As described in part one of this 2-part series (September 2017, Dentistry Today), the Continuous Wave (CW) of Obturation Technique is known to be a very effective way to fill root canal systems in all their complexity.1-5 Done correctly, it is also a very efficient technique, albeit complex in the details that must come together to achieve an ideal fill. An important aspect of the technique is understanding how variations of endodontic anatomy are best handled, ie, what type of backfill is best used for small, medium, and large root canals. This matters since it determines how the downpack is to be ended: with removal of the gutta-percha alongside the plugger or with the intent that all condensed gutta-percha in the canal remains in place. Once these and other nuances are understood, CW Obturation can be completed nearly as fast as single-cone and carrier-based filling methods.
Preparation for CW Procedure Cone Fit
Cone fitting used to be somewhat of an art form. Before the advent of variably tapered rotary files, the predominant method of cutting tapered shapes in root canals was Schilder’s Serial Step-Back shaping technique. Tapered canal shapes were indirectly created by using increasingly larger K-files progressively further back from the terminus, and, because of this, the accuracy of the resulting taper depended on the accuracy of the increments of step-back between instruments. Not surprisingly, every canal ended up with slightly different shapes, making the selection of the ideal cone size a challenge. With the wide array of rotary files that are now available—and with a bit of training—clinicians can cut remarkably ideal shapes, and, as a happy result, cone fitting has become fairly rote. Tapered shaping procedures revolve primarily around the creation of a continuous taper in the apical third of the canal so that a slightly less-tapered gutta-percha cone can be confidently fit just at its tip, 0.5 mm from the end of the canal, as this is the key to obturation accuracy with a cone fit technique.
In this method, feather-tipped master cones are selected only for their tapers, not their tip diameters. Thus, canals with 20-.06, 30-.06, and 40-.06 shapes are all fit with the same .06 gutta-percha cone; likewise, canals with 30-.08 or 40-.08 canal shapes are all fit with .08 gutta-percha cones. The cones are actually one-degree less tapered than their named sizes, so when they are fit in a slightly larger taper shape, they will inevitably bind only at their tips in the terminal region of the canal.
After picking a cone of the appropriate taper, its tip is inserted into the die in a gutta-percha gauge that matches the final terminal preparation diameter and is clipped on the reverse side with a scalpel blade (Figure 1). For instance, if the canal to be conefit was cut to a 30-.06 shape, the .06 gutta-percha cone would be placed in the size No. 30 die and the extra length would be cut off. This initial sizing is seldom exactly the right diameter; rather, it is only done to reduce the cone to a length between 0.5 and 1.0 mm beyond that canal terminus. Once the tip is sized, the cone is placed in a wet canal to its binding point, the shank end is carefully grasped with locking cotton pliers perpendicular to the cone, and it is measured on a millimeter gauge and cut to a length 0.5 mm short of terminal length.
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| Figure 1. The Gutta-Percha Gauge (Dentsply Sirona Endodontics) is used to presize the tips of master cones before fitting them in shaped canals. | Figure 2. Illustration showing a paper point extending slightly beyond the terminus of a root canal and heme staining its tip to that point. (Courtesy of Dr. David Rosenberg.) |
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| Figure 3. The elementsfree cordless Continuous Wave (CW) Downpack Handpiece (Kerr Endodontics). |
At first glance, this tapered cone fit method seems more complicated than standardized cone fitting by tip size. However, a No. 35 gutta-percha cone seldom fits a root canal preparation cut with a No. 35 K-file, because No. 35 files cut a shape somewhat larger than 0.35 mm. Rather than choose the cone by tip size, when we really never know the exact size of an apical preparation, this tapered cone fit procedure first confirms that the slightly-less-tapered cone fits the slightly-more-tapered canal with the desired tugback. Then the tip is adjusted to length with no consideration for the diameter the canal was actually prepped to or the exact diameter of gutta-percha that will give the desired fit at the end of said canal.
Choosing when intraoperative radiographs are taken is up to the clinician; however, even though I don’t take length-determination radiographs, I do recommend taking cone fit images, as it is the second-to-last chance to get the apical extent of filling just right.
Sealer
Choosing a biocompatable sealer for 3-D obturation is more important than many clinicians understand. Using a sealer that is chemically toxic for the 72 hours it takes to set (AH Plus and Thermaseal [Dentsply Sirona]) is a good strategy when 2-D filling methods are used since it will wage “chemical warfare” for that 3-day period on any remaining bacteria or pulp remnants. However, when used with 3-D obturation techniques that consistently place surplus sealer puffs at the root surface next to periradicular tissues, these kinds of sealers cause patients needless suffering.
Kerr’s Pulp Canal Sealer is the primary sealer used by clinicians who heat up gutta-percha and push on it to fill lateral canal complexities, partly because it sets within 15 minutes in canals, rendering it relatively biocompatible and reducing a patient’s postoperative discomfort after root canal therapy to a minimum. The other characteristic of this zinc oxide eugenol sealer is that it can be mixed to a very viscous state (one drop of liquid to one scoop of powder) due to its Canada balsam component. Mixed to a consistency that will cause the sealer to string off the mixing pad an inch and hang there, it is ideal for warm gutta-percha cone fit obturation as it helps to prevent the gutta-percha cone from being pulled out on a plugger or heat carrier. I also use this sealer for carrier-based obturation, but in a less viscous state (2 drops of eugenol to one scoop of powder) than for cone fit filling methods.
Drying Canals and Confirming Lengths
When tapered shaping objectives are met, procedures necessary to dry canals can also be used as final confirmation of canal length if small-tipped paper points are used. After 2 to 3 paper points are used to dry a root canal, another paper point can be dropped to and through the terminus of the canal, grasped carefully in cotton pliers, pulled out immediately, and its dry length measured (Figure 2). This will provide final confirmation of length just before filling, so if length has changed during shaping, the cone can be clipped to the perfect length before it is condensed into the canal. Usually, the periapical tissue fluids that wet the paper point when it slips through the end of the canal will be clear, so touching the end of the paper point will cause the wet part to bend, making it easier to measure the dry part. Occasionally, the tissue fluids will stain the end of the paper point with heme, making it easier to see and measure canal length.
Cementing Master Gutta-Percha Cones
The easiest way to place sealer to the end of the canal preparation is to butter the apical half of the master cone with it, slowly insert the sealer into the canal so surplus has time to escape coronally, pump the cone 3 to 4 times, and pull it out to look at its tip. If it is coated to its tip, simply place the cone back in the canal. If the sealer is at all wiped off the tip (this happens 50% of the time), recoat it with sealer and then replace it in the canal. The sealer always goes to length the second time.
CW Downpack Technique in Small Canals
The CW downpacking technique used in small canals nearly always removes the gutta-percha alongside the electric heat plugger (EHP), so it is necessary to do a syringe backfill of the space vacated by the plugger and gutta-percha.
The CW downpacking technique is as follows:
1. Pre-fit the .06 and .08 EHPs, pushing apically as you rock them back and forth so that the canal bends the plugger, which allows it to reach its ideal length. Adjust the stops on the pluggers to the same reference points gutta-percha master cones fit to, and compare their fit lengths to the fit gutta-percha cone to determine the largest EHP that fits within 4.0 to 6.0 mm of the terminus. Place it into the working end of the elementsfree cordless CW downpack handpiece (Kerr Endodontics) (Figure 3). No tightening of a collet is needed.
2. Cement the master gutta-percha cone (cut to fit 0.5 mm from full length in the canal) with Kerr’s Pulp Canal Sealer.
3. Activate the heat switch on the EHP handpiece for at least 2 seconds, then sear the master cone off at the canal orifice. Activating the EHP for less time can cause luting, rather than searing, of the gutta-percha cone to the orifice plugger—a very frustrating result as the cone will pull out of the canal. If this happens, let the EHP cool, straighten the gutta-percha cone on its end, return it to the canal, heat for the recommended time and it should stay in the canal when the EHP is removed before orifice condensation of the heated gutta-percha.
4. Condense the thermosoftened gutta-percha at the orifice with the stainless steel (SS) end of the No. 1 Buchanan Hand Plugger (opposite the red color ring end, as it has a 0.9 mm D) just until the gutta-percha has been folded into the canal in preparation for the CW downpack.
5. Press the now-cold tip of the EHP into the gutta-percha at the orifice.
6. While pushing apically, activate the heat switch—the EHP will move into the canal immediately. When the preset stop on the plugger gets 2.0 mm from the reference point, release the activation switch but continue pushing firmly in a apical direction. The plugger should come to a stop 1.0 mm from binding length (Figure 4).
7. Hold apical pressure on the EHP for 5 seconds. The Elements Obturation Unit (EOU) (Kerr Endodontics) or elementsfree device will give an audible “beep” at 5 seconds after handpiece switch release and 2 “beeps” after 10 seconds.
8. Activate the heat switch again—this time for a full “one thousand one” count, pause for another “one thousand two,” and withdraw the EHP from the canal. Most all of the EHP should be coated with gutta percha and sealer.
9. Bring the smaller NiTi end of the No. 1 Hand Plugger (its red ring is at the end with the 0.4 mm NiTi plugger) to the end of the downpack space and condense the apical mass of gutta-percha until it sets (Figure 5). The canal is now ready for syringe backfilling.
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| Figure 4. Illustration of the CW technique after an electric heat plugger (EHP) is in final downpack position. | Figure 5. Illustration of the CW technique showing a CW Hand Plugger condensing an apical mass of gutta-percha after the completion of the downpack in preparation for the backfill. |
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| Figure 6. The elementsfree backfill extruder cartridge with its new unbreakable needle. | Figure 7. The elementsfree cordless CW Backfilling Extruder (Kerr Endodontics). |
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| Figure 8. Illustration of the CW Technique showing the elementsfree extruder needle in place and binding 2.0 to 3.0 mm from the apical mass of gutta-percha. After placement of the needle, it is critical to wait for 5 seconds before extruding gutta-percha, so the needle (chilled by contact with the canal wall as well as the gutta-percha) can reheat before the backfill begins. |
Syringe Backfilling in Small Canals
The syringe backfilling technique is as follows:
1. Place a backfill cartridge (Figure 6) in the end of the EOU (corded) or the elementsfree cordless CW backfilling (gutta-percha) extruder (Kerr Endodontics) (Figure 7), and rotate it 90° clockwise to secure. I typically set the extruder up before cementing the master cone and executing the downpack so that it is already heated and ready to go when it’s time for the backfill.
2. Once the actuator button lights up, the extruder and cartridge are heated and ready to operate. Before placing the needle in the canal to begin the backfill, it is important to run the extruder piston forward until gutta-percha is seen coming out of the end of the needle. This can be accomplished by holding the actuator button continuously or by “double tapping” the button, which switches the extruder motor to continuous mode without the need to hold the button during this procedure. The reasons for this nuance in technique are that it takes up to 15 seconds for the extruder motor to push the heated gutta-percha in the cartridge to the tip of the needle, when holding the needle in the canal for that length of time could overheat the root.
3. The cartridge needle is placed to its binding point in the backfill space—in small canals, this is usually 2.0 to 4.0 mm short of the apical mass of gutta-percha—and is held there for 5 seconds before actuating the extruder motor (Figure 8). This wait time is critical as the needle is chilled when placed in contact with the canal wall (the extruder needle needs to be at least 100°C [212°F] and body temperature is 37°C [98.6°F]), which thickens the gutta-percha before extrusion, thereby increasing the chance of leaving a backfilling void.
4. Once the wait time is over, the extruder motor is switched on while the needle is held in the canal with a light pressure. The extruder motor will be felt to be operating for several seconds, and then the needle, having filled the empty space ahead of it, will bump back in the canal (Figure 9).
5. The extruder needle is removed from the canal and the smaller end of the blue No. 2 Buchanan Hand Plugger is brought into the canal to condense the first “squirt” of extruded gutta-percha with a single firm stroke. This end of the No. 2 plugger is 0.7 mm in diameter and the end of the 23-gauge extruder needle is 0.65 mm in diameter, so when the extruder needle bumps back after filling the space ahead of it, the gutta-percha left in the backfill space condenses to a canal level with a diameter of about 0.75 mm, making the 0.7 mm NiTi end of the No. 2 plugger the perfect size to create a very effective condensation stroke. This first backfill condensation stroke and the 5-second wait time before extrusion are the most potent defenses against leaving a backfill void (which is, ironically, the least clinically important but most disappointing backfilling mistake).
6. The extruder needle is replaced in the backfill space and is now in contact with the gutta-percha mass. Another 5-second wait time is held, after which the canal is syringe backfilled to the orifice level. A good suggestion is to wait for 2 seconds after syringing to the orifice level, move the needle circumferentially in the orifice, remove the needle, and finish the backfill with the larger SS end of the red No. 1 Buchanan Hand Plugger—brought to bear with a firm, 10-second, sustained condensation stroke. Holding this sustained, 10-second condensation stroke at the orifice level densifies the backfill in a way that “bouncing” condensation strokes can never accomplish in an elastic medium like gutta-percha. After the end of the sustained stroke at the orifice, moving the end of the plugger sideways to cut surplus gutta-percha against the wall of the orifice is the easiest and most effective way to remove unwanted filling material from the pulp chamber.
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| Figure 9. Illustration of the CW Technique showing the elementsfree extruder needle being bumped back by the extruded gutta-percha. | Figure 10. Microphotograph of condensed gutta-percha left in a large canal in preparation for a single-cone backfill. Because this is a virtual impression of the downpack plugger, simply cementing a like-tapered Autofit Backfill Gutta-Percha (Kerr Endodontics) point in the space fills that space and provides a very low probability of a backfill void. |
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| Figure 11. The Autofit Backfill Gutta-Percha cones come in .06, .08, .10, and .12 tapers, and they all have tip diameters of 0.5 mm to match the tip diameters of the CW EHPs that precede them. | Figure 12. A maxillary molar obturated with the CW Technique. Note the mid-root bifurcation of the MB canal, as well as the secondary canal bifurcating itself before exiting the root. This case, done as a live demonstration at the Chicago Midwinter Meeting many years ago (note the large coronal shapes that were common in the 1990s), is an excellent example of how 3-D filling can improve success rates. Despite vigorous irrigation, it is unlikely that I was able to kill all the bacteria 7.0 to 8.0 mm away from the primary MB canal. In my opinion, the reason this case was successful was because any bacteria left near the end of this uninstrumented space were most likely entombed by the bolus of sealer and gutta-percha driven past them during the downpack. |
Removing Syringe Backfilling Voids
The easiest method to remove a backfill void is to downpack into it and do a single-cone backfill as described later (see Single-Cone Backfilling Procedures). Attempting to strip gutta-percha from the canal when a void has occurred so another syringe backfill can be done nearly always results in yet another backfill void. This most likely occurs because it isn’t possible to remove all of the gutta-percha particles out of the backfill space with a heat plugger; these particles are then gathered by the hot extruder needle reentering the canal and are then carried to the end of the backfilling space to be extruded against, causing yet another annoying backfilling void. A much easier, more consistently successful method is to remove the void with a single downpack stroke, followed by the very predictable single-cone backfill.
Downpacking Medium and Large Canals
Syringe backfilling small canals without voids is the most challenging part of CW Obturation. The downpack routine in medium and large canals is different, however. Because medium and large canals are larger in internal diameter and are much less curved than small canals, it is possible to downpack, then carefully break the plugger loose from the gutta-percha along its sides and remove it without removing any of the condensed gutta-percha. In large canals with lateral fins (common in single-canal premolars), the downpacked gutta-percha typically remains in the canal after removal of the EHP, even when a separation burst of heat is used, because of the mechanical lock of the condensed gutta-percha into the undercuts of the lateral fins.
This downpacking technique is as follows:
1. The prefit EHP is preheated for 2 seconds, then is used to sear the master cone off at the orifice, and the remaining gutta-percha is condensed with the SS end of either the red No. 1 (0.9 mm D) or the blue No. 2 (1.35 mm D) Buchanan Hand Plugger, depending on the original orifice diameter.
2. After it is cool again, the EHP is wiped with an alcohol swab to lightly lubricate it for the retrieval to follow, it is pushed against the gutta-percha at the orifice, the heat switch is activated, and the plugger immediately heads into the canal.
3. When the EHP is within 2.0 to 3.0 mm of its preset length (4.0 to 6.0 mm short of full canal length), condensation pressure is maintained as the plugger slows its apical movement to, hopefully, 1.0 mm short of the preset length. If the heat has been terminated too soon and the plugger is more than 1.0 mm short of the intended depth of the downpack, a short, additional burst of heat will allow the plugger to achieve its desired depth.
4. Firm apical pressure is maintained as the condensed gutta-percha cools, taking up the inevitable shrinkage vertically rather than allowing it to shrink away from the canal walls. Five seconds after release of the switch, a beep will be heard, but in larger canals, apical condensation pressure is further held until a double beep is heard 5 seconds later (ie, 10 seconds after release of the heat switch).
5. Apical pressure is held as the EHP is rotated back and forth to break it loose from the gutta-percha condensed around it, and then, with a modest backward removal force, the EHP is teased out of the canal with the intention of leaving all of the condensed gutta-percha in the canal rather than readhering it to the plugger (Figure 10). If heat is mistakenly reapplied, another 10-second wait should be allowed, and then the previous release routine is repeated after the gutta-percha has cooled. On occasion, the gutta-percha will not release but will be dislodged in the canal or removed with the withdrawn EHP when it is meant to be left in place. In this case, simply reapply apical pressure, rotate the EHP more aggressively, and re-attempt removal of the EHP and leaving the condensed gutta-percha in the canal.
The release of the plugger from the gutta-percha is made more difficult by to the following factors:
• Irregularly bent EHPs. When initially fitting the downpack plugger, be certain to straighten any previously set curvatures not needed to downpack to length in the canal to be obturated.
• EHPs with the sealer baked onto the plugger surfaces. Use a bur brush to clean EHPs prior to downpacking these larger canals.
• EHPs levered away from their final positions. Attempting to remove the EHP when it has been even slightly levered away from its final position after downpacking will be difficult. It is actually not that easy to hold the plugger in an angularly passive alignment as the handpiece is a long lever arm in relation to the plugger. When frustrated by an EHP not releasing from the gutta-percha along its sides, I have found it helpful to place a hand instrument under the crook of the plugger with a light upward force while slightly rotating the EHP. This trick rarely fails.
• Dislodged condensed gutta-percha. Whenever the condensed gutta-percha appears to have been dislodged during retrieval, let the EHP cool completely. Then use an alcohol swab to clean it off of the sealer, and place it back in the space left by the plugger in the gutta-percha. Finally, with firm pressure, do a 10-second, sustained condensation stroke to return it into place and to densify the gutta-percha against the canal wall.
Single-Cone Backfilling Procedures
After the downpack in larger canals is completed and the condensed gutta-percha is secured in place, the space left by the EHP is ready for the single-cone backfill. I usually select and adjust the tip diameter of the backfill cone before cementing the master cone and beginning the downpack procedure. I use Kerr Endodontics’ Autofit Backfill Gutta-Percha Cones (Figure 11), which come in the 5 plugger sizes of .04, .06, .08, .10, and .12 tapers. However, standard taper gutta-percha points can also be used if they are tip-adjusted with a gutta-percha gauge to a 0.5mm diameter. Check and adjust the Autofit Backfill Cones, if necessary, as they are occasionally sized too small at their tip ends.
The single-cone backfill technique is as follows:
1. The backfill cone is coated with Kerr’s Pulp Canal Sealer (mixed to a viscosity that will string an inch above the mixing pad without dripping back to the pad), is taken into place in the backfill space and moved in and out 3 or 4 times, removed, recoated with a bit more sealer at the cone tip, and reinserted to final position. Reapplication of sealer ensures that it is carried to the end of the backfill space.
2. The EHP is preheated for at least 2 seconds; the backfill cone is seared at or slightly below the orifice level of the canal; and the larger SS end of the No. 1 or No. 2 Buchanan Hand Plugger is brought to bear with a firm, 10-second, sustained condensation stroke. Any gutta-percha that has moved beside the tip of the plugger during this sustained condensation stroke is folded back into the gutta-percha mass at the orifice and is carefully condensed to a flat surface, ideally a millimeter below the orifice level, to allow a void-free placement of glass ionomer against it during the post-endodontic restorative procedure.
CW Obturation in medium and large canals is more efficient than carrier-based obturation. There is a principal difference between small and large downpack procedures. The downpack for small canals ends with a separation burst of heat and removal of the EHP along with the condensed gutta-percha glued to it. The downpack for larger canals ends with the careful removal of the EHP while leaving the condensed gutta-percha in the canal.
IN SUMMARY
In this 2-part article series, the case has been made for both the efficacy as well as the efficiency of the Continuous Wave Obturation Technique. When used to 3-dimensionally fill medium and large root canals to their full apical and lateral extents, this method is faster to execute than carrier-based obturation, especially when cleanup of the pulp chamber is included in the equation. The most complex root canal systems, with a little bit of training, can be predictably filled with the CW Obturation Technique, often showing dramatic results (Figure 12).
References
- Buchanan LS. The Continuous Wave of Obturation technique: ‘centered’ condensation of warm gutta-percha in 12 seconds. Dent Today. 1996;15:60-67.
- DuLac KA, Nielsen CJ, Tomazic TJ, et al. Comparison of the obturation of lateral canals by six techniques. J Endod. 1999;25:376-380.
- Goldberg F, Artaza LP, De Silvio A. Effectiveness of different obturation techniques in the filling of simulated lateral canals. J Endod. 2001;27:362-364.
- Lea CS, Apicella MJ, Mines P, et al. Comparison of the obturation density of cold lateral compaction versus warm vertical compaction using the continuous wave of condensation technique. J Endod. 2005;31:37-39.
- Gencoglu N, Helvacioglu D, Gundogar M. Effect of six obturation techniques on filling of lateral canals. Journal of Research and Practice in Dentistry. 2014;2014:807624 (doi: 10.5171/2014.807624).
Dr. Buchanan is a Diplomate of the American Board of Endodontics, a Fellow of the National and International Colleges of Dentists, and part-time faculty in the graduate endodontic programs of the University of California, Los Angeles, and the University of Southern California. He is the founder of Dental Education Laboratories, a hands-on teaching center in Santa Barbara, Calif, where he also maintains a practice limited to conventional/microsurgical endodontic therapy and implant surgery. He can be reached by visiting his company websites delendo.com and endobuchanan.com.
Disclosure: Dr. Buchanan designed, patented, and licenced the CW hand and electric heat pluggers and the elementsfree Obutration System (Kerr Endodontics).
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