ENDODONTOLOGY. Introduction. Original Research ABSTRACT

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1 Original Research Push-out bond strengths of the dentine - sealer interface with and without a main cone: A comparative study using different sealers and cone systems LAKSHMI AMARA * VASUNDHARA SHIVANNA ** LODHA VISHAL RAJESH *** ABSTRACT Objectives: The objective of the study was to compare the bond strength of Epoxy resin based and UDMA based sealers and to assess the relative bond strengths between Dentin-Sealer and Sealer-main cone, by testing canals filled with and without a main cone. Materials and method: Thirty extracted maxillary premolar teeth with two separate canals were prepared using 0.06 taper K3 instruments to size 35. Teeth were divided into three groups for filling using AH Plus, EndoREZ or Realseal sealers. In each tooth, one canal was filled with a matching single-cone technique, and other was filled with sealer alone. A 1 mm slice of mid-root dentine was prepared for the push-out test. Failure modes after push-out were examined under stereomicroscopy and scanning electron microscopy. Results: Overall, the epoxy resin-based sealer provided the highest push-out bond strengths. Push-out bond strengths were significantly higher (p < 0.001)when canals were filled with sealer alone than those filled with main cone and sealer. Sealers failed in cohesive mode within the thin film, leaving a layer of sealer on the canal surface. Bulk sealer showed predominantly adhesive failure at the dentine sealer interface, with a clean dentine wall and with resin tags either partially pulled out or sheared off at the interface. Interpretation and Conclusion: i) Epoxy resin based sealer had the highest push-out bond strength compared with UDMA based sealers when used with main cone. ii)the bond strengths after filling with sealer alone were higher than those with main cone and sealer and may reflect different patterns of behavior when the sealer is present in thin layer. Keywords: push-out bond strength test; AH Plus; EndoREZ; RealSeaL; bond failure; SEM analysis Introduction Successful root canal treatment depends on the thorough debridement of the root canal system, the elimination of pathogenic microorganisms and finally, the complete sealing of the canal space to prevent ingress of the bacteria from the oral environment and spread to the apical tissue. 1 The steps in endodontic treatment thus comprises of gaining an access to the root canal system, accomplishing debridement through a meticulous biomechanical preparation, disinfection of the root canal space and finally obturation of the same. * Professor, ** Professor & Head of the Department, *** Post Graduate Student, Department of Conservative Dentistry & Endodontics, College of Dental Sciences, Davangere

2 LAKSHMI AMARA, VASUNDHARA SHIVANNA, LODHA VISHAL RAJESH The American Association of Endodontist defines obturation as a three dimensional filling of the root canal system as close to the cementoenamel junction as possible. 2, 3 The use of a solid core in conjunction with a sealer is the most frequently used method of obturation. In order to give a fluid tight or a fluid impervious seal a sealer should exhibit certain properties like insolublility,low shrinkage, bacteriostatic, hermetically sealing etc. Also the bond strength of the root canal sealers is important for maintaining the integrity of the seal in the root canal filling. 4 Therefore, sealers should also demonstrate adhesive properties to dentin. This adhesive property may lead to greater strength of the restored tooth and may provide greater resistance to tooth fracture thus, decreasing the chances of endodontic failure and increasing the clinical longevity of an endodontically treated tooth. 5 The development of resin based sealers and improvements in adhesive technology have fostered attempts to incorporate adhesive dentistry in endodontics by introducing obturation systems with a specific focus on obtaining a monoblock in which the core material, sealing agent and root canal dentin form a single cohesive unit. 3,6-7 Thus, the present study was intended to assess the extent to which the resin based sealers and the corresponding main cones are bonded to each other as well as to the root canal wall. Objectives The objective of the study was: 1. To compare the bond strength of Epoxy resin based and UDMA based sealers and 2. To assess the relative bond strengths between Dentin-Sealer and Sealer-Main cone, by testing canals filled with and without a main cone. Methodology Selection of Teeth: The study sample comprised of 30 freshly extracted maxillary first premolar teeth with two separate canals. The criterion for selection was that the teeth were extracted for orthodontic reasons from patients within the age groups years. Preparation of specimens: Instrumentation and Obturation: The teeth were decoronated at the cementoenamel junction using a low speed contra angled hand piece and diamond disc under water coolant. Each root canal was checked for patency using a size 10 K-file.Sixty canals were then prepared at working length 0.5 mm short of the patency length using 0.06 taper K3 Ni-Ti rotary instrument to master apical rotary (MAR) size 35 in crown down technique as recommended by the manufacturer. 1% Sodium hypochlorite was used to irrigate each canal and 5 ml of 15% EDTA was used as a final rinse to minimize the residual effect of NaOCl on free radical polymerization. A final rinse of 5ml of normal saline was used to remove any remnant of the irrigating solutions. The canals were dried using paper points. Teeth were randomly divided into 3 groups for filling with three resin sealers containing 10 teeth each: 57

3 PUSH-OUT BOND STRENGTHS OF THE DENTINE - SEALER INTERFACE WITH AND WITHOUT A MAIN CONE: A COMPARATIVE STUDY USING DIFFERENT SEALERS AND CONE SYSTEMS Group 1: AH Plus taper Gutta-percha points Group 2: EndoREZ taper EndoREZ points Group3: RealSeal-0.06 taper Resilon points For each tooth, buccal and lingual canals were randomly allocated to a main cone plus sealer or sealer only. For the canal filled using a main cone, a master cone was matched to the final MAR file size. The master cones were checked in the canal prior to obturation by tugback method. After mixing the sealers according to the manufacturer s instructions, one canal was filled with a main cone using a single cone technique and the second canal was completely filled with the sealer only. For EndoREZ and Resilon groups, after filling the roots was light cured for 40 seconds to create a coronal seal according to manufacturer s instructions. All specimens were stored at 100% humidity at 37ºC for a period of one week. Preparation for Push-out bond testing: Teeth were embedded in clear acrylic resin and then cross-sectioned using hard tissue microtome. 1mm slices of mid-root dentin were made to achieve a main cone diameter slightly greater than 1 mm (based on the main cone taper). Apical and coronal aspects of each sample were photographed and examined using stereomicroscope to confirm a circular shape of thecanal and to check for voids. The canal diameters of both the coronal and apical aspects were measured using Image Proplus software (USA). The filling material was then loaded with a 0.75mm diameter stainless steel plunger selected. The plunger was mounted on the upper part of a universal testing machine. The samples were aligned over a support jig in an apical to coronal direction to avoid any constriction interference.the tests were conducted at a cross head speed of 0.5 min -1 using a 100N load cell set at 50N maximum load using universal testing machine. The highest value recorded was taken as the push-out bond strength. The thicknesses of the samples were measured using a digital calliper towithin 0.01 mm. The area under load was calculated by: Area = ½ (circumference of coronal aspect + circumference of apical aspect) thickness. The push-out value in MPa was calculated from force (N) divided by area in mm 2. After the push-out bond strength test, both sides of the sample including the main cone sealer plug were examined under stereomicroscopy to determine the mode of failure. Each sample was evaluated at 20X magnification and put into one of the following categories. Bond failure types were coded as follows: Code Type of failure Adhesive failure at the D/S interface Combination adhesive failure at both the D/S and S/M interface Adhesive failure at the S/M interface Cohesive failure within the sealer Mixed failure in both adhesive and cohesive modes within the sealer Scanning Electron Microscopic examination: Representative samples from each group were split vertically. Samples were mounted on stubs and 58

4 LAKSHMI AMARA, VASUNDHARA SHIVANNA, LODHA VISHAL RAJESH sputter coated with gold and examined under scanning electron microscope to look for sealer penetration within the dentinal tubules Results From the present in vitro study following results were obtained: The data of push out bond strength were analyzed by one way ANOVA followed by Tukeys post hoc test for multiple comparisons. It was seen that Group 1 showed the highest push-out bond strength compared to Group 2 and 3 in both only sealer (S) and sealer with main cone (M) groups. (Graph-I) The Students paired t test was used within the same sealer type with and without a main cone. When intra group comparison of the push out bond strengths of all three groups amongst only sealer (S) and sealer with main cone (M) groups was done, Group 1 and 2 showed highly significant (p <0.001) difference of the push out bond strength between only sealer (S) and sealer with main cone (M) groups where as in Group 3 this difference was non-significant (p>0.05).(table-1) Inter group comparison of bond strength in only sealer (S) groups showed highly significant difference between Groups 1 & 2 and Groups 1 & 3(p<0.001). Inter group comparison of bond strength in sealer with main cone (M) groups showed highly significant difference between Groups 1 & 2 and Groups 1 & 3(p<0.001). Analysis of the failure types of different groups for the canals containing sealer only (S) showed that in Group 1: 70% samples had adhesive failure between dentin and sealer whereas 30% mixed failure between both adhesive and cohesive types. Group 2 showed 80% adhesive failure between dentin and sealer and 20% showed mixed failure. Group 3 showed 90% adhesive failure and 10 % mixed failure. (Graph-II) Analysis of the failure types of different groups for the canals containing sealer with a main cone (M) showed that in Group 1: 30% samples had an adhesive failure between dentin and sealer where as 70% combined failure at dentin sealer and sealer main cone interface. Group 2 &3 showed 70% adhesive failure and 30 % combined failure at dentin sealer and sealer main cone interface. (Graph-III) There were no instances of purely cohesive failure within the sealer or purely adhesive failure at the sealer main cone interface. Results of SEM Analysis When samples were examined under Scanning electron microscope following observations were made. In Epoxy resin based sealer i.e. AH Plus and gutta-percha group, the surface of the canal wall was coated with a layer of sealer cement with filler particles embedded in the matrix and projecting above its surface. Resin particles seemed to totally obscure the dentinal tubule orifices and there was no evidence of resin tags pulling out of dentinal tubules. The sealer layer appeared depleted of resin matrix, with filler particles prominent on the fractured site of both the canal wall and the pushed out main cone.the failure was observed mainly as predominantly cohesive failure within the sealer itself. 59

5 PUSH-OUT BOND STRENGTHS OF THE DENTINE - SEALER INTERFACE WITH AND WITHOUT A MAIN CONE: A COMPARATIVE STUDY USING DIFFERENT SEALERS AND CONE SYSTEMS In the EndoREZ and Resilon groups, in canals filled with sealer only, failure was predominantly adhesive at the dentin sealer interface. This was evidenced by the presence of resin tags that had been pulled out from the dentin surface. Clear dentin surfaces were found where some tags had sheared off but remained in the dentin tubules. The pushed-out sealer plug had matrix surrounding filler particles however;any resin tags on the pushed out sealer plug could not be seen. Graph I - push-out bond strength comparison amongst all groups in both only sealer(s) and sealer with main cone (m). Graph II - analysis of the failure types for the canals containing sealer only (s). Graph III - analysis of the failure types for the canals containing sealer with a main cone (m). Table1 - intra group comparison of the push out bond strengths of all three groups amongst only sealer (s) and sealer with main cone (m) groups. Sealer (S) Sealer+Main cone (M) Groups Mean SD Mean SD Mean Difference t* value p Value, sig Group p< HS Group p< HS Group p> 0.05 NS *Student s paired t tes Figure 1:Set up for push out test (schematic diagram) Figure 2:Stereomicroscopic image of sample before push-out 60

6 LAKSHMI AMARA, VASUNDHARA SHIVANNA, LODHA VISHAL RAJESH any space that allows the percolation of fluids between the filling and the wall. In a dynamic situation, it is needed to resist dislodgement of the filling during subsequent manipulation: 4 for example, the sealer is subjected to dislocating forces if it is necessary to accommodate a post. 8 Figure 3:Stereomicroscopic image of sample before push- out Figure 4: SEM image of AH Plus-Guttapercha group Bond-strength testing has become a popular method for determining the effectiveness of adhesion between endodontic materials and tooth structure.various tests used to measure bond strength are micro-tensile strength test, shear strength test and push-out bond strength test. The push-out test design was selected due to the following advantages over other tests: It is easy to align samples for testing. It is less sensitive to small variations among specimens and to the variations in stress distribution during load application. 1 Discussion Figure 5:SEM image of EndoREZ group Figure 6: SEM image of RealSeal-Resilon group. The ideal root canal filling is that the entire root canal space is filled with no voids or gaps. 1 Adhesion of root canal filling material to dentinal walls is important in both static and dynamic situations. In a static situation, it should eliminate The model has been shown to be effective and reproducible. Another advantage of this method is that it allows root canal sealers to be evaluated even when bond strengths are low. 4 For the present study, intact maxillary premolar teeth from patients aged 14 to 20 years were used in order to minimize the effect of continued dentin deposition in older teeth. In the present study maxillary premolar teeth with two separate canals were selected because the purpose of this study was to measure the bond strength of the Dentine-Sealer interface and the Sealer-Main cone interface separately. One canal was completely filled with sealer (to measure the 61

7 PUSH-OUT BOND STRENGTHS OF THE DENTINE - SEALER INTERFACE WITH AND WITHOUT A MAIN CONE: A COMPARATIVE STUDY USING DIFFERENT SEALERS AND CONE SYSTEMS Dentine-Sealer bond strength) and the other canal was filled with sealer plus main cone (to include both Dentine-Sealer and Sealer-Main cone interface). A canal that is completely filled with sealer is equivalent to a thicker layer of sealer. The use of sealer alone is not recommended but was included only to permit the separate measurement of thedentine-sealer bond strength. During the chemomechanical preparation, a layer of debris, the smear layer is formed. The role of smear layer in endodontics has been the subject of considerable debate since it was first described in 1975 by Mc.Comb et al. It has been suggested that high bond strengths cannot be achieved unless the smear layer is removed. 9 Different irrigants have been recommended to remove the inorganic component of root dentine, for example EDTA solutions at a concentration of 15-17%. 10 Studies have shown that EDTA solution alone was not effective in removing smear layer completely but when used in combination with NaOCl it was found to be effective. 11 In the present study 1% Sodium hypochlorite was used to irrigate each canal after every file using a 27 gauge irrigating needle.after completion of the preparation, canals were rinsed with 5 ml of 15% EDTA as a final rinse. Results of the push out tests: All resin sealers showed a two to eight fold higher push out bond strengths of the dentin sealer interface [canals filled with sealer alone-(s)] than of the combined Dentine-Sealer and Sealer-Main cone interfaces [sealer with main cone (M)].Thus it is reasonable to speculate that all resin sealers bond much strongly to dentin than to main cone. In the present study Group 1:AH Plus taper Gutta-percha points showed the highest push out bond strength at the dentin sealer interface and the difference was highly significant when compared to Group 2 and Group 3. The probable reasons of higher push out strength for AH Plus and gutta-percha could be 3 : Formation of a covalent bond by an open epoxide ring to any exposed amino groups in collagen. Very low shrinkage while setting. Long term dimensional stability. Inherent volumetric expansion of AH Plus may have contributed to the superior bond strength of AH Plus In the present study, Group 2 EndoREZ points and EndoREZ sealer demonstrated low push out bond strength as compared to Group 1, with the difference being highly significant.the reasons for low strength could be: Due to the polymerization shrinkage of the 4, 12 methacrylate-based sealer. Also, the sealer bonds weakly to the prepolymerized proprietary coating, as the latter lacks free radicals for bonding because of the removal of 8, 13 the oxygen inhibition layer for packing purposes. EndoREZ has good hydrophilic properties, thus helping create long resin tags in radicular dentin. However, these tags appeared unbounded and exhibited insufficient adhesive strength to resist polymerization shrinkage, resulting in gap 62

8 LAKSHMI AMARA, VASUNDHARA SHIVANNA, LODHA VISHAL RAJESH formation between sealer and canal wall 3 this may help to explain the low bond strength for this group in the present study. The long resin tags, together with the thin layer of hybridized dentin, could not completely prevent gap formation and silver leakage. 14 In the present study the Realseal and Resilon group (Group 3) showed low push-out bond strength as compared to AH Plus and gutta-percha. The reasons for its low bond strength could be: Due to the presence of voids between the dentinal walls and the endodontic obturation. Voids could have been caused by incorporation of primer and / or sealer. Polymerization shrinkage of the sealer might also contribute to thelower bond strength value observed in Resilon group. The amount of shrinkagedepends on the type, size, and content of filler particles as well as thetype of matrix used. The stress associated with this shrinkage may resultin separation of the resin-based sealer from the dentinal walls and consequently, the bond strength value of this interface would decrease. It has also been suggested that low concentration of dimethacrylates that is present in matrix componentof Resilon. 15 Another possible reason could be the absence of freeradicals within the well-polymerized resilon material for effective couplingwith the sealer might be the reason for the debonding between the sealer and Resilon thus resulting in the low bond 3, 15 strength in Epiphany and Resilon. The present study found a difference in the modes of failure between thin film and bulk layer of the sealer. Within thin filmà failure was mainly cohesive within the sealer itself. With bulk sealerà failure was adhesive between dentin and sealer. be 1 : The probable reasons for such a result could The distinctive thin film failure might be explained by an insufficient amount of resin in a thin setting layer. Resin based sealers have been shown to 7, 14 penetrate dentinal tubules extensively. This could be possible because of resin matrix preferentially penetrating the dentinal tubules, leaving a sealer layer that is enriched with filler particles that are larger than the dentinal tubules diameter. This leaves a sealer with a resin depleted layer and filler particle enriched interphase. Within thin film à loss of resin in the tubules may not be compensated for thus resulting in a weak bond as a result of the excessively high particle ratio in the sealer layer. With bulk sealer a much greater supply of resin is available without depleting its presence around the filler particles, thus holding the sealer together and maintaining cohesive strength. In the present study AH Plus and gutta-percha had the highest push out bond strength which correlates with dye penetration tests and fluid filtration tests. Studies have shown that the leakage of Resilon was either equal or less to AH Plus. 63

9 Conclusion Based on the employed methodology and according to the results obtained in the present in vitro study, following conclusions can be drawn: Epoxy resin based sealer had the highest push-out bond strength compared with UDMA based sealers when used with main cone & sealer Bond strengths after filling with sealer alone were higher than those with main cone & sealer and may reflect different patterns of behavior when the sealer is present in thin layer. However bond strength to dentin is only one of the factors that should be considered while evaluating the quality of root canal sealer. Other factors like microleakage test and fracture resistance of the materials needs to be further investigated by additional in-vivo and in-vitro studies to further establish the correlation between bond strength and leakage and to substantiate the findings of this study. References: 1. Jainaen A., Palamara J. E. A. & Messer H. H. Push-out bond strengths of the dentine sealer inter - face with and without a main cone. IntEndod J 2007;40: An Association of Endodontists: Appropriateness of care and quality assurance guidelines. Chicago: The association, Fisher M. A., Berzins D.W., Bahcall J.K. An In Vitro Comparison of bond strengths of various obturation materials to root canal dentin using a Push-out test design. 2007;33: Ungor M., Onay E. O. &Orucoglu H. Push-out bond strengths: the Epiphany-Resilon endodontic obturation system PUSH-OUT BOND STRENGTHS OF THE DENTINE - SEALER INTERFACE WITH AND WITHOUT A MAIN CONE: A COMPARATIVE STUDY USING DIFFERENT SEALERS AND CONE SYSTEMS compared with different pairings of Epiphany, Resilon, AH Plus and gutta-percha. IntEndod J 2006;39: Sly M.M., Moore B. K., Platt J.A. & Brown C.E. Push-Out Bond Strength of a New Endodontic Obturation System (Resilon/Epiphany).J Endod 2007;33: Onay E.O.,Ungor M., Ari H., Belli S.,Ogus E. Push out bond strength and SEM evaluation of new polymeric root canal fillings. Oral Surg Oral Med Oral Pathol Oral RadiolEndod 2009;107: Shipper G., Ørstavik D., Teixeira F.B. & Trope M. An Evaluation of Microbial Leakage in Roots Filled with a Thermoplastic Synthetic Polymer-Based Root Canal Filling Material (Resilon). J Endod 2004;30(5): Wennberg A. &Orstavik A. Adhesion of root canal sealers to bovine dentine and gutta-percha. Intendod J 1990;23: Bodrumlu E. &Tunga U. The apical sealing ability of a new root canal filling material. Am J Dent 2007;20: Heredia M. P., Luque C.M.F, Rodriguez M.P.G, Peinado F.J.M. & Lopez S.G. Decalcifying effect of 15% EDTA, 15% citric acid, 5% phosphoric acid and 2.5% sodium hypochlorite on root canal dentine. IntEndod J 2008;41: Saleh I. M., Ruyter I. E., Haapasalo M. &Orstavik D.The effects of dentine pretreatment on the adhesion of root-canal sealers. IntEndod J 2002;35: Bergmans L., Moisiadis P., De Munck J., Van Meerbeek B., Lambrechts P. Effect of polymerization shrinkage on the sealing capacity of resin fillers for endodontic use. J Adhes Dent 2005; 7: Hiraishi N.et al. Is an oxygen inhibited layer required for bonding of resin-coated gutta-percha to a methacrylate-based root canal sealer? J Endod 2006; 32: Tay F.R. 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(9): Lee B.S., Lai E.H.H, Liao K.H., Lee C.Y., Hsieh K.H. & Lin C.P. A novel polyurethane-based root canal obturation Material and Urethane-acrylate based root canal selaler-part2: Evaluation of push-out bond strengths. J Endod 2008; 34(5):