- Email: [email protected]
New endodontic obturation systems and their interfacial bond strength with intraradicular dentine – ex vivo studies
· Advances in Medical Sciences · Vol. 56 · 2011 · pp 327-333 · DOI: 10.2478/v10039-011-0031-1 © Medical University of Bialystok, Poland
New endodontic obturation systems and their interfacial bond strength with intraradicular dentine – ex vivo studies Pawińska M1*, Kierklo A2, Tokajuk G3, Sidun J4 1 Department of Conservative Dentistry, Medical University of Bialystok, Bialystok, Poland 2 Department of Dentistry Propaedeutics, Medical University of Bialystok, Bialystok, Poland 3 Department of Periodontal and Oral Mucosa Diseases, Medical University of Bialystok, Bialystok, Poland 4 Department of Materials Science and Biomedical Engineering, Bialystok University of Technology, Bialystok, Poland
* CORRESPONDING AUTHOR: Department of Conservative Dentistry, Medical University of Bialystok 24a M. Skłodowskiej-Curie Str., 15-276 Bialystok, Poland tel. + 48 85 7421774, fax. + 48 85 7421774 e-mail: [email protected] (Małgorzata Pawińska)
Received 25.10.2010 Accepted 18.05.2011 Advances in Medical Sciences Vol. 56 · 2011 · pp 327-333 DOI: 10.2478/v10039-011-0031-1 © Medical University of Bialystok, Poland
ABSTRACT Purpose: To comparatively evaluate adhesive properties of selected root canal fillings through the measurement of the materialdentine interfacial bond strength. Material and Methods: Fifty extracted single-rooted human teeth with one canal each were prepared using Hero instruments to size 30.04. Teeth were divided into four subgroups depending on the root canal filling material and the method of obturation: Resilon/Epiphany - a thermoplastic method (IA), Resilon/Epiphany - a matching single-point method (IB), gutta-percha/Roeko Seal Automix - a thermoplastic method (IIA) and gutta-percha/Roeko Seal Automix - a matching single-point method (IIB). The obturated roots were cut perpendicular to the long axis to create 1.7 mm thick slices. The bond strength was measured for each test slice with push –out testing machine. Results: The highest push-out bond strength was registered in subgroup IB (3.98 ± 1.33 MPa). Significantly lower bond strength was observed in subgroups IA (0.50 ± 0.24 MPa), IIA (0.33 ± 0.18 MPa) and IIB (0.08 ± 0.03 MPa) (p<0.001). No statistically significant differences in material-dentine interfacial bond strength values were observed between IA and IIA, IA and IIB, IIA and IIB subgroups (p > 0.05). Conclusions: The push-out bond strength of the material-dentine interface was dependent on the type of material used and the root canal filling technique. The R/E system exhibited better adhesion ability to intraradicular dentine than G/RSA. The highest bond strength was observed for Resilon/Epiphany introduced with the single-cone technique. Key words: endodontic sealers, adhesion, push-out bond strength, Resilon
INTRODUCTION Endodontics is one of the dental branches, which has made constant progress in the recent years. Due to the dynamic development of modern technology and innovative solutions, it crosses many borders between the fields of dentistry, for example, in search for more perfect obturation materials [1]. The filling of the root canal should meet certain standards. Treatment efficacy is dependent upon precise threedimensional root canal filling. Durable and fluid-tight filling protects the tooth from bacterial microleakage and further complications. Ideal adherence of the filling to the root canal dentine is one of the critical factors, for it eliminates leakages
in static conditions, which could endanger the tooth by the fluid penetration into the cavity. In dynamic conditions, however, it prevents the material from being translocated by the occlusal load [2]. To evaluate the adherence force (adhesion) of the filling to the root canal walls, the strength of the material-dentine interfacial bond is measured. There are several measurement methods to assess the adhesion: shear bond strength, tensile bond strength, push-out bond strength, but none of them is recognised as a standard method [3-6]. The latter seems to provide the most similar conditions as those observed in clinical reality, as it measures the material-dentine interfacial bond strength along the entire length of the root canal [6-8].
328
New endodontic obturation systems and their interfacial bond strength with intraradicular dentine – ex vivo studies
Table 1. Compositions of materials tested for push-out bond strength. Material
Source
Gutta-percha
VDW® GmbH Munchen, Germany
Active ingredients Gutta-percha, zinc oxide, barium sulfate, pigment agent
Roeko Seal Automix
Coltene/Whaledent GmbH+Co. KG, Langenau, Germany
Polydimethylsiloxane, silicone oil, paraffin-base oil, platinum catalyst, zirconium dioxide
Resilon
Pentron® Clinical Technologies, LLC Wallingford CT, USA
Organic part: thermoplastic synthetic polymer – polycaprolactone, Inorganic part: biactive glass, bismuth oxychloride, barium sulphate
Epiphany
Pentron® Clinical Technologies, LLC Wallingford CT, USA
Organic part: BisGMA, ethoxylated BisGMA, UDMA, hydrophilic difunctional methacrylates Inorganic part: calcium hydroxide, barium sulphate, barium glass, bismuth oxychloride, silica
Table 2. Number of teeth and number of slices in experimental groups and subgroups. Group I – Resilon/Epiphany subgroup A
Group II – Gutta-percha/RSA subgroup B
subgroup A
subgroup B
thermoplastic method
single-point method
thermoplastic method
single-point method
number of teeth
number of slices
number of teeth
number of slices
number of teeth
number of slices
number of teeth
number of slices
10
8
15
15
10
8
15
15
Moreover, it provides repetitive results, allows for testing of materials with low bond strength with dentine and the samples for testing are easy to align [9]. This test is also less sensitive to differences in sample sizes and differentiated stress distribution during load application [10]. According to Skidmore et al. [11], during the test, a trend to decrease the actual adhesion values and heterogeneous load distribution in samples of considerable thickness in observed. The latter disadvantage may be overcome by using thin dentine slices (approx. 1 mm) [7]. One of the new sealers used with gutta-percha cones, receiving good clinical outcomes, is polysiloxane-based Roeko Seal Automix (RSA) [12]. Its particular strength lies in the low sensitivity to moisture, no shrinkage, and even 0.2% expansion during the first few weeks after application, after which the volume becomes stable, ensuring good sealing [13, 14]. Five years ago, a material called Resilon was introduced to market. It was based on a thermoplastic composite resin, which is used with a methacrylate sealer - Epiphany. The potential ability of this system to penetrate into the dentine tubules is emphasised. It results in creating a monoblock, provides resistance to bacterial microleakage, low shrinkage during thermal plasticisation and leads to the strengthening of the tooth structure [15-17]. The aim of this study was to comparatively evaluate adhesive properties of selected root canal fillings through the measurement of the material-dentine interfacial bond strength.
MATERIAL AND METHODS A total of fifty single-rooted human teeth (with one canal each), extracted from periodontal reason, enrolled into the study after their evaluation in the endodontic microscope, which aimed at selecting only roots without any signs of hard tissue structure damage. The teeth were decoronated at the cement-enamel junction using a turbine and a diamond burr under water coolant. The root canal treatment was performed by two dentists. The root canals were prepared using crowndown method with rotary nickel-titanium instruments Hero 642 (MicroMega) until the master apical rotary (MAR size 30/04) an appropriate work length (1 mm short of the patency length) was achieved. During instrumentation, the root canals were irrigated with sodium hypochlorite (1%), 17% ethylenediaminetetraacetic acid (EDTA) and distilled water with subsequent drying with standardised paper points. The first group of 25 roots was filled with Resilon/Epiphany (R/E) system and the second group (remaining 25 roots) with gutta-percha with Roeko Seal Automix sealer (G/RSA). Tab. 1 shows the composition of the studied materials. Two subgroups were defined in each group, depending on the root canal filling method (A – thermoplastic method using System B and Obtura II; B – paste and single-cone (with a 0.04 taper master cone) technique. Tab. 2 shows the number of teeth in respective groups and subgroups. Radiographs were taken to confirm length and density of the root canal obturation in each case. All samples were stored in a moist environment at 37°C for 1 week. Each root was subsequently cut perpendicular to the long axis into transverse slices of 1.7 mm thick by using Minitom slow speed saw with water cooling. The number of slices in respective groups and subgroups is presented in
329
Pawińska M et al.
Figure 1. The root slice and interfacial area of root filling prepared to an image analysis software.
Figure 2. Schematic representation of calculating of the root filling interfacial area.
Table 3. Push-out bond strength values expressed in MPa ( mean, SD) with respect to the material and method of root canal filling. Group
Mean (MPa)
SD
IA* (Resilon/Epiphany) thermoplastic method
0.50
0.24
IB *#$ (Resilon/Epiphany) single-point method
3.98
1.33
IIA # (Gutta-percha/RSA) thermoplastic method
0.33
0.18
IIB $ (Gutta-percha/RSA) single-point method
0.08
0.03
SD – standard deviation *the statistically significant differences between IB and IA, p<0.001 # the statistically significant differences between IB and IIA, p<0.001 $ the statistically significant differences between IB and IIB, p<0.001
Tukey’s HSD (honestly significant difference) test for posthoc comparisons was used to evaluate the differences among experimental groups. The level of significance was set at p<0.05. Tab. 2. From each root one slice from the coronal side of the root was obtained. In the case of four teeth (2 from group I and 2 from group II), fillings using the thermoplastic condensation technique, we were unable to obtain undamaged slices when cutting the samples. Each slice was then measured, photographed from both apical and coronal side and subjected to computer processing using Corel DRAW 9.0 and MicroMeter software for the calculation of the circumference and surface area of the filling on both sides of each slices (Fig. 1). Once we obtained these values, and bearing in mind the thickness of each slice, we calculated the actual interfacial area of the root filling (P), similar in shape to a cylinder, using the following formula [5] (Fig. 2): P = (Ca + Cc) x ½ H Ca – circumference of the apical aspect Cc – circumference of the coronal aspect H – thickness of slice The material-dentine interfacial bond strength, which is the adhesion force of the endodontic material to the root canal wall, was performed using testing machine Instron TM-SM (Instron) and push-out test [5, 8, 9]. The filling was pushed out of the slice, placed in the specially constructed device with a piston, in an apical-coronal direction with a speed of 1 mm/min and simultaneous registration of the applied force. Adhesion of the canal filling to the dentine was calculated for each slice by dividing the force in newtons [N], needed to push a material out of the slice, by the interfacial area of the root filling calculated earlier [in mm2]. The obtained result was expressed in megapascals [MPa].
Statistical analysis Statistical analysis was performed using the software package Statistica 8.0 (StatSoft). The push-out bond strength results were evaluated using one-way analysis of variance ANOVA.
RESULTS The obtained results are summarized in Tab. 3. and Tab. 4. The highest push-out bond strength value was registered for the teeth filled with Resilon/Epiphany system using the singlecone technique (group IB) and amounted to 3.98 ± 1.33 MPa. Significantly lower bond strength was observed for the teeth filled with the same material, but using the thermoplastic method (group IA, 0.50 ± 0.24 MPa), and both subgroups, where the obturation was performed using gutta-percha and RSA paste (group IIA – 0.33 ± 0.18 MPa; group IIB – 0.08 ± 0.03 MPa) (p<0.001). No statistically significant differences in material-dentine interfacial bond strength values measured in the push-out test were observed between IA and IIA, IA and IIB, IIA and IIB subgroups (p>0.05). In order to estimate the influence of the used material and canal obturation technique on the dentine-material bond strength identified with adhesion, a regression model was created in the studied groups, the correctness of which was statistically confirmed (p<0.05) (Tab. 4). This model explained 63.1% of the adhesion variation (adjusted R2 coefficient = 0.631). Additionally, basing on the regression model, the absolute influence of the used material and obturation technique on dentine-material interface bond strength was estimated. Statistical analysis revealed that the Resilon/Epiphany system increased the material adhesion by 2.608 MPa (regression coefficient B=2.608) in comparison to gutta-percha/RSA system. This increase has proven to be statistically significant (p<0.001). The root canal filling with paste and single cone increased the filling adhesion by 1.235 MPa (regression coefficient B=1.235) in comparison to thermoplastic technique. The differences were statistically significant
330
New endodontic obturation systems and their interfacial bond strength with intraradicular dentine – ex vivo studies
Table 4. The regression model presenting the influence of the material and the application method on the material-dentine interfacial bond strength, that is the filling adhesion. Regression coefficient B
Standardised regression p coefficient β
Significance of regression model
Adjusted R2 coefficient
Material (Resilon/Epiphany vs.Gutta-percha/ RSA)
2.608
0.683
p < 0.001
p < 0.05
0.631
Method (single-point method vs. thermoplastic method)
1.235
0.308
p < 0.05
(p<0.05) (Tab. 4). Moreover, the involvement of the respective parameters (material type, obturation technique) in altering the materialdentine bond strength value in the created model was established using a standardised regression coefficient β. The absolute value of this coefficient defines the importance of the respective parameter. The statistical analysis revealed that it was the type of material used followed by canal filling technique that had the greatest and concurrently statistically most significant influence on material-dentine adhesion (β = 0.683, p<0.001 and β = 0.308, p<0.05, respectively) (Tab. 4).
DISCUSSION It was expected that the results of this ex-vivo study would indicate which of the tested endodontic materials can provide a tight seal of the canal system. However, it is hard to unequivocally determine this fact. Knowledge of adhesion of the above-described materials to the root canal dentine was rather sparse. Our studies showed that it is the adherence forces that are decisive for the material-intraradicular dentine bond strength and both systems studied demonstrate different inclinations to create such bonds. The R/E system applied to the root canal using the single-cone technique showed the highest values of the push-out bond strength. The bond strength was significantly weaker in teeth, where the material was applied using the thermoplastic method. On the other hand, in the G/RSA group, the material exhibited higher push-out bond strength after being applied using the thermoplastic method than after being sealed with the single cone, but the differences were statistically insignificant. R/E system introduced the use of the single-cone method demonstrated significantly higher adhesion values to the dentine rather than the G/RSA applied using either techniques. There is no unanimity among the authors using the pushout test as to the evaluation of the bond strength between the intraradicular dentine and R/E systems after the obturation using the single-cone technique. Nagas et al. [18] obtained similar results as we did (from 2.1 ± 0.9 to 3.9 ± 0.8 MPa, depending on the localisation of the slice), yet their material was light cured. On the other hand, other authors obtained 10-times lower bond strength of the methacrylate sealer with the dentine [10, 19]. Our own results, concerning the R/E system applied using the thermoplastic method, are identical
with those of Sly et al. [20] and Gesi et al. [5], yet lower than the material-dentine interfacial bond strength values acquired by Skidmore et al. [11] (1.51 ± 1.22 MPa) and Bouillaguet et al. [21] (5.0 MPa), despite the fact that all authors used the same push-out test. The above-mentioned discrepancies may result from different methods of sample preparation for the experiment (addition of the thinning resin to the sealer, different tooth storing time after root filling, different root slices thickness used in the test). Higher push-out bond strength in teeth filled with R/E system using the single-cone method should be explained by the presence of the thicker layer of the sealing paste [22] applied between Resilon and the dentine. Jainaen et al. [10] and Rahimi et al. [22] observed higher adhesion force values for thicker sealer layers, regardless of the sealer type. According to the authors, the weaker adherence of the thinner sealer layer to the dentine may be attributed to the small resin amount in comparison to the filler, that remains on the canal surface after its part has penetrated the dentine tubules. The thicker sealer layer provides better availability to resin components; therefore, no excessive depletion takes place and filler particles can be bonded, leading to the maintenance of the sealer cohesion [10, 22]. The results of the current studies reveal, however, that the thickness of the sealer layer plays a significant role in adhesion only in the case of resin-based materials and is not that important for polydimethylsiloxanes. The filling technique influences the bonding strength as well. The single-cone technique is considered to be less reliable than other methods due to the unfavourable sealer to guttapercha ratio, which facilitates the microleakage and quality decrease of interfacial integrity of root canal fillings [23, 24]. Recently, this conception has been modified. Nowadays, the sealer volume is smaller due to the use of cones of increased conicity, which are adjusted precisely to the geometry of the root canal prepared with NiTi rotary instruments, with identical convergence angle as cones [25]. In oval cross-section canals, it is recommended to introduce several gutta-percha cones apart from the main one (without the condensation with spreader), which increases the proportional amount of guttapercha in pericoronal part of the filling [26]. Thermoplastic methods may, on the other hand, lead to more damage of adhesive bond with dentine, due to the faster sealer polymerisation at higher temperatures [27, 28]. This phenomenon could have had significant importance for obtaining worse results in root canals, which were filled with
331
Pawińska M et al.
Resilon and Epiphany using the thermoplastic technique. In the presented studies, the R/E system was not light cured in order to create comparative conditions for both groups. Nagas et al. [18], however, studied the Resilon/ Epiphany-dentine bond strength after they had been cured with different light curing units (quartz-tungsten-halogenQTH, light-emitting diode-LED, plasma-arc- PAC). The authors observed that the highest bond strength was obtained for curing of the root canal filling with the QTH light curing unit, which is associated with slower polymerisation process, longer duration of the sealer liquid phase and associated smaller polymerisation shrinkage. The lowest adhesion values were observed also for root canal fillings cured with the PAC light curing unit. The authors consider that the increase in light output and the decrease in the curing time unfavourably influence the adherence of the Epiphany to the dentine. They emphasise the significance of the decrease in bond strength toward the apical direction of the root canal, which indicates limited light penetration. Such phenomenon was not observed for self-cured root canal fillings [19-21]. The available literature does not provide much insight into the evaluation of the adhesive properties of the RSA paste. This sealer is a silicone polymer and does not contain any free, reactive oxygen-containing groups, which could bond the dentine calcium. It results in no adhesion between the paste and tooth tissues [29], which was confirmed in our own current studies. The bond strength between the root canal wall and RSA sealer with single gutta-percha cone was 0.08 MPa. The experiments of Gambarini et al. [30], showed that the siloxane sealer is characterised by significantly lower disperse ability than polymethacrylate, and the capability to flow and low surface tension are very desired features, as they improve the adaptation of the filling to the canal walls. Saleh et al. [31] proved that RSA binds more strongly with root dentine in the presence of the smear layer and experimental primer. Therefore, the removal of the former and material condensation without prior primer application in their own studies could have contributed to worse results obtained for the group of RSA-filled roots. The latest studies of Saleh et al. [32] prove that the presence of the smear layer inhibits the bacterial leakage both in root canals filled with gutta-percha and Resilon. It should therefore be borne in mind that certain types of sealers may need different smear layer processing to obtain optimal bond with root canal dentine [31]. Resin sealers exhibit better penetration of the dentine tubules after the removal of the smear layer [5, 8, 18, 22]. This phenomenon may be desired, as it increases the surface of material-dentine adherence, provides its mechanical fixation, better canal sealing, and blocks the dentine tubules as well, preventing the bacteria from colonising the dentine. Saleh et al. [31] and Jainaen et al. [10] conclude that the presence of the sealer tags does not increase the bond strength with the dentine. It is even assumed that the sealer tags may cause unfavourable tensions resulting from load and lead to damage of the adhesive bonds [5, 8].
The bond strength of the methacrylate sealer-dentine interface is dependent on physico-chemical phenomena during the polymerisation of the material as well. Beriat et al. [33] proved that the conversion degree of the Epiphany sealer (transformation of monomers to polymers through the conversion of the double bonds between carbon atoms into single ones) after light curing reached the level of only 60% after two weeks from curing. Ureyen-Kaya et al. [34] achieved significantly higher bond strength after filling the root canal with combined Epiphany sealer and gutta-percha than with Resilon (G/E 2.22 ± 0.94 MPa vs. R/E 1.49 ± 1.06 MPa). The authors suggested combining the Epiphany sealer rather with gutta-percha, which seems more susceptible to condensation, than with Resilon, particularly during the material introduction with the so-called “cold” techniques. The material-dentine interfacial bond strength is only one of the aspects of the quality evaluation of the root canal fillings. Despite the fact that in most cases, the results of laboratory studies cannot be directly extrapolated to clinical conditions, the laboratory tests (ex-vivo) are helpful in examining and comparing the new materials. The information obtained in our study extends knowledge on endodontic materials science and is of significant importance from a practical point of view.
CONCLUSIONS Within the limits of this study, it may be concluded as following: the push-out bond strength of the material-dentine interface was dependent on the type of material used and the root canal filling technique. The R/E system exhibited better adhesion ability to intraradicular dentine than G/RSA. The highest bond strength was observed for Resilon/Epiphany introduced with the single-cone technique.
ACKNOWLEDGEMENTS The work was supported by the Medical University of Bialystok, by grant No 3-91766 L.
REFERENCES 1. Schwartz RR. Adhesive dentistry and Endodontics. Part 2: bonding in the root canal system – the promise and the problems: a review. J Endod. 2006 Dec; 32(12):1125-34. 2. Tagger M, Tagger E, Tjan AHL, Bakland LK. Measurement of adhesion of endodontic sealers to dentin. J Endod. 2002 May; 28(5):351-4. 3. Bouillaguet S, Troesch S, Wataha JC, Krejci I, Meyer JM, Pashley DH. Microtensile bond strength between adhesive cements and root canal dentin. Dent Mater. 2003 May; 19(3):199-205. 4. Erdemir A, Ari H, Gungunes H, Belli S. Effect of
332
New endodontic obturation systems and their interfacial bond strength with intraradicular dentine – ex vivo studies
medications for root canal treatment on bonding to root canal dentin. J Endod. 2004 Feb; 30(2):113-6. 5. 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 Nov; 31(11):809-3. 6. Gogos C, Theodorou V, Economides N, Beltes P, Kolokouris J. Shear bond strength of AH 26 and Epiphany to composite resin and Resilon. J Endod. 2008 Nov; 34(11):1385-7. 7. Goracci C, Tavares AE, Fabianelli A, Monticelli F, Rafaelli O, Cardoso PC, Tay F, Ferrari M. The adhesion between fiber posts and root canal walls: comparison between microtensile and push-out bond strength measurements. Eur J Oral Sci. 2004 Aug; 112(4):353-61. 8. Lee BS, Lai EH, Liao KH, Lee CY, Hsieh KH, Lin CP. A novel polyurethane-based root canal obturation material and urethane-acrylate-based root canal sealer – part 2: evaluation of push-out bond strengths. J Endod. 2008 May; 34(5): 594-8. 9. Ungor M, Onay EO, Orucoglu H. Push-out bond strengths: the Epiphany-Resilon endodontic obturation system compared with different pairings of Epiphany, Resilon, AH Plus and gutta-percha. Int Endod J. 2006 Aug; 39(8):643-7. 10. Jainaen A, Palamara JEA, Messer HH. Push-out bond strengths of dentin-sealer interface with and without a main cone. Int Endod J. 2007 Nov; 40(11):882-90. 11. Skidmore LJ, Berzins DW, Bahcall JK. An in vitro comparison of the intraradicular dentin bond strength of Resilon and gutta-percha. J Endod. 2006 Oct; 32(10):963-6. 12. Gencoglu N, Turkmen C, Ahiskali R. A new siliconebased root canal sealer Roekoseal®-Automix. J Oral Rehabil. 2003 Jul; 30(7):753-7. 13. Wu MK, Tigos E, Wesselink PR. An 18-month longitudinal study on a new silicon-based sealer, RSA RoekoSeal: A leakage study in vitro. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2002 Apr; 94(4):499-502. 14. Özok AR, van der Sluis LW, Wu MK, Wesselink PR. Sealing ability of a new polydimethylsiloxane-based root canal filling material. J Endod. 2008 Feb; 34(2):204-7. 15. Lin ZM, Jhugroo A, Ling JQ. An evaluation of the sealing ability of a polycaprolactone-based root canal filling material (Resilon) after retreatment. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2007 Dec; 104(6):846-51. 16. 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 May;30(5): 342-7. 17. Tay FR, Pashley DH. Monoblocks in root canals: A hypothetical or a tangible goal. J Endod. 2007 Apr; 33(4):391-8. 18. Nagas E, Cehreli ZC, Durmaz V, Vallittu PK, Lassilla LVJ. Regional push-out bond strength and coronal microleakage of Resilon after different light-curing methods. J Endod. 2007 Dec; 33(12):1464-8.
19. 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 Jul; 33(7):856-8. 20. Sly MM, Moore KB, Platt JA, Brown CE. Push-out bond strength of new endodontic obturation system (Resilon/ Epiphany). J Endod. 2007 Feb; 33(2):160-2. 21. Bouillaguet S, Bertossa B, Krejci I, Wataha JC, Tay FR, Pashley DH. Alternative adhesive strategies to optimize bonding to radicular dentin. J Endod. 2007 Oct; 33(10):1227-30. 22. Rahimi M, Jainaen A, Parashos P, Messer HH. Bond of resin-based sealers to root dentin. J Endod. 2009 Jan; 35(1):121-4. 23. De-Deus G, Couthinho-Filho T, Reis C, Murad C, Paciornik S. Polymicrobial leakage of four root canal sealers at two different thicknesses. J Endod. 2006 Oct; 32(10):998-1001. 24. Kontakiotis EG, Wu MK, Wesselink PR. Effect of sealer thickness on long-term sealing ability: a 2-year followup study. Int Endod J 1997 Sep; 30(12):307-12. 25. Monticelli F, Sword J, Martin RL, Schuster GS, Weller RN, Ferrari M, Pashley DH, Tay FR. Sealing properties of two contemporary single-cone obturation systems. Int Endod J. 2007 May; 40(5):374-85. 26. Wu MK, van der Sluis LWM, Wesselink PR. A 1-year follow-up study on leakage of single-cone fillings with RoekoRSA sealer. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2006 May; 101(5):662-7. 27. Tay FR, Loushine RJ, Lambrechts P, Weller RN, Pashley DH. Geometric factors affecting dentin bonding in root canals: A theoretical modeling approach. J Endod. 2005 Aug; 31(8):584-9. 28. Tay FR, Loushine RJ, Weller NR, Kimbrough W, Pashley DH, Mak YF, Lai C-NS, Raina R, Williams C. Ultrastructural evaluation of the apical seal in roots filled with a polycaprolactone-based root canal filling material. J Endod. 2005 Jul; 31(7):514-9. 29. Lee KW, Williams MC, Camps JJ, Pashley DH. Adhesion of endodontic sealers to dentin and gutta-percha. J Endod. 2002 Oct; 28(10):684-8. 30. Gambarini G, Testarelli L, Pongione G, Gagliani M. Radiographic and rheological properties of a new endodontic sealer. Aust Dent J. 2006 Jan; 32(1):31-4. 31. Saleh IM, Ruyter IE, Haapasalo MP, Ørstavik D. The effect of dentine pretreatment on the adhesion of root-canal sealers. Int Endod J. 2002 Sep; 35(10):859-66. 32. Saleh IM, Ruyter IE, Haapasalo MP, Ørstavik D. Bacterial penetration along different root canal filling materials in the presence or absence of smear layer. Int Endod J. 2008 Jan; 41(1):32-40. 33. Beriat NC, Ertan A, Cehreli ZC, Gulsahi K. Time-dependent conversion of methacrylate-based sealer polymerized with different light-curing units. J Endod. 2009 Jan; 35(1):110-2.
Pawińska M et al.
34. Ureyen-Kaya B, Kececi AD, Orhan H, Belli S. Micropush-out bond strengths of gutta-perch versus thermoplastic synthetic polymer-based systems – an ex vivo study. In. Endod J. 2008 Mar; 41(3):211-318 .
333
New endodontic obturation systems and their interfacial bond strength with intraradicular dentine – ex vivo studies Pawińska M1*, Kierklo A2, Tokajuk G3, Sidun J4 1 Department of Conservative Dentistry, Medical University of Bialystok, Bialystok, Poland 2 Department of Dentistry Propaedeutics, Medical University of Bialystok, Bialystok, Poland 3 Department of Periodontal and Oral Mucosa Diseases, Medical University of Bialystok, Bialystok, Poland 4 Department of Materials Science and Biomedical Engineering, Bialystok University of Technology, Bialystok, Poland
* CORRESPONDING AUTHOR: Department of Conservative Dentistry, Medical University of Bialystok 24a M. Skłodowskiej-Curie Str., 15-276 Bialystok, Poland tel. + 48 85 7421774, fax. + 48 85 7421774 e-mail: [email protected] (Małgorzata Pawińska)
Received 25.10.2010 Accepted 18.05.2011 Advances in Medical Sciences Vol. 56 · 2011 · pp 327-333 DOI: 10.2478/v10039-011-0031-1 © Medical University of Bialystok, Poland
ABSTRACT Purpose: To comparatively evaluate adhesive properties of selected root canal fillings through the measurement of the materialdentine interfacial bond strength. Material and Methods: Fifty extracted single-rooted human teeth with one canal each were prepared using Hero instruments to size 30.04. Teeth were divided into four subgroups depending on the root canal filling material and the method of obturation: Resilon/Epiphany - a thermoplastic method (IA), Resilon/Epiphany - a matching single-point method (IB), gutta-percha/Roeko Seal Automix - a thermoplastic method (IIA) and gutta-percha/Roeko Seal Automix - a matching single-point method (IIB). The obturated roots were cut perpendicular to the long axis to create 1.7 mm thick slices. The bond strength was measured for each test slice with push –out testing machine. Results: The highest push-out bond strength was registered in subgroup IB (3.98 ± 1.33 MPa). Significantly lower bond strength was observed in subgroups IA (0.50 ± 0.24 MPa), IIA (0.33 ± 0.18 MPa) and IIB (0.08 ± 0.03 MPa) (p<0.001). No statistically significant differences in material-dentine interfacial bond strength values were observed between IA and IIA, IA and IIB, IIA and IIB subgroups (p > 0.05). Conclusions: The push-out bond strength of the material-dentine interface was dependent on the type of material used and the root canal filling technique. The R/E system exhibited better adhesion ability to intraradicular dentine than G/RSA. The highest bond strength was observed for Resilon/Epiphany introduced with the single-cone technique. Key words: endodontic sealers, adhesion, push-out bond strength, Resilon
INTRODUCTION Endodontics is one of the dental branches, which has made constant progress in the recent years. Due to the dynamic development of modern technology and innovative solutions, it crosses many borders between the fields of dentistry, for example, in search for more perfect obturation materials [1]. The filling of the root canal should meet certain standards. Treatment efficacy is dependent upon precise threedimensional root canal filling. Durable and fluid-tight filling protects the tooth from bacterial microleakage and further complications. Ideal adherence of the filling to the root canal dentine is one of the critical factors, for it eliminates leakages
in static conditions, which could endanger the tooth by the fluid penetration into the cavity. In dynamic conditions, however, it prevents the material from being translocated by the occlusal load [2]. To evaluate the adherence force (adhesion) of the filling to the root canal walls, the strength of the material-dentine interfacial bond is measured. There are several measurement methods to assess the adhesion: shear bond strength, tensile bond strength, push-out bond strength, but none of them is recognised as a standard method [3-6]. The latter seems to provide the most similar conditions as those observed in clinical reality, as it measures the material-dentine interfacial bond strength along the entire length of the root canal [6-8].
328
New endodontic obturation systems and their interfacial bond strength with intraradicular dentine – ex vivo studies
Table 1. Compositions of materials tested for push-out bond strength. Material
Source
Gutta-percha
VDW® GmbH Munchen, Germany
Active ingredients Gutta-percha, zinc oxide, barium sulfate, pigment agent
Roeko Seal Automix
Coltene/Whaledent GmbH+Co. KG, Langenau, Germany
Polydimethylsiloxane, silicone oil, paraffin-base oil, platinum catalyst, zirconium dioxide
Resilon
Pentron® Clinical Technologies, LLC Wallingford CT, USA
Organic part: thermoplastic synthetic polymer – polycaprolactone, Inorganic part: biactive glass, bismuth oxychloride, barium sulphate
Epiphany
Pentron® Clinical Technologies, LLC Wallingford CT, USA
Organic part: BisGMA, ethoxylated BisGMA, UDMA, hydrophilic difunctional methacrylates Inorganic part: calcium hydroxide, barium sulphate, barium glass, bismuth oxychloride, silica
Table 2. Number of teeth and number of slices in experimental groups and subgroups. Group I – Resilon/Epiphany subgroup A
Group II – Gutta-percha/RSA subgroup B
subgroup A
subgroup B
thermoplastic method
single-point method
thermoplastic method
single-point method
number of teeth
number of slices
number of teeth
number of slices
number of teeth
number of slices
number of teeth
number of slices
10
8
15
15
10
8
15
15
Moreover, it provides repetitive results, allows for testing of materials with low bond strength with dentine and the samples for testing are easy to align [9]. This test is also less sensitive to differences in sample sizes and differentiated stress distribution during load application [10]. According to Skidmore et al. [11], during the test, a trend to decrease the actual adhesion values and heterogeneous load distribution in samples of considerable thickness in observed. The latter disadvantage may be overcome by using thin dentine slices (approx. 1 mm) [7]. One of the new sealers used with gutta-percha cones, receiving good clinical outcomes, is polysiloxane-based Roeko Seal Automix (RSA) [12]. Its particular strength lies in the low sensitivity to moisture, no shrinkage, and even 0.2% expansion during the first few weeks after application, after which the volume becomes stable, ensuring good sealing [13, 14]. Five years ago, a material called Resilon was introduced to market. It was based on a thermoplastic composite resin, which is used with a methacrylate sealer - Epiphany. The potential ability of this system to penetrate into the dentine tubules is emphasised. It results in creating a monoblock, provides resistance to bacterial microleakage, low shrinkage during thermal plasticisation and leads to the strengthening of the tooth structure [15-17]. The aim of this study was to comparatively evaluate adhesive properties of selected root canal fillings through the measurement of the material-dentine interfacial bond strength.
MATERIAL AND METHODS A total of fifty single-rooted human teeth (with one canal each), extracted from periodontal reason, enrolled into the study after their evaluation in the endodontic microscope, which aimed at selecting only roots without any signs of hard tissue structure damage. The teeth were decoronated at the cement-enamel junction using a turbine and a diamond burr under water coolant. The root canal treatment was performed by two dentists. The root canals were prepared using crowndown method with rotary nickel-titanium instruments Hero 642 (MicroMega) until the master apical rotary (MAR size 30/04) an appropriate work length (1 mm short of the patency length) was achieved. During instrumentation, the root canals were irrigated with sodium hypochlorite (1%), 17% ethylenediaminetetraacetic acid (EDTA) and distilled water with subsequent drying with standardised paper points. The first group of 25 roots was filled with Resilon/Epiphany (R/E) system and the second group (remaining 25 roots) with gutta-percha with Roeko Seal Automix sealer (G/RSA). Tab. 1 shows the composition of the studied materials. Two subgroups were defined in each group, depending on the root canal filling method (A – thermoplastic method using System B and Obtura II; B – paste and single-cone (with a 0.04 taper master cone) technique. Tab. 2 shows the number of teeth in respective groups and subgroups. Radiographs were taken to confirm length and density of the root canal obturation in each case. All samples were stored in a moist environment at 37°C for 1 week. Each root was subsequently cut perpendicular to the long axis into transverse slices of 1.7 mm thick by using Minitom slow speed saw with water cooling. The number of slices in respective groups and subgroups is presented in
329
Pawińska M et al.
Figure 1. The root slice and interfacial area of root filling prepared to an image analysis software.
Figure 2. Schematic representation of calculating of the root filling interfacial area.
Table 3. Push-out bond strength values expressed in MPa ( mean, SD) with respect to the material and method of root canal filling. Group
Mean (MPa)
SD
IA* (Resilon/Epiphany) thermoplastic method
0.50
0.24
IB *#$ (Resilon/Epiphany) single-point method
3.98
1.33
IIA # (Gutta-percha/RSA) thermoplastic method
0.33
0.18
IIB $ (Gutta-percha/RSA) single-point method
0.08
0.03
SD – standard deviation *the statistically significant differences between IB and IA, p<0.001 # the statistically significant differences between IB and IIA, p<0.001 $ the statistically significant differences between IB and IIB, p<0.001
Tukey’s HSD (honestly significant difference) test for posthoc comparisons was used to evaluate the differences among experimental groups. The level of significance was set at p<0.05. Tab. 2. From each root one slice from the coronal side of the root was obtained. In the case of four teeth (2 from group I and 2 from group II), fillings using the thermoplastic condensation technique, we were unable to obtain undamaged slices when cutting the samples. Each slice was then measured, photographed from both apical and coronal side and subjected to computer processing using Corel DRAW 9.0 and MicroMeter software for the calculation of the circumference and surface area of the filling on both sides of each slices (Fig. 1). Once we obtained these values, and bearing in mind the thickness of each slice, we calculated the actual interfacial area of the root filling (P), similar in shape to a cylinder, using the following formula [5] (Fig. 2): P = (Ca + Cc) x ½ H Ca – circumference of the apical aspect Cc – circumference of the coronal aspect H – thickness of slice The material-dentine interfacial bond strength, which is the adhesion force of the endodontic material to the root canal wall, was performed using testing machine Instron TM-SM (Instron) and push-out test [5, 8, 9]. The filling was pushed out of the slice, placed in the specially constructed device with a piston, in an apical-coronal direction with a speed of 1 mm/min and simultaneous registration of the applied force. Adhesion of the canal filling to the dentine was calculated for each slice by dividing the force in newtons [N], needed to push a material out of the slice, by the interfacial area of the root filling calculated earlier [in mm2]. The obtained result was expressed in megapascals [MPa].
Statistical analysis Statistical analysis was performed using the software package Statistica 8.0 (StatSoft). The push-out bond strength results were evaluated using one-way analysis of variance ANOVA.
RESULTS The obtained results are summarized in Tab. 3. and Tab. 4. The highest push-out bond strength value was registered for the teeth filled with Resilon/Epiphany system using the singlecone technique (group IB) and amounted to 3.98 ± 1.33 MPa. Significantly lower bond strength was observed for the teeth filled with the same material, but using the thermoplastic method (group IA, 0.50 ± 0.24 MPa), and both subgroups, where the obturation was performed using gutta-percha and RSA paste (group IIA – 0.33 ± 0.18 MPa; group IIB – 0.08 ± 0.03 MPa) (p<0.001). No statistically significant differences in material-dentine interfacial bond strength values measured in the push-out test were observed between IA and IIA, IA and IIB, IIA and IIB subgroups (p>0.05). In order to estimate the influence of the used material and canal obturation technique on the dentine-material bond strength identified with adhesion, a regression model was created in the studied groups, the correctness of which was statistically confirmed (p<0.05) (Tab. 4). This model explained 63.1% of the adhesion variation (adjusted R2 coefficient = 0.631). Additionally, basing on the regression model, the absolute influence of the used material and obturation technique on dentine-material interface bond strength was estimated. Statistical analysis revealed that the Resilon/Epiphany system increased the material adhesion by 2.608 MPa (regression coefficient B=2.608) in comparison to gutta-percha/RSA system. This increase has proven to be statistically significant (p<0.001). The root canal filling with paste and single cone increased the filling adhesion by 1.235 MPa (regression coefficient B=1.235) in comparison to thermoplastic technique. The differences were statistically significant
330
New endodontic obturation systems and their interfacial bond strength with intraradicular dentine – ex vivo studies
Table 4. The regression model presenting the influence of the material and the application method on the material-dentine interfacial bond strength, that is the filling adhesion. Regression coefficient B
Standardised regression p coefficient β
Significance of regression model
Adjusted R2 coefficient
Material (Resilon/Epiphany vs.Gutta-percha/ RSA)
2.608
0.683
p < 0.001
p < 0.05
0.631
Method (single-point method vs. thermoplastic method)
1.235
0.308
p < 0.05
(p<0.05) (Tab. 4). Moreover, the involvement of the respective parameters (material type, obturation technique) in altering the materialdentine bond strength value in the created model was established using a standardised regression coefficient β. The absolute value of this coefficient defines the importance of the respective parameter. The statistical analysis revealed that it was the type of material used followed by canal filling technique that had the greatest and concurrently statistically most significant influence on material-dentine adhesion (β = 0.683, p<0.001 and β = 0.308, p<0.05, respectively) (Tab. 4).
DISCUSSION It was expected that the results of this ex-vivo study would indicate which of the tested endodontic materials can provide a tight seal of the canal system. However, it is hard to unequivocally determine this fact. Knowledge of adhesion of the above-described materials to the root canal dentine was rather sparse. Our studies showed that it is the adherence forces that are decisive for the material-intraradicular dentine bond strength and both systems studied demonstrate different inclinations to create such bonds. The R/E system applied to the root canal using the single-cone technique showed the highest values of the push-out bond strength. The bond strength was significantly weaker in teeth, where the material was applied using the thermoplastic method. On the other hand, in the G/RSA group, the material exhibited higher push-out bond strength after being applied using the thermoplastic method than after being sealed with the single cone, but the differences were statistically insignificant. R/E system introduced the use of the single-cone method demonstrated significantly higher adhesion values to the dentine rather than the G/RSA applied using either techniques. There is no unanimity among the authors using the pushout test as to the evaluation of the bond strength between the intraradicular dentine and R/E systems after the obturation using the single-cone technique. Nagas et al. [18] obtained similar results as we did (from 2.1 ± 0.9 to 3.9 ± 0.8 MPa, depending on the localisation of the slice), yet their material was light cured. On the other hand, other authors obtained 10-times lower bond strength of the methacrylate sealer with the dentine [10, 19]. Our own results, concerning the R/E system applied using the thermoplastic method, are identical
with those of Sly et al. [20] and Gesi et al. [5], yet lower than the material-dentine interfacial bond strength values acquired by Skidmore et al. [11] (1.51 ± 1.22 MPa) and Bouillaguet et al. [21] (5.0 MPa), despite the fact that all authors used the same push-out test. The above-mentioned discrepancies may result from different methods of sample preparation for the experiment (addition of the thinning resin to the sealer, different tooth storing time after root filling, different root slices thickness used in the test). Higher push-out bond strength in teeth filled with R/E system using the single-cone method should be explained by the presence of the thicker layer of the sealing paste [22] applied between Resilon and the dentine. Jainaen et al. [10] and Rahimi et al. [22] observed higher adhesion force values for thicker sealer layers, regardless of the sealer type. According to the authors, the weaker adherence of the thinner sealer layer to the dentine may be attributed to the small resin amount in comparison to the filler, that remains on the canal surface after its part has penetrated the dentine tubules. The thicker sealer layer provides better availability to resin components; therefore, no excessive depletion takes place and filler particles can be bonded, leading to the maintenance of the sealer cohesion [10, 22]. The results of the current studies reveal, however, that the thickness of the sealer layer plays a significant role in adhesion only in the case of resin-based materials and is not that important for polydimethylsiloxanes. The filling technique influences the bonding strength as well. The single-cone technique is considered to be less reliable than other methods due to the unfavourable sealer to guttapercha ratio, which facilitates the microleakage and quality decrease of interfacial integrity of root canal fillings [23, 24]. Recently, this conception has been modified. Nowadays, the sealer volume is smaller due to the use of cones of increased conicity, which are adjusted precisely to the geometry of the root canal prepared with NiTi rotary instruments, with identical convergence angle as cones [25]. In oval cross-section canals, it is recommended to introduce several gutta-percha cones apart from the main one (without the condensation with spreader), which increases the proportional amount of guttapercha in pericoronal part of the filling [26]. Thermoplastic methods may, on the other hand, lead to more damage of adhesive bond with dentine, due to the faster sealer polymerisation at higher temperatures [27, 28]. This phenomenon could have had significant importance for obtaining worse results in root canals, which were filled with
331
Pawińska M et al.
Resilon and Epiphany using the thermoplastic technique. In the presented studies, the R/E system was not light cured in order to create comparative conditions for both groups. Nagas et al. [18], however, studied the Resilon/ Epiphany-dentine bond strength after they had been cured with different light curing units (quartz-tungsten-halogenQTH, light-emitting diode-LED, plasma-arc- PAC). The authors observed that the highest bond strength was obtained for curing of the root canal filling with the QTH light curing unit, which is associated with slower polymerisation process, longer duration of the sealer liquid phase and associated smaller polymerisation shrinkage. The lowest adhesion values were observed also for root canal fillings cured with the PAC light curing unit. The authors consider that the increase in light output and the decrease in the curing time unfavourably influence the adherence of the Epiphany to the dentine. They emphasise the significance of the decrease in bond strength toward the apical direction of the root canal, which indicates limited light penetration. Such phenomenon was not observed for self-cured root canal fillings [19-21]. The available literature does not provide much insight into the evaluation of the adhesive properties of the RSA paste. This sealer is a silicone polymer and does not contain any free, reactive oxygen-containing groups, which could bond the dentine calcium. It results in no adhesion between the paste and tooth tissues [29], which was confirmed in our own current studies. The bond strength between the root canal wall and RSA sealer with single gutta-percha cone was 0.08 MPa. The experiments of Gambarini et al. [30], showed that the siloxane sealer is characterised by significantly lower disperse ability than polymethacrylate, and the capability to flow and low surface tension are very desired features, as they improve the adaptation of the filling to the canal walls. Saleh et al. [31] proved that RSA binds more strongly with root dentine in the presence of the smear layer and experimental primer. Therefore, the removal of the former and material condensation without prior primer application in their own studies could have contributed to worse results obtained for the group of RSA-filled roots. The latest studies of Saleh et al. [32] prove that the presence of the smear layer inhibits the bacterial leakage both in root canals filled with gutta-percha and Resilon. It should therefore be borne in mind that certain types of sealers may need different smear layer processing to obtain optimal bond with root canal dentine [31]. Resin sealers exhibit better penetration of the dentine tubules after the removal of the smear layer [5, 8, 18, 22]. This phenomenon may be desired, as it increases the surface of material-dentine adherence, provides its mechanical fixation, better canal sealing, and blocks the dentine tubules as well, preventing the bacteria from colonising the dentine. Saleh et al. [31] and Jainaen et al. [10] conclude that the presence of the sealer tags does not increase the bond strength with the dentine. It is even assumed that the sealer tags may cause unfavourable tensions resulting from load and lead to damage of the adhesive bonds [5, 8].
The bond strength of the methacrylate sealer-dentine interface is dependent on physico-chemical phenomena during the polymerisation of the material as well. Beriat et al. [33] proved that the conversion degree of the Epiphany sealer (transformation of monomers to polymers through the conversion of the double bonds between carbon atoms into single ones) after light curing reached the level of only 60% after two weeks from curing. Ureyen-Kaya et al. [34] achieved significantly higher bond strength after filling the root canal with combined Epiphany sealer and gutta-percha than with Resilon (G/E 2.22 ± 0.94 MPa vs. R/E 1.49 ± 1.06 MPa). The authors suggested combining the Epiphany sealer rather with gutta-percha, which seems more susceptible to condensation, than with Resilon, particularly during the material introduction with the so-called “cold” techniques. The material-dentine interfacial bond strength is only one of the aspects of the quality evaluation of the root canal fillings. Despite the fact that in most cases, the results of laboratory studies cannot be directly extrapolated to clinical conditions, the laboratory tests (ex-vivo) are helpful in examining and comparing the new materials. The information obtained in our study extends knowledge on endodontic materials science and is of significant importance from a practical point of view.
CONCLUSIONS Within the limits of this study, it may be concluded as following: the push-out bond strength of the material-dentine interface was dependent on the type of material used and the root canal filling technique. The R/E system exhibited better adhesion ability to intraradicular dentine than G/RSA. The highest bond strength was observed for Resilon/Epiphany introduced with the single-cone technique.
ACKNOWLEDGEMENTS The work was supported by the Medical University of Bialystok, by grant No 3-91766 L.
REFERENCES 1. Schwartz RR. Adhesive dentistry and Endodontics. Part 2: bonding in the root canal system – the promise and the problems: a review. J Endod. 2006 Dec; 32(12):1125-34. 2. Tagger M, Tagger E, Tjan AHL, Bakland LK. Measurement of adhesion of endodontic sealers to dentin. J Endod. 2002 May; 28(5):351-4. 3. Bouillaguet S, Troesch S, Wataha JC, Krejci I, Meyer JM, Pashley DH. Microtensile bond strength between adhesive cements and root canal dentin. Dent Mater. 2003 May; 19(3):199-205. 4. Erdemir A, Ari H, Gungunes H, Belli S. Effect of
332
New endodontic obturation systems and their interfacial bond strength with intraradicular dentine – ex vivo studies
medications for root canal treatment on bonding to root canal dentin. J Endod. 2004 Feb; 30(2):113-6. 5. 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 Nov; 31(11):809-3. 6. Gogos C, Theodorou V, Economides N, Beltes P, Kolokouris J. Shear bond strength of AH 26 and Epiphany to composite resin and Resilon. J Endod. 2008 Nov; 34(11):1385-7. 7. Goracci C, Tavares AE, Fabianelli A, Monticelli F, Rafaelli O, Cardoso PC, Tay F, Ferrari M. The adhesion between fiber posts and root canal walls: comparison between microtensile and push-out bond strength measurements. Eur J Oral Sci. 2004 Aug; 112(4):353-61. 8. Lee BS, Lai EH, Liao KH, Lee CY, Hsieh KH, Lin CP. A novel polyurethane-based root canal obturation material and urethane-acrylate-based root canal sealer – part 2: evaluation of push-out bond strengths. J Endod. 2008 May; 34(5): 594-8. 9. Ungor M, Onay EO, Orucoglu H. Push-out bond strengths: the Epiphany-Resilon endodontic obturation system compared with different pairings of Epiphany, Resilon, AH Plus and gutta-percha. Int Endod J. 2006 Aug; 39(8):643-7. 10. Jainaen A, Palamara JEA, Messer HH. Push-out bond strengths of dentin-sealer interface with and without a main cone. Int Endod J. 2007 Nov; 40(11):882-90. 11. Skidmore LJ, Berzins DW, Bahcall JK. An in vitro comparison of the intraradicular dentin bond strength of Resilon and gutta-percha. J Endod. 2006 Oct; 32(10):963-6. 12. Gencoglu N, Turkmen C, Ahiskali R. A new siliconebased root canal sealer Roekoseal®-Automix. J Oral Rehabil. 2003 Jul; 30(7):753-7. 13. Wu MK, Tigos E, Wesselink PR. An 18-month longitudinal study on a new silicon-based sealer, RSA RoekoSeal: A leakage study in vitro. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2002 Apr; 94(4):499-502. 14. Özok AR, van der Sluis LW, Wu MK, Wesselink PR. Sealing ability of a new polydimethylsiloxane-based root canal filling material. J Endod. 2008 Feb; 34(2):204-7. 15. Lin ZM, Jhugroo A, Ling JQ. An evaluation of the sealing ability of a polycaprolactone-based root canal filling material (Resilon) after retreatment. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2007 Dec; 104(6):846-51. 16. 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 May;30(5): 342-7. 17. Tay FR, Pashley DH. Monoblocks in root canals: A hypothetical or a tangible goal. J Endod. 2007 Apr; 33(4):391-8. 18. Nagas E, Cehreli ZC, Durmaz V, Vallittu PK, Lassilla LVJ. Regional push-out bond strength and coronal microleakage of Resilon after different light-curing methods. J Endod. 2007 Dec; 33(12):1464-8.
19. 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 Jul; 33(7):856-8. 20. Sly MM, Moore KB, Platt JA, Brown CE. Push-out bond strength of new endodontic obturation system (Resilon/ Epiphany). J Endod. 2007 Feb; 33(2):160-2. 21. Bouillaguet S, Bertossa B, Krejci I, Wataha JC, Tay FR, Pashley DH. Alternative adhesive strategies to optimize bonding to radicular dentin. J Endod. 2007 Oct; 33(10):1227-30. 22. Rahimi M, Jainaen A, Parashos P, Messer HH. Bond of resin-based sealers to root dentin. J Endod. 2009 Jan; 35(1):121-4. 23. De-Deus G, Couthinho-Filho T, Reis C, Murad C, Paciornik S. Polymicrobial leakage of four root canal sealers at two different thicknesses. J Endod. 2006 Oct; 32(10):998-1001. 24. Kontakiotis EG, Wu MK, Wesselink PR. Effect of sealer thickness on long-term sealing ability: a 2-year followup study. Int Endod J 1997 Sep; 30(12):307-12. 25. Monticelli F, Sword J, Martin RL, Schuster GS, Weller RN, Ferrari M, Pashley DH, Tay FR. Sealing properties of two contemporary single-cone obturation systems. Int Endod J. 2007 May; 40(5):374-85. 26. Wu MK, van der Sluis LWM, Wesselink PR. A 1-year follow-up study on leakage of single-cone fillings with RoekoRSA sealer. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2006 May; 101(5):662-7. 27. Tay FR, Loushine RJ, Lambrechts P, Weller RN, Pashley DH. Geometric factors affecting dentin bonding in root canals: A theoretical modeling approach. J Endod. 2005 Aug; 31(8):584-9. 28. Tay FR, Loushine RJ, Weller NR, Kimbrough W, Pashley DH, Mak YF, Lai C-NS, Raina R, Williams C. Ultrastructural evaluation of the apical seal in roots filled with a polycaprolactone-based root canal filling material. J Endod. 2005 Jul; 31(7):514-9. 29. Lee KW, Williams MC, Camps JJ, Pashley DH. Adhesion of endodontic sealers to dentin and gutta-percha. J Endod. 2002 Oct; 28(10):684-8. 30. Gambarini G, Testarelli L, Pongione G, Gagliani M. Radiographic and rheological properties of a new endodontic sealer. Aust Dent J. 2006 Jan; 32(1):31-4. 31. Saleh IM, Ruyter IE, Haapasalo MP, Ørstavik D. The effect of dentine pretreatment on the adhesion of root-canal sealers. Int Endod J. 2002 Sep; 35(10):859-66. 32. Saleh IM, Ruyter IE, Haapasalo MP, Ørstavik D. Bacterial penetration along different root canal filling materials in the presence or absence of smear layer. Int Endod J. 2008 Jan; 41(1):32-40. 33. Beriat NC, Ertan A, Cehreli ZC, Gulsahi K. Time-dependent conversion of methacrylate-based sealer polymerized with different light-curing units. J Endod. 2009 Jan; 35(1):110-2.
Pawińska M et al.
34. Ureyen-Kaya B, Kececi AD, Orhan H, Belli S. Micropush-out bond strengths of gutta-perch versus thermoplastic synthetic polymer-based systems – an ex vivo study. In. Endod J. 2008 Mar; 41(3):211-318 .
333