3. Iman F.doc J Bagh College Dentistry Vol. 25(1), March 2013 Push-out bond Restorative Dentistry 14 Push-out bond strength of different root canal obturation materials Sundus H. Naser, B.D.S. (1) Iman M. Al-Zaka, B.D.S., M.Sc. (2) ABSTRACT Background: The aim of this study was to evaluate the push-out bond strength of four different obturation materials to intraradicular dentin and to determine the failure mode. Materials and method: forty straight palatal roots of the maxillary first molars teeth were used in this study, the roots were instrumented using crown down technique and rotary EndoSequence system, the roots were randomly divided into four groups according to the materials used for obturation (n=10).Group (1): AH Plus sealer and gutta-percha. Group (2): Activ GP glass ionomer sealer and Activ GP gutta-percha (Activ GP system). Group (3): Bioceramic sealer and Bioceramic gutta-percha. Group (4): GuttaFlow2 sealer and gutta-percha. For all groups single cone obturation technique was used. After incubation period of one week, the roots were embedded in clear acrylic resin and each root sectioned into three levels apical, middle and cervical. The bond strength was measured using computerized universal testing machine, each section fixed in the machine so that the load applied from apical to coronal direction at 0.5mm/min speed and the computer drew curve to show the higher bond force before dislodgment of the filling material. After de-bonding each sample was examined under Stereomicroscopic and the type of failure mode was recorded. Results: showed a non significant difference between AH plus group and Bioceramic group. AH Plus group showed a very highly significant difference with Activ GP group and a highly significant difference with GuttaFlow2 group. There were significant differences between coronal level and both apical and middle levels with no significant differences between apical and middle levels within each group. Conclusion: AH plus group showed the highest mean of bond strength in comparing to other tested groups. Keywords: Bond strength, push-out test, adhesive sealer, obturation materials. (J Bagh Coll Dentistry 2013; 25(1):14-20). INTRODUCTION Successful root canal treatment depends on the thorough debridement of the root canal system, the elimination of pathogenic organisms and finally the complete sealing of the canal space to prevent ingress of bacteria from the oral environment and spread to the periapical tissue (1). The physical properties necessary for this function include adaptation and adhesion of the filling material to the root canal wall, because gutta- percha does not directly bond to the dentin surface, the sealer should be capable of producing a bond between core material and dentin wall (2). Different types of sealer have been introduced to endodontics, including those based on zinc oxide eugenol, calcium hydroxide, glass–ionomer cement and a range of resins. Epoxy resin-type sealers have been used for many years. They showed higher bond strength to dentin than zinc oxide eugenol types and calcium hydroxide-based sealer (3). In recent years, different filling materials and sealers have been developed on the basis of dentin adhesion technology in an attempt to seal the root canal more effectively, and to increase fracture resistance of root filled teeth (4). Furthermore, manufacturers have further incorporated adhesive dentistry in endodontics by introducing obturation systems with a specific focus on obtaining a “monobloc” in which the core material, sealing agent, and root canal dentin form a single cohesive unit (5). Both Activ GP Precision system and Bioceramic sealer are based on adhesion technology (6). Activ GP is a system which utilizes improved glass ionomer (GI) technology (both as a sealer and as a special GI coated gutta percha cone) to create a true single cone monoblock obturation (7). Activ GP sealer is superior to previous GI-based systems in terms of handling characteristics, working time, radiopacity (8) and seal, because of the increased of its flowability (9,10). Bioceramic sealer (BC) is a new premixed sealer, ready-to-use injectable and hydraulic cement paste. It is composed of calcium phosphate, calcium silicate, calcium hydroxide, zirconium oxide, filler, and thickening agents. Bioceramic sealer have dimensional stability and don’t shrink upon setting, consequently, remains non restorable inside the root canal (6). GuttaFlow®2 sealer is an alternative root filling material introduced into the endodontic practice. GuttaFlow®2 is a cold flowable filling system for root canals, combining sealer and gutta-percha in one product. Adhesion properties of root canal sealers to dentin are determined by several mechanical tests. Push-out test has been described to measure the bond between sealer, canal wall and the core material (11,12). The aim of this study was to compare the bond strength of different root canal obturation materials. MATERIALS AND METHODS Forty freshly extracted maxillary first molars teeth with straight palatal root were selected from (1)M.Sc. student. Department of Conservative Dentistry, College of Dentistry, Al-Mustanseria University. (2)Assistant Professor. Department of Conservative Dentistry, College of Dentistry, Al-Mustanseria University. J Bagh College Dentistry Vol. 25(1), March 2013 Push-out bond Restorative Dentistry 15 different health centers for this study according to specific criteria. After extraction, all teeth were stored in 0.1% thymol solution at room temperature. The roots surfaces were verified with a magnifying eye lens (10X) and light cure device for any visible cracks or fractures. Using diamond disc mounted on straight hand-piece and under water coolant the palatal root of teeth was sectioned perpendicular to the long axis of the root at the furcation area to facilitate straight line access for canal instrumentation and filling procedure. The length of the root was determined by digital caliper and marker to (10) mm from apex to cement-enamel junction. The exact location of the apical foramen and the patency of the canals were verified by insertion of a No.15 K-file into the canal and advancing until it is visualized at the apical foramen. The root canals were prepared with Crown-Down technique to master apical file #40 using 0.06 taper EndoSequence NiTi rotary instruments (Brasseler USA, Savannah) at 500 rpm and 1.2 N/c torque. Five millimeter of 2.5% NaOCL with 27-G syringe was used for irrigation between each file size with a final rinse of 5 ml, 17% EDTA (PD Swiss quality) for 1min. Followed by copious amounts of distilled water to remove any remnant of the irrigation solutions (13,14). Samples grouping The roots were randomly divided into four groups (n=10) according to type of obturation materials, for all groups single cone obturation technique was used: Group (1): In this group, the AH Plus sealer (Dentsply, Germany) mixed according to the manufacture's instructions. The tip of master cone #40/.06 was coated with the AH plus sealer and placed into canal to full working length (fig.1). Group (2): Canals were obturated with Activ GP root canal obturation system (Brasseler USA, Savannah), (fig.2). After the root canals were dried with master paper points, Activ GP sealer powder and liquid in (3:1) ratio mixed following the manufacture's instructions. Then the apical half of Activ GP master cone #40/.06 was coated with sealer and inserted slowly in the canal with circular motion until it reach full working length. Group (3): In this group the EndoSequence BC sealer and EndoSequence BC gutta-percha were used (Brasseler USA, Savannah), (fig.3). The obturation was performed with a #40/.06 BC gutta-percha master cone in combination with BC Sealer according to the manufacturer's instructions. Then the master BC gutta percha cone was coated with a thin layer of sealer, and very slowly inserts it into the canal. Group (4): Canals were obturated with #40/.06 gutta-percha and GuttaFlow2 sealer (Coltene,Germany) according to the manufacturer's instructions (fig.4). GuttaFlow®2 was spread on a mixing slab and inserted into the root canal with the master file #40 then the master cone #40/.06 coated with sealer and inserted to the working length. For all groups excess gutta-percha was removed with hot plugger 1mm below the orifice. All obturated roots of all groups were wrapped in saline moistened gauze in closed plastic vial allowing the sealer to set for 7 days at 37°C in an incubator (19). After the storage period, the roots were embedded in clear orthodontic resin (15). The sectioning of root was made by using Diamond Cut-off Saw. Four cut was made horizontally to obtain three sections (apical, middle, and coronal) of 2 mm in thickness , three sections were obtained (2), (4.5), and (7) mm from true anatomical apex. The thickness of each section was measured with a digital caliper, thus, each study group of (10) roots provided a total of (30) test specimens, consisting of (10) specimens from each root region. Push-out bond strength test Push-out test was performed by applying a compressive load to the apical aspect of each slice via a cylindrical plunger mounted on Tinius-Olsen Universal Testing Machine managed by computer software. Samples were examined under the Nikon metallurgical microscope (magnification 50X) and pictures of both sides of each section are taken with digital camera which was connected with microscope, and measurements calculated using LUCIA G software analysis program. The obturated area of the section at each level was measured from the apical side to determine the size of punch pin (16).Three different sizes of punch pins were used, 0.7 mm diameter for the coronal slices, 0.55 mm diameter for the middle slices and 0.4 mm diameter for the apical slices. The punch pins should provide almost complete coverage over the main cone without touching the canal wall and sealer (13,16) . The root filling in each section subjected to loading using a universal testing machine (WDW50) at a speed of 0.5 mm / min in an apical-coronal direction until the first dislodgment of obturating material and a sudden drop along the load deflection. The maximum failure load was recorded in Newton (N) and was used to calculate the push-out bond strength in megapascals (MPa) according to the following formula (17): Push-out bond strength (MPa) = J Bagh College Dentistry Vol. 25(1), March 2013 Push-out bond Restorative Dentistry 16 ANOVA test and LSD test was performed as statistical analysis for push-out bond strength. Analysis of failure modes After the push-out bond strength test, each sample was inspected with a Stereomicroscope (Kruss, Germany) at 40x magnification to determine the failure mode. Each sample was evaluated and placed into one of 3 failure modes (16, 18): Type I: adhesive failure, either at the sealer-dentin (S/D) or between the sealer-core (S/C) interfaces, Type II: cohesive failure, within the filling material (sealer or core material), Type III: mixed failure, which contains both adhesive and cohesive failures. RESULTS Mean values and standard deviation for all groups presented in (table-1). AH Plus group has the highest mean values at all levels in comparison with other groups followed by BC group, then GuttaFlow2 group, while Activ GP group has the lowest mean value at all levels. The coronal level in all groups has the highest mean push-out bond strength values, followed by middle and then the apical level (fig.5). Analysis of variance (ANOVA) test was performed and showed that there were very highly significant differences (p≤0.001) at all levels (table-2). There was no significant difference between Group1 (AH Plus) and Group3 (Bioceramic) at all levels (P ≥ 0.05). And also there was no significant difference between Group2 (Activ GP) and Group4 (GuttaFlow2) at all levels (P ≥ 0.05). Group1 (AH Plus) showed a very highly significant difference (P ≤ 0.001) with group2 (Activ GP) and a highly significant difference (P ≤ 0.01) with group4 (GuttaFlow2) at all levels (table-3). ANOVA test between different levels within each group showed that there was a highly significant difference (P ≤ 0.01) among different levels within each group (table-4). The least significance difference test (LSD) was performed to confirm the results of ANOVA test between each two levels for each groups and showed a significant difference between coronal level with both middle and apical levels and there was a non significance difference between apical and middle level in all groups (table-5). Analysis of failure mode The analysis of failure mode for push-out test was shown that the predominant mode of failure in AH-Plus group was adhesive failure (S/G) and mixed failure. In the Activ GP group the failure mode was predominantly cohesive failure within the gutta-percha itself and adhesive failure at S/D interface. The failure mode in the BC group was a cohesive failure mainly within the gutta-percha and mixed failure. Finally the failure mode in the GuttaFlow2 group was adhesive failure mainly at S/G with some failure at S/D interface (table-6). DISCUSSION Many obturation systems were proposed to the endodontics as to approach the good sealing ability and adhesion to dentin. Despite the inadequate levels of bond strength between most current endodontic sealers and root dentin and gutta-percha (19,20) the adhesion of sealers to intra- radicular dentin via frictional resistance, chemical bond, or micromechanical retention is still necessary in maintaining the integrity of the sealer-dentin interface during mechanical stresses caused by; tooth flexure, operative procedures, or subsequent preparation of a post space (21, 22). The AH Plus group showed the highest mean of push- out bond strength. The highest bond strength of AH Plus could be explained by the formation of a covalent bond by an open epoxide ring to any exposed amino groups in collagen (23). Other investigations have further shown high-quality properties with epoxy resin–based sealers, including very low shrinkage while setting, long- term dimensional stability, flow, and long setting time, AH Plus sealer penetrates deeper into the surface microirregularities (24). This agrees with the finding of Fisher et al.(13) and Sagsen et al.(25) . A highly significant difference was shown between AH Plus group and the Activ GP group, like other self-curing GI cements and resin composites, may have undergone shrinkage during its setting phase creating gaps between the sealer and root dentin(26) . This result may be also attributed to the non homogeneous mix of GI sealer which is questionable which might have an adverse effect on it is properties. Moreover when comparing Activ GP group with AH Plus group in mechanisms of bonding, different mechanisms of bonding of both sealers played a role. The removal of the smear layer, by EDTA improves micromechanical retention of AH Plus sealer but also depleted calcium ions which are necessary for the Activ GP bonding. This result is in agreement with Fisher et al (13), Hashem et al. (27) and Elsheikh et al (18). When comparing the AH Plus group with BC group no significant difference was found between them at all levels. Shokouhinejad et al. (14) also found a non significant difference in the push-out bond strength between AH Plus and BC sealer. This could be related to the combined effect of the chemical and mechanical bonding of J Bagh College Dentistry Vol. 25(1), March 2013 Push-out bond Restorative Dentistry 17 the BC sealer to dentin wall (formation of hydroxyapatite during the setting) as well as the chemical bonding between the sealer and BC core material might have resulted in a significantly increased push out bond strength of BC sealer (28,29). GuttaFlow2 group showed a significant difference with AH Plus group and BC group. According to Tummala et al.(30) the wettability of the root canal sealers influences its adaptability to the radicular dentin. AH Plus sealer was shown to wet the root dentin surface better than the GuttaFlow sealer and this could be attributed to its ability to penetrate into the micro-irregularities better. GuttaFlow showed poor wetting on the root dentin surface because of the presence of silicone, which possibly produces high surface tension forces, making the spreading of these materials less (30). The bond strength value decreased in a coronal to apical direction and showed significant difference between the coronal and apical level with no significant difference between apical and middle levels. The explanation for this may be that the apical dentine contains less patent tubules than coronal dentine and the more complex structure of tubular dentine apparently yields itself better to infiltration compared to the sclerotic apical counterpart. This agrees with the finding of Nagas et al. (31) and Al-Hamed et al. (32). The predominant mode of failure for AH Plus group was adhesive failure at S/G. Elsheikh et al.(18), showed that the failure mode for AH Plus was adhesive mainly between sealer and main cone and partially between sealer and dentin. Furthermore Nagas et al.(33) revealed that the failure mode was adhesive mainly between the gutta-percha and the AH Plus sealer. The predominant mode of failure for Activ GP group was adhesive at S/D interface and cohesive failure within the core material itself which might be due to weakening in the gutta-percha when sialinated with coating (18), and the nonhomogeneous coating of GI particle on the surface of the Activ GP cone which may be contributed to less favorable bonding(34). In BC group the predominant mode of failure was also cohesive within the BC cone and this may be also attributed to weak and unfavorable distribution of the BC coating on the surface of BC cone. The predominant mode of failure for GuttaFlow2 group was adhesive failure mainly at S/G and some adhesive failure at S/D interface and this could be attributed to the lack of chemical union between sealer and gutta-percha or sealer and dentin. Within the limitation of the present study the push-out bond strength of AH Plus group was higher than other groups tested and the bond strength were affected by the tooth levels. REFERENCES 1. Sundqvist G, Figdor D, Persson S, Sjo¨gren U. Microbiologic analysis of teeth with failed endodontic treatment and the outcome of conservative re- treatment. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1998; 85(1):86-93. 2. Skinner RL, Himel VT. The sealing ability of injection molded thermoplasticized gutta-percha with and without the use of sealers. J Endod 1987; 13(7):315-7. 3. Lee KW, Williams MC, Camps JJ, Pashley DH. Adhesion of endodontic sealers to dentin and gutta- percha. J Endod 2002; 28(10):684-2. 4. 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(11):809-13. 5. Tay FR, Pashley DH. Monoblocks in root canals: a hypothetical or a tangible goal. J Endod 2007; 33(4):391-8. 6. Koch K, Brave D. Bioceramic technology-the game changer in endodontics. Endod Pract. 2009; 2:17-27. 7. Koch, Brave D. A new endodontic obturation technique. Dent Today. 2006; 25(102):104-7. 8. Fransen JN, He J, Glickman GN, Rios A, Shulman JD, Honeyman A. Comparative assessment of ActiV GP/Glass Ionomer sealer, Resilon/Epiphany, and Gutta-Percha/AH Plus obturation: a bacterial leakage study. J Endod 2008; 34(6):725-6. 9. Kontakiotis EG, Tzanetakis GN, Loizides AL. A comparative study of contact angles of four different root canal sealers. J Endod 2007; 33(3):299-302. 10. Faria-Júnior N, Massi S, Croti H, Gutierrez J, Dametto F, Vaz L. Comparative assessment of the flow rate of root canal sealers. Rev. odonto ciênc 2010; 25(2):170- 3. 11. Thompson JI, Gregson PJ, Revell PA. Analysis of push-out test data based on interfacial fracture energy. J Mat Science: Materials in Medicine 1999; 10:863–8. 12. Chandra N, Ghonem H. Interfacial mechanics of push- out tests: theory and experiments. Composites Part A: Appl Sc & Manufact 2001; 32(3):575. 13. Fisher MA, Berzins DW, Bahcall JK. An in vitro comparison of bond strength of various obturation materials to root canal dentin using a push-out test design. J Endod 2007; 33(7):856-8. 14. Shokouhinejad N, Gorjestani H, Nasseh AA, Hoseini A, Mohammadi M, Shamshiri AR. Push-out bond strength of gutta-percha with a new bioceramic sealer in the presence or absence of smear layer. Aust Endod J 2011; 37(2):1-6. 15. Eguchi D, Peters D, Hollinger J, Lorton L. A comparison of the area of the canal space occupied by gutta-percha following four gutta-percha obturation techniques using Procosol sealer. J Endod 1985; 11(4):166-75. 16. Jainaen A, Palamara J & Messer H. Push-out bond strengths of the dentine–sealer interface with and without a main cone. Int Endod J 2007; 40(11):882- 90. 17. Nagas E, Cehreli ZC, Durmaz V. Regional push out bond strength and coronal micro leakage of resilon after different light curing methods. J Endod 2007; 33(8):1464-70. J Bagh College Dentistry Vol. 25(1), March 2013 Push-out bond Restorative Dentistry 18 18. Elsheikh AM, Mohamed GE and Saba AA. Push out bond strength of glass ionomer-Impregnated gutta percha/glass ionomer sealer System to root canal dentin conditioned with Different endodontic irrigants. Eygpt Dent J 2011; 57(3):2351-55. 19. Schwartz R. Adhesive dentistry and endodontics. part 2: bonding in the root canal system.the promise and the problems: A Review. J Endod 2006; 32:1125-34. 20. Bouillaguet S, Bertossa B, Krejci I, Wataha JC, Tay FR, Pashley DH. Alternative adhesive strategies to optimize bonding to radicular dentin. J Endod 2007; 33(10):1227-30. 21. Saleh IM, Ruyter IE, Haapasalo MP, Ørstavik D. Adhesion of endodontic sealers: scanning electron microscopy and energy dispersive spectroscopy. J Endod 2003; 29(9): 595-6. 22. Ayad MF, Farag AM, Garcia-Godoy F. Effect of lactic acid irrigant on shear bond strength of Epiphany adhesive sealer to human dentin surface. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2010; 109(5): e100. 23. Nunes VH, Silva RG, Alfredo E, Sousa MD, Sousa YT. Adhesion of Epiphany and AH Plus sealers to human root dentin treated with different solutions. Braz Dent J 2008; 19(1):46-85. 24. Flores D, Rached-Júnior F, Versiani M1, Guedes D, Sousa-Neto M, Pécora J. Evaluation of physicochemical properties of four root canal sealers. Int Endod J 2011; 44(2):126-35. 25. Sagsen B, Ustun Y, Demirbuga S & Pala K. Push-out bond strength of two new calcium silicate-based endodontic sealers to root canal dentine. Int Endod J 2011; 44(12):1088-91. 26. Monticelli F, Sadek FT, Schuster GS, Volkmann KR, Looney SW, Ferrari Toledano M, Pashley DH, and Tay FR. Efficacy of two contemporary single-cone filling techniques in preventing bacterial leakage. Int Endod J 2007(a); 33(3):310-3. 27. Hashem AA, Ghoneim AG, Lutfy RA, Fouda MY. The effect of different irrigating solutions on bond strength of two root canal-filling systems. J Endod 2009; 35(4):537-40. 28. Ghoneim AG, Lutfy RA, Sabet NE and Dalia M. Fayyad DM. Resistance to fracture of roots obturated with novel canal-filling systems. J Endod 2011; 37(11):1590-2. 29. Candeiro G, Correia F, Duarte M, Siqueira D. Evaluation of radiopacity, ph, release of calcium ions, and flow of a bioceramic root canal sealer. J Endod 2012; 36(6):842-5. 30. Tummala M, Chandrasekhar V, Rashmi S, Kundabala M, Ballal V. Assessment of the wetting behavior of three different root canal sealers on root canal dentin. J Conserv Dent 2012; 15(2):109-12. 31. Nagas E, Cehreli ZC, Durmaz V. Effect of light- emitting diode photopolymerization modes on the push-out bond strength of a methacrylate-based sealer. J Endod 2011(a); 37(6):832-5. 32. Al-Hamed MJ, Fouda MY and Ahmed GM. Effect of different irrigates on the bond strength of bioceramic sealer to root canal dentin. Egypt Dent J 2011; 57(3): 2269-75. 33. Nagas E, Uyanik O, Eymirli A, Cehreli ZC,Vallittu P, Lassila LV,and Durmaz V. Dentin moisture conditions affect the adhesion of root canal sealers. J Endod 2012; 38(2):240-4. 34. Monticelli F, Sword J, Martin RL, Schuster GS, Weller RN, Ferrari M. Sealing properties of two contemporary single-cone obturation systems. Int Endod J 2007(b); 40(5):374-85. Table 1: Descriptive statistics of Push-out bond strength values (MPa) at three levels for all groups. Groups Level No. Mean SD. SE. Min. Max. Group1 (AH Plus) Coronal 10 1.664 0.304 0.096 1.04 2.11 Middle 10 1.276 0.319 0.101 0.81 1.81 Apical 10 1.260 0.324 0.102 0.93 1.87 Group2 (Activ GP) Coronal 10 1.105 0.314 0.099 0.83 1.85 Middle 10 0.824 0.115 0.036 0.67 1.00 Apical 10 0.817 0.170 0.054 0.59 1.12 Group3 (Bioceramic) Coronal 10 1.591 0.283 0.089 1.25 2.08 Middle 10 1.191 0.136 0.043 0.95 1.33 Apical 10 1.155 0.121 0.038 1.02 1.40 Group4 (GuttaFlow2) Coronal 10 1.256 0.270 0.085 0.99 1.69 Middle 10 0.950 0.216 0.068 0.67 1.33 Apical 10 0.913 0.193 0.061 0.58 1.21 Table 2: ANOVA test for mean push-out bond strength among groups at each level level ANOVA SS df MS F P-value Sig. Coronal Level Between group 2.133 3 0.711 8.289 0.000 *** Within group 3.095 36 0.086 Total 5.228 39 Middle level Between group 1.313 3 0.438 9.717 0.000 *** Within group 1.627 36 0.045 Total 2.941 39 Apical level Between group 1.274 3 0.425 9.149 0.000 *** Within group 1.671 36 0.046 Total 2.946 39 *** Very highly significant J Bagh College Dentistry Vol. 25(1), March 2013 Push-out bond Restorative Dentistry 19 Table 3: LSD test for mean push-out bond strength between four groups at each level Level Groups P-value Sig. Coronal Level Group1 Group 2 0.000 *** Group 3 0.581 N.S Group 4 0.004 ** Group2 Group 3 0.001 ** Group 4 0.257 N.S Group3 Group 4 0.015 * Middle Level Group1 Group 2 0.000 *** Group 3 0.377 N.S Group 4 0.002 ** Group2 Group 3 0.000 *** Group 4 0.193 N.S Group3 Group4 0.016 * Apical Level Group1 Group 2 0.000 *** Group 3 0.283 N.S Group 4 0.001 ** Group2 Group 3 0.001 ** Group 4 0.326 N.S Group3 Group 4 0.017 * *Significant; ** highly significant difference; *** Very highly significant; N.S Non-significant difference. Table 4: ANOVA test for mean push-out bond strength among the different levels within each group Groups ANOVA SS df MS F-test P-value Sig. Group1 Between group 1.047 2 0.523 5.245 0.012 * Within group 2.694 27 0.1 Total 3.741 29 Group2 Between group 0.54 2 0.27 5.738 0.008 ** Within group 1.27 27 0.047 Total 1.81 29 Group3 Between group 1.171 2 0.586 15.563 0.000 *** Within group 1.016 27 0.038 Total 2.187 29 Group4 Between group 0.709 2 0.354 6.774 0.004 ** Within group 1.413 27 0.052 Total 2.121 29 *Significant; ** highly significant difference; *** Very highly significant Table 5: LSD test for mean push-out bond strength between the different levels within each group Groups Level P-value Sig. Group1 Coronal & Middle 0.011 * Coronal & apical 0.008 *(* Middle & apical 0.911 N.S Group2 Coronal & Middle 0.007 ** Coronal & apical 0.006 ** Middle & apical 0.943 N.S Group3 Coronal & Middle 0.000 *** Coronal & apical 0.000 *** Middle & apical 0.631 N.S Group4 Coronal & Middle 0.006 ** Coronal & apical 0.002 ** Middle & apical 0.72 N.S *Significant; ** highly significant difference; *** Very highly significant; N.S Non-significant difference. J Bagh College Dentistry Vol. 25(1), March 2013 Push-out bond Restorative Dentistry 20 Table 6: Failure modes for different groups Groups Mode of failure (No.) Adhesive Cohesive Mixed S/D S/G Within sealer Within gutta-percha Cohesive & adhesive Group1 6 13 ---------- ----------- 11 Group2 10 --------- -------- 14 6 Group3 7 ----------- ------- 13 10 Group4 10 14 ------- -------- 6 Fig. 5: Bar chart graph for mean Push-out bond strength at each level of different groups