|Year : 2015 | Volume
| Issue : 2 | Page : 75-81
The effect of the nanofilled adhesive systems on shear bond strength of all-ceramics to dentin
Filiz Keyf1, Sencan Ozlu1, Tayfun Vural2, Emir Baki Denkbas2
1 Department of Prosthodontics, Faculty of Dentistry, Hacettepe University, Ankara, Turkey
2 Department of Chemistry, Biochemistry Division, Nanotechnology and Nanomedicine and Biochemistry Division, Hacettepe University, Ankara, Turkey
|Date of Web Publication||20-Apr-2015|
Department of Prosthodontics, Faculty of Dentistry, Hacettepe University, Sihhiye, 06100 Ankara
Source of Support: This investigation was supported by grant No. 09 D 06 201001 from the Hacettepe University Scientific Research and Development Office, Conflict of Interest: None
Aim: This study evaluated shear bond strength between three all-ceramic systems to dentin using six different adhesives, of which three of them contain nanofillers. Materials and Methods: Ceramic discs were prepared from each of Ceramco, IPS Empress 2 and Copran Zr. Different dentin surfaces were prepared with adhesives. Adper Single Bond Plus, Nano-bond, Prime & Bond NT (PB), Excite Bond, One Step Plus, Opti Bond Solo Plus were applied to the conditioned dentin surfaces. Ceramic discs were luted to the dentin with resin cement. All specimens were kept in water at 37°C for 1-week and thermal cycled for 500 cycles in 5°C and 55°C. Shearing test was conducted, and statistical analyses were performed using nonparametric tests (α = 0.05). Fractured surfaces of each specimen were inspected with Scanning Electron Microscope. Furthermore, distribution of nanofillers into the nanofilled adhesives was examined by transmission electron microscope. Results: Significant differences were observed in bond strength values of the adhesives (P < 0.05). For each ceramic, PB showed the highest bond strength values. Failure mode was cohesive in nanofilled adhesives resin and mixed failure for the others. Nanofillers were aggregated in some areas for each nanofilled adhesive. Ceramco showed the highest bond strength values while Copran Zr showed the lowest. Conclusion: Nanofilled adhesive systems would suggest for good clinical performance together with all-ceramics system. Furthermore, felspathic ceramics is better than the other all-ceramics systems.
Keywords: Adhesion, all-ceramic, cohesive, dental adhesives, nanofilled dental adhesive, shear bond strength
|How to cite this article:|
Keyf F, Ozlu S, Vural T, Denkbas EB. The effect of the nanofilled adhesive systems on shear bond strength of all-ceramics to dentin. SRM J Res Dent Sci 2015;6:75-81
|How to cite this URL:|
Keyf F, Ozlu S, Vural T, Denkbas EB. The effect of the nanofilled adhesive systems on shear bond strength of all-ceramics to dentin. SRM J Res Dent Sci [serial online] 2015 [cited 2022 Jul 5];6:75-81. Available from: https://www.srmjrds.in/text.asp?2015/6/2/75/155457
| Introduction|| |
The cementation process is important for the clinical success of all-ceramic restorations. The restoration may be cemented with glass ionomer or resin cements. Resin cements are the most preferred because of their ability to reduce fracture of the ceramic structures and the range of shades available to produce an optimal esthetic appearance. ,, Long-term survival of adhesive ceramic restorations depends on reliable bond between the ceramic, the resin cement, and the dental substrates. According to the literature, creating a porous ceramic surface texture, which is then silanated, is essential to obtain a reliable bond. ,,, Due to the specific properties of human dentin, including high organic content, the tubular structure variations and its intrinsic wetness, bonding to dentin is more difficult to enamel.  In spite of these difficulties, dentin bonding has become more successful with the development of new dentin adhesive systems over the last 10 years. ,,,,
The addition of filler particles into the dental adhesives should increase the viscosity, this would result in a thicker bonding resin layer. Based on this idea, filled adhesives have been introduced, which have included various types of fillers; such as conventional glass, ion leachable glass or silica fillers. ,,,,, Nanofilled dental adhesives have been produced containing unique and dispersible nanoparticles. ,, The manufacturers have claimed that this extremely small size, discrete particles prevents agglomeration in nanofillers reinforced resin for a reliable bond. ,,
This study was used three types of all-ceramic restorative systems. To select the most appropriate type of systems for clinical use, the clinician must be familiar with the differences between systems. Feldspathic ceramics is indicated for onlays, three-quarter crowns, and veneers, but their strength limits their use to complete coverage crowns in the anterior segment, only. Lithium-disilicate glass ceramics can perform successfully in the posterior segment for single crowns and 3-unit fixed partial prosthesis in the anterior area. Zirconium oksit ceramics has superior mechanical properties as a core material for posterior crowns and fixed partial prosthesis, implant abutments, and implant-supported restorations.
The purpose of our study was to evaluate the shear bond strength of the nanofilled adhesives between three type all-ceramic systems and dentin. The distribution of nanofillers was also examined by transmission electron microscopy (TEM). The null hypothesis tested was that nanofilled adhesive systems would not improve the bond strength of all-ceramics to dentin.
| Materials and methods|| |
This study investigates the bond strength of three all-ceramic systems (Ceramco, IPS Empress 2 and Copran Zr) retained on dentin with six different adhesive systems which three of them contain nanofillers. The adhesives used in this study are Adper Single Bond Plus (ASB), Nano-bond (NB), Prime & Bond NT (PB), Excite Bond (EB), One Step Plus (OSP), Opti Bond Solo Plus (OBS). Composition and manufacturer information is shown in [Table 1]. ASB, NB, and PB are nanofilled adhesive systems.
Sixty ceramic specimens (diameter of 4 mm, height of 2 mm and shade of A 1 ) were prepared from each of feldspathic ceramic (Ceramco, Dentsply, USA), lithium disilicate ceramic (IPS Empress 2, Ivoclar, Vivadent, Liechtenstein) and zirconium-oxide ceramic (Copran Zr, Whitepeaks Dental Systems, Essen, Germany). Ceramco and IPS Empress 2 seramic discs were etched with 9.5% hydrofluoric acid (Porcelain Etch; Ultradent, South Jordan, Utah, USA) for 20 s, Copran Zr seramic discs were air abraded with 110 μm alumina particles (Korox, Bego, Bremen, Germany). Then ceramic discs were silanated (Silane; Ultradent, USA).
Tooth specimens of 180 sound human molars were embedded in autopolymerizing acrylic resin (Meliodent; Heraeus Kulzer GmbH, Hanau, Germany) in rectangular silicone molds, such that the coronal portion would be exposed. The buccal surfaces of the tooth specimens were prepared with a water-irrigated precision saw (IsoMet 1000, Buehler, Germany) to obtain a flat dentin surface parallel to the long axis of the tooth. 180 vertical planar dentin-bonding surface were divided into 18 groups (n = 10). The prepared dentin surfaces were etched with 37% orthophosphoric acid (Ultraetch; Ultradent, South Jordan, USA) for 15 s, rinsed and dried until a frosty white appearance was observed. Different adhesives (ASB, NB, PB, EB, OSP, OBS) were applied to each group in accordance with the manufacturer's recommendations. All adhesives were used utilize dry bonding technique. Polymerization was performed with a light curing unit (Hilux Dental Curing Light Unit, 800 mW/cm 2 , Optimax, Benlioglu Dental Inc., Ankara, Turkey) for 20 s. The prepared all-ceramic specimens were luted to the dentin surfaces with a dual-polymerizing resin cement (PermaFlo DC, Ultradent, South Jordan, USA) and polymerized for 40 s from each of two opposite directions. The finger pressure applied on ceramic specimens during light curing of the cement [Figure 1].
Dentin-ceramic specimens were stored in distilled water at 37°C for 1-week before being thermal cycled 500 times in 5 ± 2°C and 55 ± 2°C, with a dwell time of 20 s in each bath and 10 s transfer time (Thermal cycling, Nüve, Akyurt, Ankara, Turkey). ,,, The specimens were then loaded axially in a universal testing machine (Llyod Universal Testing Machine, AMETEK, Inc., Hampshire, England) with a crosshead speed of 0.05 mm/min until fracture [Figure 2]. Shear bond strength at failure was measured and recorded for each group in MPa. The data were analyzed with nonparametric one-way analysis of variance (Kruskal-Wallis), Mann-Whitney U-test were also used. Differences were considered significant at α = 0.05.
|Figure 2: Schematic diagram of the test assembly for determining shear bond strength|
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After debonding, fractured dentin surfaces were sputter coated with gold (Agar Sputter Coater; Agar Scientific Ltd., Stansted, UK) for scanning electron microscopy (SEM, JEOL JSM 6400, Tokyo, Japan) evaluation of the fracture pattern. The specimens fracture mode was classified as adhesive (fracture anywhere within the adhesive interface), cohesive in dentin, cohesive in adhesive resin, or mixed. Furthermore, distribution of nanofillers into the nanofilled adhesive solutions was evaluated using TEM (TEM, FEI Tecnai G2 Spirit, Holland). Nanofilled adhesives were diluted 1:5 with ethanol prior to analysis. A bulk of the adhesive solution put on a copper grid and allowed the sample to dry at room temperature. Prepared samples were examined by TEM operating at 120 kv.
| Results|| |
The mean shear bond strength values and standard deviation of adhesives for each all-ceramic type are given in [Table 2].
|Table 2: Mean shear bond strengths (MPa) and standard deviations between adhesive systems|
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For Ceramco ceramic system, PB (X−0 = 17.26 ± 3 MPa) had the highest shear bond strength among the adhesives tested, while OSP had the lowest. When the bond strengths were compared among the adhesive system tested, ASB was significantly different from OSP; NB was significantly different from OSP; PB was significantly different from EB, OSP and OBS (P < 0.05).
For IPS Empress 2, PB (X− = 15.03 ± 3.11 MPa) had the highest shear bond strength and OSP had the lowest. ASB was significantly different from PB; NB was significantly different from OSP and OBS; PB was significantly different from EB, OSP and OBS (P < 0.05).
For Copran Zr, PB (X− = 6.79 ± 2 MPa) had the highest shear bond strength, while OBS were the lowest. ASB was significantly different from OBS; NB was significantly different from OSP and OBS; PB was significantly different from EB, OSP and OBS (P < 0.05).
There were significant differences between three all-ceramic systems for each adhesive group [Table 3]. The highest shear bond strength values were recorded for Ceramco, and the lowest were recorded for Copran Zr for each of the adhesive. For ASB, NB, EB, OSP, and OBS adhesives, Ceramco was significantly different from IPS Empress 2 and Copran Zr; IPS Empress 2 was significantly different from Copran Zr. For PB, Ceramco was significantly different from Copran Zr; IPS Empress 2 was significantly different from Copran Zr (P < 0.05).
|Table 3: Mean shear bond strengths (MPa) and standard deviations between all-ceramic systems|
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Failure modes and number of occurrences are presented in [Table 4]. SEM observation revealed that failure mode was cohesive in adhesive resin for ASB, NB and PB mostly. Adhesive remains on fractured dentin surface are shown in [Figure 3],[Figure 4] and [Figure 5]. Mixed failure mode was observed for EB, OSP and OBS mostly. [Figure 6],[Figure 7] and [Figure 8] show tubular obliteration with resin tags and an adhesive layer on the dentin surface. From the TEM evaluation, nanofillers were aggregated easily in all the adhesives containing nanofillers. For the specimen of ASB and NB, larger clusters were observed than PB [Figure 9].[Figure 10] and [Figure 11]. Failure mode of debonded specimens of nanofilled adhesives was cohesive failure in resin that remnants of adhesive resin covering the dentin surface. The TEM image of each nanofilled adhesives showed that the nanofillers were aggregated into clusters.
|Figure 3: Scanning electron microscopy image of dentin surface after shear test using Adper Single Bond Plus. Cohesive in adhesive resin failure mode can be observed, with remnants of adhesive resin covering the fractured surface (original magnification ×1000)|
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|Figure 4: Scanning electron microscopy image of dentin surface after shear test using Nano-bond. Cohesive in adhesive resin failure mode can be observed, with remnants of adhesive resin covering the fractured surface (original magnification ×1000)|
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|Figure 5: Scanning electron microscopy image of dentin surface after shear test using Prime & Bond NT. Cohesive in adhesive resin failure mode can be observed, with remnants of adhesive resin covering the fractured surface (original magnification ×1000)|
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|Figure 6: Scanning electron microscopy image of debonded surface after shear test using Excite Bond. Mixed failure mode can be observed, adhesive remains and resin tags in dentin tubules were seen. A: Adhesive remains. D: Dentin. Arrows: Fractured resin tags in dentin tubules (original magnification ×1000)|
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|Figure 7: Scanning electron microscopy image of debonded surface after shear test using One Step Plus. Mixed failure mode can be observed, adhesive remains and resin tags in dentin tubules were seen. A: Adhesive remains. D: Dentin. Arrows: Fractured resin tags in dentin tubules (original magnification ×1000)|
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|Figure 8: Scanning electron microscopy image of debonded surface after shear test using Opti Bond Solo Plus. Mixed failure mode can be observed, adhesive remains and resin tags in dentin tubules were seen. A: Adhesive remains. D: Dentin. Arrows: Fractured resin tags in dentin tubules (original magnification ×1000)|
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|Figure 9: Transmission electron microscopy image of nanofillers of Adper Single Bond Plus specimen. The large clusters distributed throughout the adhesive specimen. Arrows: Aggregation of nanofillers|
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|Figure 10: Transmission electron microscopy image of nanofillers of Nano-bond specimen. Large clusters distributed densely. Arrows: Aggregation of nanofillers|
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|Figure 11: Transmission electron microscopy image of nanofillers of Prime & Bond NT specimen. Some small clusters were followed. Arrow: Aggregation of nanofillers|
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| Discussion|| |
In the present study, PB significantly improved the shear bond strength between dentin and all-ceramic systems, and the other nanofilled adhesives had higher shear bond strength values too. Therefore, the null hypothesis of the study was rejected.
The addition of fillers to the adhesives has been intended to increase their viscosity to prevent the occurrence of too thin adhesive layer, to increase the elastic modulus for providing a flexible intermediate shock-absorber layer that can resist the polymerization shrinkage stress, and distribute the occlusal loads, and accordingly to increase the dentin bond strength. ,,,,,, Adding fillers that are larger than the interfibrillar spaces (15-20 nm) of the etched dentin increase the viscosity of the adhesive, but also filler accumulation occur on the top of the etched dentin substrate. Therefore, it might reduce the adhesive penetration into the dentin and produce a defective hybrid layer. ,, But, in the case of additional nanofillers being smaller than the interfibrillar spaces, the nanofillers can penetrate into the hybrid layer. ,
Three nanofilled adhesives were used in the present study. For each all-ceramic systems, nanofilled adhesives had higher shear bond strength values. ASB has 10% by weight of 5 nm diameter silica filler.  The load by volume and filler size of NB is unknown since the manufacturer does not release quantitative data on the composition of their product.  PB include nanoscale silica fillers (Aerosil® . Degussa Corp., Ridgefield Park, New Jersey, USA) which have 7 nm average particle size and 1% filler ratio, also they have been functionalized by a special silanization process.  PB had the highest shear bond strength values for each all-ceramics. This may be attributed to not only the nanofiller content but also, the difference in the monomer type (PENTA) of PB. Because PENTA is an acidic phosphonated monomer, and it is possible that these phosphate groups could have some kind of interaction with the calcium ions left on the dentin surface or even with the underlying dentin. 
Toledano et al.  evaluated the bond strength of five adhesive systems (Single Bond, PB, EB, Clearfil SE Bond, Etch and Prime 3.0) to either superficial or deep dentin. On superficial dentin, microtensile bond strength of Single Bond, PB, EB was similar. But on deep dentin, the highest microtensile bond strength to dentin were attained with PB and Clearfil SE Bond (adhesives containing nanofillers). They are suggested that these nanofilled adhesives formed thick intermediate layers between the hybrid layer and the resin that may offer the resin-dentin interface a sufficient strain capacity to accommodate tensions generated by the polymerization shrinking stresses. This was more evident on deep dentin, in which adhesives diffuse faster and deeper into the dentin.  In addition, Perdigγo et al.  are defined that PB has a low viscosity because of its nanofilled composition. According to their TEM and SEM evaluation, the nanofillers penetrated the dentin tubules and infiltrated the microspaces between the collagen fibers within the hybrid layer. 
From SEM evaluation, debonded specimens of nanofilled adhesives showed adhesive remains on the dentin surface indicating cohesive failure in resin. This is related to high values of bond strength, predicting an effective bonding. , When failure occurs within the resin, dentinal tubules are filled with the resin tags. Thus, if debonding happens clinically, the actual debonding site is less critical as long as the underlying dentin is sealed with resin.  It is also indicating a normal distribution of stresses during mechanical testing of bond strength. 
The manufacturers have claimed that silane-treated nanoparticles prevent agglomeration. ,, When adhesives were examined by TEM, the nanofillers were easily observed as clusters, which were formed by the aggregation of the nanofillers. The specimens of ASB and NB, larger clusters were showed than PB. This may be attributed to the increased filler ratio. Kim et al.  and Kasraei et al.  evaluated the filler size and characteristics into the adhesive systems. Authors concluded that when nanofilller content increases, they aggregated easily into large clusters, and these clusters could act as flaws which may induce cracks and cause a decrease in the bond strength. In addition, they reported that fillers with larger dimensions than the interfibrillar space (15-20 nm) of the etched dentin might cause filler accumulation over the top of etched dentin surface. Further studies would be needed to prevent aggregation of nanofillers in dental adhesives.
In this study, lithium disilicate and zirconium-based ceramics show lower bond strength values, this can be explained that its harder to change surface characteristics by surface treatment methods than feldspathic ceramics as indicated in the literature. ,,,
One of the limitations of this study is that the study was conducted under static conditions. Fatigue loading of the specimens would better simulate intraoral conditions. Furthermore, the specimens were thermal cycled in water, which does not fully represent the dynamic environment of the oral cavity presented by saliva. Further studies that subject the specimens to dynamic loading in artificial saliva before loading would more closely resemble intraoral conditions.
| Conclusion|| |
The adhesives tested between all-ceramic materials, and dentin had significantly different bond strength values. Bond strength of the dentin-resin-ceramic joint was increased by the use of nanofilled adhesives. Chemical content of the adhesive such as filler size, filler volume, and monomer type and surface treatment methods of ceramics and dentin may affect the bond strength.
| Acknowledgments|| |
This investigation was supported by grant No. 09 D 06 201001 from the Hacettepe University Scientific Research and Development Office.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11]
[Table 1], [Table 2], [Table 3], [Table 4]