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An In Vitro Comparison of the Intraradicular Dentin Bond Strength of Resilon and Gutta-Percha
Basic Research—Technology
An In Vitro Comparison of the Intraradicular Dentin Bond Strength of Resilon and Gutta-Percha Lance J. Skidmore, DDS, David W. Berzins, PhD, and James K. Bahcall, DMD, MS Abstract The purpose of this study was to compare the micropush-out bond strength of Resilon to that of guttapercha. Extracted human anterior teeth were used for evaluation. The crowns were removed and the root canals were instrumented with Gates Glidden drills and 0.06 Profile rotary files. Instrumentation was performed with 5.25% sodium hypochlorite irrigation and a final rinse of 17% EDTA. The teeth were randomly divided into two groups. Gutta-percha group: obturation with gutta-percha and Kerr Pulp Canal Sealer EWT. Resilon group: obturation with Resilon points, Epiphany Primer, and Root Canal Sealant. The teeth were cut perpendicular to their long axis to obtain a series of 1.0 mm thick disks (n ⫽ 15 per group). Micropush-out bond strengths to root canal dentin were measured. The results show that the mean bond strength to root canal dentin was significantly higher (p ⬍ 0.05) in the Resilon/Epiphany group as compared to the gutta-percha/ Kerr Pulp Canal Sealer EWT group. (J Endod 2006;32: 963–966)
Key Words Bond strength, Epiphany, micropush-out, Resilon
From the Department of Endodontics, Marquette University, School of Dentistry, Milwaukee, Wisconsin. Address requests for reprint to Dr. Lance J. Skidmore, Marquette University, School of Dentistry, Department of Endodontics, 1801 West Wisconsin Avenue, Room 245, Milwaukee, WI 53233. E-mail address: lance.skidmore@ marquette.edu. 0099-2399/$0 - see front matter Copyright © 2006 by the American Association of Endodontists. doi:10.1016/j.joen.2006.03.020
JOE — Volume 32, Number 10, October 2006
T
he principal objectives of endodontic therapy are to first chemomechanically clean and shape the root canal system, and second to completely obturate the canal system in three dimensions (1). Because bacteria and their byproducts have been shown to cause apical periodontitis and root canal failure (2– 4), the objective of three dimensional obturation is to completely seal the canal system from any bacterial ingress from the oral cavity and periradicular tissues. Additionally, the obturating materials seal within the canal system any irritants that are not removed during chemomechanical preparation. Gutta-percha and traditional sealers have been the most commonly used and accepted materials for the obturation of endodontically treated teeth. However, leakage and recontamination of the root-canal system continue to cause post treatment complications (5). Khayat et al. (6) examined the microbial leakage of extracted maxillary and mandibular molars and found that canals were completely contaminated on average within 28 days regardless of the gutta-percha obturation method. To minimize the likelihood of contamination, new materials and methods are continually developed to improve the seal of endodontic obturation. Resilon (Resilon Research LLC, Madison, CT) is a new material that has been introduced for the obturation of endodontically treated teeth. Resilon is a synthetic polycaprolactone polymer based on the polymers of polyester. This material contains dimethacylates and can bond to methacrylate-based resin sealers (7). Resilon points look and handle like gutta-percha, and when used with a self etch primer and a resin sealer, the manufacturer claims a bonded obturation between the intraradicular dentin and the root canal filling is formed. Several studies have evaluated this material (8 –12). Shipper et al. (8) used a split chamber microleakage test to compare the resistance to leakage of Resilon and Epiphany sealer to that of gutta-percha and AH26 sealer and found Resilon had significantly less leakage over 30 days. The results of Tay et al. (11) are in contrast to those of Shipper et al. (8). Tay et al. found that the quality of apical seal with Resilon was not superior to gutta-percha and a conventional epoxy-resin sealer when compared using a silver tracer penetration technique. Teixeira et al. (9) evaluated the fracture resistance of endodontically treated teeth filled with either gutta-percha or Resilon and found that the mean fracture loads of the gutta-percha groups were lower than the Resilon groups. However, the results of Gesi et al. (12) challenge the concept of the ability to increase fracture resistance of root canal treated teeth using Resilon, because their Resilon/ Epiphany group exhibited significantly lower interfacial strength compared with guttapercha/AH Plus group. One of the main claims of those advocating the use of Resilon is its ability to produce a bonded monoblock filling. This is created by the adhesion of the Resilon cone to the resin based sealer, which adheres to the dentinal wall and penetrates the dentinal tubules. Shipper et al. (10) referred to this bonded root canal filling as the Resilon “Monoblock” System (RMS). In their study, a dog model was used to compare the efficacy of gutta-percha and AH26 sealer versus RMS in preventing apical periodontitis after coronal microbial inoculation. The results showed the RMS was associated with significantly (p ⬍ 0.05) less periapical inflammation. An improved bond and the creation of a monoblock root canal obturation would be the main advantages of this new material. Therefore, the purpose of this study was to evaluate the bondability of this new material by comparing the micropush-out bond strength of Resilon/Epiphany filled teeth to that of teeth filled with gutta-percha and Kerr Pulp Canal Sealer EWT (Kerr Corporation, Orange, CA). The null hypothesis is that there
Comparing Bond Strength of Resilon and Gutta-Percha
963
Basic Research—Technology is no difference in the micropush-out bond strength of Resilon and gutta-percha based obturating systems.
Materials and Methods Twelve recently extracted human anterior teeth with straight roots were used in this study. The crowns were removed at the cementoenamel junction using a high-speed carbide bur with water coolant. A #15 K-type file was inserted until it could be seen at the apical foramen, and then 1 mm was subtracted from this to determine the working length. The root canals were instrumented with Gates Glidden burs and 0.06 Profile nickel-titanium rotary instruments (Dentsply Tulsa Dental, Tulsa, OK) to a size 40 file at working length. To remove the smear layer, instrumentation was performed with 5.25% sodium hypochlorite irrigation and a final rinse of 17% ethylene diamine tetra-acetic acid (EDTA) as per manufacturer’s instructions. Sodium hypochlorite was not used for final irrigation because it may negatively alter the bond of the sealer to the dentinal wall. The teeth were dried with paper points then randomly divided into two equal groups. Gutta-percha group: Obturation with gutta-percha and Kerr Pulp Canal Sealer EWT using a warm vertical compaction technique. Resilon group: Obturation with Resilon Points, Epiphany Primer, and Root Canal Sealant (Pentron Clinical Technologies, Wallingford, CT) using a warm vertical compaction technique. In the gutta-percha group, a #40 .06 tapered cone (Dentsply Tulsa Dental) was fit with tug back. The point was coated with Kerr Pulp Canal Sealer EWT (mixed according to manufacturer’s instructions) and introduced into the canal and pumped a few times. The cone was removed, re-coated with sealer, and inserted again to ensure adequate sealer coverage. A downpack and backfill were completed using a System B (System B, SybronEndo, Orange, CA) and Obtura II (Obtura Corp., Fenton, MO). In the Resilon group, the Epiphany self-etch primer was brought into the canal by the insertion of a saturated fitted paper point. This step was done two times to ensure adequate primer placement. Excess primer, if any, was removed with a dry paper point. The sealer was then expressed using the auto mix syringe tip. The fitted master cone was coated with the sealer and placed into the canal and pumped. The cone was removed, re-coated with sealer, and inserted again to ensure adequate sealer coverage. The downpack and backfill were then completed using the same technique as the gutta-percha group. All bonded samples were stored in 100% humidity for 24 h at 37°C. The samples were cut perpendicular to their long axis using an Isomet saw (Buehler Ltd., Lake Bluff, IL) with water lubrication. The samples in both groups were collected from the middle and coronal thirds of the canal. Because of the small size of the filling material in the apical 3 mm of the root, this portion was not evaluated using the micropush-out technique. If the sample contained filling material of a noncircular shape, it was discarded, as this would result in nonuniform stress distributions during testing and inaccurate measurements. Overall, this step produced a series of 1.0 mm thick disks (n ⫽ 15 per group) with seven and six of the 15 disks for the gutta-percha and Resilon groups, respectively, arising from the middle third of the teeth. The exact dimensions of each disk were measured with a digital caliper to within 0.01 mm. The filling material was loaded with a 0.76 mm diameter cylindrical stainless steel plunger that provided the most extended coverage over the filling material without touching the canal wall (Fig. 1). The teeth were marked as to ensure that the direction of the plunger push was in the apical to coronal direction, to avoid any interference owing to any root canal taper. Micropush-out bond strengths to root canal dentin were measured using a universal-testing machine 964
Skidmore et al.
Figure 1. Schematic representation of tooth sample preparation and micropush-out set-up used for testing the bond strength.
(Instron Corp., Norwood, MA) at a speed of 0.5 mm/min until bond failure occurred. The bond strength expressed in MPa at failure was calculated by dividing the load in Newtons by the area of the bonded interface. The area of the bonded interface was calculated with the formula, area ⫽ 2r ⫻ h, where is the constant 3.14 and r and h are the measured radius and height in millimeters of the filling material that was pushed out. The bond strength results were statistically evaluated using the Shapiro-Wilk test to determine whether the data were normally distributed. As the data were not normally distributed, the MannWhitney test was performed with statistical significance set at 95% (p ⬍ 0.05). For each group, bond strength data for the middle and coronal levels of the root were pooled as no difference (p ⬎ 0.10) was found between the different areas. After the measurement of bond strength, both sides of the failed bond were evaluated microscopically to determine modes of bond failure. Each sample was evaluated and placed into one of 3 failure modes: type I, adhesive failure, at sealer and dentin interface; type II, cohesive failure, within sealer or dentin; type III, mixed failure, failure in both the sealer and dentin. Four randomly selected intact and failed samples were prepared for scanning electron microscopy (SEM) evaluation. Each sample was sputter coated with gold (Hummer I, Technics Electron Microscopy Systems, Inc., Munich, Germany) and evaluated under SEM (JSM-35, Jeol Ltd. Tokyo, Japan) at magnifications ranging from 300 to 2000⫻.
Results The mean micropush-out bond strength of the Resilon group (1.51 ⫾ 1.22 MPa) was significantly higher (p ⬍ 0.05) than that of the gutta-percha group (0.66 ⫾ 0.39 MPa). Modes of failure are shown in Table 1. Inspection of the samples revealed the bond failure to be predominantly adhesive between the sealer and dentin interface for
JOE — Volume 32, Number 10, October 2006
Basic Research—Technology TABLE 1. Mean Micropush-Out Bond Strength Resilon Group
Gutta-Percha Group
1.51 ⫾ 1.22 MPa
0.66 ⫾ 0.39 MPa
both groups. SEM evaluation of intact samples revealed incomplete bond formation at the resin/dentin interface (Fig. 2) and empty dentinal tubules (Fig. 3) could be seen on the dentinal surface of the tested samples.
Discussion The results show that there is a significant difference between the Resilon and gutta-percha groups, and thus the null hypothesis is rejected. The results of this study should be viewed in conjunction with those of Gesi et al. (12). They found that the bond strength of the Resilon system was significantly lower than that of gutta-percha and an epoxyresin sealer. Other research has established that the bond strengths of zinc oxide eugenol based sealers, as used in this study, to dentin are lower than those of the polymer and epoxy based sealers (13). Therefore, the Resilon system may be viewed as having intermediate bond strengths compared to gutta-percha with other types of sealers commonly used. Although interstudy comparison of data may be problematic, it may be worth noting that the Resilon group had a mean bond strength of (0.50 ⫾ 0.41 MPa) in the Gesi et al. (12) study compared to (1.51 ⫾ 1.22 MPa) in this study, despite similar methodologies. A possible explanation for the differences and that may require further investigation, is that in their study, the coronal surface was light cured for 40 s. Light curing of a composite resin causes rapid polymerization and prevents stress relief by resin flow which has been shown to introduce interfacial stresses because of polymerization shrinkage (14, 15). They also included six premature failures in the calculation of the mean bond strength. Using the thin slice method of sample preparation, we had no premature failures in either the Resilon or gutta-percha groups.
Figure 2. Lower magnification view of an intact Resilon sample showing both complete bond formation (A) and lack of bonding (B).
JOE — Volume 32, Number 10, October 2006
Bond strength evaluations have become popular to determine the effectiveness of the adhesion of dental materials to root canal dentin. In this study, a micropush-out bond strength test was used. There is no generally accepted superior test for bond strength evaluation. Another test frequently used is the microtensile test (16, 17). However, in a preliminary study, the microtensile method produced an excessive amount of premature bond failures during the cutting phase of the sample preparation, and it was not found to be a reliable test method for this study. Similar difficulties were reported by Goracci et al. (18) when comparing microtensile and push-out bond strength measurements. It was then decided to use the micropush-out test to evaluate bond strength. Some have objected to the use of the push-out test due the possible nonuniform stress distribution (19). In this study, we sought to overcome this limitation by using thin-slice samples, only 1-mm thick. Using this method, it was possible to reliably produce a sample capable of bond strength evaluation. Sodium hypochlorite was not used as the final irrigation solution because several studies have shown that exposure to sodium hypochlorite results in reduced resin bond strengths (20, 21). It is believed that this occurs because sodium hypochlorite is an oxidizing agent that leads to the oxidation of some component of the dentin matrix. Oxygen also has been shown to inhibit the polymerization of resins (21). In this study, as part of the final rinse, dentin was treated with 17% EDTA to remove the smear layer and to provide better adhesion of the sealers to the root canal dentin. The removal of the smear layer permits the penetration of the sealer into the dentinal tubules, and has been shown to increase the dentin bond strength of resin based sealers and an enhanced seal (22, 23). However, in this study, SEM evaluation showed successful removal of smear layer (Fig. 3), but Resilon was still not able to form a complete monoblock bond in some areas. The finding that the Resilon-filled canals had more than two times the mean micropush-out bond strength of the gutta-percha group, suggests that, though it is a weak bond, there is bonding occurring. Specimen evaluation by SEM revealed gaps between the sealer and dentin in the Resilon-filled root canals (see Fig. 2). This point of weakness was also evidenced by the finding that 14 of 15 specimens experienced adhesive failure at the sealer-dentin interface (Table 2). This finding suggests that the weak link in Resilon-filled root canals lies at the sealerdentin interface, which is in agreement with others (11).
Figure 3. SEM image showing open dentinal tubules (arrow) of failed interface of Resilon group.
Comparing Bond Strength of Resilon and Gutta-Percha
965
Basic Research—Technology TABLE 2. Modes of bond failure Failure mode
Gutta-Percha group
Resilon group
I - Adhesive II - Cohesive III - Mixed Total samples
13 0 2 15
14 0 1 15
In conclusion, the Resilon/Epiphany filled root canals have significantly (p ⬍ 0.05) higher mean micropush-out bond strength to intraradicular dentin than that of gutta-percha and Pulp Canal Sealer EWT. However, SEM evaluation challenges the idea of producing a complete monoblock obturation without gaps. The clinical significance of these findings will require further in vivo evaluation.
Acknowledgments The authors wish to thank Jim Brozek for the drawing and Dr. Raymond A. Fournelle, Department of Mechanical and Industrial Engineering, Marquette University, for use of the SEM.
References 1. Schilder H. Filling root canals in three dimensions. Dent Clin North Am 1967; 1:723– 44. 2. Kakehashi S, Stanley HR, Fitzgerald RJ. The effects of surgical exposures of dental pulps in germ-free and conventional laboratory rats. Oral Surg Oral Med Oral Path 1965;20:340 –9. 3. Siqueira JF Jr. Aetiology of root canal treatment failure and why well-treated teeth can fail. Int Endod J 2001;34:1–10. 4. Lin LM, Skribner JE, Gaengler P. Factors associated with endodontic treatment failures. J Endod 1992;18:625–7. 5. Torabinejad M, Ung B, et al. In vitro bacterial penetration of coronally unsealed endodontically treated teeth. J Endod 1990;16:566 –9. 6. Khayat A, Lee SJ, Torabinejad M. Human saliva penetration of coronally unsealed obturated root canals. J Endod 1993;19:458 – 61.
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7. Jia WT, Alpert B. Root canal filling material. United States Patent & Trademark Office, United States Patent Application 20030113686, June 19, 2003. 8. Shipper G, Orstavik D, Teixeira FB, Trope M. An evaluation of microbial leakage in roots filled with a thermoplasitic synthetic polymer based root canal filling material (Resilon). J Endod 2004;30:342–7. 9. Teixeira FB, Teixeira ECN, Thompson JY, Trope M. Fracture resistance of roots endodontically treated with a new resin filling material. JADA 2004;135:646 –52. 10. Shipper G, Teixeira FB, Arnold R, Trope M. Periapical inflammation after coronal microbial inoculation of dog roots filled with gutta-percha or Resilon. J Endod 2005;31:91– 6. 11. Tay FR, Loushine R, Weller N, et al. Ultrastructural evaluation of the apical seal in roots filled with a polycaprolactone-based root canal filling material. J Endod 2005;31:514 –9. 12. Gesi A, Raffaelli O, Goracci C, Pashley DH, Tay FR, Ferrari M. Interfacial strength of Resilon and gutta-percha to intraradicular dentin. J Endod 2005;31:809 –13. 13. Lee KW, Williams BS, Camps JJ, Pashley DH. Adhesion of endodontic sealers to dentin and gutta-percha. J Endod 2002;28:684 – 8. 14. Alster D, Feilzer AJ, de Gee AJ, Davidson CL. Polymerization contraction stress in thin resin composite layers as a function of layer thickness. Dent Mater 1997;13:146 –50. 15. Ferracane JL. Developing a more complete understanding of stresses produced in dental composites during polymerization. Dent Mater 2005;21:36 – 42. 16. Erdemir A, Eldeniz AU, Belli S, Pashley DH. Effect of solvents on bonding to root canal dentin. J Endod 2004;30:589 –92. 17. Pashley DH, Carvalho RM, Sano H, et al. The microtensile bond test: a review. J Adhes Dent 1999;1:299 –309. 18. Goracci C, Tavares AU, Fabianelli A, et al. The adhesion between fiber posts and root canal walls: comparison between microtensile and push-out bond strength measurements. Eur J Oral Sci 2004;112:353– 61. 19. Sudsangiam S, Van Noort R. Do dentin bond strength tests serve a useful purpose? J Adhes Dent 1999;1:57– 67. 20. Morris MD, Lee KW, Agee KA, Bouillaguet S, Pashley DH. Effects of sodium hypochlorite and RC-Prep on bond strengths of resin cement to endodontic surfaces. J Endod 2001;27:753–7. 21. Ari H, Yasar E, Belli S. Effects of NaOCl on bond strengths of resin cements to root canal dentin. J Endod 2003;29:248 –51. 22. Eldeniz AU, Erdemir A, Belli S. Shear bond strength of three resin based sealers to dentin with and without the smear layer. J Endod 2005;31:293– 6. 23. Behrend GD, Cutler CW, Gutmann JL. An in-vitro study of smear layer removal and microbial leakage along root-canal fillings. Int Endod J 1996;29:99 –107.
JOE — Volume 32, Number 10, October 2006
An In Vitro Comparison of the Intraradicular Dentin Bond Strength of Resilon and Gutta-Percha Lance J. Skidmore, DDS, David W. Berzins, PhD, and James K. Bahcall, DMD, MS Abstract The purpose of this study was to compare the micropush-out bond strength of Resilon to that of guttapercha. Extracted human anterior teeth were used for evaluation. The crowns were removed and the root canals were instrumented with Gates Glidden drills and 0.06 Profile rotary files. Instrumentation was performed with 5.25% sodium hypochlorite irrigation and a final rinse of 17% EDTA. The teeth were randomly divided into two groups. Gutta-percha group: obturation with gutta-percha and Kerr Pulp Canal Sealer EWT. Resilon group: obturation with Resilon points, Epiphany Primer, and Root Canal Sealant. The teeth were cut perpendicular to their long axis to obtain a series of 1.0 mm thick disks (n ⫽ 15 per group). Micropush-out bond strengths to root canal dentin were measured. The results show that the mean bond strength to root canal dentin was significantly higher (p ⬍ 0.05) in the Resilon/Epiphany group as compared to the gutta-percha/ Kerr Pulp Canal Sealer EWT group. (J Endod 2006;32: 963–966)
Key Words Bond strength, Epiphany, micropush-out, Resilon
From the Department of Endodontics, Marquette University, School of Dentistry, Milwaukee, Wisconsin. Address requests for reprint to Dr. Lance J. Skidmore, Marquette University, School of Dentistry, Department of Endodontics, 1801 West Wisconsin Avenue, Room 245, Milwaukee, WI 53233. E-mail address: lance.skidmore@ marquette.edu. 0099-2399/$0 - see front matter Copyright © 2006 by the American Association of Endodontists. doi:10.1016/j.joen.2006.03.020
JOE — Volume 32, Number 10, October 2006
T
he principal objectives of endodontic therapy are to first chemomechanically clean and shape the root canal system, and second to completely obturate the canal system in three dimensions (1). Because bacteria and their byproducts have been shown to cause apical periodontitis and root canal failure (2– 4), the objective of three dimensional obturation is to completely seal the canal system from any bacterial ingress from the oral cavity and periradicular tissues. Additionally, the obturating materials seal within the canal system any irritants that are not removed during chemomechanical preparation. Gutta-percha and traditional sealers have been the most commonly used and accepted materials for the obturation of endodontically treated teeth. However, leakage and recontamination of the root-canal system continue to cause post treatment complications (5). Khayat et al. (6) examined the microbial leakage of extracted maxillary and mandibular molars and found that canals were completely contaminated on average within 28 days regardless of the gutta-percha obturation method. To minimize the likelihood of contamination, new materials and methods are continually developed to improve the seal of endodontic obturation. Resilon (Resilon Research LLC, Madison, CT) is a new material that has been introduced for the obturation of endodontically treated teeth. Resilon is a synthetic polycaprolactone polymer based on the polymers of polyester. This material contains dimethacylates and can bond to methacrylate-based resin sealers (7). Resilon points look and handle like gutta-percha, and when used with a self etch primer and a resin sealer, the manufacturer claims a bonded obturation between the intraradicular dentin and the root canal filling is formed. Several studies have evaluated this material (8 –12). Shipper et al. (8) used a split chamber microleakage test to compare the resistance to leakage of Resilon and Epiphany sealer to that of gutta-percha and AH26 sealer and found Resilon had significantly less leakage over 30 days. The results of Tay et al. (11) are in contrast to those of Shipper et al. (8). Tay et al. found that the quality of apical seal with Resilon was not superior to gutta-percha and a conventional epoxy-resin sealer when compared using a silver tracer penetration technique. Teixeira et al. (9) evaluated the fracture resistance of endodontically treated teeth filled with either gutta-percha or Resilon and found that the mean fracture loads of the gutta-percha groups were lower than the Resilon groups. However, the results of Gesi et al. (12) challenge the concept of the ability to increase fracture resistance of root canal treated teeth using Resilon, because their Resilon/ Epiphany group exhibited significantly lower interfacial strength compared with guttapercha/AH Plus group. One of the main claims of those advocating the use of Resilon is its ability to produce a bonded monoblock filling. This is created by the adhesion of the Resilon cone to the resin based sealer, which adheres to the dentinal wall and penetrates the dentinal tubules. Shipper et al. (10) referred to this bonded root canal filling as the Resilon “Monoblock” System (RMS). In their study, a dog model was used to compare the efficacy of gutta-percha and AH26 sealer versus RMS in preventing apical periodontitis after coronal microbial inoculation. The results showed the RMS was associated with significantly (p ⬍ 0.05) less periapical inflammation. An improved bond and the creation of a monoblock root canal obturation would be the main advantages of this new material. Therefore, the purpose of this study was to evaluate the bondability of this new material by comparing the micropush-out bond strength of Resilon/Epiphany filled teeth to that of teeth filled with gutta-percha and Kerr Pulp Canal Sealer EWT (Kerr Corporation, Orange, CA). The null hypothesis is that there
Comparing Bond Strength of Resilon and Gutta-Percha
963
Basic Research—Technology is no difference in the micropush-out bond strength of Resilon and gutta-percha based obturating systems.
Materials and Methods Twelve recently extracted human anterior teeth with straight roots were used in this study. The crowns were removed at the cementoenamel junction using a high-speed carbide bur with water coolant. A #15 K-type file was inserted until it could be seen at the apical foramen, and then 1 mm was subtracted from this to determine the working length. The root canals were instrumented with Gates Glidden burs and 0.06 Profile nickel-titanium rotary instruments (Dentsply Tulsa Dental, Tulsa, OK) to a size 40 file at working length. To remove the smear layer, instrumentation was performed with 5.25% sodium hypochlorite irrigation and a final rinse of 17% ethylene diamine tetra-acetic acid (EDTA) as per manufacturer’s instructions. Sodium hypochlorite was not used for final irrigation because it may negatively alter the bond of the sealer to the dentinal wall. The teeth were dried with paper points then randomly divided into two equal groups. Gutta-percha group: Obturation with gutta-percha and Kerr Pulp Canal Sealer EWT using a warm vertical compaction technique. Resilon group: Obturation with Resilon Points, Epiphany Primer, and Root Canal Sealant (Pentron Clinical Technologies, Wallingford, CT) using a warm vertical compaction technique. In the gutta-percha group, a #40 .06 tapered cone (Dentsply Tulsa Dental) was fit with tug back. The point was coated with Kerr Pulp Canal Sealer EWT (mixed according to manufacturer’s instructions) and introduced into the canal and pumped a few times. The cone was removed, re-coated with sealer, and inserted again to ensure adequate sealer coverage. A downpack and backfill were completed using a System B (System B, SybronEndo, Orange, CA) and Obtura II (Obtura Corp., Fenton, MO). In the Resilon group, the Epiphany self-etch primer was brought into the canal by the insertion of a saturated fitted paper point. This step was done two times to ensure adequate primer placement. Excess primer, if any, was removed with a dry paper point. The sealer was then expressed using the auto mix syringe tip. The fitted master cone was coated with the sealer and placed into the canal and pumped. The cone was removed, re-coated with sealer, and inserted again to ensure adequate sealer coverage. The downpack and backfill were then completed using the same technique as the gutta-percha group. All bonded samples were stored in 100% humidity for 24 h at 37°C. The samples were cut perpendicular to their long axis using an Isomet saw (Buehler Ltd., Lake Bluff, IL) with water lubrication. The samples in both groups were collected from the middle and coronal thirds of the canal. Because of the small size of the filling material in the apical 3 mm of the root, this portion was not evaluated using the micropush-out technique. If the sample contained filling material of a noncircular shape, it was discarded, as this would result in nonuniform stress distributions during testing and inaccurate measurements. Overall, this step produced a series of 1.0 mm thick disks (n ⫽ 15 per group) with seven and six of the 15 disks for the gutta-percha and Resilon groups, respectively, arising from the middle third of the teeth. The exact dimensions of each disk were measured with a digital caliper to within 0.01 mm. The filling material was loaded with a 0.76 mm diameter cylindrical stainless steel plunger that provided the most extended coverage over the filling material without touching the canal wall (Fig. 1). The teeth were marked as to ensure that the direction of the plunger push was in the apical to coronal direction, to avoid any interference owing to any root canal taper. Micropush-out bond strengths to root canal dentin were measured using a universal-testing machine 964
Skidmore et al.
Figure 1. Schematic representation of tooth sample preparation and micropush-out set-up used for testing the bond strength.
(Instron Corp., Norwood, MA) at a speed of 0.5 mm/min until bond failure occurred. The bond strength expressed in MPa at failure was calculated by dividing the load in Newtons by the area of the bonded interface. The area of the bonded interface was calculated with the formula, area ⫽ 2r ⫻ h, where is the constant 3.14 and r and h are the measured radius and height in millimeters of the filling material that was pushed out. The bond strength results were statistically evaluated using the Shapiro-Wilk test to determine whether the data were normally distributed. As the data were not normally distributed, the MannWhitney test was performed with statistical significance set at 95% (p ⬍ 0.05). For each group, bond strength data for the middle and coronal levels of the root were pooled as no difference (p ⬎ 0.10) was found between the different areas. After the measurement of bond strength, both sides of the failed bond were evaluated microscopically to determine modes of bond failure. Each sample was evaluated and placed into one of 3 failure modes: type I, adhesive failure, at sealer and dentin interface; type II, cohesive failure, within sealer or dentin; type III, mixed failure, failure in both the sealer and dentin. Four randomly selected intact and failed samples were prepared for scanning electron microscopy (SEM) evaluation. Each sample was sputter coated with gold (Hummer I, Technics Electron Microscopy Systems, Inc., Munich, Germany) and evaluated under SEM (JSM-35, Jeol Ltd. Tokyo, Japan) at magnifications ranging from 300 to 2000⫻.
Results The mean micropush-out bond strength of the Resilon group (1.51 ⫾ 1.22 MPa) was significantly higher (p ⬍ 0.05) than that of the gutta-percha group (0.66 ⫾ 0.39 MPa). Modes of failure are shown in Table 1. Inspection of the samples revealed the bond failure to be predominantly adhesive between the sealer and dentin interface for
JOE — Volume 32, Number 10, October 2006
Basic Research—Technology TABLE 1. Mean Micropush-Out Bond Strength Resilon Group
Gutta-Percha Group
1.51 ⫾ 1.22 MPa
0.66 ⫾ 0.39 MPa
both groups. SEM evaluation of intact samples revealed incomplete bond formation at the resin/dentin interface (Fig. 2) and empty dentinal tubules (Fig. 3) could be seen on the dentinal surface of the tested samples.
Discussion The results show that there is a significant difference between the Resilon and gutta-percha groups, and thus the null hypothesis is rejected. The results of this study should be viewed in conjunction with those of Gesi et al. (12). They found that the bond strength of the Resilon system was significantly lower than that of gutta-percha and an epoxyresin sealer. Other research has established that the bond strengths of zinc oxide eugenol based sealers, as used in this study, to dentin are lower than those of the polymer and epoxy based sealers (13). Therefore, the Resilon system may be viewed as having intermediate bond strengths compared to gutta-percha with other types of sealers commonly used. Although interstudy comparison of data may be problematic, it may be worth noting that the Resilon group had a mean bond strength of (0.50 ⫾ 0.41 MPa) in the Gesi et al. (12) study compared to (1.51 ⫾ 1.22 MPa) in this study, despite similar methodologies. A possible explanation for the differences and that may require further investigation, is that in their study, the coronal surface was light cured for 40 s. Light curing of a composite resin causes rapid polymerization and prevents stress relief by resin flow which has been shown to introduce interfacial stresses because of polymerization shrinkage (14, 15). They also included six premature failures in the calculation of the mean bond strength. Using the thin slice method of sample preparation, we had no premature failures in either the Resilon or gutta-percha groups.
Figure 2. Lower magnification view of an intact Resilon sample showing both complete bond formation (A) and lack of bonding (B).
JOE — Volume 32, Number 10, October 2006
Bond strength evaluations have become popular to determine the effectiveness of the adhesion of dental materials to root canal dentin. In this study, a micropush-out bond strength test was used. There is no generally accepted superior test for bond strength evaluation. Another test frequently used is the microtensile test (16, 17). However, in a preliminary study, the microtensile method produced an excessive amount of premature bond failures during the cutting phase of the sample preparation, and it was not found to be a reliable test method for this study. Similar difficulties were reported by Goracci et al. (18) when comparing microtensile and push-out bond strength measurements. It was then decided to use the micropush-out test to evaluate bond strength. Some have objected to the use of the push-out test due the possible nonuniform stress distribution (19). In this study, we sought to overcome this limitation by using thin-slice samples, only 1-mm thick. Using this method, it was possible to reliably produce a sample capable of bond strength evaluation. Sodium hypochlorite was not used as the final irrigation solution because several studies have shown that exposure to sodium hypochlorite results in reduced resin bond strengths (20, 21). It is believed that this occurs because sodium hypochlorite is an oxidizing agent that leads to the oxidation of some component of the dentin matrix. Oxygen also has been shown to inhibit the polymerization of resins (21). In this study, as part of the final rinse, dentin was treated with 17% EDTA to remove the smear layer and to provide better adhesion of the sealers to the root canal dentin. The removal of the smear layer permits the penetration of the sealer into the dentinal tubules, and has been shown to increase the dentin bond strength of resin based sealers and an enhanced seal (22, 23). However, in this study, SEM evaluation showed successful removal of smear layer (Fig. 3), but Resilon was still not able to form a complete monoblock bond in some areas. The finding that the Resilon-filled canals had more than two times the mean micropush-out bond strength of the gutta-percha group, suggests that, though it is a weak bond, there is bonding occurring. Specimen evaluation by SEM revealed gaps between the sealer and dentin in the Resilon-filled root canals (see Fig. 2). This point of weakness was also evidenced by the finding that 14 of 15 specimens experienced adhesive failure at the sealer-dentin interface (Table 2). This finding suggests that the weak link in Resilon-filled root canals lies at the sealerdentin interface, which is in agreement with others (11).
Figure 3. SEM image showing open dentinal tubules (arrow) of failed interface of Resilon group.
Comparing Bond Strength of Resilon and Gutta-Percha
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Basic Research—Technology TABLE 2. Modes of bond failure Failure mode
Gutta-Percha group
Resilon group
I - Adhesive II - Cohesive III - Mixed Total samples
13 0 2 15
14 0 1 15
In conclusion, the Resilon/Epiphany filled root canals have significantly (p ⬍ 0.05) higher mean micropush-out bond strength to intraradicular dentin than that of gutta-percha and Pulp Canal Sealer EWT. However, SEM evaluation challenges the idea of producing a complete monoblock obturation without gaps. The clinical significance of these findings will require further in vivo evaluation.
Acknowledgments The authors wish to thank Jim Brozek for the drawing and Dr. Raymond A. Fournelle, Department of Mechanical and Industrial Engineering, Marquette University, for use of the SEM.
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7. Jia WT, Alpert B. Root canal filling material. United States Patent & Trademark Office, United States Patent Application 20030113686, June 19, 2003. 8. Shipper G, Orstavik D, Teixeira FB, Trope M. An evaluation of microbial leakage in roots filled with a thermoplasitic synthetic polymer based root canal filling material (Resilon). J Endod 2004;30:342–7. 9. Teixeira FB, Teixeira ECN, Thompson JY, Trope M. Fracture resistance of roots endodontically treated with a new resin filling material. JADA 2004;135:646 –52. 10. Shipper G, Teixeira FB, Arnold R, Trope M. Periapical inflammation after coronal microbial inoculation of dog roots filled with gutta-percha or Resilon. J Endod 2005;31:91– 6. 11. Tay FR, Loushine R, Weller N, et al. Ultrastructural evaluation of the apical seal in roots filled with a polycaprolactone-based root canal filling material. J Endod 2005;31:514 –9. 12. Gesi A, Raffaelli O, Goracci C, Pashley DH, Tay FR, Ferrari M. Interfacial strength of Resilon and gutta-percha to intraradicular dentin. J Endod 2005;31:809 –13. 13. Lee KW, Williams BS, Camps JJ, Pashley DH. Adhesion of endodontic sealers to dentin and gutta-percha. J Endod 2002;28:684 – 8. 14. Alster D, Feilzer AJ, de Gee AJ, Davidson CL. Polymerization contraction stress in thin resin composite layers as a function of layer thickness. Dent Mater 1997;13:146 –50. 15. Ferracane JL. Developing a more complete understanding of stresses produced in dental composites during polymerization. Dent Mater 2005;21:36 – 42. 16. Erdemir A, Eldeniz AU, Belli S, Pashley DH. Effect of solvents on bonding to root canal dentin. J Endod 2004;30:589 –92. 17. Pashley DH, Carvalho RM, Sano H, et al. The microtensile bond test: a review. J Adhes Dent 1999;1:299 –309. 18. Goracci C, Tavares AU, Fabianelli A, et al. The adhesion between fiber posts and root canal walls: comparison between microtensile and push-out bond strength measurements. Eur J Oral Sci 2004;112:353– 61. 19. Sudsangiam S, Van Noort R. Do dentin bond strength tests serve a useful purpose? J Adhes Dent 1999;1:57– 67. 20. Morris MD, Lee KW, Agee KA, Bouillaguet S, Pashley DH. Effects of sodium hypochlorite and RC-Prep on bond strengths of resin cement to endodontic surfaces. J Endod 2001;27:753–7. 21. Ari H, Yasar E, Belli S. Effects of NaOCl on bond strengths of resin cements to root canal dentin. J Endod 2003;29:248 –51. 22. Eldeniz AU, Erdemir A, Belli S. Shear bond strength of three resin based sealers to dentin with and without the smear layer. J Endod 2005;31:293– 6. 23. Behrend GD, Cutler CW, Gutmann JL. An in-vitro study of smear layer removal and microbial leakage along root-canal fillings. Int Endod J 1996;29:99 –107.
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