered master cone of gutta-percha. The heat plugger is placed through the master cone to within 5mm of the predetermined working length. This creates a 5mm apical plug of gutta-percha.9 The apical plug of gutta-percha is then condensed with a hand plugger creating an extremely reliable apical seal (Figure 3 and Figure 4). In order for the continuous wave of condensation method to be most effective, gutta-percha cones matching the taper size of the final shaping instrument need to be used. There are two types of greater tapered gutta-percha available for this technique, non-standardized tapered gutta-percha cones (Figures 5A) and ISO sized tapered gutta-percha cones (Figure 5B).
Non-standardized greater tapered gutta-percha cones are manufactured according to taper size only. They come to a feather tip and do not have a predetermined tip size. These cones need to be custom trimmed in order to adapt to the prepared canal. ISO sized greater tapered gutta-percha cones are manufactured to a specific taper size as well as tip diameter to match the taper and diameter of the prepared canal.
When using non-standardized gutta-percha cones it is necessary for the clinician trim the tip of the gutta-percha cone to match the apical diameter of the prepared canal. This is termed "customizing the gutta-percha cone." This is accomplished using a gutta gauge (Figure 6). A gutta gauge is a device with predetermined openings corresponding with apical diameters from ISO size 20 to size 140.
Customizing the gutta-percha cone is accomplished by placing an non-standardized gutta-percha cone through the opening in the gutta gauge that directly corresponds to the apical diameter of the prepared canal (Figure 7). Once placed in the gauge, the guttapercha cone will bind at a level orresponding to the desired diameter. The excess gutta-percha will pass through the gauge and can be visualized on the underside (Figure 8). The excess guttapercha is then removed by passing a #15 scalpel blade across the bottom of the gutta gauge until the remaining gutta-percha cone is flush with the bottom of the gauge (Figure 8-11). The nonstandardized gutta-percha cone is now ready to be fit into the prepared canal. A working image should obtained to verify proper placement and length of the gutta-percha cone prior to heat application
Although either a customized non-standardized gutta-percha cone or an ISO sized greater tapered gutta-percha cone can be used for the continuous wave technique, it is the opinion of the author that a custom trimmed non-standardized gutta-percha cone lends to a more predictable outcome. This rationale is mainly due to the degree of taper manufactured into the gutta-percha cones.
Figure 12 shows two gutta-percha cones. The cone on the left is a .06 tapered ISO gutta-percha cone, whereas the cone on the right is a .06 tapered custom trimmed non-standardized gutta-percha cone. The tip size of both cones corresponds to a size 30. The visual difference between the two types of cones is apparent. Even though both cones exhibit a tip size of 30 and a taper rate of .06, the cone on the left appears larger. This visual difference is due to the constant taper rate of the ISO sized gutta-percha cone throughout its length, where as the non-standardized gutta-percha cone's taper is limited to the apical extent only. Limiting the taper to the apical extent of the cone prevents premature coronal binding of the gutta-percha upon placement. It is for this reason custom trimmed non-standardized gutta-percha cones are preferred for the continuous wave method.
There are several electric heat carriers available to perform the continuous wave down pack of gutta-percha. One example of a heat source is the System B (Figure 13). Common features to most heat systems include the ability to adjust the temperature setting of the delivered heat, as well as pluggers of various tapers to ccommodate a wide variety canal types (Figure 14). It is important for the clinician to pre-fit the heat plugger prior to performing the down pack. In order to determine the appropriate plugger size, the clinician is looking for the largest tapered plugger that fits to within 5mm of the predetermined working length. The suggested heat setting for the down packing process is 200 degrees Celsius.11
Immediately following the down pack of gutta-percha, a hand plugger is used to further condense the apical plug of gutta-percha while it is still warm. (Figure 15) Many different different styles of hand pluggers are available and can be used for this technique. The clinician should choose a hand plugger with an appropriate diameter so that the apical extent of gutta-percha can be reached passively without binding on the lateral walls of the root canal system. Vertical pressure is applied to the gutta-percha during the cooling process thus creating a reliable apical seal.
The theory behind this technique is directly related to the thermomechanical properties of guttapercha. The thermo-mechanical properties of gutta-percha dictate that the heat will carry several millimeters beyond the apical extent of the heat source.10 This will allow the apical 5mm of gutta-percha to be softened and condensed for a better adaptation of material. The application of heat and apical pressure to a well adapted master gutta-percha cone will also create hydraulic pressure within the canal. The hydraulic pressure created will in turn move the heated gutta-percha and sealer apically and laterally to further seal canal irregularities.
Once the apical plug of gutta-percha has been established, the remaining canal space can be obturated with thermo-plasticized injectable gutta-percha. This is termed the "backfill" (Figure 16). There are two main types of delivery systems available to deliver thermo-plasticized guttapercha, manual and automated.
A manual delivery system consists of a "gun-like" unit which the clinician needs to squeeze in order to activate the flow of gutta-percha (Figures 17A and 17B). An automated delivery system takes on the appearance of a "wand." The flow of gutta-percha is activated by pressing a button. Although both ystems are equally reliable to perform the backfill, it is the opinion of the author that an automated delivery system improves the clinician's ergonomics.
The tip of the delivery system should be placed as apically as allowable (preferably butting up with the apical plug of GP). The tip is allowed to sit in the canal for 5 seconds. This rewarms the apical plug of gutta-percha. Once the flow of gutta-perch is activated, the thermoplastic gutta-percha will utomatically back the delivery unit out of the canal. In some canals, this can be done in one fluid movement. In longer roots, incremental placement may be indicated to prevent voids (Figures 18 and 19).
Immediately following the backfilling process, larger hand pluggers are placed on the coronal extent of the warm gutta-percha and apical pressure is applied as the gutta-percha cools. This will vertically condense the gutta-percha, creating a homogeneous mass of obturation material. The gutta-percha should extend coronally to the orifice level at the extent of the pulpal floor, thus completing obturation. Due to the predictable nature of this obturation method, it remains the obturation technique of choice among most endodontic practitioners.
Carrier based obturation
Carrier based obturation is a method that introduces heated gutta-percha into the canal via a solid core carrier. Traditionally the carrier consists of a solid plastic core, but recently Denstply Tulsa Dental Specialties introduced a carrier based obturation product that consists of a cross-lined gutta-percha core. This product is called GuttaCore™. Like the continuous wave of condensation, carrier based obturation takes advantage of the thermoplastic properties of gutta-percha. The solid core delivery system allows the clinician to introduce warm gutta-percha to the root canal system and create a reliable seal in one fluid motion.
The author is aware that other carrier based obturation systems exist. Most carrier based systems use similar obturation techniques. For the purpose of this article, the discussion and examples of carrier based obturation are limited to GuttaCore™ due to the author’s extensive knowledge and experience with this product.
Obturation with a carrier based obturator begins with size verification. The size verifier is a non-end-cutting NiTi tool that resembles a file at a 0.45 taper (Figure 20 and Figure 21). This instrument is used to gauge the prepared canal. This step is designed to determine if the prepared canal is able to accept the corresponding size obturator. With irrigant in place, a size verifier equivalent to the last size rotary file used at length is measured and passively placed in the canal. It is strongly recommended to obtain a working radiograph with the size verifier in place so that corrections can be made prior to obturator placement if necessary (Figure 22).
Following size verification, the clinician must now prepare the obturator. There are two methods of obturator preparation available to the clinician.
The Manufacturer's Recommended Instructions
Most obturators have predetermined calibration markings (calibration rings) that correspond to the exact distance to the tip of the internal carrier (Figure 23). This should NOT be confused with the distance to the tip of the gutta-percha on the arrier. The guttapercha on the carrier extends approximately 1mm beyond the terminus of the internal carrier (Figure 24). The calibration markings are set at 18, 19, 20, 22, 24, 27 and 29mm. The silicone stopper should be placed on the calibration ring that corresponds with the predetermined working length. Because the gutta percha extends approximately 1mm beyond the internal carrier, it is important to place the TOP of the silicone stopper BELOW the calibration ring (Figure 25). Failing to set the silicone stopper in this fashion may cause the obturator to extend beyond the desired length.
Adjusting the silicone stopper according to the manufacturer’s recommendation is reliable when the working length is a whole number. This method becomes very arbitrary when the working length contains 1/2 mm or 1/4 mm measurements. In order to adjust for 1/2 mm increments, the manufacturer suggests setting the of silicone stopper between the calibration rings. There is no recommended method to adjust for 1/4 mm increments. For this
reason the author recommends the second method for obturator preparation.
The clinician must first remove the excess gutta-percha from the coronal end of the carrier. The excess gutta-percha will be termed the "button" of gutta-percha (Figure 26). The button of gutta-percha can be removed by placing the index finger and thumb on the button. With the index finger and thumb in position, the button of guttapercha is rotated around the carrier (Figure 27). Removing the button of gutta-percha accomplishes two objectives. 1) The obturator will be able to lie flush against the measuring device giving the clinician a more accurate measurement and 2) there will be less gutta-percha
remaining in the chamber following placement.
The obturator should be placed flush against the measuring device (Figure 28). The silicone stopper is adjusted so that the tip of the gutta-percha on the obturator measures to the exact working length. This is the same measuring method most clinicians use to adjust the working length of the silicone stopper during the instrumentation process. Using this method to prepare the obturator allows the clinician to maintain a level of consistency during the measuring process. This method also allows for greater precision. The clinician has the ability to measure the 1/2 mm or 1/4 mm if desired.
Sealer placement when using carrier based obturation is a critical step. Placing too much sealer (in most cases) will cause an abundance of sealer to be forced beyond the apical terminus. Placing too little sealer will have an adverse effect on the seal of the obturation material. In order to fully grasp the importance of sealer placement, the clinician must first understand the relationship between sealer and gutta-perch during the obturation process.
During root canal obturation, hydrodynamic forces are created within the root canal system. These hydrodynamic forces can push gutta-percha and ealer into remote areas of the root canal system. These same forces can push obturation material into unwanted places as well. A basic Law of Physics states that "two objects can not occupy the same space at the same time." It is this law that dictates the movement of material during obturation.
When obturating with the continuous wave of condensation technique, the heat carrier is applied in the apical direction through the gutta-percha cone. If excess sealer is present, it will most likely be displaced coronally. The coronal displacement of sealer occurs because of space between the canal walls and the heat carrier. This space acts to vent excess sealer. The sealer will take the "path of least resistance" and flow coronally towards the orifice. If the clinician has maintained patency during the instrumentation process, some sealer may also be displaced apically (but very little) creating an apical "puff" of sealer (Figure 29).
When obturating with a carrier based obturator, as the carrier/guttapercha complex is inserted into the canal, there is no space between the obturation material and the walls of the canal. Therefore there is no space available to "vent" excess sealer. This creates a "squeegee effect." The "path of least resistance" rationale causes the sealer to be displaced apically only. If too much sealer has been applied to the canal, the displacement will occur into the periapical tissues creating an undesirable outcome (Figure 30).
Proper sealer placement for carrier based obturation is performed with a paper point. A paper point of one taper size smaller than the taper of the prepared canal should be coated with sealer and applied to the predetermined working length. (Example: if the final shape of the canal is a size 30 with an .06 taper, a size 30 paper point with an .04 taper should be used.) This will prevent coronal binding of the paper point. A lateral and vertical motion can be used during this process to ensure proper sealer distribution. The sealer can be applied liberally, but do not flood the canal. Excess sealer needs to
be removed from the canal with additional dry paper points. These subsequent paper points can be use in the same manor as if you are drying the canal. Continue this process until the paper point appears blotted with sealer upon removal, not coated (Figures 31 and 32). Blotting the excess sealer from the canal will ensure minimal sealer displacement during obturator placement.
Carrier based obturation systems use a heating oven to warm the gutta-percha prior to placement. The obturator should be placed in the appropriate slot and the arm pushed down to activate the oven cycle (Figure 33). The oven will begin to warm the gutta-percha as the internal carrier remains stiff. Allow time for the oven to go through the predetermined heating cycle. The oven will beep when the obturator is ready. After the oven beeps, press the activation arm again and the warmed obturator will automatically be removed from the oven. The obturator is now ready for insertion into the canal.
Transferring the obturator from the warming oven to the canal can be accomplished one of two ways: 1) the obturator handle can be grasped with the thumb and index finger and taken directly to the canal (Figure 34), or 2) using a cotton forceps, the shaft of the carrier can be grasped and taken to the canal (Figure 35).
In some cases, the clinician may be working on a patient with a limited opening or a working environment that may not be able to accommodate the entire "carrier/handle complex." The obturator can be modified to accommodate the clinician in these difficult situations. When using GuttaCore™ obturators, the shaft of the carrier can be grasped above the silicone stopper and below the handle. The handle can be removed by bending the carrier at a right angle above the cotton forceps (Figure 36). Other types of obturators may require other means to remove the carrier/handle complex.
Removing the handle will give the clinician more flexibility in
limited access situations.
When working in multi-rooted teeth, the clinician may be faced with some additional challenges. One such challenge is related to visibility. The obturation of one canal may obstruct the clinician’s view to other canals, therefore making it more difficult to obturate the additional canal(s). This can be address ed by removing the handle portion and the silicone stopper from the carrier following its placement. When using GuttaCore™, the handle and silicone stopper can be removed by placing lateral pressure on the handle with the index finger or thumb until the carrier breaks. Other carrier based obturation systems may require other means of handle removal. In most cases there will still be enough carrier remaining in the chamber to retrieve the obturator if a correction is needed at a later point. Once removed, visibility to the additional canal(s) should be improved (Figures 39-41).
Another challenge when working on multi-rooted teeth is related to orifice proximity and canal confluency. Preventing excess guttapercha from blocking other canals in close proximity or flowing into canals that are confluent can be accomplished by "protecting" the additional canals with a paper point. If the canals have separate portals of exit, the paper point can be placed to length. If the canals are confluent, the paper point should be placed to the level of confluence. (In confluent canals, if the paper point is placed to the working length, the apical advancement of the obturator will be blocked). Once the obturator is in place, the paper point can be removed and the remaining canal(s) can be safely obturated. This process can be repeated for additional canals if needed (Figures 42-44).
Following complete obturation, the clinician will be left with a surplus of gutta-percha and carrier remaining in the pulp chamber. When using GuttaCore™, this excess carrier/gutta-percha can be addressed with a long spoon excavator. The spoon excavator is placed between the axial wall of the pulp chamber and the residual carrier extending beyond the orifice. While applying apical and lateral pressure, the spoon will sever the carrier at the orifice level. Bulk gutta-percha can be removed with the spoon. It is important to remember NOT to use the spoon in a "scooping" manor when severing the carrier. The "scooping" motion will create leveraging forces that will lift the core of the obturator out of the canal effecting the seal of the obturation material. Again, force should be applied in a lateral and apical direction (Figure 45).
It may prove difficult to completely rid the pulp chamber from all residual gutta-percha and sealer following obturation with either continuous wave and/or carrier based obturators. This issue can be addressed with the use of gutta-percha softener (chloroform). Although some clinicians may be oncerned with toxicity levels and/or carcinogenicity of chloroform,12 there is no ban on its use in dentistry.13 When used carefully and in small amounts, chloroform can be a safe and effective guttapercha solvent.13, 14
Following bulk obturation material removal (and post space preparation if indicated), a microbrush with a small amount of chloroform is used to loosen residual gutta-percha and sealer from the pulpal floor and axial walls. This step may need to be repeated depending on the amount of remaining bturation material. In some extreme cases a cotton pellet soaked with softener can be used to wick up bulk gutta-percha and sealer. Phosphoric acid (acid etch) can then be placed in the pulp chamber and with a separate microbrush the chamber is scrubbed. Following acid etch placement, the canal should be thoroughly rinsed with water and dried (Figure 46).
It is strongly recommended that the chamber should be sealed/restored immediately following obturation. It is extremely advantageous to place the final restoration or at the very least, seal the canal orifices with an orifice barrier for the following reasons: 1) Proper isolation and moisture control measures are in place via rubber dam isolation and 2) The risk of contamination from a leaky temporary is eliminated.
Chosing an obturation method
The rationale for choosing an obturation method is directly related to the anatomy of the canal being treated and driven by the thermoplastic properties of gutta-percha. Prior to the obturation phase (during instrumentation), the clinician should have developed a strong knowledge and understanding of the internal nuances of the root canal system being treated. Knowledge of these canal nuances may suggest one obturation method over another.
The primary obturation technique used by the author remains to be the continuous wave of condensation method. As previously mentioned, in order to achieve a successful result with the continuous wave method, the heated plugger must fit to within 5mm of the established working length. This is not always possible. On several occasions, canals being treated will possess tortuous curvatures preventing plugger penetration to the desired depth. If the
continuous wave method is used without adequate plugger penetration, heat will fail to transfer far enough into the apical plug, thus compromising the adaptation of gutta-percha in the apical extent of the canal. If the clinician accepts this, the continuous wave technique now becomes a glorified single cone obturation method. (Single cone obturation methods, like cold lateral condensation, relies more on sealer rather that the thermoplastic properties of gutta-percha). When faced with these types of canals, a carrier based obturator may be a better choice. Heated gutta-percha wrapped round a solid core carrier placed to length will ensure that thermoplastic gutta-percha is delivered to the apical extent of the root canal system.
Ultimately, the decision as to the method of obturation and materials used will fall solely in the hands of the treating clinician. These decisions are made based on the knowledge and skill set of the individual practitioner. It is strongly suggested and encouraged for every clinician to understand and be competent with multiple methods of obturation. Having multiple options available lends to more clinical versatility and a more predictable outcome.