Written by Edward Lowe, DMD Tuesday, 31 October 2006 19:00
The advances in endodontics in the last 20 years have truly made it an easier and enjoyable process from a general practitioner’s point of view. Apex locators, rotary Ni-Ti instrumentation, and carrier-assisted warm gutta-percha are but a few of the many innovations that continue to make endodontics more user-friendly.
The use of carrier-assisted warm gutta-percha has been around for more than 15 years. The first systems introduced involved the use of a metal carrier. While this seemed like a good choice for a carrier, the metal’s drawback was the challenges it presented to retreating the canal if it was required as well as to placing a post and core. The advent of plastic carriers has met these challenges by being easier to remove and trim. The 4% shrinkage factor of warm gutta-percha is negligible, and the inclusion of a plastic core further minimizes shrinkage.
Figure 1. The Soft-Core System: verifier (top), obturator (middle), and obturator with pin removed (bottom).
A Soft-Core Endodontic Obturator (Axis Dental) is a core of biocompatible plastic that is sized according to ISO standards and coated with thermoplastic gutta-percha. A single unit is all that is needed to totally obturate a root canal (Figure 1). The Soft-Core system (Axis Dental) introduces a removable handle, which allows the operator to place several obturators and still maintain visibility of the coronal openings. The length of all the obturators is 27 mm, with the apical 18 mm of the plastic carrier core being solid and the coronal 6 mm being hollow to accommodate the handle and pin. The pin can be pulled out to create a 31-mm obturator. The taper of the carriers is .03 so they can easily be inserted to length, and they come in tip sizes 20 to 100. The black carrier is radiopaque and does not discolor the tooth structure. The gutta-percha is reversible thermoplastic. This means that it becomes soft and highly adhesive when heated to temperatures above approximately 100°C. When cooled, it returns to a firm, rigid state. Reheating will once again make the gutta-percha soft and adhesive.
This article follows a Soft-Core system retreatment of a failed endodontic case and the subsequent restoration of the tooth with a post and core buildup and an IPS e.max CAD crown (Ivoclar Vivadent).
|Figure 2. Mandibular left first premolar (No. 21) with 16-year-old PFM crown and fistula.||Figure 3. Radiograph showing caries under the crown and a radiolucent area around the failing endodontic fill.|
A 44-year-old female patient presented with a persistent fistula in the apical region of her mandibular left first premolar (tooth No. 21), as shown in Figure 2. The tooth was asymptomatic with slight mobility. Hot and cold tests were negative, and the patient felt discomfort during percussion. Pulp vitality readings for tooth No. 21 were a maximum of 80 using an Elements Diagnostic Unit and Apex Locator (SybronEndo). Tooth No. 22 tested positive for hot and cold, and the vitality reading was 19. Tooth No. 27 was vitality tested for a control and yielded a reading of 22.
Periapical radiographs revealed an 8-mm periapical radiolucency around the apex and mesial root surface of tooth No. 21 extending to the distal root surface and apex of tooth No. 22 (Figure 3). The radiograph revealed the presence of recurrent caries under the existing porcelain-fused-to-metal crown on tooth No. 21. This tooth had been endodontically treated 16 years earlier, and a post, core, and crown were placed at about the same time. The post appeared to be a very short metal post, and the endodontic fill appeared to be failing. One can assume that all these factors contributed to the existing condition of tooth No. 21.
Figure 4. A fine Axis diamond (NTI 392-016) is used to remove the cement around the post.
Figure 5. The .12-taper K3 shaper was used to remove the bulk of gutta-percha.
The treatment plan involved retreatment of the tooth with removal of the short post and replacement of the PFM crown.
At the initial appointment, the patient was isolated with a rubber dam, and an access opening was made through the crown with an NTI KS2 diamond bur (Axis Dental). At this point, the caries-riddled tooth relinquished both the crown and a portion of the core. The short post was carefully removed using a combination of hand instruments and a fine-tipped diamond (NTI 392-016 [Axis Dental]; Figure 4). The original PFM crown was recem-ented as a provisional for aesthetic reasons.
Access to the apex was obtained by using a combination of hand and rotary instruments. A 17-mm .12-taper K3 shaper (Sybron-Endo) was used to remove the initial bulk of gutta-percha (Figure 5). A small amount of purulent exudate emerged as the apical third was negotiated. Once a 21-mm size 35 Hedstrom file was worked down to the vicinity of the apex, the Elements Diagnostic Unit and a radiograph were used to confirm the working length of 18.5 mm. From this point on, removal of the old gutta-percha was carried out using a 21-mm K3 G-Pack (SybronEndo). The black gutta-percha that was removed was an indication of the extensive microleakage invading the original endodontic fill. The canal was irrigated with sodium hypochlorite and thoroughly dried with paper points. A cotton pellet and Cavit (3M ESPE) were placed in the coronal access, and the patient was dismissed.
One week later, the patient’s fistula had subsided to a great degree and the tooth was less mobile. The tooth was reopened, and the crown-down technique using the K3 files began with a No. 25 file with a .08 taper and ended with a No. 25 with a .02 taper. Patency between rotary files was constantly confirmed. The canal was irrigated frequently with 3% hydrogen peroxide and 0.2% chlorhexidine gluconate. A No. 35 K-Flex file (SybronEndo) was placed alongside a No. 70 K-Flex file to check for the possibility of a second canal; however, it was determined radiographically that there was only one large canal. The final apical instrument was a No. 70 K-Flex file.
Prior to obturating the canal, large paper points were used to dry it thoroughly after final irrigation with chlorhexidine. A size 70 Soft-Core verifier was fitted in the canal to check if a size 70 Soft-Core obturator would fit to length. A size verifier is basically an obturator without gutta-percha. You use it to verify whether the chosen obturator size will fit in the root canal. A somewhat loose fit in the apical third is important to allow clearance for back-filling of the gutta-percha. A tight fit may impede seating of the obturator to the working distance. The filling with the obturator will proceed accurately and without problems if the size verifier can be placed to the working distance without resistance.
Figure 6. Introducing the sealer into the canal with the canal verifier.
Equal amounts of Seal-apex (SybronEndo) non-eugenol calcium hydroxide polymeric root canal sealer catalyst and base were mixed. The No. 70 verifier was used to introduce enough sealer to liberally coat the canal walls to the apex (Figure 6). The use of sealer is imperative. It not only helps seal the canal but also acts as a lubricant for the obturator by minimizing friction upon inserting it.
The No. 70 obturator was placed in one of the slots in the top of the Soft-Core oven, and the green “on” portion of the control button was pressed. The Soft-Core oven utilizes a replaceable 150-W halogen bulb as the heat source. A thermo sensor automatically monitors the temperature inside the oven and increases and/or decreases the light intensity during the cycle. The temperature will be maintained at a constant 110°C plus/minus 5°C. When the obturator has reached the proper temperature,
the oven will sound a tone and shut off.
Figure 7. The obturator seated to the working length.
Figure 8. The Soft-Core Core Removal kit.
Figure 9. The plastic core is removed to the length of the intended post.
Figure 10. MultiCore composite core is built and shaped around the post.
The obturator was removed from the oven and inserted into the canal to the working distance without twisting the handle (Figure 7). A radiograph to confirm the position of the fill was taken at this time. After allowing the gutta-percha to cool for 3 to 4 minutes, the handle was carefully removed and the black plastic core cut back with an NTI KS2 diamond to 1 mm inside the access opening. The opening to the PFM crown was sealed with Cavit, and the patient was sent home.
One week later the patient returned for the restorative portion of her treatment. The fistula had completely disappeared. The PFM crown was removed and the pulp chamber cleared of excess Cavit with a diamond bur. The Soft-Core Core Remover is a tapered, pointed, noncutting instrument that was developed specifically to ensure safe and fast removal of the plastic core and gutta-percha in the canal (Figure 8).
With the plastic core removed to the length of the intended post with the Soft-Core Core Remover (Figure 9), a No. 4 PeerlessPost drill was used to drill a post space for a No. 4 PeerlessPost fiber post (SybronEndo). The post was cemented with a dual- cure resin cement (Multilink [Ivoclar Vivadent]), and a composite core (MultiCore [Ivoclar Vivadent]) was built on top of it.
After light- and self-curing, the tooth and core were shaped into a full crown prep using a coarse NTI KS2 and a fine NTI 846-020 diamond (Axis Dental; Figure 10). The prep was polished with Sof-Lex discs (3M ESPE), and an impression was taken with a Gripper quadrant triple tray (Discus Dental) and Precision extra light- and medium-body polyvinyl siloxane impression material (Discus Dental). An acrylic provisional crown was made with Luxatemp (Zenith/
DMG), and a preoperative PVS impression taken of the existing crown. The crown was cemented provisionally with Systemp.link (Ivoclar Vivadent).
A crown was fabricated from IPS e.max CAD, a new, high-strength, highly aesthetic glass ceramic for the CAD/CAM technique. The block is blue in color and is in a precrystalline form that is ideal for milling. It is indicated for single-unit anterior copings, premolar copings, and 3-unit bridges from the premolars forward. From a lab perspective, it is very efficient. After milling the IPS e.max CAD as a blue block, it is crystallized in a porcelain furnace for about 35 minutes. The material undergoes a dramatic color change as final physical properties are established. The resulting coping is then layered with a dentin and enamel buildup using a nano-fluorapatite glass ceramic layering ceramic (IPS e.max Ceram [Ivoclar Vivadent]). The definitive restoration is contoured, stained, and finally hand-polished to match the adjacent natural dentition’s shade and texture.
Figure 11. The IPS e.max Ceram crown from different views.
Figure 12. Multilink primer applied to the crown prep.
Figure 13. Multilink dual-cure resin cement applied to the crown.
Figure 14. Crown spot-tacked into place.
Figure 15. One-month postoperative view of IPS e.max CAD crown in place. Note healing of fistula in periapical tissue.
Figure 16. Occlusal view of preoperative PFM crown in place.
Figure 17. Occlusal view of postoperative IPS e.max CAD crown in place.
Figure 18. One-month postoperative radiograph of completed endodontic and restorative procedures.
Figure 19. Preoperative radiograph of an abscessed molar with multiple canals.
Figure 20. Postoperative radiograph with the canals obturated with Soft-Core obturators.
When the crown was returned from the lab, it was inspected for fit on the working model and uncut model (Figure 11). The patient’s provisional crown was removed, and the tooth surface was cleaned with 3% hydrogen peroxide and rinsed with water. The crown was tried in to confirm fit. The inside of the crown was coated with silane (Monobond-S [Ivoclar Vivadent]) for 1 minute and air-dried. Multi-link primer A and B were mixed and placed on the crown prep for 15 seconds with a microbrush (Figure 12). Multilink transparent dual-cure resin cement was spread inside the crown, which was seated onto the tooth (Figure 13). After spot-tacking the crown in place with a 2-mm tacking tip, the contacts were flossed, and excess cement was removed (Figure 14). Final curing of the crown was done with a bluephase C8 LED curing light (Ivoclar Vivadent) for 10 seconds on the buccal, occlusal, and lingual surfaces. A fine, 8-bladed finishing carbide (NTI TDF 9 [Axis Dental]) was used to remove excess cement around the margins. The occlusion was checked with Madame Butterfly Silk (Almore International), and the adjustments were polished with a yellow CeraGlaze porcelain polisher (Axis Dental). Note the absence of the fistula in the postoperative photo (Figure 15).
Acknowledgment The author would like to acknowledge Juan and Nelson Rego of Smile Designs by Rego, Santa Fe Springs, Calif, for the exquisite ceramic work.
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