The Future of Root Canal Obturation

INTRODUCTION
The use of core carriers with attached gutta-percha for root canal obturation is not new, as there was evidence in the late 1800s that indicates gutta-percha was softened and adapted to gold wires and placed in the root canal system.¹ In the past 40 years, there have been additional attempts to use this approach to obturate prepared root canal systems, namely the use of silver cones wrapped in gutta-percha^2,3 and the formation of softened gutta-percha on root canal files.⁴ In each historical attempt to devise a better obturator or technique, a hard core material was used that often created challenges if treatment revision was necessary.^5,6 Likewise, post space preparation posed numerous difficulties for clinicians.^7,8
To meet these challenges, a plastic core obturator was created in the early- to mid-1990s that was flexible, had sufficient strength for placement in the canal, was easily softened with chemicals or heat, and could be removed for treatment revision. However, as with any technique or material, improper usage created numerous clinical impasses. These included the inability to remove the carrier in small tortuous canals, stripping of the gutta-percha from the carrier with subsequent binding of the plastic in the improperly shaped root canal, and the potential for root perforation during post space preparation.

STRONG CROSS-LINKED CORE DEVELOPED
To eliminate these challenges, and to develop core obturators that would provide the clinician with the best possible canal filling technique, advances in materials science and polymer chemistry enabled the development of a strong core that is made from a cross-linked, thermoset elastomer of gutta-percha (GuttaCore Crosslinked Gutta-Percha Obturator [DENTSPLY Tulsa Dental Specialties]) (Figure 1).
This core, when coated with regular gutta-percha, allows clinicians to achieve their desired goal, bypassing all the previous challenges to this obturation technique. This technology allows the movement of warm gutta-percha 3-dimensionally into all areas of the properly shaped root canal system. While many obturation techniques rely on lateral or vertical compaction techniques, the hydraulic force from these techniques sends gutta-percha in one or 2 unequal and unpredictable directions (laterally or apically). With GuttaCore, the vectors of force for the movement of softened gutta-percha during placement are in all directions within the canal (Figure 2). This outcome, however, is based on proper canal shaping and thorough irrigation. Preparation of root canals with this approach is paramount to the removal of pulp tissue and dentinal debris, and for a more effective volume of disinfecting irrigant to penetrate, circulate and clean all areas of the root canal’s system.^9,10 The resulting shaped and cleaned space permits a maximization of the hydraulic force and flow of gutta-percha into the canal system with the placement of GuttaCore.

Figure 1. Animated representation of polymer chains of a thermoset elastomer of gutta-percha (blue) being cross-linked (red) to enhance strength and stability of the newly formed core material.	Figure 2. Animated representation of softened GuttaCore obturators (DENTSPLY Tulsa Dental Specialties) in the root canals of a mandibular molar showing flow and adaptation to the canal irregularities and communications.

Generally, applications of GuttaCore are somewhat similar to those used with other gutta-percha core carriers. However, there are some important aspects to the delivery of GuttaCore that require attention. Prior to obturation, canals should be shaped and enlarged to a minimum of a 25/.06 or greater if possible,^11,12 to ensure not only thorough canal debridement but also to provide sufficient space and taper for the GuttaCore material to flow into the canal intricacies (Table). In a recent long-term cohort study, the presence or absence of sufficient taper of the root canal preparation was the main factor associated the development of periapical lesions following treatment.¹³ When using a rotary file with a taper equal to or greater than .06, the GuttaCore Crosslinked Gutta-Percha Core Obturator that is the same apical size as the last file taken to working length is selected. When using a .04 tapered rotary file, the GuttaCore obturator that is one apical size smaller than the last file taken to working length is selected.
GuttaCore is a notable advancement in endodontics, in that polymer chemistry has enabled the development of a cross-linked gutta-percha core that has sufficient strength to be placed into demanding anatomical confines, such as severely curved canals or canals that are difficult to reach. It requires minimal heating to be effective in its flow and adaptation to the prepared canal’s walls. While it cannot be bent prior to placement, as a clinician might wish to do in difficult canal access situations, it can be placed easily when positioned at the correct angle in by utilizing a pair of locking cotton forceps.

GUTTA CORE TECHNIQUE
Prior to use, each shaped and cleaned canal must be verified as to its size and taper (Figure 3). This is done with a metal size verifier, which is most effective in guiding the clinician in choosing the correct size of GuttaCore obturator. When properly sized, the softened material can reach to the full extent of the canal preparation. This is especially helpful in long root canals.
As with all gutta-percha obturation procedures, a sealer is essential. However, its placement is somewhat different than with other filling techniques. With GuttaCore, the sealer is placed in the coronal half of the canal and wicked out with a paper cone if too much is placed. There should be a thin layer on the walls in the coronal half of the canal that will ultimately be carried to the apical extent of the canal with minimal extrusion (Figures 4a to 4c).

Figure 3. Use of size verifier is essential to ensure the proper GuttaCore obturator is chosen.	Figure 4a. A small amount of sealer is placed to create a thin layer on the root canal walls prior to placement of the heated GuttaCore obturator.
Figure 4b. Obturation of a 2-root maxillary first premolar using GuttaCore obturators. Note the material adapation to the walls with no evidence of a core within the root canal filling.	Figure 4c. Obturation of root canals in a mandibular second molar with GuttaCore obturators and sealer. A small amount of sealer is extruded apically.
Figure 5. A new GuttaCore oven is used to simplify the heating of the core carrier. Two cores may be heated simultaneously.	Figure 6. The arm that will contain the carrier is easily depressed, and when ready, the heated core is slowly lifted from the heating cylinder.
Figure 7. Animated representation of the cutting of the core at the canal orifice with a small round bur. A sharp, endodontic spoon excavator may also be used.	Figure 8. In teeth that present with difficult canal access, following the heating of the GuttaCore obturator, the handle can easily be snapped off (left) and the obturator is then positioned in a locking cotton forceps at the desired angle for delivery to the canal (right).
Figure 9. Mandibular second molar with 3 canals at lengths of 24.5 mm filled with GuttaCore obturators and sealer using the technique described in Figure 8.	Figure 10. Due to the chemical cross-linking of the GuttaCore obturator, it is generally impervious to the use of chemicals for softening, although the gutta-percha that surrounds the obturator is susceptible to softening with chemical agents.

The carrier is heated in the GuttaCore oven (Figure 5) that is designed to provide the proper softening of the material while maintaining core integrity and strength. Once heated in this contemporary and easy-to-use oven (Figure 6), the heated carrier is gently lifted from the supportive oven arm. In fact, with this new oven, 2 cores can be heated simultaneously if desired, or heating can be staggered to enhance clinical delivery in a timely fashion.
Once the carrier is placed in a slow, nontwisting movement, it is held firmly by one finger, and a sharp endodontic spoon excavator can be used to cut off the handle. In lieu of this, the handle can be moved side to side until it breaks free from the shaft. A third method is to use a rotating bur, which will take one to 2 seconds or less to remove the coronally extruding shaft and handle. Once removed, the remaining shaft, which is light gray in color, can be compacted for one to 2 seconds if necessary (Figure 7).

Figure 11. Animated representation of the use of rotary retreatment files to remove the GuttaCore obturator and surrounding gutta-percha when necessary.

THE CHALLENGE OF POSTERIOR APPLICATIONS
The placement of GuttaCore obturators can be challenging in the posterior part of the mouth, where placement of the heated carrier at a specific angle is necessary to provide a smooth and easy entry into a canal orifice. In this case, 2 options present themselves. First, if there is sufficient access to the tooth, upon removal of the core from the oven with the index finger and thumb, the core below the handle is grasped with a locking cotton forceps, while the handle is adjusted in the clinician’s grasp to achieve the desired angle for delivery to the prepared canal (Figure 8). Second, if there is insufficient access due to the inability of the patient to open or due to an abnormal tooth position, upon removal of the heated carrier, the core below the handle is grasped with a locking cotton forceps and the handle of the core is removed with a slight bending action. The heated carrier is then repositioned in the locking forceps to the desired angle for delivery. In both situations, the placement of the core is done slowly with minimal pressure to the desired length (Figure 9).

PREVIOUS CHALLENGES WITH CORE OBTURATION
Three of the major challenges with previously used core obturation have been removal of the coronal portion for post space, the entire removal for treatment revision, and management of canals with wide buccal-lingual canals or C-shaped canals.13 Because the core in the GuttaCore obturator is a form of gutta-percha, removal is quite easy for post space preparation using: (1) the post space drill that comes with each post kit; (2) Peeso reamers; (3) files used for gutta-percha removal (ProTaper retreatment files [DENTSPLY Tulsa Dental Specialties]); or (4) application of heat in the canal to soften the gutta-percha around the carrier followed by use of a rotating file or hand Hedström file. A chemical softening agent can also be used to soften the gutta-percha, although the core itself is impervious to chemical degradation due to being cross-linked (Figure 10).
The second challenge is the potential need for core removal during treatment revision. Here again the use of the ProTaper retreatment files is indicated and usually will work quite well over the entire length of the canal (Figure 11). An additional option can be to use the same files that were used during canal shaping and enlarging. A third option would be to soften the gutta-percha that surrounds the core with either chemicals or heat to enhance penetration with a rotary or hand instrument. Finally, removal of the coronal one-half to two-thirds of the filling material with rotary instruments followed by the use of heat, chemicals and hand K or Hedström files to remove filing material from the apical third is also effective.
Canals with wide, irregular anatomy and completed apical constrictions have always posed problems for any obturation technique.14 The approach to obturation often involved the tedious formation of a custom gutta-percha cone for the apical portion of the canal; however, the middle and coronal portions required a wide range of techniques to achieve the desired canal obturation. With GuttaCore, the filling of these canals is straightforward and 2 options exist: (1) a compacting instrument, such as a plugger or speader can be placed in the canal prior to the placement of the first obturator. Subsequently, this instrument can be used for compacting the filling material without removing the instrument, thereby preserving the space for a second or even third obturator when indicated; or (2) after placement of the obturator, the spreader or compacting instrument is then plunged into the canal alongside the carrier and space is created to add additional gutta-percha cones or segments of gutta-percha, followed by further compaction until further penetration cannot be achieved.

CLOSING COMMENTS
The development of a cross-linked gutta-percha carrier for the GuttaCore obturators represents a major breakthrough for root canal obturation that will enable any clinician to achieve a well-filled, properly prepared root canal system on a predictable basis. As with the advent of nickel-titanium rotary instruments for more ideal canal shaping and ultimate cleaning, the GuttaCore addition to root canal obturation techniques provides the clinician with confidence that the highest level of root canal obturation will be attained.

References

1. Perry SG. Preparing and filling the roots of teeth. Dent Cosmos. 1883;25:182-194.
2. Welch SE. Gutta percha coated silver cones as root canal filling material. Ill Dent J. 1978;47:604-610.
3. Negm MM. Filling root canals with silver-percha cones: a clinical study. Oral Surg Oral Med Oral Pathol. 1983;55:81-85.
4. Johnson WB. A new gutta-percha technique. J Endod. 1978;4:184-188.
5. Gutmann JL, Battrum DE. Challenges in retreatment of thermafil obturated root canals. Lebanese Dent J. 1994;33:57-66.
6. Machtou P, Reit C. Non-surgical retreatment. In: Bergenholtz G, Hørsted-Bindslev P, Reit C, eds. Textbook of Endodontology. Oxford, England: Blackwell Munksgaard; 2003.
7. Ibarrola JL, Knowles KI, Ludlow MO. Retrievability of Thermafil plastic cores using organic solvents. J Endod. 1993;19:417-418.
8. Dalat DM, Spångberg LS. Effect of post preparation on the apical seal of teeth obturated with plastic thermafil obturators. Oral Surg Oral Med Oral Pathol. 1993;76:760-765.
9. Boutsioukis C, Gogos C, Verhaagen B, et al. The effect of apical preparation size on irrigant flow in root canals evaluated using an unsteady Computational Fluid Dynamics model. Int Endod J. 2010;43:874-881.
10. Boutsioukis C, Gogos C, Verhaagen B, et al. The effect of root canal taper on the irrigant flow: evaluation using an unsteady Computational Fluid Dynamics model. Int Endod J. 2010;43:909-916.
11. Khademi A, Yazdizadeh M, Feizianfard M. Determination of the minimum instrumentation size for penetration of irrigants to the apical third of root canal systems. J Endod. 2006;32:417-420.
12. Paqué F, Ganahl D, Peters OA. Effects of root canal preparation on apical geometry assessed by micro-computed tomography. J Endod. 2009;35:1056-1059.
13. Santos SM, Soares JA, Costa GM, et al. Radiographic parameters of quality of root canal fillings and periapical status: a retrospective cohort study. J Endod. 2010;36:1932-1937.
14. Gutmann JL, Lovdahl PE. Problem Solving in Endodontics: Prevention, Identification, and Management. 5th ed. St. Louis, MO: Elsevier; 2011.

     

Dr. Gutmann is professor emeritus in Restorative Sciences, Baylor College of Dentistry, Texas A&M University Health Science Center, Dallas, Tex. He is a Diplomate of the American Board of Endodontics and past president of the American Association of Endodontists. He has presented more than 800 lectures, papers, and continuing education courses internationally. Additionally he has authored or co-authored more than 275 articles in dental journals and 3 text books that address scientific, research, educational, and clinical topics. Dr. Gutmann has taught full-time for more than 27 years at 3 major universities. Presently, he is in private practice limited to endodontics in Dallas, Tex. He can be reached at jlg4570@aol.com.

Disclosure: Dr. Gutmann has no financial interest in the product or technique discussed and he serves as a consultant to DENTSPLY Tulsa Dental Specialties.