An evaluation of the sealing ability of a polycaprolactone-based root canal filling material (Resilon) after retreatment

An evaluation of the sealing ability of a polycaprolactone-based root canal filling material (Resilon) after retreatment

An evaluation of the sealing ability of a polycaprolactone-based root canal filling material (Resilon) after retreatment Zheng-Mei Lin, DDS, PhD,a Ash...

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An evaluation of the sealing ability of a polycaprolactone-based root canal filling material (Resilon) after retreatment Zheng-Mei Lin, DDS, PhD,a Ashroy Jhugroo, BDS, DDS,b and Jun-Qi Ling, DDS, MD, PhD,c Guangzhou, China DEPARTMENT OF ENDODONTICS AND CONSERVATIVE DENTISTRY, GUANGHUA COLLEGE OF STOMATOLOGY, SUN YAT-SEN UNIVERSITY

Objective. The aim of this study was to evaluate the sealing ability of Resilon after retreatment. Study design. Sixty-six single-rooted mandibular premolars were enlarged to apical size 45 and then obturated with Resilon. The roots were randomly divided into 3 groups (n ⫽ 22/group). In group 1 no further treatment was done. Groups 2 and 3 were reinstrumented to apical size 60 using K-files and ProFile, respectively. In each group, 4 samples were kept for environmental scanning electron microscopy (ESEM) analysis. The remaining roots from groups 2 and 3 were refilled with Resilon. Sixteen roots from each group were then evaluated for microleakage; two roots served as controls. Data were analyzed statistically by Kruskall-Wallis test. Results. There were no significant differences between the experimental groups (P ⬎ .05). The ESEM showed new attachment of resin tags on the dentin surface of retreated roots. Conclusion. Resilon can be used for retreatment, but it still allowed microleakage. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2007;104:846-51)

During the past few decades the number of patients seeking nonsurgical endodontic retreatment has increased considerably. Teeth with inadequate obturation, unfilled root canals, or underextended root fillings may require retreatment before coronal restoration.1 The main goal of orthograde retreatment is regaining access to the apical foramen by complete removal of the root canal filling material, thus facilitating sufficient cleaning and shaping of the complete root canal system and final obturation.2 Recently, a new thermoplastic synthetic polymer– based root canal filling material, Resilon (RealSeal; SybronEndo, Orange, CA), has been developed to perform like gutta-percha with the same handling properties. For retreatment purposes, it may be softened with heat or dissolved with a solvent such as chloroform. Based on polymers of polyester, Resilon contains bioactive glass, bismuth oxychloride, and barium sulphate.3 It is supplied in varying tapers and as pellets for heated obturation methods. A primer is used for conditioning of the dentinal wall surface of the canal. A dual-curing resin sealer that bonds to the primer and the soft resin filling material creates a secondary monoblock system.4 a

Associate Professor. Resident. c Dean and Head of Department. Received for publication Mar 6, 2007; returned for revision Apr 28, 2007; accepted for publication May 15, 2007. 1079-2104/$ - see front matter © 2007 Mosby, Inc. All rights reserved. doi:10.1016/j.tripleo.2007.05.020 b

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The most commonly used root filling material is gutta-percha in combination with a sealer. Many materials have been assessed as root canal fillings. However, none fulfills all the requirements for an ideal material. Resilon may have properties superior to gutta-percha,3,5-11 but not much is known about its capacity to undergo retreatment. For Resilon to be considered as a superior root filling material, it is essential that it be easily removed from the root canal and retains its bonding capacity to the canal wall and the core resin material during retreatment. Recently published articles have suggested that Resilon, along with its sealer, were removed more effectively than gutta-percha and AH Plus sealer.7,11 To date, there has been no publication evaluating the sealing capacity of Resilon after retreatment. The aims of the present study were to compare the in vitro microleakage of root canal fillings and to analyze the extent of resin tags formation at the resin-dentin interface by environmental scanning electron microscopy (ESEM) before and after retreatment with Resilon. MATERIALS AND METHODS A total of 66 single-rooted mandibular premolars were selected and stored for less than 1 month in 0.02% sodium azide containing isotonic saline (0.9% NaCl). All teeth were examined under a microscope for root fractures and cracks. The crowns were removed at the cementoenamel junction by means of a diamond saw (Isomet; Buehler, Lake Bluff, IL). The length was

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determined by inserting a size #15 Flex-o-file (Dentsply Maillefer, Tulsa, OK) into the root canal until it was visible at the apex. The working length was established by subtracting 1 mm from the real length. The initial apical size of the each tooth was gauged by identifying the first instrument that fitted snugly at the working length. Those that had apical root canal diameters more than ISO size #25 were rejected. The roots were then instrumented in a crown-down fashion with ProFile nickel-titanium rotary instruments with 0.04 taper (Dentsply Maillefer). The apical third was prepared with a ProFile hand instrument up to size #45, 0.04 taper (Dentsply Maillefer). The patency of the canals was maintained with ISO size #15 Flex-o-files. Each root canal was irrigated with 10 mL 1.25% sodium hypochlorite followed by 5 mL 17% EDTA. Repeated recapitulations were made to keep the canals patent. After final instrumentation all teeth received a final irrigation of 15 mL 1.25% sodium hypochlorite and 5 mL EDTA. The canals were then flushed with 10 mL sterile water to remove any remaining sodium hypochlorite (per the instructions of the manufacturer). When all the teeth were dried with paper points, the self-etching RealSeal Primer was introduced into the canals to working length with the microbrush supplied by the manufacturer. Excess primer was removed with dry paper points. Then the dual sealer was spread into the canal walls with a lentulo spiral at low rpm. A master cone, size #45, 0.02 taper RealSeal point, was fitted to working length with the use of a spreader, and the medium-fine accessory cones coated in resin sealer were used for lateral condensation. Excess material was removed and condensation accomplished with a plugger. Regardless of the tooth length, the root canal fillings were limited to 15 mm so that the volume of Resilon filling was uniform in each tooth. After the procedure, the coronal portion of the obturation was light cured for 40 seconds (3M curing light 2500; ESPE Dental Products, St. Paul, MN), and radiographs were taken to verify the quality and apical extent of the root fillings. The teeth were randomly divided into 3 groups, and the samples were kept at 100% humidity for 1 month. Experimental groups Group 1: Original Resilon obturation. The first group consisted of 22 roots of teeth filled with Resilon. Of these, 16 were selected for microleakage evaluation and 4 for ESEM analysis; the remaining 2 served as controls. Group 2: Reinstrumentation with a K-file and chloroform and refilling with Resilon. The original Resilon filling material was removed from each of the roots (n ⫽ 22) with a K-file and chloroform totaling 1.0 mL.

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The coronal portions of the canals were filled with chloroform and a size #15 K-type file (Dentsply Maillefer) was used to remove the softened material, thus creating a larger space for chloroform. This process proceeded until sufficient space was available for use of larger-size files. With the serial use of larger files, the chemically softened Resilon in the apical portion of the root filling was reached. Removal of the Resilon was considered to be complete when no material was evident on the files. The roots were then instrumented up to a size #60 K-file to remove all residual Resilon sealer or filling materials that might have remained in the irregularities of the canal walls. Two roots were selected at this stage for ESEM evaluation. The root canals were then refilled with Resilon following the initial procedure. All the samples were kept in 100% humidity for 1 month. Two roots were then selected at this stage for ESEM evaluation, 2 roots served as controls, and the remaining 16 roots were used for the microleakage test. Group 3: Reinstrumentation with ProFile 0.04 taper Ni-Ti rotary instruments and chloroform and refilling with Resilon. Removal of Resilon from the roots (n ⫽ 22) was conducted using crown-down technique with ProFile 0.04 taper Ni-Ti rotary instruments (Dentsply Maillefer). The coronal part was removed with a size #40 file to allow for the creation of the reservoir for the chloroform. A total of 1.0 mL chloroform was used in each tooth. By decreasing sequentially to size #35, size #30, and size #25 files, the full working length of canal could be instrumented. The files were cleaned each time before being reintroduced in the canal. One series of ProFile instruments was used for this group. A final instrumentation size #60, 0.04 taper ProFile was used to remove any material potentially remaining on the canal wall. Two samples were selected for ESEM analysis. The remaining roots were then refilled with Resilon following the initial procedure and were kept at 100% humidity for 1 month. Two roots were then selected for ESEM evaluation, 2 roots served as controls, and the remaining 16 roots were used for the microleakage test. Control group. The control group consisted of 6 roots obtained from the 3 experimental groups. They were sealed with layers of nail varnish covering the root canal orifices, as well as the apical foramen, and evaluated for microleakage. Regardless of the tooth length, the root canal fillings were limited to 15 mm so that the volume of Resilon filling was uniform in each of the teeth. All teeth were prepared and retreated by the same experienced operator. The roots of the experimental groups were also covered with sticky wax, except for the canal orifices and the apical 2 mm.

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with a glucose kit (Diasys, Shanghai, China) in a UVVis recording spectrophotometer (Schimadzu, Kyoto, Japan). Differences between the means of each group were analyzed using the Kruskall-Wallis test for analysis of variance. When the difference of leakage in term of glucose concentration among groups was significant, further comparisons by use of the Nemenyi test were performed.

Fig. 1. Model used to assess microleakage.

Description of the leakage model The device for evaluating leakage was based on the filtration of glucose along the root canal filling, as described by Xu et al.12 The device was composed of 2 parts (Fig. 1). The lower part consisted of an Eppendorf vial in which a small hole had been prepared to receive the coronal portion of the root. The tooth was inserted into the vial in such a way that half of it protruded through the vial. A hole was made in the cap of the vial to accommodate a 15-mm-long plastic tube. All junctions in the model were sealed with cyanoacrylate and sticky wax and ensured to be airtight by means of compressed air forced from the opened end of the tube. The vial and the plastic tube were filled with 5 mL of 1 mol/L glucose solution maintained at a pH of 7.0 and density of 1.09 ⫻ 103 g/L. The solution also contained 0.01% NaN3 to inhibit the growth of microorganisms. The assembly was then placed in a small sterile glass bottle so that at least 2 mm of the tip of the root was immersed in 1 mL of distilled water. The preparations were maintained in an incubator at a constant temperature of 37°C and 100% humidity. From each glass vial, 10 ␮L of the solution was removed on the 1st, 3rd, 4th, 7th, 10th, 15th, 20th, and 30th days. Then 10 ␮L distilled water was added into the bottle so that a constant volume of 1.0 mL of solution was maintained. The samples were analyzed

ESEM The specimens selected from groups 1, 2, and 3 were analyzed by use of the Philips XL 30 ESEM (Eindhoven, The Netherlands). Using a slow-speed saw (Isomet) under water cooling, each specimen was cut longitudinally into 2 parts. One part was examined under ESEM without prior decalcification. The other part had its exposed dentin-filling interface polished with 1200-grit silicon carbide paper and brought into relief by etching with 10% phosphoric acid for 15 seconds followed by deproteinization in 5% sodium hypochlorite for 10 minutes, as described by Tay et al.13 The specimens were examined wet and uncoated for penetration of resin into the dentinal tubules and for presence of gaps in the resin-dentin interface. Most of the ESEM images were taken in the apical regions of the samples, because these were the most inaccessible regions for instrumentation, irrigation, and sealer application and were most likely to show differences in sealing. RESULTS All of the samples from each of the experimental groups (1, 2, and 3) leaked from the first day of the experiment. The leakage gradually increased with time. The control (nail varnish) teeth showed no leakage. Comparison of groups by the Kruskall-Wallis test showed no significant differences between the reinstrumentation/refilling groups and the original Resilon group (P ⬎ .05). The Nemenyi test also indicated that there were no significant differences among the experimental groups (P ⬎ .05). The mean microleakage values from the different groups are summarized in Table I and Fig. 2. A low-magnification view of specimens from group 1 (no reinstrumentation/refill) showed intimate contact between the Resilon, the sealer, and the dentinal wall (Fig. 3, A). A decalcified sample from group 1 revealed that long and uniform resin tags with lateral branches were evident upon higher magnification (Fig. 3, B). Resilon and sealer clearly appeared to bind together, with resin tags penetrating the dentin. The presence of Resilon/sealer deep within the dentinal tubules in roots was also observed in samples from groups 2 and 3 (Fig. 3, C). Refilled samples clearly showed the presence of

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Table I. Mean microleakage values from the different experimental groups

Time (days) 1 2 3 4 7 10 15 20 30

Original Resilon

Reinstrumentation with K-file and refilling with Resilon

Resinstrumentation with ProFile and refilling with Resilon

0.05 ⫾ 0.07 0.11 ⫾ 0.08 0.26 ⫾ 0.10 0.36 ⫾ 0.14 0.64 ⫾ 0.13 0.84 ⫾ 0.19 1.56 ⫾ 0.31 2.03 ⫾ 0.52 3.60 ⫾ 0.77

0.07 ⫾ 0.08 0.15 ⫾ 0.09 0.30 ⫾ 0.16 0.42 ⫾ 0.11 0.72 ⫾ 0.19 0.90 ⫾ 0.71 1.72 ⫾ 0.33 2.63 ⫾ 0.78 4.01 ⫾ 1.09

0.06 ⫾ 0.07 0.12 ⫾ 0.10 0.27 ⫾ 0.27 0.38 ⫾ 0.23 0.68 ⫾ 0.21 0.84 ⫾ 0.32 1.66 ⫾ 0.54 2.38 ⫾ 0.66 3.95 ⫾ 0.89

new microtags deep within the dentinal tubules (Fig. 3, D and E). Gap-containing regions were not seen in the ESEM images from any of the different experimental groups. This suggests that roots subjected to instrumentation and refill form seals similar to those formed during the preliminary root canal filling. DISCUSSION The superior sealing capacity of Resilon may be attributed to the adhesion of the Resilon cone/sealer into the dentin walls and tubules of the root canal system. While this property of Resilon indicates that it can be used for primary root canals, it was previously unknown whether this material would form an effective seal in retreated teeth. Leakage tests are an accepted method for comparing the seal formed by filling materials, although a universally accepted procedure does not exist.14 Glucose was used as the tracer because of its size and physicochemical properties. It is sensitive and nondestructive and can be used repeatedly.12 However, a glucose solution without any preservative presents a risk of contamination by bacteria and subsequent decomposition of the glucose. Xu et al.12 used the glucose solution containing 0.2% NaN3 in their microleakage model. At this concentration, however, the glucose solution was alkaline (pH 7.83). Preliminary tests were performed to determine the concentration of NaN3 most suitable for the present experiment. Small disks of the core material and sealer were prepared and placed in glucose solutions containing different concentrations of NaN3 for 30 days. With a concentration of 0.01% NaN3, there was only slight degradation of the Resilon core material (⬍0.1% of its weight) and bacterial growth could be prevented. The pH value of the solution was essentially neutral (pH 6.96). Because of possible degradation of the Resilon in an alkaline medium, a concentration of

0.01% of NaN3 was preferred.15 This was in accordance with ISO standard 6876:2001(E). Similar to previous studies,3,6,8-10 Resilon-filled roots demonstrated leakage. Removal of Resilon from the specimens in the retreatment groups and enlargement of the apical diameter of all the roots in the experimental groups to ISO size #60 ensured that almost all existing root fillings were removed. The method for removal of the filling material from the root canals did not appear to affect the extent of the leakage, because the rates for the 2 retreatment groups were essentially the same. There were no statistical differences between the groups. However, there was a continuous and increasing leakage in all of the experimental groups during the 30 days experimental period. A consistent hermetic seal was not achieved when roots were filled or refilled with Resilon using this microleakage model. Apart from possible reasons such as naturally occurring irregularities, root canal spaces that were untouched during chemomechanical preparation, apical deltas, and variability of the thickness of the sealer during obturation, microleakage could be explained by the high solubility and dimensional changes of the sealer.16 Polymerization shrinkage may also be responsible for possible formation of gaps leading to increasing apical leakage, even though we could not clearly identify these gaps in the ESEM images.17 Environmental scanning electron microscopy allows the examination of fully hydrated specimens in their natural state with no prior specimen preparation. This procedure eliminates artifacts caused by vacuum desiccation during conventional SEM.13 The ESEM images of the sections confirmed the creation of a new resin sealer bonding/tag layer after retreatment. The resin tags were well extended into the dentinal wall, and new resin tags meshed with remnants could be seen. This indicates that Resilon is able to penetrate the dentin after reinstrumentation to form a seal, as seen in specimens from group 1. For reinstrumentation and complete Resilon material removal in groups 2 and 3, the apical third was prepared to ISO size #60. This is 2 sizes larger than that used for initial instrumentation of the roots. Masiero and Barietta18 enlarged the apical sizes of mandibular premolars by only 0.05 mm during retreatment. Removal of condensed Resilon from the dentinal walls with hand files was more time consuming and difficult than with rotary instruments. With both methods, there were areas on the dentinal surface where the removal of the material was not complete during reinstrumentation. However, visible gap-containing regions were not seen in the ESEM samples from any of the experimental groups. The main advantage of Resilon is its ability to adhere

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Fig. 2. Graph showing microleakage of the experimental and control groups.

Fig. 3. Esem micrographs showing attachment of resin tags before (A-C) and after re-treatment (D, E).

to the dentin walls, but Shipper et al.3 questioned its capacity to withstand retreatment. The aim of the present study was to compare the sealing capacity of canals filled with Resilon and of canals refilled with Resilon. We found no statistical difference between the experimental groups, which suggests that the sealing capacity after reinstrumentation and refilling of root canals with Resilon is almost the same as the initial filling. Because in the different groups glucose leaked

at approximately the same rate, we concluded that the capacity of Resilon to form resin tags was retained after retreatment. The presence of gaps could be expected because of the presence of residual sealer on the dentinal surface after reinstrumentation. However, none of the specimens showed regions that could clearly be identified as gaps. Although Resilon/Epiphany system may to be a good root filling material, recent studies have shown that the

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seal obtained may be no better than gutta-percha/sealer.19,20 In the present study, a continuous and increasing rate of leakage occurred from the first day onward in all of the experimental groups. However, the clinical significance of in vitro microleakage has been questioned.21 The amount of leakage in in vitro studies comparing the sealing ability of endodontic materials does not take into consideration the tissue response expected in an in vivo situation. Moreover, the amount of leakage in vivo may also be influenced by the presence or absence of coronal restorations, quality of root canal filling, and number and virulence of the microorganisms.22 Because of limitations of in vitro studies, these results should be treated with caution. Further studies should be performed to compare in vivo the sealing ability of Resilon/Epiphany and gutta-percha/ sealer systems after retreatment. CONCLUSION Under the present experimental conditions, Resilon could be successfully used to refill root canals. There were no statistical differences in leakage between roots after preliminary Resilon filling and refilling after reinstrumentation. However, this new filling material also allowed leakage to occur before and after retreatment. REFERENCES 1. Friedman S, Stabholz A. Endodontic retreatment— case selection and technique. Part 1: criteria for case selection. J Endod 1986;12:28-33. 2. Stabholz A, Friedman S. Endodontic retreatment— case selection and technique. Part 2: treatment planning for retreatment. J Endod 1988;14:607-14. 3. Shipper G, Ørstavik D, Teixeira FB, Trope M. An evaluation of microbial leakage in roots filled with a thermoplastic synthetic polymer– based root canal filling material (Resilon). J Endod 2004;30:342-7. 4. Tay FR, Pashley DH. Monoblocks in root canals: a hypothetical or a tangible goal. J Endod 2007;33:391-8. 5. Teixeira FB, Teixeira EC, Thompson JY, Trope M. Fracture resistance of roots endodontically treated with a new resin filling material. J Am Dent Assoc 2004;135:646-52. 6. Shipper G, Teixeira FB, Arnold RR, Trope M. Periapical inflammation after coronal microbial inoculation of dog roots filled with gutta-percha or Resilon. J Endod 2005;31:91-6. 7. Ezzie E, Fleury A, Solomon E, Spears R, He J. Efficacy of retreatment techniques for a resin-based root canal obturation material. J Endod 2006;32:362-4. 8. Stratton RK, Apicella MJ, Mines P. A fluid filtration comparison of gutta-percha versus Resilon, a new soft resin endodontic obturation system. J Endod 2006;32:642-5. 9. Tunga U, Bodrumlu E. Assessment of the sealing ability of a new root canal obturation material. J Endod 2006;32:876-8.

Lin et al 851 10. Bodrumulu E, Tunga U. Apical leakage of Resilon obturation material. J Contemp Dent 2006;7:45-52. 11. Schirrmeister JF, Meyer KM, Hermanns P, Altenburger MJ, Wrbas KT. Effectiveness of hand and rotary instrumentation for removing a new synthetic polymer-based root canal obturation material (Epiphany) during retreatment. Int Endod J 2006;39: 150-6. 12. Xu Q, Ming-wen F, Bing F, Gary SPC, Han-lin H. A new quantitative method using glucose for analysis of endodontic leakage. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2005;99:107-11. 13. Tay FR, Loushine RJ, Weller RN, Kimbrough WF, Pashley DH, Mak YF, 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. 14. Wu MK, Wesselink PR. Endodontic leakage studies reconsidered. Part I. Methodology, application and relevance. Int Endod J 1993;26:37-43. 15. Tay FR, Pashley DH, Williams MC, Raina R, Loushine RJ, Weller RN, et al. Susceptibility of a polycaprolactone-based root canal filling material to degradation. I. Alkaline hydrolysis. J Endod 2005;31:593-8. 16. Versiani MA, Carvalho-Junior JR, Padilha MI, Lacey S, Pascon EA, Sousa-Neto, MD, et al. A comparative study of physicochemical properties of AH Plus and Epiphany root canal sealants. Int Endod J 2006;39:464-471. 17. Tay FR, Sidhu SK, Watson TF, Pashley DH. Water-dependent interfacial transition zone in resin-modified glass-ionomer cement-dentin interfaces. J Dent Res 2004;83:644-9. 18. Masiero AV, Barietta FB. Effectiveness of different techniques for removing gutta-percha during retreatment. Int Endod J 2005;38:2-7. 19. Biggs SG, Knowles KI, Ibarrola JL, Pashley DH. An in vitro assessment of the sealing ability of Resilon/Epiphany using fluid filtration. J Endod 2006;32:759-61. 20. Aptekar A, Ginnan K. Comparative analysis of microleakage and seal for 2 obturation materials: Resilon/Epiphany and guttapercha. J Can Dent Assoc 2006;72:245a-d. 21. Karagenç B, Gençogˇlu N, Ersoy M, Cansever G, Külekçi G. A comparison of four different microleakage tests for assessment of leakage of root canal fillings. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2006;102:110-3. 22. Siqueira JF Jr, Rocas IN, Faviere A, Abad EC, Castro AJ, Gahyva SM. Bacterial leakage in coronally unsealed root canals obturated with 3 different techniques. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2000;90:647-50.

Reprint requests: Jun-Qi Ling, DDS, MD, PhD Endodontics and Conservative Dentistry Guanghua College of Stomatology Sun Yat-sen University 56, Ling Yuan west road Guangzhou 510055 China [email protected]