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Bonding Comes to the Root Canal System Richard E. Mounce, DDS

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The Importance of Coronal Seal and the Limitations of Gutta Percha
Obturation and coronal seal, traditionally, have not been accorded the importance they deserve in comparison to cleaning and shaping procedures. Dogma and mythology such as “what you take out is more important than what you put in” has predominated endodontic thinking. While what you take out is important, what you put in, both into the canals and access cavity, is every bit as important.

Gutta percha (GP), while the time honored “gold standard” for endodontic obturation, has limitations. GP has maintained its utility over the decades since its introduction into dentistry because of its relative lack of toxicity, biocompatibility, and ability to be thermosoftened, economy and ready availability. It neither bonds to sealers nor to dentin. GP, in and of itself, does not provide a barrier to bacterial movement along the canal. Bacteria that challenge GP as a result of coronal leakage can and does migrate along its length unobstructed from crown to apex.

GP depends almost entirely on the presence of a coronal seal to prevent bacterial contamination, as GP, over the long term, forms no barrier to its apical migration. Clinically, there is a direct correlation in the endodontic literature between adequate post endodontic restoration and long-term clinical success. Adequate coronal seal increases clinical success.1-4

GP has also been shown to degrade in root canal systems when harvested from root canals, even those that have a coronal seal.5 GP leakage occurs via two pathways, between the sealer and canal wall and between the GP and the sealer. Even if the clinician is using a resin based sealer and clearing the smear layer, the avenue of leakage between the GP and the sealer is left open with GP. In addition, GP shrinks five to seven percent upon cooling when using warm GP obturation techniques.

Bonded Obturation: A New and Exciting Alternative to Gutta Percha
The landscape of endodontics changed forever in 2003 with the introduction of Resilon (Pentron) in 2003. SybronEndo licensed the use of Resilon at that time and marketed the same material with the name, RealSeal (RS).* SybronEndo bought Pentron in 2008 and the product is sold today exclusively as RS. In my full time endodontic practice, I have used only RS since January 2004.

RealSeal has been described as “a thermoplastic synthetic resin material based on the polymers of polyester and contains a difunctional methacrylate resin, bioactive glass and radio opaque fillers. RealSeal sealer contains UDMA, PEGDMA, EBPADMA and BisGMA resins, silane treated barium borosilicate glasses, barium sulfate, silica, calcium hydroxide, bismuth oxychloride with amines, peroxide, photo initiator, stabilizers and pigment. RealSeal Primer is an acidic monomer solution in water. RealSeal is non-toxic, FDA approved and non mutagenic. With its radio opaque fillers, RealSeal is a highly radio opaque material. The sealer is resorbable.” 6

RS is available in two forms, as master cones and in the form of RS1BO. RS master cones are trimmed, fit and used just as GP master cones are. RS master cones look, handle and are retreated exactly as GP master cones. RS1BO and RS act to fulfill the primary functions of a root canal obturation material:
  1. To stop or minimize the movement of periapical tissue fluids into the canal and/or the movement of bacteria from within the canal toward the apex.
  2. To act as a barrier to coronal microleakage and prevent secondary infection of the canal.
  3. To make the root stronger. There is evidence in the endodontic literature (although not conclusive) that RS strengthens roots and minimizes the risk of vertical root fracture.
RS has been tested extensively in the endodontic literature. The preponderance of findings in scientific refereed journals in in-vitro7-11 and in-vivo12-13 studies has shown RS to resist coronal leakage to a statistically significant degree greater than GP. Clinical case studies with limited recall periods published thus far have shown that RealSeal is better or equal to GP with regard to clinical success in the measure time periods, but no worse.14-15

In vitro, in the first study published on RS1BO, their sealing ability has been verified relative to warm carrier based GP techniques.16 Using a fluid filtration measuring technique, Testarelli, et. al., stated, “Statistical analysis showed a significant difference about the RS1 group, the Thermafil and One/Step group, while no significant differences were noted between these last two groups. Results show that the number of teeth that had no (=0) leakage was higher in the RS1 group (eight specimens) than in the remaining ones (1 and 1 specimen, respectively).” They further conclude that “under the conditions of the present experimental test, the new RS1 material (carrier-based Resilon) provided excellent preliminary results showing sealing ability at 24 hours significantly better than traditional carrier-based guttapercha systems.”

RealSeal has been proven biocompatible in the endodontic literature.17-19

Steps Common to Both RealSeal Master Cones and RealSeal 1 Bonded Obturators
1) The canal is prepared with the clinicians chosen canal enlargement technique. I use the Twisted File* (TF) due to its ability to shape canals to larger tapers with fewer insertions and files. The average mesial root of a lower molar is taken to a .08 TF taper to the apex. The average palatal root of an upper molar is taken to a .10 TF taper to the apex. TF is available in .04/25/40/50, .06/25/30/35, .08/25, .10/25 and .12/25 taper and tip sizes. The master apical diameter can be enhanced as desired using TF, making it a complete rotary nickel titanium system for any type of canal anatomy encountered.

2) Both RS master cones and RS1BO are used after the smear layer has been removed. A liquid EDTA solution such as SmearClear* is used as a rinse for approximately two minutes in the canal as the final irrigant. SmearClear can also be ultrasonically activated if desired. After the liquid EDTA rinse, the canal is rinsed with distilled water.

3) RS self-etching sealer is used for obturation. In both cases, a thin sealer film thickness is used. Sealer is not allowed to pool in the canal. Sealers other than the RS self-etching sealer are not recommended for use with RS obturation.

RealSeal Master Cone Technique
The simplest, most efficient and economical way to utilize master cones, irrespective of the obturation technique is to use one common master cone and trim it to fit the preparation’s master apical diameter. For me, that master cone is the .06/20 RS master cone. If for example, the master apical diameter is an ISO size #50. Trimming 5mm off of the end of a .06/20 RealSeal master cone provides a #50 size at the tip of the .06/20 master cone. The mathematics are simple, 2mm back from the tip of a .06/20 master cone the tip diameter is a 32, 4 mm back it is a 44 and 5mm back a #50 ISO tip diameter.

Tug back should be obtained before obturation. If the master cone resists vertical displacement both with and without sealer at the true working length, the canal is ready to obturate. Once tugback has been achieved with the master cone as per above, the canal can be obturated with either SystemB or vertical compaction.

Smaller tapered objects fit into larger tapered objects. With regard to cone fit, a .04, .06 tapered master cone fits easily inside a .08 TF preparation. When these master cones are down packed into the apical third of the canal, the tugback gained previously will keep the master cone from sliding beyond the minor constriction of the apical foramen. After down packing in a technique such as SystemB or vertical compaction, the coronal two thirds of the canal can be back filled with a device such as the Elements Obturation Unit (EOU).*

The guiding principles for clinicians who are using RS1BO are essentially the same as above for master cones. The RS1BO is .04 tapered and fits easily inside the larger taper of the .06 or .08 TF preparation. The difference in taper between the .04 RS1BO taper and the larger TF preparation taper, .08 for example, is filled by the RS material surrounding the obturator. As the RS1BO is inserted, the RS surrounding the obturator is moved with hydraulic vectors of force, apically and laterally, in essence filling the prepared canal space and all of the ramifications of the canal anatomy that have not been touched with RNT files.

The RS1BO system has:

  1. A .04-tapered obturators made of polysulfone that is surrounded by RS.
  2. #20-90 tip sizes.
  3. An oven that is custom designed with regard to heat and time for the various RS1BOs.
  4. A corresponding size verifier to tell the clinician the required RS1BO size that should be utilized. Before attempting to insert a given RS1BO, the clinician should find the size verifier that can be inserted to the true working length passively. The verifier that provides this ease of insertion is the correct RS1BO for the given canal.
  5. Size correlations to TF as follows: .06/25-30 TF: 25-30 RS1BO, .08/25 TF: 30-35 RS1BO, .10/25 TF: 35-40 RS1BO. Using the given TF instrument to the apex should result, after size verification in the listed RS1BO sizes listed here.
RS1BO have several characteristics that distinguish them from existing warm GP carrier based obturation products. These include:
  1. All RS1BO are dissolvable in GP solvents such as chloroform in all sizes.
  2. RS1BO can be shredded out of a canal at 900-1200 rpm with TF, although caution is advised. Removal of RS1BO should generally be performed passively with the .06 TF. After the removal of the bulk of the obturator, the tags of polysulfone that remain can often be removed with Hedstrom files or dissolved from the canal.
  3. The obturation is bonded throughout the entire obturation due to the chemical similarity of the self-etching sealer, RS core material and polysulfone obturator.
  4. RS1BO provides clinicians using cold obturation techniques a simple and efficient means to provide both a warm obturation as well as a bonded one. Warm obturation will move a heat-softened mass of RS into the narrowing cross sectional diameters of the prepared canal, in essence to thermally replicate the internal anatomy of the root. RS1BO are simple in concept and application. Clinicians who are using warm carrier based GP devices will be able to quickly adapt to RS1BO and yet provide a bonded obturation with its advantages.
RealSeal is physically absorbed onto the polysulfone surface of the RS1BO. RS1BO are injection molded improving the hydraulics of obturator placement. In essence, the obturator will predictably stay centered in the canal as it is inserted because the obturator begins the heating and insertion process in the center of the RealSeal.

FAQ
Can I cure RealSeal with a curing light?
Yes, although RealSeal sealer has a dual cure. The depth of cure will be several millimeters from the occlusal surface. The self-etching RealSeal sealer will self-cure in 40 to 60 minutes.

How do I know when to use a RS1BO or a master cone based RS technique?
Use of RS1BO or a master cone based form of RS is a matter of personal preference. This said, there are several considerations that might guide clinical decisions. For example, the greater the extent to which the apex is open, the less indication there would be for RS1BO. Specifically, if the apex was open to a 50 ISO or above (which is relatively large), different techniques such as custom fitting a master cone would become more clinically relevant. Use of RS1BO in an open apex will lead to unnecessary extrusion of sealer and obturation material. Fortunately, the vast majority of apices encountered in general practice are smaller, approximately ISO 35 and smaller.

How can I control extrusion of sealer and RealSeal at the apex with RS1BOs?
Extrusion can be minimized by:
  1. Precise apical control in preparation.
  2. Correct determination of true working length.
  3. Correct speed and depth of RS1BO insertion to the minor constriction of the apical foramen.
  4. Using the correct amount of sealer and having a thin sealer thickness before insertion.
The degree of extrusion in SystemB technique and with RS1BO is relatively similar.

How does the cost of RS1BO compare to GP master cones?
The endodontic literature is absolutely clear that coronal leakage is one mechanism of endodontic failure. Any steps that can be taken to diminish the degree of coronal leakage, be that in providing an excellent coronal seal or bonding the obturation, has a direct clinical value relative to the alternative offered by GP. Bonding makes the obturation functional relative to GP, a material that acts only as a space filler. Providing a seal from crown to apex (through placement of the coronal seal and bonded obturation) that minimizes or stops the movement of bacteria within a canal cannot be overstated in clinical significance.
Can I use my existing oven with RS1BO? Can I use different sealers with RS and RS1BO?
“No” to both questions. The working temperatures for RS are lower than for GP. The RS ovens operate at 175-180 degrees Celsius. The sealer is chemically compatible with the RS and RS1BO. These products are not designed to be used with other sealers.

Can RealSeal and RealSeal 1 be retreated?
RS is retreated in the same manner as GP using solvents, heat and mechanical means. RS1BO can be mechanically removed using TF at enhanced speeds, 900-1200 rpm. TF at these RPMs shred the obturator quite efficiently. It is noteworthy that the obturator is entirely soluble in chloroform making it simpler to retreat than warm GP alternatives.

What technique modifications are required to bond obturation?
The only required modification from existing GP techniques is the need to remove the smear layer detailed above. Using a self-etching sealer, with either RS master cones or RS1BO, the techniques are identical to those employed with GP.

How do I treat merging canals using RS1BO?
The straighter of the two canals is obturated first with RS1BO and then the second obturator is placed into the second orifice. The second obturator will not obviously advance as far apically as the first.

Does my canal preparation need to change to use RS1BO?
No, canal preparation is exactly the same using either RS master cones or RS1BO. I use either a trimmed .06/20 RS master cone with tug back to obturate the canal or a size verifier to determine which RS1BO is the correct size for the given preparation.

A clinically relevant review of bonded obturation with RealSeal in master cone form and RealSeal 1 Bonded Obturators has been presented. Emphasis has been placed on the clinical advantages of both bonding obturation and the efficiency that using a tandem of the Twisted File* and RealSeal* in both forms can provide the astute clinician. I welcome your comments and questions.

*SybronEndo, Orange, California

Dr. Mounce lectures globally and is widely published. He is in private practice in Endodontics in Vancouver, Washington.		 RealSeal 1 Bonded Obturator Clinical Technique

1) After the smear layer has been removed and the canal dried, the RealSeal self-etching sealer is applied. The smear layer is removed with a two-minute rinse of a liquid EDTA solution such as SmearClear.*

2) A size verifier is used to tell the clinician the ideal RS1BO size. The size verifier that fits passively to the apex is the correct ISO tip size RS1BO for insertion.

3) RS Sealer is applied in the canal. Sealer is not allowed to pool in the canal. It is applied and then dispersed to leave only a minimal film thickness.

4) The chosen RS1BO is placed into the RealSeal Oven* after the oven has been allowed to heat up for the appropriate time to be made ready to thermosoften the obturator.

5) Once the correct heating period takes place for the chosen RS1BO, the obturator is taken out of the oven and inserted into the prepared canal within six seconds. RS1BO should slide easily and passively to the true working length. It is advisable to practice in extracted teeth to gain fluency in canal preparation, use of the size verifiers and RS1BO insertion.

6) The excess portion (handle) of the RS1BO extending beyond the orifice can be removed either with heat or a bur. The Elements Obturation Unit* makes an excellent heat source for such removal.

7) Either using a heat source such as the EOU or any of the drills that accompany post kits makes post space.
Bibliography
  1. Lazarski, et al. Epidemiological evaluation of the outcomes of nonsurgical root canal treatment in a large cohort of insured dental patients. JOE 2001 Dec;27(12):791-6.
  2. Salehrabi R, et al Endodontic treatment outcomes in a large patient population in the USA: an epidemiological study. JOE 2004, Dec;30(12):846-50.
  3. Tilashalski, et al Root canal treatment in a population-based adult sample: status of teeth after endodontic treatment. JOE 2004, Aug;30(8):577-81.
  4. Aquilino, et al. Relationship between crown placement and the survival of endodontically treated teeth. JPD 2002, Mar;87(3):256-63.
  5. C. Maniglia-Ferreira, et al. Degradation of trans-polyisoprene over time following the analysis of root fillings removed during conventional retreatment. Int Endod J. 2007 Jan;40(1):25-30.
  6. Mounce RE, Glassman, G, Bonded Endodontic Obturation, Another Quantum Leap Forward for Endodontics, Oral Heath Canada, July 2004, p 13-22.
  7. Silveira, et al Negative influence of continuous wave technique on apical sealing of the root canal system with Resilon. J Oral Sci June 2007 Jun;49(2):121-8.
  8. Bodrumlu, et al Apical leakage of Resilon obturation material J Contemp Dent Pract. Sept 2006 2006 Sep 1;7(4):45-52.
  9. Tunga U, Bodrumlu E. Assessment of the sealing ability of a new root canal obturation material. J Endod. 2006 Sep;32(9):876-8. Epub 2006 May 6.
  10. Aptekar, et al Comparative analysis of microleakage and seal for 2 obturation materials: Resilon/Epiphany and gutta-percha. J Can Dent April 2006 Apr;72(3):245.
  11. Stratton, et al A fluid filtration comparison of gutta-percha versus Resilon, a new soft resin endodontic obturation system. J Endod. 2006 Jul;32(7):642-5.
  12. Leonardo MR, et al. Root canal adhesive filling in dogs’ teeth with or without coronal restoration: a histopathological evaluation. J Endod. 2007 Nov;33(11):1299-303. 1
  13. Shipper G, et al. Periapical inflammation after coronal microbial inoculation of dog roots filled with gutta-percha or resilon. J Endod. 2005 Feb;31(2):91-6.
  14. Two- and four-year outcome of biologically-based treatment protocol of endodontically treated teeth filled with Resilon. Prospective outcome of endodontic treatment performed in private practice by a single clinican using a standardized protocol with Resilon as the filling material; 2 and 4 year follow-up results. Debelian G. Oslo, Norway. In-manuscript.
  15. Cotton, TP, et al. A Retrospective Study Comparing Clinical Outcomes after Obturation with Resilon/Epiphany or Gutta-Percha/Kerr Sealer Volume 34, Issue 7, Pages 789-797 (July 2008)
  16. Testarelli L, et al. Sealing ability of a new carrier-based obturating material. Minerva Stomatol. 2009 May;58(5):217-22.
  17. Merdad, et al Short-term cytotoxicity assessment of components of the epiphany resin-percha obturating system by indirect and direct contact millipore filter assays. JOE January 2007 Jan;33(1):24-7.
  18. Onay, et al In vivo evaluation of the biocompatibility of a new resin-based obturation system. OOO July 2007 Sep;104(3):e60-6.
  19. Key, et al Cytotoxicity of a new root canal filling material on human gingival fibroblasts JOE August 2006 Aug;32(8):756-8.
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