==== Front J Conserv DentJ Conserv DentJCDJournal of Conservative Dentistry : JCD0972-07070974-5203Medknow Publications & Media Pvt Ltd India JCD-21-35010.4103/JCD.JCD_201_16Original ArticleBond strength of composite resin to white mineral trioxide aggregate: Effect of different surface treatments Samimi Pouran Kazemian Mehrdad 1Shirban Farinaz 2Alaei Samane 1Khoroushi Maryam Dental Materials Research Center and Department of Operative Dentistry, Isfahan University of Medical Sciences, Isfahan, Iran1 Department of Operative Dentistry, Isfahan (Khorasgan) Branch, Islamic Azad University, Isfahan, Iran2 Dental Research Center, Department of Orthodontics, School of Dentistry, Isfahan University of Medical Sciences, Isfahan, IranAddress for correspondence: Prof. Maryam Khoroushi, Dental Materials Research Center and Department of Operative Dentistry, Isfahan University of Medical Sciences, Isfahan, Iran. E-mail: khoroushi@dnt.mui.ac.irJul-Aug 2018 21 4 350 353 01 9 2016 11 8 2017 22 2 2018 Copyright: © 2018 Journal of Conservative Dentistry2018This is an open access journal, and articles are distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 License, which allows others to remix, tweak, and build upon the work non-commercially, as long as appropriate credit is given and the new creations are licensed under the identical terms.Background: The main aim of restorative dentistry is to restore and preserve dental health with the use of appropriate restorative modalities to protect the pulp and restore its function. This study compared the effect of different surface treatments of mineral trioxide aggregate (MTA) on the bond strength of composite resin to MTA. Materials and Methods: Forty cylindrical acrylic blocks with a hole were prepared and filled by ProRoot MTA. The samples were assigned to four groups: Group 1 – no surface treatment; Group 2 – phosphoric acid etching; Group 3 – sandblasting; and Group 4 – hydrofluoric acid (HF) etching, rinsing, and silane application. OptiBond Solo Plus adhesive was utilized in all the groups. Then, composite resin cylinders were bonded to sample surfaces. The samples were thermocycled and tested for microshear bond strength using a universal testing machine at a crosshead speed of 1 mm/min. Data were analyzed with Kruskal–Wallis and Mann–Whitney tests. Scanning electron microscopy images were prepared for each study group after surface treatments. Results: Means and standard deviations of bond strength values in study groups 1–4 were 14.83 ± 7.76, 21.85 ±7.99, 6.48 ± 3.89, and 26.01 ± 11.09 Mpa, respectively. Conclusions: Within the limitations of this study, phosphoric acid etching or HF etching plus silanization was preferred to surface treatment of MTA before composite resin bonding. Keywords: Composite resins; mineral trioxide aggregate; shear strengthhydrofluoric acidacid etchingdental ==== Body INTRODUCTION Mineral trioxide aggregate (MTA) has been confirmed and used as an apical barrier in cases of open apices, repair of perforations, treatment of internal/external root resorption, and direct pulp capping (DPC).[1] Provision of a coronal seal during restorative procedures of root-filled teeth, especially in cases of perforation or DPC, is very important. In such cases, the use of a secondary intracoronal seal has been suggested with the application of adhesive materials due to inadequate sealing of the perforations or exposure areas.[23] Furthermore, in most cases with furca perforations or DPC, it is not possible to achieve retention from the intracanal post or secondary retention features. As a result, the advantages of applying an adhesive restoration over MTA consist of achieving secondary retention and secondary seal. In many cases, composite resin is recommended because it exerts lower forces on the pulp capping biomaterial during placement of the final restoration.[4] Since the goal is to obtain a monolithic restoration and to have a more durable, sealed, and successful restoration, the bond strength between the composite resin and MTA is of utmost importance. The composite resin with favorable bond strength can establish the MTA. There are little data available on the bond strength between MTA and adhesives or various surface treatments.[567] Therefore, this study was undertaken to compare the effect of different surface treatments on the microshear bond strength of composite resin to the MTA. MATERIALS AND METHODS Forty cylindrical acrylic blocks with a hole as mold were prepared.[89] Holes with 4 mm in diameter and 2 mm in height were filled with ProRoot MTA (ProRoot MTA, Dentsply Tulsa Dental, USA). The blocks were stored in an incubator at 37°C under 100% humidity for 72 h for final setting. The specimens were divided into four groups, with a specific surface treatment in each performed as follows: Group 1: No surface treatment was performed on MTA Group 2: The surface of MTA was etched with 37.5% phosphoric acid gel (Kerr, Karlsruhe, Germany) for 20 s Group 3: The surface of MTA was sandblasted using an intraoral sandblasting device, Dento-Prep (DK-8721, Daugaard, Denmark), at 7 mm from the surface using 50-μ Al2O3powder under 30 Psi air pressure for 15 s. The surface was rinsed with air/water syringe and then dried Group 4: The surface of MTA was treated with 9% hydrofluoric acid (HF) (Ultradent, USA) for 90 s. Then, one layer of silane (Ultradent, USA) was applied and allowed to dry. In all the groups, OptiBond Solo Plus (OBSP) adhesive resin (Kerr, Karlsruhe, Germany) was applied to the specimen and then light-cured for 20 s, using an light-emitting diode light-curing unit (Ivoclar Vivadent, FL-9494 Schaan, Liechtenstein) at an intensity of 650 mW/cm2. Then, 1 mm length of prepared Tygon tube, 0.7 mm internal diameter, was placed on the bonding area, and resin composite (Point 4, 3M ESPE, USA) was packed into the tube and light-cured for 40 s. After being stored at 37°C distilled water for 24 h, all the specimens underwent a 1000-cycle thermocycling procedure at 5/55°C. Microshear bond strength tests were carried out using a universal testing machine (Zwick, Roell Z020, Germany), with a shearing force at a strain rate of 1 mm/min and a 0.5-mm wide chisel. The failure modes were then evaluated under a stereomicroscope (Nikon, Tokyo, Japan) at ×30. Data were analyzed with Kruskal–Wallis and Mann–Whitney tests. Statistical significance was defined at P < 0.05. Scanning electron microscopy analysis Two specimens from each group were prepared using the same special surface treatment for scanning electron microscope (SEM) evaluation. Subsequent to surface treatment, the specimens were evaluated under SEM (XL30, PHILIPS, Netherlands) after gold-sputtering. RESULTS Mean values and standard deviations of microshear bond strength are presented in Table 1. Kruskal–Wallis test showed a statistically significant difference in microshear bond strength values between the four study groups (P < 0.05). The maximum microshear bond strength was observed in Group 4, which was prepared with HF and silane (26.0 ± 11.0), and the minimum value was observed in Group 3, where sandblasting was used for surface treatment (6.4 ± 3.8). Table 1 Mean values, standard deviations, and 95% confidence intervals of microshear bond strength The results of Mann–Whitney test are presented in Table 1. There were significant differences in bond strength values between Group 1 and Groups 3 and 4. In addition, there were significant differences in bond strength values between Group 2 and Group 3 and Group 3 and Group 4. The majority of fracture modes in the experimental groups were adhesive (82.5%); other fracture modes were cohesive (MTA) in Groups 2 and 4. SEM images of specimens with different surface treatments are shown in Figure 1. Figure 1 (a) SEM of MTA (no surface treatment). (b) SEM of treatment with phosphoric acid. (c) SEM of sandblasted MTA. (d) SEM of MTA treated with hydrofluoric acid (×1000) (SEM: Scanning electron micrograph, MTA: Mineral trioxide aggregate) DISCUSSION In addition to biocompatibility, bioactivity, and remineralization properties of pulp capping materials, the bond strength of these materials to restorative materials is important. Proper bonding of composite resins to pulp capping biomaterials produces an adhesive interface, which is capable of distributing stresses relatively evenly over the entire bonding area.[10] In this study, different surface treatments were carried out on MTA to bond the composite resin. The principal ingredients of white MTA include calcium oxide, silica, and bismuth oxide;[11] phosphorous is present in very small amounts in MTA.[12] However, hydroxyapatite crystals are precipitated in phosphate-buffered solution.[13] Although the chemical composition of MTA precipitates was not examined in the present study, the composition of crystalline structures created on MTA surfaces could be deduced. It was assumed that they are calcium hydroxide and calcium silicate hydrate, which are the principal bonding phases in a hydrated Portland cement-based material.[1415] Under SEM, Group 1 with no surface treatment showed two structural phases, including a crystal phase of calcium phosphate and an amorphous phase of calcium oxide with a granular view [Figure 1a], which is consistent within the results of some previous studies.[11161718] The mean microshear bond strength in this group was significantly higher than that in Group 3 (sandblasting and OBSP). The presence of intracrystalline spaces on the MTA surface results in a spongy appearance, which helps in infiltration of resin and results in micromechanical bonding. In this study, application of phosphoric acid etch on the MTA surface resulted in the removal of crystals and amorphous structures, creating a rough and porous surface that improved adhesion of the resin materials [Figure 1b]. The microshear bond strength in Group 2 was higher than that in Groups 1 and 3. There were no statistically significant differences between phosphoric acid-etched and nonetched groups (Groups 1 and 2). In a study by Oskoee et al.,[10] no significant differences were reported between the shear bond strength of etched and nonetched groups. A study used scanning electron microscopy to evaluate the effects of acid etching on surface characteristics of MTA and showed that the disordered structure and spindle-shaped crystals were removed during the process;[19] therefore, the selective removal of the matrix surrounding the crystals results in a sponge-like surface suitable for bonding to composite resins with no significant effect on MTA structure. Phosphoric acid treatment eroded the crystalline structure on the white MTA surface, creating a cracked surface that contained internal pores. Consistent with the results of the present study, the characteristic etching pattern on MTA as a result of phosphoric acid treatment was reported previously,[19] suggesting that phosphoric acid might contribute to a reliable micromechanical bonding of the etch-and-rinse adhesive system to MTA.[7] Based on the results of this study, the minimum bond strength was recorded in Group 3. Sandblasting of the surface with 50-μ alumina resulted in a homogeneous appearance with lower pore depths compared to acid-etching under SEM [Figure 1c]. The low bond strength value in this group was attributed to fewer pores, which can be a result of sandblasting without the use of silane because as noted previously, application of silane for the preservation of bonding is critical after sandblasting.[202122] Maximum bond strength was recorded in Group 4 in the present study. Application of 9% HF for 90 s resulted in a homogenously porous appearance under SEM [Figure 1d]. HF can remove all the smear layers on the surface and etch the silica and the boundaries between the phases. Application of silane after etching improved the wetting and served as a chemical bonding agent. It is a bifunctional molecule, reacting with the hydroxyl groups of the silica phases on one side and bonding to copolymerized resin from the other side.[23] It seems that the stronger acidic treatment resulted in a more destructive surface than the weaker acidic treatment, and the eroded surface enhanced the bond strength.[7] Several studies have reported the presence of different amounts of silica in the MTA phase. Torabinejad et al. showed 2.47% and 6% silica in the crystal and amorphous phases, respectively.[17] In addition, Dammaschke et al. reported the presence of tricalcium and dicalcium silicate in MTA crystals.[16] In the present study, the highest bond strength value (26.01 MPa) was recorded in Group 4, which was attributed to the combination of the chemical bond between silane and the etched silica groups on MTA, as well as the micromechanical bonding caused by the rough MTA surface. In this study, cohesive (MTA) fracture modes were seen in Groups 2 and 4. A previous study reported that the bond is acceptable when fracture occurs within each material rather than in the bonded interface (i.e., cohesive rather than adhesive).[24] CONCLUSIONS High values of microshear bond strength means obtained in this study can be explained by surface porosities and micromechanical bonding mechanism. Maximum bond strength in HF and silane treated group could be related to the chemical bonding between silica groups on MTA surface and the silane molecules. Financial support and sponsorship This report is based on a Grant (#385071) submitted to the Vice Chancellery for Research, Isfahan University of Medical Sciences, Isfahan, Iran. Conflicts of interest There are no conflicts of interest. Acknowledgments The authors thank Vice Chancellery for Research, Isfahan University of Medical Sciences, for financial support (#385071). ==== Refs REFERENCES 1 Parirokh M Torabinejad M Mineral trioxide aggregate: A comprehensive literature review – Part III: Clinical applications, drawbacks, and mechanism of action J Endod 2010 36 400 13 20171353 2 Wolanek GA Loushine RJ Weller RN Kimbrough WF Volkmann KR In vitro bacterial penetration of endodontically treated teeth coronally sealed with a dentin bonding agent J Endod 2001 27 354 7 11485256 3 Galvan RR Jr West LA Liewehr FR Pashley DH Coronal microleakage of five materials used to create an intracoronal seal in endodontically treated teeth J Endod 2002 28 59 61 11833689 4 Savadi Oskoee S Bahari M Kimyai S Motahhari P Eghbal MJ Asgary S Shear bond strength of calcium enriched mixture cement and mineral trioxide aggregate to composite resin with two different adhesive systems J Dent (Tehran) 2014 11 665 71 25628696 5 Jaberi-Ansari Z Mahdilou M Ahmadyar M Asgary S Bond strength of composite resin to pulp capping biomaterials after application of three different bonding systems J Dent Res Dent Clin Dent Prospects 2013 7 152 6 24082986 6 Altunsoy M Tanrıver M Ok E Kucukyilmaz E Shear bond strength of a self-adhering flowable composite and a flowable base composite to mineral trioxide aggregate, calcium-enriched mixture cement, and Biodentine J Endod 2015 41 1691 5 26238526 7 Shin JH Jang JH Park SH Kim E Effect of mineral trioxide aggregate surface treatments on morphology and bond strength to composite resin J Endod 2014 40 1210 6 25069935 8 Kasraie S Shokripour M Safari M Evaluation of micro-shear bond strength of resin modified glass-ionomer to composite resins using various bonding systems J Conserv Dent 2013 16 550 4 24347892 9 Knight GM McIntyre JM Mulyani Bond strengths between composite resin and auto cure glass ionomer cement using the co-cure technique Aust Dent J 2006 51 175 9 16848267 10 Oskoee SS Kimyai S Bahari M Motahari P Eghbal MJ Asgary S Comparison of shear bond strength of calcium-enriched mixture cement and mineral trioxide aggregate to composite resin J Contemp Dent Pract 2011 12 457 62 22269237 11 Asgary S Parirokh M Eghbal MJ Brink F Chemical differences between white and gray mineral trioxide aggregate J Endod 2005 31 101 3 15671818 12 Asgary S Eghbal MJ Parirokh M Ghoddusi J Kheirieh S Brink F Comparison of mineral trioxide aggregate's composition with Portland cements and a new endodontic cement J Endod 2009 35 243 50 19166783 13 Asgary S Eghbal MJ Parirokh M Ghoddusi J Effect of two storage solutions on surface topography of two root-end fillings Aust Endod J 2009 35 147 52 19961453 14 Smith JB Loushine RJ Weller RN Rueggeberg FA Whitford GM Pashley DH Metrologic evaluation of the surface of white MTA after the use of two endodontic irrigants J Endod 2007 33 463 7 17368340 15 Reyes-Carmona JF Felippe MS Felippe WT Biomineralization ability and interaction of mineral trioxide aggregate and white Portland cement with dentin in a phosphate-containing fluid J Endod 2009 35 731 6 19410094 16 Dammaschke T Gerth HU Züchner H Schäfer E Chemical and physical surface and bulk material characterization of white ProRoot MTA and two Portland cements Dent Mater 2005 21 731 8 15935463 17 Torabinejad M Hong CU McDonald F Pitt Ford TR Physical and chemical properties of a new root-end filling material J Endod 1995 21 349 53 7499973 18 Camilleri J Montesin FE Di Silvio L Pitt Ford TR The chemical constitution and biocompatibility of accelerated Portland cement for endodontic use Int Endod J 2005 38 834 42 16218977 19 Kayahan MB Nekoofar MH Kazandaǧ M Canpolat C Malkondu O Kaptan F Effect of acid-etching procedure on selected physical properties of mineral trioxide aggregate Int Endod J 2009 42 1004 14 19732179 20 Kussano CM Bonfante G Batista JG Pinto JH Evaluation of shear bond strength of composite to porcelain according to surface treatment Braz Dent J 2003 14 132 5 12964658 21 Güler AU Yilmaz F Ural C Güler E Evaluation of 24-hour shear bond strength of resin composite to porcelain according to surface treatment Int J Prosthodont 2005 18 156 60 15889665 22 Ozcan M Evaluation of alternative intra-oral repair techniques for fractured ceramic-fused-to-metal restorations J Oral Rehabil 2003 30 194 203 12535148 23 Powers JM Sakaguchi RL Craig's Restorative Dental Materials 2006 13th ed India Elsevier 24 Tate WH Friedl KH Powers JM Bond strength of composites to hybrid ionomers Oper Dent 1996 21 147 52 8957904