Bond degradation resistance of self adhesive sealer bonded to radicular dentin using an alternative adhesive strategy

Available online at www.sciencedirect.com

H O S T E D BY

ScienceDirect Tanta Dental Journal 12 (2015) 124e131 www.elsevier.com/locate/tdj

Bond degradation resistance of self adhesive sealer bonded to radicular dentin using an alternative adhesive strategy R.E. Hassan a,1, M.I. Riad b,*, M.A. Kataia c,2 b

a Endodontic Department, Faculty of Dentistry, Minia University, Egypt Conservative Dentistry Department, Faculty of Oral and Dental Medicine, Cairo University, EL Manial, Egypt c Endodontic Department, Faculty of Oral and Dental Medicine, Cairo University, EL Manial, Egypt

Received 3 March 2015; revised 18 April 2015; accepted 20 April 2015 Available online 23 May 2015

Abstract Objective: This study was carried out to evaluate the effect of an alternative adhesive strategy; double layering dentin bonding procedure in root canal obturation on the durability of root canal sealing using Resilon/Epiphany dual cure resin composite sealer system. Materials and methods: One hundred and twenty freshly extracted human upper central incisors teeth with straight root canals were used. The crowns were removed at the level of Cemento-Enamel Junction (CEJ). All roots were instrumented with a crowndown technique. The root canals were filled with either single or double layering bonding techniques, aged for 7 days and 3 months, and then sectioned perpendicular to the longitudinal axis of each root into a series of 1.0 mm thick cross-sectional slices. Durability of sealing was tested by both micropush out and nanoleakage tests. For the micropush out test, each root slice was subjected to compressive loading via a computer controlled materials testing machine, while for nanoleakage, the slices were immersed in the tracing solution of ammoniacal silver nitrate for 24 h in complete darkness. Photomicrographs were obtained by Environmental Scanning Electron Microscope. Results: The micropush out bond strength increased significantly with the double layering technique. On the other hand, it was not affected by aging. Only one nanoleakage pattern start to emerge as early as 7 days after sealing and continue after that. Conclusions: The current study supports the concept that double layering bonding strategy might be successfully adapted to endodontics to optimize bond strength of endodontic self-adhesive sealers to radicular dentin and to reduce nanoleakage. © 2015, Hosting by Elsevier B.V. on behalf of the Faculty of Dentistry, Tanta University.

Keywords: Double layering technique; Adhesive sealer; Micropush out; Nanoleakage

* Corresponding author. Operative Dentistry Department, Faculty of Oral and Dental Medicine, Cairo University, 15 El Saray St., EL Manial 11451, Egypt. Tel.: þ20 02 01006608683; fax: þ20 02 27538831. E-mail addresses: [email protected] (R.E. Hassan), [email protected] (M.I. Riad), [email protected] (M.A. Kataia). Peer review under the responsibility of the Faculty of Dentistry, Tanta University. 1 Tel.: þ20 01001542529. 2 Tel.: þ20 01223118296, þ20 01006609395. http://dx.doi.org/10.1016/j.tdj.2015.04.002 1687-8574/© 2015, Hosting by Elsevier B.V. on behalf of the Faculty of Dentistry, Tanta University.

R.E. Hassan et al. / Tanta Dental Journal 12 (2015) 124e131

125

Table 1 Materials' specifications, composition, manufacturers and batch number. Materials

Specification

Composition

Manufacturer

Batch no

Epiphany

Soft Resin Endodontic Obturation system. Self-Etch Root Canal Sealer

Pentron Clinical Wallingford, CT 06492 USA

173157

Resilon points

Root canal filling material.

Benzoyl Peroxide, Tertiary Amine, EBPADMA, BIS-GMA, HEMA, Proprietary acidic, Silane treated Barium glass, Ca3(PO4), Bismuth oxychloride, Luting system Polyester, Difunctional methacrylate resin, Bioactive glass, Bismuth oxychloride, Barium sulfate, Coloring agent.

Pentron Clinical Wallingford, CT 06492 USA

162850

Abbreviations: Bis-GMA: Bisphenol A diglycidyl methacrylate; HEMA: 2-Hydroxyethyl methacrylate; EBPADMA: Ethoxylated Bisphenol Dimethacrylate-based Amorphous Calcium Phosphate Composites.

1. Introduction Root canal obturation ideally confers prevention of coronal ingress of bacteria, and accumulation of fluid apically that could serve as nutrients for bacteria [1]. Success in endodontic treatment is predominantly determined by complete obturation of the canal system. Gutta-percha is considered the gold standard root canal filling material. However it does not bond to the internal tooth structure, resulting in the absence of a complete seal leading to leakage that takes place at the interface between the sealer and gutta-percha or the sealer and dentin [2]. Thus, finding a gutta-percha substitute that would provide a superior seal of the root canal system has become a challenge in modern endodontics. The materials and techniques currently used for adhesive bonding to dentin in restorative dentistry have been developed over many years. The latest generation of dentin bonding systems achieved high bond strength and reduced microleakage by micromechanical bonding or forming a hybrid layer between the dentin and the resin. Studies have examined the potential of adhesive resin root canal filling materials as possible improvements in decreasing the amount of leakage when compared with conventional gutta-percha fillings and an improvement on the root fracture resistance as a consequence to establishing monoblock between the intraradicular dentin and adhesive root fillings [3]. Resilon/Epiphany3 is a resin-based obturation system that utilizes a dentin adhesive. It utilizes a resinous obturating material and an adhesive resin sealer, creating a monoblock of dentin/adhesive/obturating material [4]. Nanoleakage was originally used to describe microporous zones beneath or within the hybrid layer that permitted tracer penetration to occur in the 3

Pentron Clinical Wallingford, CT 06492, USA.

absence of interfacial gap, it occurs through submicrometer-sized spaces within dentin hybrid layer where disparities existed between the depths of demineralization and monomer diffusion [5]. Nanoleakage may allow the penetration of bacterial products which may result in hydrolytic breakdown of either the adhesive resin or collagen within the hybrid layer, thereby compromising the stability of the resinedentin bond [6]. One of the advantages of the incremental technique used in cavities filled with resin composite is that the volume reduction of each increment could be compensated for by the next, and thus the consequence of polymerization shrinkage would be less harmful since only the volume reduction of the last layer would effectively damage the bond surface [7]. In a trial to mimic the benefits of this technique, a double layering technique was tried in obturation of endodontically treated teeth. Therefore, it is of value to shade a light on the bond degradation resistance of Resilon/epiphany obturation system to dentin using single and double layering techniques as assessed by micropush out bond strength and nanoleakage tests. 2. Materials and methods

One hundred and twenty freshly human upper central incisors teeth with straight root canal, fully developed apices and free of cracks, caries or fractures and had no previous root canal treatment extracted due to periodontal disease were selected. The crowns of the teeth were removed at the level of CEJ to obtain a 12-mm long root. Canal patency was determined by passing a size 10 K file through the apical foramen. The pulp tissue was first removed with barbed broach4. Canal working lengths (WL) were established 1.0 mm short of the apex. All teeth were instrumented with a 4

Dentsply Maillefer, Ballaigues, Switzerland.

126

R.E. Hassan et al. / Tanta Dental Journal 12 (2015) 124e131

Fig. 1. Steps of preparation of Teflon pluggers used for double layering filling technique.

crown-down technique [8] using a set of ProTaper rotary instruments3 following the manufacturer's instructions till size F3. Irrigation was performed using 3 mL of 2.5% NaOCl after every change of instrument. Following biomechanical preparation 17% EDTA was used for 1 min, followed by distilled water for 1 min. The specimens were divided into two groups according to the filling modalities of 60 teeth each, where in the first group roots were obturated with the sealer (Table 1) according to the manufacturer instructions with the single layer bonding technique, while the second group was obturated using an alternative adhesive strategy; double layering bonding technique. Again, each group was subdivided into two subgroup of 30 teeth each according to aging periods of one week and 3 months. 2.1. Single layer bonding technique

The sealer was applied to the canal wall. The master cone was coated with Epiphany sealer3 and introduced into the canal to the full working length. Lateral compaction was performed; accessory cones coated with sealer were inserted into the canal. The excess points were then cut with a heated instrument. As soon as the filling was completed, light cure was applied for 40 s from the top with LED curing unit5. This ensures an immediate coronal seal. 2.2. Double layering bonding technique

The sealer was applied to the canal in two layers; the first layer was applied to the canal wall, and then a fabricated Teflon plugger was introduced in the canal 5

Ivoclar Vivadent, Schaan, Liechtenstein.

to the full working length. The Teflon plugger had to be of the same size and taper of a Protaper F3 file in order to fit in the canal and leave a space for the sealer. Cylindrical Teflon rod (30 cm length  1 cm diameter) was chosen and cut into smaller rods (3.5 cm length) with the aid of diamond disk. 2 cm of each rod was reduced by a trimming machine to 3 mm diameter. Trials for size reduction more than this by the machine led to rod bending and fracture (Fig. 1a). With the aid of manufacturer's specifications of the Protaper file taper and diameter, the rod was grinded by diamond stone mounted on a slow speed hand piece, to reach the specified measurement of the file number F3. The plugger taper and thickness was measured and repeatedly checked while grinding by means of a digital caliper (0.01 mm). The other unreduced 1.5 cm of the rod was used as a handle (Fig. 1b). The first layer was light cured from the top for 40 s with the Teflon plugger inside the canal. Because there was no bonding of the Teflon material to methacrylatebased resins, the Teflon plugger was easily withdrawn, and at the same time it is light-conducting material. Light can pass through the Teflon material so cannot prevent complete curing. This step was performed to keep the canal space for the Resilon point's placement. Another layer of the sealer was applied to the Resilon point, inserted and bonded in situ by light-curing for another 40 s. All samples were stored in gauze dampened with aqueous solution for 72 h at 37  C to allow the sealer to set. 2.3. Incubating storage container

A ready-made plastic container with a lid, to minimize heat loss and water evaporation during the

R.E. Hassan et al. / Tanta Dental Journal 12 (2015) 124e131

127

Fig. 4. The roots mounted on the pipeline system fixed to a plastic base. Fig. 2. The incubation storage box closed and the temperature control unit.

long-term storage periods, was used. A digital temperature control unit, a heater for warming the water to the desired temperature [37  C ± 0.1  C] and a fan mixer connected to an electric motor to circulate the water for keeping the temperature well distributed and to prevent stagnation (Fig. 2). 2.4. Mounting of the teeth to the pipelines

The pipeline system used in the experiment had two directions of liquid flow; one horizontal with two opening for inter connection of the extensions, and the other direction perpendicular to it with three opening for mounting of the teeth (Fig. 3). After mounting the teeth to the pipelines through plastic hoses surrounding the root, the pipelines rows each representing a test group were immersed in a distilled water bath; which was renewed every week. Water level was kept below the coronal end of the root by 2 mm to insure hydration over the aging periods, at the same time no water can pass through the canal from its coronal end (Fig. 4).

Fig. 3. Pipeline unit.

2.5. Specimen's preparation for micropush and nanoleakage tests

The roots were sectioned perpendicular to the longitudinal axis of each root into a series of crosssectional slices of 1.0 mm thick disks. 2.6. Micro-push out bond strength testing

Each root slice was mounted in custom made loading fixture; metallic block with circular cavity at the middle, this cavity for specimen housing having a central whole to facilitate displacement of extruded filling material, then subjected to compressive loading at a crosshead speed of 1 mm/min via a computer controlled materials testing machine. After securing to a loading fixture, the filling material was loaded with different diameter cylindrical fabricated stainless steel plunger that provided the most extended coverage over the filling material without touching the canal wall, of 1.0, 0.76, 0.50, and 0.35 mm. The plunger tip was sized and positioned to touch only the filling, without

Fig. 5. Specimen mounted on materials testing machine.

128

R.E. Hassan et al. / Tanta Dental Journal 12 (2015) 124e131

Table 2 The means, standard deviation (SD) values of micropush out bond strength of the tested sealer. Technique

Aging

Mean

SD

P-value

Single layer

7 3 7 3

1.02 2.58 3.30 4.05

0.6 1 1.4 1.2

0.011* 0.423 <0.001* 0.332

Double layering *

days m days m

Significant at P  0.05.

stressing the surrounding dentin, in apical coronal direction to push the filling toward the larger diameter, thus avoiding any limitation to the filling movement possibly owing to the canal taper. Each slice was so marked on its coronal side with an indelible marker to ensure that the direction of plunger push was in the apical to coronal direction (Fig. 5). The maximum failure load was recorded in N and converted into MPa. The bond strength was calculated from the recorded peak load divided by the computed surface area as calculated by the following formula: ½A ¼ ð3:14  r 1  3:14  r 2 ÞL; where r1 apical radius, r2 coronal one L ¼ ½ðr 1  r 2 Þ2 þ h2 0:5 h is the thickness of the sample in millimeters.

Failure manifested by extrusion of filling piece and confirmed by sudden drop along load-deflection curve recorded by Nexygen computer software. 2.7. Nanoleakage test: specimens preparation for silver nitrate uptake

The slices were immersed in a 50 wt% ammoniacal silver nitrate tracer solution for 24 h in a light proof container in total darkness. The silver-stained slices were rinsed thoroughly with distilled water and

immersed in photo-developing solution for eight hours under a fluorescent light, to reduce the diamine silver ions into metallic silver grains within voids along the bonded interfaces [9,10]. Evaluation of silver uptake was done using Quanta Environmental Scanning Electron Microscope (FEI Quanta 200 ESEM, 2003). 3. Results Table 2 showed that after aging for 7 days, and 3 months, the mean micropush out bond strength in MPa with double layering technique showed statistically significantly higher values than that with single layer technique. The results showed that the increase in Micropush bond strength with 3 months aging was not statistically significantly different from that of 7 days with both techniques. Results of observation of environmental scanning electron microscope (ESEM) showed that with the single layer technique at 7 days aging time, the hybrid layer showed scanty scattered deposited silver grains that took the spotted appearance. Epiphany showed a good seal as all dentinal tubules were free from silver droplets. (Fig 6 right). With double layering technique the hybrid layer showed numerous very small and few deposits of silver grains of spotted pattern. The hybrid layer was approximately 3e4 mm thick (Fig. 6 left). At three months aging time, the same spotted appearance of that 7 days aging appeared, where the hybrid layer showed scanty scattered isolated deposits of silver grains located throughout its whole thickness with both tested sealing techniques (Fig. 7). 4. Discussion Endodontic sealers should demonstrate adhesive properties to dentin to reach the objectives of the obturation of the canal space and seal the canal space

Fig. 6. ESEM Photomicrograph of the single layer technique (left) and double layers (right) of Epiphany sealer dentin interface at 7 days aging period.

R.E. Hassan et al. / Tanta Dental Journal 12 (2015) 124e131

129

Fig. 7. ESEM Photomicrograph of the single layer technique (left) and double layers (right) of Epiphany sealer dentin interface at 3 months aging period.

both apically and coronally, thus decreasing the chance of endodontic treatment failure [11]. However, bonding to root dentin is compromised by volumetric changes that occur in methacrylate resin-based sealers during polymerization. Polymerization shrinkage stresses developed along the root dentin-sealer interface might result in debonding of the sealer. These stresses are exacerbated inside the root canal because the bonding area is high relative to the volume of canal filling materials; canal walls cannot compensate for shrinkage stresses by elastic deformation. Resin based restorative materials shrink from 2 to 7%, depending on the volume occupied by filler particles and the test method. The force of polymerization contraction often exceeds the bond strength of dentin adhesives to dentin, resulting in gap formation along the surfaces with the weakest bonds. Separation often occurs within the hybrid layer, but can occur in other areas. Resins in thin layers generate very high forces from polymerization contraction [12]. An alternative adhesive strategy, also known as incremental technique that is used usually in restorative procedures; to reduce the polymerization shrinkage of resin composite restorations, was tried in this study in root canal obturation, in a trial to enhance bonding to radicular dentin. Adopting double layering technique may compensate for polymerization stresses. With this bonding procedure, a first step coats the canal walls with a hybridized resin, and then a second step bonds the core material to the cured resin film. Thus, the polymerization shrinkage that occurs during the initial adhesive coating step may reduce the effects of stress imposed when the core material polymerizes, thereby preserving the bond integrity [13]. Specimens were aged for 7 days and 3 months. Loss of bond strength was first detectable in the laboratory at 3 months [14]. By introducing an aging factor into the study design, one can assess the durability of adhesion, to test the effect of time degradation as well

as the effect of the hydrolytic degradation of the adhesive polymer and water sorption that causes swelling and plasticization of the polymers, resulting in a reduction of their mechanical properties and a decrease in strength of the resin bond. Bond-strength testing has become a popular method for determining the effectiveness of adhesion between endodontic materials and tooth structure. There are many methods for measuring the adhesion of endodontic root canal sealers, but none has yet been widely accepted [15]. The tensile strength test is sensitive, with the result that small alterations in the specimen or in stress distribution during load application have a substantial influence on the results [16]. However the push-out test provides a better evaluation of the bonding strength than the conventional shear test because with the push-out test fracture occurs parallel to the dentine-bonding interface, which is a true shear test for parallel-sided samples [17]. It has the benefit of more closely simulating the clinical condition. Another advantage of this method is that it allows root canal sealers to be evaluated even when bond strength are low. Non-uniform stress distribution is a drawback of the push-out test when it is performed on the whole post or on thick root sections [18]. To overcome this problem, the original push-out technique was modified by slicing the root into 1-mm-thick specimens [19]. Adhesive materials are frequently compared using either bond strength or/and microleakage tests. Even if a material has relatively low bond strength to dentin it may be a good obturating material if it is effective in preventing microleakage. None of the current adhesive materials provide a leak proof seal [12]. Leakage has been shown to occur at the margins of sealer dentin interface, but may also be limited to internal aspects of the sealer dentin interface. Thus, both the marginal seal; microleakage and the internal dentinal seal; nanoleakage are important to the longevity of resinbased endodontic filling materials. Nanoleakage was

130

R.E. Hassan et al. / Tanta Dental Journal 12 (2015) 124e131

originally used to describe micro porosities within hybrid layers that allow silver nitrate penetration to occur in the absence of gap formation between resin composite and the hybrid layer. Ammoniacal silver nitrate is the most used tracer for evaluation of the nanoleakage phenomenon, this solution can penetrate the dentin due to the small silver ion size (0.059 nm in diameter), contrasting the size of this ion with the size of some bacteria (0.5e1.0 mm) yields considerable information about the results obtained in evaluating the nanoleakage phenomenon. Comparison between the results of different test groups indicated that while Epiphany/Resilon groups showed low bond strength but it performs well especially when the double layering technique was used, that appeared in long aging time with no degradation in bond strength, especially that all specimens were soaked in distilled water to accelerate the experiment so if degradation will occur it will happen rapidly. The results of the micropush bond strength values of the tested obturating techniques revealed that obturating techniques had a significant effect on the bond strength; where the modified double layering technique showed statistically significantly higher mean push out bond strength than that of single layer one (Table 2). A possible explanation for this difference was that, in the single layer technique, 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 [20]. With a double layering bonding procedure, a first step coats the canal walls with hybridized resins, and then a second step bonds the core material to the cured resin film. Thus, the polymerization shrinkage that occurs during the initial adhesive coating step will reduce the effects of stress imposed when the core material polymerizes with the sealer, thereby preserving the bond integrity. Also resins in thin layers generate high forces from polymerization contraction [12]. The results showed that the increase in Micropush bond strength with 3 months aging was not statistically significantly different from that of 7 days with both techniques. The inherent volumetric expansion, may have contributed to the superior bond strength found in this study. Physicochemical properties such as solubility and dimensional change after setting of the root canal filling materials are associated with the integrity and dimensional stability of the canal wall/sealer or sealer/core, being directly related to the desired hermetical sealing [21].

The mean linear shrinkage of the sealer shall not exceed 1% or 0.1% in expansion (ANSI/ADA Specification 57). This dimensional alteration could be explained by water sorption suffered by these types of resins after polymerization. Water sorption in resin composite materials is a diffusion-controlled process and occurs mainly in the resin matrix that can be explained by the presence of hydrophilic difunctional methacrylates. Polymerized materials from mixtures of hydrophilic monomers will show high water sorption. Diffusion of water, however, has belated beneficial effects. Swelling of the resin matrix results in expansion of the composite that compensates for the polymerization stresses that are created during shrinkage [1]. At the meantime, the non-significant difference in the bond strength results between the two aging periods might indicate absence of hydrolysis degradation of resin composite and the depletion of collagen fibrils. Different patterns of nanoleakage could be observed, through which the extent of nanoleakage was determined. It starts with spotted pattern where the silver particles appear as isolated spots consisting of very small (5e10 nm) silver grains dispersed randomly throughout both the adhesive and the hybrid layers, that indicates the first grade of nanoleakage and end with silver bands that indicates extensive nanoleakage. The observation of the photomicrographs revealed that there was nanoleakage manifested by silver penetration that had only spotted pattern with in both aging periods. This finding was in agreement with [5,22]. Epiphany selfetch sealer contains HEMA and Bis GMA. Several reports indicated that BisGMA does not infiltrate into acid-etched dentin as well as HEMA, creating a HEMArich, BisGMA-poor lower half of such hybrid layers. HEMA, mixing with water in the bottom half of the hybrid layer, may produce hydro gels and that silver uptake in these sites reflects the presence of such water. One disadvantage of hydrophilic HEMA resin systems is that they attract water [5]. Nanoleakage might also result from the incomplete diffusion of high molecular weight resin monomers into the primed collagen network. As Epiphany resin sealer contains fillers, and then its ability to penetrate the network is further compromised. The exposed collagen network may make the resinecollagen hybrid layer more susceptible to hydrolytic degradation over the long term [6]. Epiphany behave perfectly when applied in double layering technique where only very few spots of silver were apparent in the hybrid layers. The manipulation of the partially polymerized sealer during condensation

R.E. Hassan et al. / Tanta Dental Journal 12 (2015) 124e131

in single layer technique might disrupt developing bonds between self-etching primer and root dentin. In addition, the manufacturer's instruction for immediately light-curing the coronal root filling created a coronal seal that might limit the flow of resin sealer for stress relief. This result contradicts that of Tay et al. [8] who observed heavy silver deposits between the methacrylate resin sealer and root dentin, In areas that exhibited severe leakage, continuous bands of silver were present along the interface.

[7]

[8]

[9]

5. Conclusions

[10]

The current study supports the concept of double layering strategy, which greatly affects the resistance to degradation with positive effect on both the bond performance and the nanoleakage profile of Resilon/ Epiphany system.

[11]

[12]

6. Recommendations [13]

1. Keeping in consideration the possible clinical life, more studies are needed for the double layering bonding technique. 2. Further development should be done regarding the Teflon plugger if this alternative bonding strategy proved to be an effective method. 3. It is worthwhile to examine in future studies the self-etching potential of this self-adhesive sealer to ensure that it is aggressive enough to etch through smear layers and demineralize the intact radicular dentin without the adjunctive use of EDTA.

[14]

[15]

[16]

[17]

[18]

References [19] [1] Depraet FJHW, De Bruyne MAA, De Moor RJG. The sealing ability of an epoxy resin root canal sealer after Nd: YAG laser irradiation of the root canal. Int Endod J 2005;38:302e9. [2] Economides N, Kokorikos I, Kolokouris I, Panagiotis B, Gogos CP. Comparative study of apical sealing ability of a new resin-based root canal sealer. J Endod 2004;30:403e5. [3] De-Deus G, Namen F, Galan JJ. Reduced long-term sealing ability of adhesive root fillings after water-storage stress. J Endod 2008;34:322e5. [4] Pentron Clinical Technologies, Wallingford, CT, U.S.A, Epiphany® Newsletter, July 2005. [5] Li H, Burrow MF, Tyas MJ. Nanoleakage patterns of four dentin bonding systems. Dent Mater 2000 Jan;16:48e56. [6] De-Munck J, Van Landuyt K, Peumans M, Poitevin A, Lambrechts P, Braem M, et al. A critical review of the

[20]

[21]

[22]

131

durability of adhesion to tooth tissue: methods and results. J Dent Res 2005;84:118e32. Yoshida Y, Nagakane K, Fukuda R. Comparative study on adhesive performance of functional monomers. J Dent Res 2004;83:454e8. Tay FR, Loushine RJ, Monticelli F, Weller RN, Breschi L, Ferrari M, et al. Effectiveness of resin-coated gutta-percha cones and a dual-cured, hydrophilic methacrylate resin-based sealer in obturating root canals. J Endod 2005;31:659e64. Hashimoto M, De Munck J, Ito S, Sano H, Kaga M, Oguchi H, et al. In vitro effect of nanoleakage expression on resin-dentin bond strengths analyzed by microtensile bond test, SEM/EDX and TEM. Biomaterials 2004;25:5565e74. Sauro S, Pashley DH, Mannocci F, Tay FR, Pilecki P, Sherriff M, et al. Micropermeability of current self-etching and etch-and-rinse adhesives bonded to deep dentine: a comparison study using a double-staining/confocal microscopy technique. Eur J Oral Sci 2008;116:184e93. Sly MM, Moore BK, Jeffrey AP, Brown CE. Push-out bond strength of a new endodontic obturation system (Resilon/ Epiphany). J Endod 2007;33:160e2. Schwartz RS. Adhesive dentistry and endodontics Part 2: bonding in the root canal systemdthe promise and the problems: a review. J Endod 2006;32:1125e34. Bouillaguet S, Bertossa B, Krejci I, Wataha JC, Tay FR, Pashley DH. Alternative adhesive strategies to optimize bonding to radicular dentin. J Endod 2007;33:1227e30. Tay FR, Hashimoto M, Pashley DH, Peters MC, Lai SCN, Yiu CKY, et al. Aging affects two modes of nanoleakage expression in bonded dentin. J Dent Res 2003;82:537e41. Gogos C, Theodorou V, Economides N, Beltes P. Kolokouris I: shear bond strength of AH-26 and epiphany to composite resin and resilon. J Endod 2008;34:1385e7. Van Noort R, Cardew GE, Howard IC, Noroozi S. The effect of local interfacial geometry on the measurement of the tensile bond strength to dentine. J Dent Res 1991;70:889e93. Drummond JL, Sakaquchi RL, Racean DC, Wozny J, Steinberg AD. Testing mode and surface treatment effects on dentin bonding. J Biomed Mater Res 1996;32:533e41. Gallo JR, Miller T, Xu X, Burgess JO. In vitro evaluation of the retention of composite fiber and stainless steel posts. J Prosthodont 2002;11:25e9. Ungor M, Onay EO, Orucoglu H. Push-out bond strengths: the EpiphanyeResilon endodontic obturation system compared with different pairings of Epiphany, Resilon, AH plus and guttapercha. Int Endod J 2006;39:643e7. Skidmore LJ, Berzins DW, Babcall JK. An in vitro comparison of the intraradicular dentin bond strength of resilon and guttapercha. J Endod 2006;32:963e6. Donnelly A, Sword J, Nishitani Y, Yoshiyama M, Agee K, Tay FR, et al. Water sorption and solubility of methacrylate resin e based root canal sealers. J Endod 2007;33:990e4. Archegas LRP, Caldas DBM, Rached RN, Vieira S, Souza EM. Sorption and solubility of composites cured with quartztungsten halogen and light emitting diode light-curing units. J Contemp Dent Pract 2008;2:073e80.