Treatment of a maxillary second molar

Dr. L. Stephen Buchanan discusses cleaning with apical negative pressure and obturating in three dimensions using the Continuous Wave of Obturation technique

This case report demonstrates how root canals accessed in a minimally invasive manner can be successfully cleaned with apical negative pressure irrigation and then obturated in three dimensions using the Continuous Wave (CW) filling technique with elements™free Downpack and Backfill devices.

Access

In Figure 1, we see the case: an upper second molar (No. 2) with a full PFM crown and little or no pulp chamber due to the extensive calcification that occurred before the pulp became necrotic. Cutting access cavities into calcified pulp chambers is no fun for several reasons; it is difficult,1 it requires a lot of patience, and it is easy to look as though a free-range bur was used with need-less tooth structure cut and lost rather than the desired paths heading straight into each canal.2

Recently, a new type of CT guidance has been introduced for implant surgery; optically-driven dynamic CT guidance.3,4 Dr. Charles Maupin (Lubbock, Texas) and I have been experimenting with one such system (X-Nav Technologies, Lansdale, Pennsylvania) to help guide endodontic access procedures.

The result is a minimally invasive access preparation (Figure 2). At the end of each drill path, a No. 15 K-file dropped into each orifice. A rotary 25/.08 orifice opener was then used to smooth the transition path from access to the orifice. Each of the access cavities directly met each of the canals at the cementoenamel junction (CEJ) level of the tooth.

Figure 1: Maxillary second molar with total pulp chamber calcification

Figure 2: Minimally invasive access cavities — the left opening is for the palatal canal; the ovoid opening on the right side of the occlusal surface is actually the intersection of the two openings for the MB and DB canals

Treatment of canals

All three canals with lubricant (gel) in place were negotiated entirely with a single rotary glide path file. An apex locator was used with that same file to determine canal lengths. Switching to 17% liquid EDTA, the palatal (P) canal gauged slightly smaller than a No. 30 K-file, while the mesiobuccal (MB) and distobuccal (DB) canals gauged slightly larger than a No. 15 K-file. With this data in mind, I cut final shapes in the MB, DB, and P canals (slightly larger than the gauged diameters) with .06 tapered rotary files.

NaOCl irrigation was activated ultrasonically at low power for 1 minute in each canal to break loose and remove any particulate matter. This is important as it helps eliminate clogging of the apical negative pressure (ANP) MicroCannula evacuation needles (EndoVac™, Kerr Endodontics). The Endo- Vac’s MicroCannula evacuation needles are 30 GA (0.30 mm outside diameter), so its tip reached very close to the terminus of the palatal canal and within 2 mm-3 mm in the MB and DB canals. This irrigation method is especially effective in minimally invasive endodontic cases. Each canal was irrigated in this manner for 5 minutes with 8% NaOCl.

Figure 3: Working radiograph showing a tapered diamond bur placed in the guided access path for the MB cana

Matching AutoFit™ Greater Taper .06 Gutta Percha points (Kerr Endodontics) were initially trimmed with a blade and a gutta-percha gauge to a 0.2 mm tip size for the MB and DB canals and a 0.35 mm tip size for the palatal canal. Then after seating them to place in each of the canals, they were further adjusted to fit 0.5 mm short of working length. Continuous Wave Electric Heat Pluggers (Kerr Endodontics) — a .10 taper plugger for the P canal and a .06 taper plugger for the MB and DB canals — were fit to a binding point 4 mm-6 mm short of working length in each canal. Kerr Pulp Canal Sealer™ (Kerr Endodontics) was hand mixed to a viscosity that allowed it to string an inch above the mixing pad and just hang there — ideal for the Continuous Wave of Obturation filling technique. This viscosity helps hold the master cones in place when the plugger is withdrawn after the downpack. All canals were dried and their master GP cones cemented into place.

The .06 plugger was mounted in the elementsfree (Kerr Endodontics) Downpack handpiece (Figure 4). The 360-degree ring switch was activated, causing the plugger tip to reach 200ºC almost immediately. The plugger tip was then used to sever each of the GP cones at the orifice levels after which the larger stainless steel end of the No. 1 (red) CW Hand Plugger (Kerr Endodontics) was used to fold the warm gutta percha into each orifice in preparation for downpacking. The MB and DB canals were downpacked with a separation burst of heat in preparation for syringe backfilling, and the apical masses of gutta percha were condensed with the nickel-titanium end of the same #1 CW Hand Plugger used previously.

Before downpacking began, however, a gutta-percha cartridge was placed in the elementsfree Backfill device and was switched on to preheat so that it could be ready when needed later. After preheating, the Backfill extruder was “primed” by double tapping the actuator button which moves its internal piston forward until freshly heated gutta percha advanced through the end of the needle. The priming procedure is ended by hitting the button again.

Once the downpacking procedure was completed in all canals, the elementsfree Backfill device’s needle was placed to its binding point in the buccal canals, a 5-second pause was counted out, and the actuator button was pushed and held until the extruded GP bumped the needle back, and it was removed. The small NiTi end of the No. 2 (blue) CW Hand Plugger is 0.7 mm, and the extruder needle is 0.65 mm. When the needle bumped back, the 0.7 mm plugger end fit the canal at that level perfectly, so only a single sustained push was needed to eliminate any backfilling voids between the apical mass and the extruded GP. After that, the needle was returned to the remaining space to complete the backfill. The needle was placed directly onto previously extruded GP to soften it. Then after another 5-second wait, gutta percha was extruded back to the orifice level, then condensed with the larger stainless steel end of the No. 1 (red) CW Hand Plugger, thus finishing the backfill procedure.

Figure 4: Cordless elements™free Obturation System (Kerr Endodontics)

The palatal canal was downpacked in a similar fashion as the buccal canals, yet with the intention of using a single-cone backfill. For this the electric heat plugger was held in place for 10 seconds to allow the plugger to cool, the plugger was pushed apically (without reheating) and was rotated to break the plugger loose from the condensed gutta percha. The plugger was then teased out of the canal, leaving the condensed gutta percha in place with what is essentially an impression of the .10 taper plugger used in this canal. Autofit Backfill Gutta Percha Points (Kerr Endodontics) come in five sizes, matching the tapers of the pluggers, so when single-cone backfilling is to be done the same size backfill cone is chosen. It cemented in place with sealer, severed with the heated plugger, and condensed with the larger end of the #2 CW Hand Plugger. The postobturation radiograph is shown in Figure 5.

Figure 5: Post-op radiograph showing a very three-dimensional filling result, a testament to the efficacy of negative pressure irrigation and Continuous Wave Obturation in minimally invasive endodontic preparations. Note the filled apical bifurcation of the MB canal and the two apical lateral canals; one off the MB canal and one off the DB
Figure 6: Photograph of finished post-endodontic restoration

Restoration of the access cavities was done as follows:
1. Air abrasion was used to clean the filling materials off the access walls.
2. A 2 mm layer of glass ionomer was placed in each of the orifices.
3. Bonded composite material was placed and carved to the occlusal surface contours, then light-cured.
4. The restoration is polished and checked for occlusal interferences (Figure 6).

Conclusions

This case demonstrated that it is possible to find all orifices, effectively instrument and, with negative pressure irrigation, to clean complex root canal systems through minimally invasive access openings, and that the Continuous Wave of Obturation Technique, using cordless elementsfree obturation devices is very capable of delivering a dense 3D fill through these tiny access cavities as evidenced by the multiple lateral canal fills (Figure 5).