Adhesive Endodontics By: Frederic Barnett, DMD and Martin Trope, DMD

Advances in adhesive dentistry have made great contributions to cosmetic and restorative dentistry over the past few decades. However, very little research has been performed in applying the principles of adhesive dentistry to the specialty of endodontics¹. The success rates of non-surgical root canal therapy, according to university and specialty-based studies have demonstrated a high degree of clinical success^2-3. However, population-based studies have revealed success rates in approximately 50% of cases^4-6. Therefore, the search for improvements in clinical technics and materials should be continued.

Complete obturation of the root canal system plays a large role in the prognosis of endodontic therapy. Ideally, obturation of the root canal system should entomb persisting microorganisms that remain within infected dentinal tubules or within fins, cul-de-sacs, etc. Additionally, the root filling should completely seal the canal system from re-infection from the oral cavity (coronal leakage) and from apical penetration of tissue fluid⁷. However, although gutta percha and conventional sealers have been considered the “gold standard” of endodontic obturation, these materials cannot be relied upon when there is coronal leakage^8-9. In fact, the quality of the coronal seal has been shown to be of significance relative to periradicular status of root filled teeth in several studies^10-11.

A new material, Resilon™ (RealSeal™, SybronEndo, Orange, CA, USA; Epiphany™, Pentron Clinical Technologies, Wallingford, CT, USA) has been developed to replace gutta percha and traditional sealers for root canal obturation (fig. 1). This system is comprised of:

1. Resilon Primer™: a self-etch primer, which contains a sulfonic acid-terminated functional monomer, HEMA, water and a polymerization initiator.

2. Resilon Sealer™: a dual curable, resin-based composite sealer. The resin matrix is comprised of BisGMA, ethoxylated BisGMA, UDMA, and hydrophilic difunctional methacrylates. It contains fillers of calcium hydroxide, barium sulphate, barium glass, bismuth oxychloride and silica. The total filler content is approximately 70% by weight.

3. Resilon™ core material: is a thermoplastic synthetic polymer-based (polyester) root canal core material that contains bioactive glass, bismuth oxychloride and barium sulphate. The fillers content is approximately 65% by weight. The Resilon core materials, similar to gutta percha cones, are available in ISO-sizes in .02, .04 and .06 tapers, as well in accessory sizes. Additionally, pellets of this material are available for use with the Obtura II (Obtura/Spartan, Fenton, MO, USA) delivery system.

These new materials have been shown to be biocompatible, non-cytotoxic and non-mutagenic, and have been approved for endodontic use by the FDA (USA).

Shipper et al.¹² evaluated in vitro the microbial leakage in roots filled with Resilon and Resilon Sealer using lateral and warm vertical condensation. These results were compared to gutta percha with AH-26 (DENTSPLY Maillefer Tulsa, Oklahoma, USA) sealer and gutta percha with Resilon Sealer. The results indicated all of the gutta percha groups had significantly (p<.005) more leakage (more teeth) and the leakage occurred at a faster rate than when the Resilon System was used.

These in vitro results were confirmed in an in vivo investigation by Shipper et al.¹³. A dog model was used to assess and compare the efficacy of gutta percha and AH-26 sealer versus the Resilon System in preventing apical periodontitis subsequent to coronal inoculation with oral microorganisms. The results demonstrated that periapical inflammation was observed in 82% (18 of 22) of roots filled with gutta percha + AH-26 versus 19% (4 of 21) for the Resilon System. This difference was statistically different, p<0.05). The Resilon “Monoblock” System was associated with significantly less periapical inflammation that may be due to its superior resistance to coronal leakage.

The excellent sealing ability of the Resilon System may be attributed to the so-called “mono-block” that is created by the adhesion of the Resilon Cone to the Resilon Sealer, which adheres and penetrates into the dentin walls and tubules of the root canal system ^{1, 12-13} (fig. 2). As previously mentioned, leakage of gutta percha and AH-26, as well as other traditional sealers, has been shown in the dental literature. Pommel et al.¹⁴, using a fluid filtration method to evaluate apical leakage, demonstrated no statistically significant difference between AH-26, Pulp Canal Sealer, and Ketac-Endo. Additionally, no correlation was found between the sealing efficiency of the four sealers and the adhesive properties recorded in a previous study. That indicated the adhesive properties of AH-26 did not contribute towards the prevention of leakage.

One of the potential disadvantages of endodontic treatment is the weakening of the root due to iatrogenic removal of excessive amounts of dentin during instrumentation. Additionally, when excessive forces are applied with some obturation techniques, root fracture may occur. Since Resilon is a bonded resin system it has the potential to strengthen the root. Teixeira et al.¹⁵, showed that root canals filled with the Resilon System were more resistant to fracture than roots filled with gutta percha and AH-26 sealer, indicating that the “monoblock” concept is not only important to resist bacterial penetration through the material but also to hold the root together.

All methods of root canal obturation may be used with the Resilon System. The following are the clinical steps for using the Resilon System following your routine “cleaning and shaping” protocols:

1) Smear Layer Removal: NaOCl should not be the last irrigant used within the root canal system due to compatibility issues with resins^16-17. Additionally, all peroxide-based lubricants must be completely rinsed form the root canal system. Rather, liquid EDTA, SmearClear (SybronEndo, Orange, CA, USA) or chlorhexidine liquid should be used as a final rinse or soak, for 1 minute. SmearClear™ contains surfactants that enhance the wetting of the canal walls and provide for optimal smear layer removal¹⁸.

2) Placement of the Resilon Primer: After the canal is dried with paper points, the self-etch Resilon Primer is placed into the root canal system to the working length, with paper points. Dry paper points are then used to wick out the excess primer from the canal.

3) Placement of the Resilon Sealer: Next, the dual sealer-containing syringe with the auto-mixing tip attached is used to express the sealer onto a mixing pad. The sealer can then be placed into the root canal system using a lentulo spiral, the PacMac™ (at low RPM) (SybronEndo, Orange, CA, USA) or by generously coating a paper point or the master cone.

4) Obturation: The root canal system is then obturated by your preferred method (lateral, warm vertical or PacMac). Resilon Pellets for the Obtura II delivery system are available for back-filling techniques.

5) Immediate cure: The Resilon Root Filling Material can be immediately cured with a halogen curing light for 40 seconds. The use of a curing light is not required, as the material will self cure within one hour.

6) Coronal restoration: A coronal temporary or permanent restoration should then be placed to properly seal the access cavity. The use of glass ionomer or composite resin to seal the floor of the pulp chamber should also be considered.

Radiographically, Resilon is highly radiopaque and handles well with both cold lateral condensation and heated root canal filling techniques (figs. 3-5). In fact, the clinician does not need to change their obturation technic as there is essentially no learning curve. This material has considerable flow as demonstrated by the filling of accessory anatomy. Additionally, no untoward post-operative pain has been reported by clinicians using the Resilon System, and some cases have demonstrated healing within a short period of time. Re-treatment of Resilon is easily accomplished with heat, chloroform or the use of hand and/or rotary files.

The aim of this paper was to present a new resin-based endodontic root filling material, the Resilon System. Despite the fact that gutta percha and sealer have been used for many years for root canal obturation, new materials and techniques have been developed, which may increase the potential for successful outcomes by creating a better interface between the root canal walls and filling materials thus decreasing bacterial leakage. Further studies are necessary to confirm its clinical performance to replace gutta percha and traditional sealers.

Frederic Barnett received his DMD degree in 1978 and his Certificate in Endodontics in 1981, both from the University of Pennsylvania, School of Dental Medicine. He received his Board Certification in Endodontics in 1986, has served as the Director of Postdoctoral Endodontics at Penn until 1990, and is currently an Associate Professor of Endodontics at Albert Einstein Medical Center in Philadelphia. Dr. Barnett also maintains a private practice limited to endodontics.

Dr. Barnett has written numerous scientific and clinical papers and has lectured nationally and internationally on Endodontic Infections, Treatment Resistant Apical Periodontitis, Dental Traumatology and Contemporary Endodontic Treatment. He currently serves on the Advisory Board of the Dental Traumatology journal and is the Endodontics Section editor of PPAD, Endodontic Therapy and Oral Health dental journals. Additionally, he is an Associate Editor of the Journal of Endodontics. Dr. Barnett can be reached on the Dentaltown.com message boards or at fredbarnett@hotmail.com.

Dr. Martin Trope is JB Freedland Professor in the Department of Endodontics at the University of North Carolina School of Dentistry. Named in honor of one of the founding fathers of Endodontics, the Freedland Professorship recognizes significant contributions to the specialty. A noted authority in his field, Dr. Trope has been actively involved in clinical research in all phases of endodontics.

Prior to coming to UNC, Dr. Trope was Chairman, Department of Endodontology, Temple University, Philadelphia, PA. He practiced in private practice in general dentistry from 1976 to 1978 and endodontics from 1978 to 1980 and from 1987 to 1989. He earned his BDS at the University of Witwatersrand, South Africa, and his DMD and certificate of Endodontics at the University of Pennsylvania.

Dr. Trope's major research interests include dental trauma, clinical outcomes, and new diagnostic tests for pulpal and periapical disease. His work has been published in numerous journals and book chapters. In April 2002 he was awarded "The Louis I. Grossman Award " for cumulative publication of significant research by the American Association of Endodontists. Dr. Trope receives royalties on the sales of Epiphany by Petron. Dr. Trope can be reached at tropem@DENTISTRY.UNC.EDU.

Bibliogrpahy:
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