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Dr. James Gutmann highlights the changes in core-carrier obturation.
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The obturation of root canals using core-carriers with attached gutta percha has been used since the late 1800s. Evidence indicates that gutta percha was softened and adapted to gold wires and placed in the root canal system (Perry, 1883). Since the late 1970s, there have been additional attempts to use this technique to obturate prepared root canal systems with the use of silver cones wrapped in gutta percha (Welch, 1978; Negm, 1983) and the adaptation of softened gutta percha on root canal files (Johnson, 1978). Each attempt at using a core-carrier technique had its drawbacks with the hard core material often creating challenges if treatment revision (retreatment) was necessary (Gutmann, Battrum 1994; Machtou et al, 2004). Moreover, post space preparation posed numerous difficulties for clinicians in the presence of these types of core-carriers (Dalat, Spångberg, 1993; Ibarrola et al, 1993). In the early to mid-1990s, a plastic core was developed that was flexible, had sufficient strength for placement in the canal, was easily softened with chemicals or heat, and could be removed by most experienced clinicians for treatment revision (Imura et al, 1993). However, as with any techniques or materials, improper usage creates 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 (Gutmann, Battrum, 1994; Gutmann, Lovdahl, 2011). 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 have enabled the development of a strong core that is made from a cross-linked, thermoset elastomer of gutta percha (GuttaCore Brochure, 2011). Using a process called free radical polymerization, a polymer is formed from the successive addition of monomers in multiple steps to achieve the desired end result (Hammond, 2006). The polyisoprene polymer used for this process is a traditional thermal set material. Polyisoprene has been chemically cross-linked for over 150 years with such chemicals as sulphur or peroxide. To enhance this material so it could be used as a carrier, peroxide was used for the cross-linking process, since it is a cleaner chemical that left no residue. Peroxides are stable up to a specific temperature, and once it reaches that temperature, it breaks into two or more pieces called free radicals. Free radicals are very short-lived groups because they have an extra electron. The peroxide-free radicals react with a methyl group associated with a carbon-carbon double bond. This passes the extra electron onto the polyisoprene. This new free radical reacts with a new methyl group associated with a carbon-carbon double bond on different polyisoprene molecules, using up the extra electron. This links the two polyisoprene molecules together via a covalent bond, which is very strong (Billmayer, 1984). The ultimate cross-linking that occurs connects the polymer chains and transforms the gutta percha, keeping it from melting, making it subtly stronger, while retaining its best features (Figure 1). This core, when coated with regular gutta percha, allows clinicians to achieve their desired goal, eliminating all the previous technical challenges and clinician concerns to this obturation technique. This advancement in obturation technology is called the GuttaCore™ Crosslinked Obturator (Dentsply Tulsa Dental Specialties) (GuttaCore Brochure, 2011) (Figure 2). GuttaCore carriers move warmed gutta percha three-dimensionally into all areas of the properly shaped root canal system. While most obturation techniques rely on some type of compaction, the hydraulic force from these techniques sends gutta percha in one or two unequal and unpredictable directions (laterally or apically). However, with GuttaCore, the vectors of force for the movement of softened gutta percha during placement are in all directions within the canal. This desired achievement is based on proper canal shaping and thorough irrigation, which in turn, results in the removal of pulp tissue, dentinal debris and a more effective volume of disinfecting irrigant to penetrate, circulate and clean all areas of the root canal system (Boutsioukis et al, 2010a,b). The resultant shape of the canal allows a maximization of the hydraulic force and flow of gutta percha into the canal system with the placement of GuttaCore. While applications of GuttaCore are somewhat similar to those used with other gutta percha core carriers, there are some important aspects to the delivery of GuttaCore that require attention for the clinician to be successful. 1. All root canals should be shaped and enlarged to a minimum of a 25/.06 or greater if possible (Khademi et al, 2006; Paqué et al, 2009) to ensure not only thorough canal debridement (Boutsioukis et al, 2010a,b) but also to provide sufficient space and taper for the GuttaCore material to flow into the canal intricacies (Table 1). 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 (Santos et al, 2010).
2. Select a GuttaCore obturator that is the same size as the last file taken to working length (WL) when using a rotary file with a taper equal to or greater than .063. Select a GuttaCore obturator that is one size smaller than the last file taken to WL when using a .04 tapered rotary file.
Distinct characteristics of GuttaCorePolymer chemistry has enabled the development of this cross-linked gutta-percha core, which 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 canals walls. While it cannot be bent prior to placement, as a clinician might wish to do routinely in difficult canal access situations, it can be placed easily when positioned at the correct angle in a locking cotton forceps.
Clinical techniqueEach shaped and cleaned canal must be verified as to its size and taper prior to obturation. This is done with a metal size verifier, which is most effective in guiding the clinician in the choice of GuttaCore obturator (Figure 3). When properly sized, the softened material can reach to the full extent of the canal preparation. This is especially helpful in long root canals, such as those found in canines. Any good root canal sealer that is mixed properly can be used with this technique; however, its placement is somewhat different than with other filling techniques. With the GuttaCore technique, the sealer is placed in the coronal half of the canal and wicked out with a paper cone if too much is placed (Figure 4). 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 filling with minimal extrusion (Figure 5). Root canal sealers that are too thick may prevent ease of obturator placement to the desired length and should be avoided with this technique. If the obturator has an excess of gutta percha at its coronal end, careful removal is advised to minimize the amount of material in the pulp chamber after obturator placement. This is done by grasping the obturator by the handle with one hand and using the index finger and thumb of the other hand to gently pinch the gutta percha directly below the material excess (Figure 6).
The carrier is heated in the GuttaCore oven that is designed to provide both the proper softening of the material, while maintaining core integrity and strength. Once heated in the oven (Figure 7), the heated carrier is gently lifted from the supportive oven arm. In fact, in this new oven, two cores can be heated simultaneously if desired, or heating can be staggered to enhance clinical delivery in a timely fashion when obturating a multi-rooted tooth. The carrier is placed in a slow, non-twisting movement and held firmly by one finger, while a sharp endodontic spoon excavator (#31-33L/R endodontic excavator, Hu-Friedy) is used to cut off the handle. In lieu of this, the handle can be moved side-to-side without twisting until it breaks free from the shaft (Figure 8). A third method is to use a rotating round bur or small inverted cone bur, which will take 1 to 2 seconds or less to remove the coronally extruded shaft and handle (Figure 9A). Once removed, the remaining shaft, which is light grey in color, can be compacted for 1 to 2 seconds if necessary, in addition to compacting the surrounding gutta percha, if there is space to do so. For clinicians who have been practicing for a number of years and who have a wide variety of old and rarely used instruments in their offices, a wheel bur, which has been used in the past to create retention form in root-end cavity preparations when amalgam was used (Gerstein, 1984) can be used in a lateral cutting motion. This application is self-limiting by the shaft of the bur, thereby minimizing or preventing any gouging of the pulp chamber floor (Figure 9B). Other instruments that may be available to these same clinicians are small instruments that were designed to remove silver cones and have the appearance of a small fork can be used to cut the core (Figure 9C) followed by compaction at the orifice of the carrier and gutta percha.
Placement of GuttaCore obturators in the root canals of posterior teeth can be challenging due to the angle of placement, for example, the mesial buccal canal of both mandibular and maxillary molars. In these cases, two 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 10A). 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 (Figure 10B). 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 11).
Previous challenges with core obturationChallenges with previously used core obturation materials 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 (Gutmann, Lovdahl, 2011). Because the core in the GuttaCore obturator is a cross-linked form of gutta percha, removal is quite easy for post space preparation using: 1) The post space drill that comes with each post kit2) Peeso reamers3) Files used for gutta percha removal (ProTaper® D files, Dentsply Tulsa Dental Specialties) 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 somewhat impervious to chemical action due to its cross-linking. The second challenge is the potential need for core removal during treatment revision. Here again, the use of the ProTaper D files is indicated and usually will work quite well over the entire length of the canal (Figure 12). Another option may 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 both incomplete and complete apical constrictions have always posed problems for any obturation technique (Gutmann, Lovdahl, 2011). 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 obturators, the filling of these canals is straightforward and two options exist:1) A compacting instrument, such as a plugger or spreader 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. Before removing the instrument, the softened adjacent material is compacted; 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 additional compaction until further penetration cannot be achieved (Figure 13). In canals that join, such as mesial canals of mandibular molars, a paper point can be left in place while obturating the patent canal and then removed followed by obturation of that canal (Figure 14).
The development of cross-linked gutta percha and the GuttaCore Crosslinked Gutta Percha Core Obturators represent a major breakthrough for root canal obturation. As with the advent of NiTi rotary instruments and 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 can be attained.
ReferencesBillmayer FW Jr (1984) Elastomer technology, In Textbook of Polymer Science. 3rd edition, John Wiley & Sons, New York Boutsioukis C, Gogos C, Verhaagen B, et al (2010a) The effect of apical preparation size on irrigant flow in root canals evaluated using an unsteady Computational Fluid Dynamics model. Int Endod J 43: 874-81Boutsioukis C, Gogos C, Verhaagen B, et al (2010b) The effect of root canal taper on the irrigant flow: evaluation using an unsteady Computational Fluid Dynamics model. Int Endod J 43: 909-16Dalat DM, Spångberg LSW (1993) Effect of post space preparation on the apical seal of teeth obturated with plastic Thermafil obturators. Oral Surg Oral Med Oral Pathol 76: 760-5Gerstein H (1984) Surgical endodontics. In Laskin DM, Oral and Maxillofacial Surgery, Vol 2, The CV Mosby Company, St. LouisGutmann JL, Battrum, DE (1994) Challenges in retreatment of Thermafil obturated root canals. Lebanese Dent J 33: 57-66Gutmann JL, Lovdahl PE (2011) Problem Solving in Endodontics, 5th edition, Elsevier, St. LouisGuttaCore Brochure (2011) Dentsply Tulsa Dental Specialities. http://www.tulsadental.com/lit2/pdfs/BRGC12-10_GuttaCore_broch_Lo.pdf Accessed 6-24-2011Hammond P (2006) Stable free radical polymerization, atom transfer radical polymerization, controlled free radical polymerization. 10.569 Synthesis of Polymers Fall 2006 materials, MIT Open Course Ware (http://ocw.mit.edu/index.html), Massachusetts Institute of Technology, Accessed 6-24-2011Ibarrola JL, Knowles KI, Lidlow MO (1993) Retrievability of Thermafil plastic cores using organic solvents. J Endod 19: 417-8Imura N, Zuolo ML, Kherlakian D (1993) Comparison of endodontic retreatment of laterally condensed gutta percha and Thermafil with plastic carriers. J Endod 19: 609-12Johnson WB (1978) A new gutta-percha filling technique. J Endod 4: 184-8Khademi A, Yazdizaheb M, Feizianfard M (2006) Determination of the minimum instrument size for penetration of irrigants to the apical third of root canal systems. J Endod 32: 417-20Machtou P, Reit C (2003) Non-surgical retreatment. In Bergenholtz G, Hørsted-Blindslev PO, Reit C. (eds). Textbook of Endodontology, Blackwell Munksgaard, Oxford.Negm MM (1983) Filling root canals with silver percha cones: a clinical study. Oral Surg Oral Med Oral Pathol 55: 81-5Paqué F, Ganahle D, Peters OA (2009) Effects of root canal preparation on apical geometry assessed by by micro-computed tomography. J Endod 35: 1056-9Perry SG (1883) Preparing and filling the roots of teeth. Dent Cosmos 25: 185-94Santos SMC, Soares JA, Costa GM, et al (2010) Radiographic parameters of quality root canal fillings and periapical status: a retrospective cohort study. J Endod 36: 1932-7
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There remains a growing belief among clinicians that obturation is to blame for endodontic failures. This notion has more recently fallen under scrutiny as researchers have discovered that the most thorough obturation can only reflect the quality of the cleaning and shaping of the canal. In fact, a number of researchers point to the thorough use of irrigants — making sure that the debris and irrigant itself are lifted completely out of the canal, not forced out the apex — as the most important determinant in the long-term success of an endodontic procedure.
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