Push-out strength of root fillings with or without thermomechanical compaction

Transcription

1 doi: /j x Push-out strength of root fillings with or without thermomechanical compaction S. M. B. S. Carneiro 1, M. D. Sousa-Neto 2, F. A. Rached-Júnior 1, C. E. S. Miranda 1, S. R. C. Silva 1 & Y. T. C. Silva-Sousa 1 1 School of Dentistry, University of Ribeirão Preto, Ribeirão Preto, SP; and 2 Department of Restorative Dentistry, Ribeirão Preto School of Dentistry, University of São Paulo, Ribeirão Preto, SP, Brasil Abstract Carneiro SMBS, Sousa-Neto MD, Rached-Júnior FA, Miranda CES, Silva SRC, Silva-Sousa YTC. Push-out strength of root fillings with or without thermomechanical compaction. International Endodontic Journal, 45, , Aim To evaluate the influence of thermomechanical compaction (Tagger s hybrid technique THT) on the push-out strength of several root filling materials to root dentine. Methodology Root canals of eighty roots in human canines were prepared with the ProTaper system and filled with one of the following materials, using either lateral compaction (LC) (n = 40) or THT (n = 40): AH Plus/gutta-percha (GP) (n = 10), Sealer 26/GP (n = 10), Epiphany SE/Resilon (n = 10) and Epiphany SE/GP (n = 10). Three 2-mm-thick dentine slices were obtained from each third of each root. The root filling in the first slice was subjected to a push-out test to evaluate the bond strength of the materials to intraradicular dentine. Data (in MPa) were analysed using anova and post hoc Tukey s test (P < 0.05). Failure mode was determined at 25 magnification. The other two slices were prepared for scanning electron microscopy (SEM) to examine the surface of the filling materials. Results Lateral compaction (1.34 ± 1.14 MPa) was associated with a significantly higher bond strength (P < 0.05) than the THT (0.97 ± 0.88 MPa). AH Plus/ GP (2.23 ± 0.83 MPa) and Sealer 26/GP (1.86 ± 0.50 MPa) had significantly higher bond strengths than the other materials and differed significantly from each other (P < 0.05). There was a significant difference (P < 0.05) between the coronal (1.36 ± 1.15 MPa), middle (1.14 ± 1.05 MPa) and apical thirds (0.95 ± 0.83 MPa). Considering the technique and root filling material interaction, AH Plus/GP-LC was associated with the highest mean values (2.65 ± 0.66 MPa) (P < 0.05). Sealer 26/GP-LC (2.10 ± 0.46 MPa), AH Plus/GP-THT (1.81 ± 0.78 MPa) and Sealer 26/GP-TH (1.63 ± 0.44 MPa) had intermediate values that were not significantly different from each other (P > 0.05). Epiphany SE was associated with the lowest mean values (3.70 ± 0.86 MPa) (P < 0.05), regardless of the root filling technique and type of solid material (cone). Adhesive failures predominated in the specimens filled with Epiphany SE, whilst mixed and cohesive failures were more frequent in those filled with AH Plus and Sealer 26, regardless of the root filling technique. SEM analysis revealed that LC produced a dense and wellcompacted filling whilst the use of a hybrid thermomechanical technique resulted in the solid material (GP or Resilon) intermingled within sealer to form a nonhomogenous mass. Conclusion Lateral compaction was associated with higher bond strengths of the materials to intraradicular dentine than a hybrid technique using thermomechanical compaction. The greatest push-out strengths were obtained when the canals were filled with LC of AH Plus and GP cones. Keywords: push-out test, root canal filling, SEM and endodontics. Received 26 September 2011; accepted 7 February 2012 Correspondence: Manoel Damião Sousa-Neto, Rua Célia de Oliveira Meireles, 350, Jardim Canadá, , Ribeirão Preto, SP, Brasil (Tel.: ; fax: ; sousanet@forp.usp.br). ª 2012 International Endodontic Journal International Endodontic Journal, 45, ,

2 Thermomechanical root filling and adhesion to intraradicular dentine Carneiro et al. Introduction In 1979, a new concept of heat softening and compacting gutta-percha (GP) was introduced by McSpadden to accelerate root filling procedures with the development of instruments known as McSpadden compactors (Leonardo et al. 2009). This device resembled a reverse Hedström file or a reverse screw design (Leonardo et al. 2009). When rotated in the canal at a minimum speed of 8000 rpm, the heat generated by friction softens the GP, and the design of the blades forces the material apically and laterally against the canal walls, producing what has been perceived as a homogenous filling of the entire root canal system, even in the presence of irregular anatomy and lateral canals (Leonardo et al. 2009, Michelotto et al. 2010). However, the McSpadden technique has some disadvantages, such as the possibility of fracture of the instrument and displacement of the cone (Leonardo et al. 2009), extrusion of GP beyond the apex and possibility of thermal damage to the vital periodontal tissues because of an increase in temperature on the external root surface (Hopkins et al. 1986). Tagger (1984) suggested a modification in the McSpadden technique in an attempt to overcome these shortcomings. In the so-called Tagger s hybrid technique (THT), thermomechanical compaction of the filling material in the middle and coronal thirds is performed after active cold lateral compaction (LC) in the apical third, thus potentially combining the advantages of the McSpadden technique and LC in a single root canal filling method (Leonardo et al. 2009, Marciano et al. 2010). An advantage of THT is that it does not need a specific type of endodontic compactor. A McSpadden compactor, for example, can be used to produce friction between the GP and the internal root canal walls, causing the thermoplasticizing effect that promotes a good apical seal with less risk of extrusion of the filling material towards the apical third (Leonardo et al. 2009). In addition to the filling technique, the type of sealer can also influence the adhesion to root dentine (Sousa- Neto et al. 2002). Root canal sealers can be classified as calcium hydroxide-containing sealers, zinc oxide eugenol-based sealers, glass ionomer sealers and resinbased sealers. Advances in adhesive technology have led to the development of filling materials with adhesive properties, such as epoxy resin- and methacrylatebased sealers, in an attempt to reduce apical and coronal leakage by improving sealer adhesion to the root canal walls (Nunes et al. 2008, Costa et al. 2010) and increase the success rate of root canal treatment (Costa et al. 2010). The purpose of this study was to evaluate the pushout bond strength to human intraradicular dentine of root filling materials with adhesive properties using either LC or a hybrid thermomechanical compaction technique. The surface of the filling material after the use of both techniques was examined by scanning electron microscopy (SEM). Material and methods The study protocol was approved by the Institutional Ethics Committee (Process #021/10). Eighty human maxillary canines with completely formed apices and roots with curvature angles equal to or <10 (mild curvature) according to Schneider s method (Schneider 1971) were used. A series of mesiodistal radiographs was taken to confirm that all teeth had no internal calcifications, resorptions or previous endodontic treatment. The crowns were removed at the cementoenamel junction with a water-cooled diamond disc (KG Sorensen, Barueri, SP, Brazil) at low speed to obtain a standardized root length of 22 mm. A size 15 K-file (Dentsply Maillefer, Ballaigues, Switzerland) was passively introduced into each canal until its tip was just visible at the apical foramen as observed with a 4 magnifier. The working length (WL) was established by subtracting 1 mm from this length. Teeth that presented laterally displaced foramina with canal length <21 mm were replaced. The coronal and middle thirds of the canals were preflared with Gates Glidden drills (size 2, 3 and 4; Dentsply Maillefer) and then the canals were instrumented with the ProTaper rotary system (Dentsply Maillefer), according to the crown-down technique. The instruments were attached to a 64:1 gear reduction handpiece (Anthogyr, Sallanches, France) powered by an electric motor (Endo Plus VK Driller, São Paulo, SP, Brazil) and were used in the following sequence: SX, S1, S2, F1, F2, F3, F4 and F5. Throughout the chemomechanical preparation, the canals were irrigated with 2 ml of 1.0% NaOCl at each change of file. After preparation, the canals were filled with 5 ml of 17% EDTA for 3 min followed by flushing with 5 ml of distilled water and drying with absorbent paper points (Dentsply Ind. e Com. Ltda., Petrópolis, RJ, Brazil). The 80 roots had the canals filled with one of the following materials, using either LC (n = 40) or THT (n = 40): AH Plus (Dentsply DeTrey, Konstanz, Germany) with GP cones (Dentsply Ind. e Com. Ltda.) 822 International Endodontic Journal, 45, , 2012 ª 2012 International Endodontic Journal

3 Carneiro et al. Thermomechanical root filling and adhesion to intraradicular dentine (n = 10); Sealer 26 (Dentsply Ind. e Com. Ltda.) with GP cones (n = 10); Epiphany SE with Resilon cones (Pentron Clinical Technologies, LLC, Wallingford, CT, USA) (n = 10); and Epiphany SE with GP cones (n = 10) (Table 1). In the specimens filled using the LC technique, the sealer was applied to the canal with a size 40 lentulo spiral and then either a ProTaper GP cone F5 (Dentsply Maillefer) or a size 50,.06 taper Resilon cone was introduced to the WL. A size 25 finger spreader (Dentsply Maillefer) was introduced vertically to create space for the insertion of accessory GP or Resilon F cones. In the specimens filled using the hybrid technique, either a medium GP cone or a size 50, 0.06 taper Resilon cone was measured with a ruler and used as the main cone at WL. Two accessory GP or Resilon F cones coated with sealer were introduced into the canal immediately after removal of the size 25 finger spreader. Then, the size 70 McSpadden compactor (Dentsply Maillefer) coupled to a low-speed handpiece was used in a clockwise direction towards the apical third mm short of WL using brushstroke movements with approximately 1 mm of amplitude and maintaining contact of the instrument with the cones at the canal orifice. In both techniques, the sealers were mixed according to the manufacturers instructions. In the specimens filled with Epiphany SE, 40 s of photoactivation was accomplished using a halogen light source (Ultralux; Dabi Atlante, Ribeirão Preto, SP, Brazil) with a constant light intensity 600 mw cm )2, keeping the light guide tip in contact with the coronal portion of the root. Radiographs were taken to evaluate the quality of root filling in terms of homogeneity and apical extension. Excess sealer was removed with cotton pledgets, and the canal entrance was sealed with a quick-setting temporary filling (Cimpat; Septodont Brasil Ltda., Barueri, SP, Brazil). The teeth were placed immediately at 37 C and 95% humidity after a period three times greater than the regular setting time of the sealer before the bond strength test, that is, 135 min for Epiphany SE and 24 h for AH Plus and Sealer 26. For specimen preparation, the roots were fixed on acrylic plates with wax (Kota Import, São Paulo, SP, Brazil) and then sectioned in a precision cutting machine (Isomet 1000; Buehler, Lake Forest, IL, USA) at 300 rpm. Nine 2-mm-thick slices were obtained from each root (3 per root third). The first slice of each third was selected for the pushout test in an Instron 4444 universal testing machine (Instron Corporation, Canton, MA, USA) at a crosshead speed of 0.5 mm min )1. A stainless steel support was used to hold the specimens in such a way that the side with the smaller diameter of the root canal faced upwards and was aligned to the shaft that would exert pressure load on the sealer (apical-coronally). Fourmillimetre-long shafts with tip diameter of 1, 0.6 and 0.4 mm for the coronal, middle and apical third, respectively, were used. This method assured the alignment of the specimen in an accurate and reproducible manner and also maintained the shaft centralized and avoided its contact with dentine during testing, when the material was pushed and dislodged from the canal wall. The force needed to dislodge the filling material (F; in kn) was transformed into tension (r; in MPa) by dividing the force by the adhesive area of the filling material (SL; in mm 2 ), using the following equation: r = F/SL. SL was calculated using the following equation: SL = p (R + r) g, where SL = sealer bonding area; p = 3.14; R = mean radius of the coronal canal, in mm; r = mean radius of the apical canal, in mm; and g = height relative to the tapered inverted cone, in mm. Mean values of push-out bond strength were analysed statistically. The Kolmogorov Smirnov test revealed that the results were consistent Table 1 Composition of the root canal sealers Root canal sealers Composition Manufacturer AH Plus Sealer 26 Epiphany SE Self-Etch Sealer Epoxy resins, zirconium oxide, iron oxide, calcium tungstate, silicone oil Powder: calcium hydroxide, bismuth trioxide, hexamethylenetetramine, titanium dioxide Resin: bisphenol A diglycidyl ether Mixture of EBPADMA, HEMA, BISGMA and acidic methacrylate resins, silane-treated barium-borosilicate glasses, aluminium oxide, silica, hydroxyapatite, Ca-Al-F-silicate, bismuth oxychloride with amines, peroxide, photo initiator, stabilizers, and pigment. Dentsply De Trey Gmbh, Konstanz, Germany Dentsply Ind. e Com. Ltda., Petrópolis, RJ, Brazil Pentron Clinical Technologies, Wallingford, CT, USA ª 2012 International Endodontic Journal International Endodontic Journal, 45, ,

4 Thermomechanical root filling and adhesion to intraradicular dentine Carneiro et al. with a normal distribution curve and so a parametric statistical analysis was performed using three-way (root filling technique filling material root third) anova and post hoc Tukey s test with the significance level set as 5% (SPSS 17.0; SPSS Inc., Chicago, IL, USA). After the push-out test, the specimens were examined with a stereomicroscope (Stemi 2000-C; Carl Zeiss, Jena, Germany) at 25 magnification to evaluate the failure modes (adhesive, cohesive and mixed) that occurred because of the displacement of the sealer from the specimen. Failure was considered adhesive if the sealer was totally separated from dentine (dentine surface without sealer), cohesive if the fracture occurred within the sealer (dentine surface totally covered by the sealer) and mixed when a mixture of adhesive and cohesive modes (dentine surface partially covered by the sealer) occurred. SEM analysis The second and third slices obtained from roots in each third were prepared for SEM analysis after demineralization and deproteinization of intraradicular dentine to observe the ultrastructural characteristics of the filling materials (sealers and cones) after the using the two root filling techniques. The slices were decalcified in hydrochloric acid 4 N for 48 h and deproteinized in 2.5% NaOCl for 5 min, promoting the complete dissolution of dentine and exposure of the filling material. After being washed twice in distilled water for 4 min, the filling material was fixed on metallic stubs, sputter-coated with a gold palladium alloy (Bal-Tec AG, Balzers, Germany) and examined by three calibrated and experienced examiners using a scanning electron microscope (JSM 5410; JEOL Ltd, Tokyo, Japan) operating at 15 kv. SEM micrographs were obtained at 50 magnification for localization of representative areas and then at 500 magnification to evaluate the homogeneity of the filling mass. Results Push-out test Bond strength mean values and standard deviations (in MPa) for filling material displacement from root canals in each third using the push-out test in specimens with LC or the hybrid thermomechanical compaction technique are given in Table 2. There were statistically significant (P < 0.05) differences for root filling technique, filling material, root third and interaction of these factors. Regarding the root filling techniques, LC (1.34 ± 1.14 MPa) was associated with significantly higher bond strength (P < 0.05) than the hybrid technique (0.97 ± 0.88 MPa). Regarding the filling materials, AH Plus/GP (2.23 ± 0.83 MPa) and Sealer 26/GP (1.86 ± 0.50 MPa) had significantly higher bond strengths than the other materials and differed significantly from each other (P < 0.05). Epiphany SE/ Resilon (0.22 ± 0.10 MPa) and Epiphany SE/GP (0.30 ± 0.24 MPa) were associated with the lowest bond strengths and did not differ significantly from each other (P > 0.05). Comparison of the three root canal thirds revealed a significantly higher bond strength in the coronal third (1.36 ± 1.15 MPa) (P < 0.05) compared with the middle (1.14 ± 1.05 MPa) and apical thirds (0.95 ± 0.83 MPa). Considering the interaction between filling materials and root filling techniques, AH Plus/GP-LC was associated with the highest mean values (2.65 ± 0.66 MPa) (P < 0.05). Sealer 26/GP- LC (2.10 ± 0.46 MPa), AH Plus/GP-THT (1.81 ± 0.78 MPa) and Sealer 26/GP-THT (1.63 ± 0.44 MPa) had intermediate values that were not significantly different from each other (P > 0.05). Epiphany SE/ Resilon-LC (0.22 ± 0.10), Epiphany SE/GP-LC (0.39 ± 0.29 MPa), Epiphany SE/Resilon-THT (0.23 ± 0.11 MPa) and Epiphany SE/GP-THT (0.22 ± 0.13 MPa) were associated with the lowest bond strength mean values (P < 0.05) amongst all combinations of Table 2 Bond strength mean values and standard deviations (in MPa) for filling material displacement from intraradicular dentine in each third using the push-out test in specimens with lateral compaction (LC) or Tagger s hybrid technique (THT) LC THT Root canal third AH Plus/GP Sealer 26/GP Epiphany SE/Resilon Epiphany SE/GP AH Plus/GP Sealer 26/GP Epiphany SE/ Resilon Epiphany SE/GP Cervical 3.23 ± ± ± ± ± ± ± ± 0.17 Middle 2.38 ± ± ± ± ± ± ± ± 0.13 Apical 2.29 ± ± ± ± ± ± ± ± International Endodontic Journal, 45, , 2012 ª 2012 International Endodontic Journal

5 Carneiro et al. Thermomechanical root filling and adhesion to intraradicular dentine filling materials and filling techniques and did not differ significantly from each other (P > 0.05). Considering the interaction between root filling techniques and root canal thirds, LC in the coronal third was associated with the highest mean value (P < 0.05). The hybrid technique in the coronal third and LC in the middle third had intermediate values that were statistically similar to each other (P > 0.05). The hybrid technique in the middle and apical thirds and LC in the apical third had the lowest bond strength mean values and were statistically similar to each other (P > 0.05). Failure mode after the push-out test Failure mode distribution in the specimens filled with LC and the hybrid thermomechanical compaction technique is displayed in Table 3. For both techniques, there was a predominance of cohesive failures in the coronal third and mixed failures in the middle and apical thirds in the specimens filled with AH Plus/GP and Sealer 26/GP, whilst adhesive failures predominated in the specimens filled with Epiphany SE in all thirds, regardless of the technique. SEM analysis In the specimens filled with AH Plus/GP and Sealer 26/ GP using LC, the filling mass was compact and dense, with only few areas exhibiting microirregularities (Fig. 1a,c). The use of hybrid thermomechanical compaction technique resulted in a nonhomogenous mixture of GP and sealer, with an ill-compacted surface with several voids (Fig. 1b,d). In the specimens filled with Epiphany SE/GP (Fig. 2a) and Epiphany SE/Resilon (Fig. 2c) using LC, the filling mass was compact, dense and homogenous. When the hybrid technique was used, the solid material (GP or Resilon) intermingled within the sealer, forming a nonhomogenous mass. Several craters were also observed within the filling (Fig. 2b,d). Discussion The thermoplastic or thermomechanical root filling methods, based on the principles of vertical compaction of warm gutta-percha conceived and described by Schilder (1967), have been extensively investigated over time with good results regarding filling of the root canal system, homogeneity of the filling material and apical seal (Cathro & Love 2003, Gurgel-Filho et al. 2006). The present study evaluated the influence of a thermomechanical compaction technique on the adhesion of different root filling materials to root canal walls. Amongst the different thermomechanical root canal filling methods, an advantage of the hybrid technique is that it does not need a specific endodontic compactor and can be performed using a McSpadden compactor with diameter compatible with the canal, providing good apical seal and less risk of filling material extrusion towards the apex (Leonardo et al. 2009). The results of the present study revealed lower bond strength to root dentine in the specimens filled using the hybrid technique compared with LC. Previous studies have shown that vertical condensation of thermoplasticized GP can generate a force of great magnitude that promotes the filling of lateral canals and anatomic irregularities with GP and very little sealer (Schilder 1967, Brosco et al. 2003, Cathro & Love 2003, Teixeira et al. 2004, Carvalho-Sousa et al. 2010). Therefore, it may be speculated that penetration of thermoplasticized GP into the canal microirregularities and dentinal tubules promotes only mechanical interlocking because GP without sealer probably results Table 3 Distribution of failure modes (%) after the push-out test for each type of root filling technique AH Plus/GP Sealer 26/GP Epiphany SE/Resilon Epiphany SE/GP Failure mode CT MT AT CT MT AT CT MT AT CT MT AT Lateral compaction Adhesive Mixed Cohesive Tagger s hybrid technique Adhesive Mixed Cohesive GP, gutta-percha; CT, cervical third; MT, middle third; AT, apical third. ª 2012 International Endodontic Journal International Endodontic Journal, 45, ,

6 Thermomechanical root filling and adhesion to intraradicular dentine Carneiro et al. (a) (b) (c) (d) Figure 1 Scanning electron microscopy micrographs of AH Plus and Sealer 26 combined with gutta-percha (GP) cones, using either lateral compaction (LC) or Tagger s hybrid technique (THT): (a) AH Plus/GP/LC, showing a compact and dense surface with only few areas exhibiting microirregularities; (b) AH Plus/GP/THT, showing nonhomogenous mixture of GP and sealer, with an illcompacted surface with several empty spaces; (c) Sealer 26/GP/LC, exhibiting a compact but nonhomogeneous surface; and (d) Sealer 26/GP/THT, showing a material with fibrous appearance within a more porous material. (a) (b) (c) (d) Figure 2 Scanning electron microscopy micrographs of Epiphany SE combined with Resilon or gutta-percha (GP) cones, using either lateral compaction (LC) or Tagger s hybrid technique (THT): (a) Epiphany SE/Resilon/LC, showing a compact and homogeneous surface; (b) Epiphany SE/Resilon/THT, showing a material with fibrous appearance within a more porous material and large empty spaces; (c) Epiphany SE/GP/LC, showing a well-compacted surface; and (d) Epiphany SE/GP/THT, showing solid material intermingled within the sealer, forming a nonhomogenous mass. Several craters can be observed within the filling mass. 826 International Endodontic Journal, 45, , 2012 ª 2012 International Endodontic Journal

7 Carneiro et al. Thermomechanical root filling and adhesion to intraradicular dentine in lower adhesion. This also applies to Resilon cones. Moreover, in resin-based sealers, heating can accelerate the polymerization, reducing the flow of sealer (Tay et al. 2005, Kaya et al. 2008). The findings in the literature substantiate the ultrastructural analysis of filling material surface performed in the present study, in which the use of hybrid thermomechanical compaction technique resulted in a nonhomogenous mixture with an interwoven fibrous mesh within a poorly compacted material, suggesting that the plasticized solid filling material penetrated into the sealer, forming a nonuniform structure. GP and Resilon had the same behaviour. In the hybrid technique, it is likely that the plasticized and compacted solid material tends to mix with the sealer forming a nonuniform mass; upon cooling, the solid material shrinks and pulls the sealer, leaving craters that contribute to weaken the adhesive interface. In the LC technique, on the other hand, the GP is not mixed with the sealer. The SEM analysis revealed a filling material with a compact and dense surface, which was probably the resin-based sealer in contact with the dentine. It should also be mentioned that the tapered canal shape obtained with pre-flaring of the coronal and middle thirds produced root canal walls with adequate divergence, facilitating the insertion of the sealer and accessory cones. Amongst the root filling materials evaluated in the present study, the use of AH Plus with GP cones was associated with the highest bond strength mean values. Epoxy resin-based sealers penetrate deeper into the microirregularities owing to its flowability and long polymerization time, which contribute to enhancing the mechanical interlocking between sealer and dentine. In addition, the cohesion amongst the sealer molecules (Nunes et al. 2008) increases the resistance to displacement of the material from dentine surfaces, which is translated into greater adhesion (Sousa-Neto et al. 2005). It has been demonstrated that sealer polymerization in contact with dentine is influenced by the oxygen present in the root dentine walls and inside the dentinal tubules (Rached-Junior et al. 2009, Costa et al. 2010). According to Franco et al. (2002), as the oxygen inhibits vinyl polymerization in composite resins, these materials are not adequately polymerized and approximately 40 60% of the carbon bonds remain unsaturated (Finger et al. 1996). Regarding the root thirds, the highest bond strength was obtained in the coronal third, whilst Babb et al. (2009) and Costa et al. (2010) found no significant difference between the root thirds. One of the factors that could explain the different bond strengths between the root thirds is the different internal anatomy of the canals at each third because of the variation in the number and diameter of the dentinal tubules (Tao & Pashley 1988). According to Babb et al. (2009), however, the variations in tubular density along the canal are insufficient to alter sealer adhesion. Considering the interaction between root filling techniques and filling materials, the highest bond strength to root dentine was obtained with AH Plus/ GP using LC, as reported elsewhere (De-Deus et al. 2009). Epiphany SE was associated with the lowest mean values, regardless of the root filling technique and the type of solid material (cone). The claimed formation of a monoblock structure between Epiphany SE sealer, Resilon cones and dentine could not be confirmed in the present study in the same way as in a previous study (Schwartz & Fransman 2005). It appears that the amount of dimethacrylate incorporated in Resilon may not yet be optimized for effective and predictable chemical coupling to methacrylate-based sealers, which results in a weak union that does not resist polymerization shrinkage (Kaya et al. 2008). Another aspect that might interfere in the adhesion of Epiphany SE is its incomplete photoactivation because of a decrease in light exposure in the deepest regions of the root canal, which results in lower bond strengths because of reduced degree of monomer conversion (Nunes et al. 2008). The analysis of failure modes after the push-out test revealed a predominance of cohesive failures in the coronal third and mixed failures in the middle and apical thirds of specimens filled with AH Plus and Sealer 26 as well as adhesive failures in all thirds for Epiphany SE. The literature reports a predominance of mixed failures for AH Plus (Alfredo et al. 2008) and adhesive failures for Epiphany SE (Alfredo et al. 2008, Kaya et al. 2008). There was no difference between the root filling techniques with respect to failure mode. Conclusions The use of LC was associated with higher bond strength of the filling materials to root dentine than the use of a hybrid thermomechanical compaction technique. The best result was obtained when the canals were filled using LC of AH Plus and GP cones. ª 2012 International Endodontic Journal International Endodontic Journal, 45, ,

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