Materials Science and Engineering C 34 (2014) 311–317
Contents lists available at ScienceDirect
Materials Science and Engineering C journal homepage: www.elsevier.com/locate/msec
Effects of surface treatment on bond strength between dental resin agent and zirconia ceramic Ashkan Moradabadi a, Sareh Esmaeily Sabet Roudsari b, Bijan Eftekhari Yekta d, Nima Rahbar c,⁎ a
Department of Electrochemistry, Universität Ulm, Ulm, Germany Department of Optoelectonics, Universität Ulm, Ulm, Germany Department of Civil and Environmental Engineering, Worcester Polytechnic Institute, Worcester, MA 01609, USA d School of Materials Engineering, Iran University of Science and Technology, Tehran, Iran b c
a r t i c l e
i n f o
Article history: Received 19 February 2013 Received in revised form 2 August 2013 Accepted 18 September 2013 Available online 26 September 2013 Keywords: Zirconia Dental resin Bond strength Adhesion Micromechanical retention
a b s t r a c t This paper presents the results of an experimental study to understand the dominant mechanism in bond strength between dental resin agent and zirconia ceramic by investigating the effects of different surface treatments. Effects of two major mechanisms of chemical and micromechanical adhesion were evaluated on bond strength of zirconia to luting agent. Specimens of yttrium-oxide-partially-stabilized zirconia blocks were fabricated. Seven groups of specimens with different surface treatment were prepared. 1) zirconia specimens after airborne particle abrasion (SZ), 2) zirconia specimens after etching (ZH), 3) zirconia specimens after airborne particle abrasion and simultaneous etching (HSZ), 4) zirconia specimens coated with a layer of a FluorapatiteLeucite glaze (GZ), 5) GZ specimens with additional acid etching (HGZ), 6) zirconia specimens coated with a layer of salt glaze (SGZ) and 7) SGZ specimens after etching with 2% HCl (HSGZ). Composite cylinders were bonded to airborne-particle-abraded surfaces of ZirkonZahn specimens with Panavia F2 resin luting agent. Failure modes were examined under 30× magnification and the effect of surface treatments was analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). SZ and HSZ groups had the highest and GZ and SGZ groups had the lowest mean shear bond strengths among all groups. Mean shear bond strengths were significantly decreased by applying a glaze layer on zirconia surfaces in GZ and SGZ groups. However, bond strengths were improved after etching process. Airborne particle abrasion resulted in higher shear bond strengths compared to etching treatment. Modes of failure varied among different groups. Finally, it is concluded that micromechanical adhesion was a more effective mechanism than chemical adhesion and airborne particle abrasion significantly increased mean shear bond strengths compared with another surface treatments. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Demands for densely sintered ceramics as dental restorative materials have recently increased because of their outstanding properties. These oxide materials have optimized properties such as: biocompatibility [1–3] and favorable optical properties [2–7] as well as high mechanical strengths [8]. These high strength ceramics are used in dental restorations as all-ceramic crowns and bridges and in various all-ceramic core and post systems [2–4,6]. Zirconium oxide, currently the material of choice for dental application, is typically used in Yttria partially stabilized Tetragonal Zirconia Polycrystal (Y-TZP) [9]. Y-TZP has a unique toughening mechanism called “transformation toughening.” Crack propagation in Y-TZP is resisted by transformation from tetragonal to monoclinic phase through a substantial increase in volume (~4.5%) that induces compressive stresses over the crack tip [2,4,9–11]. Ceramics generally bond to resin by formation of chemical bonds and micromechanical interlocking [8,12]. Hence, long-term performance of ⁎ Corresponding author. Tel.: +1 508 831 6567; fax: +1 508 831 5808. E-mail address: [email protected] (N. Rahbar). 0928-4931/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.msec.2013.09.015
dental restoration is heavily dependent on bond durability [13]. Since, reliable chemical bonds to zirconia-based materials cannot be easily established [8,14], many studies have been focused on various surface treatments to improve bonding between zirconia and dental resin agents. Various chemical or mechanical treatments have been suggested to improve bond strength such as Silicoater [6,12], Pyrosilpen [6], tribochemical silica coating [7,11,12], Kevloc [11], sputtering [3], sandblasting [8,10,15], grinding [6], selective infiltration-etching [12,16], and additional cleaning procedures [17–22]. One of the most successful coatings with adequate values of adhesion is resin cementation [7]. Panavia F (Kuraray) is a dual-polymerizing, fluoride-releasing resin luting agent that also contains the adhesive monomer Methanediphosphonic acid (MDP) [12]. While, some researchers have suggested that high and durable bond strength was achieved on airabraded surfaces with the use of a MDP-containing composite resin, others claimed that airborne particle abrasion or chemical surface treatments such as silanization could not significantly improve bond strength. Some even claimed no surface treatment is required to achieve a durable bonding between the zirconia and dental resin [2,8,10,13,14]. Another method that has been used to establish a stronger bonding
312
A. Moradabadi et al. / Materials Science and Engineering C 34 (2014) 311–317
between the zirconia surface and the resin luting material is to fuse a thin layer of glass (porcelain) pearls to zirconia [23]. Acid etching has also been utilized to enhance the bonding between zirconia and cement by increasing micromechanical retention. While application of acidic agents, such as phosphoric and hydrofluoric acid for zirconia etching will not create the needed roughened surface for strong bonding [6,8], a solution of HF and HNO3 is reported to be more effective for etching of zirconia surface [24,25]. Hence, a correlation between different zirconia restoration surface treatments and adhesion to dental luting cements is clearly missing. The aim of this study was to improve the bond strength of MDP resin composite to zirconia ceramic using a novel chemical surface treatment by applying a thin layer of two different glaze layers on zirconia surface. The results were compared with traditional micromechanical treatments such as airborne particle abrasion and acid etching. 2. Material and methods Forty-nine square-shaped specimens of high-purity zirconiumoxide ceramic were cut from a pre-sintered ZirkonZahn zirconia block. The samples were cut by a cutting machine (Buehler, ISOMET 2000) with a diamond blade into square-shaped bars with the initial dimension of 9 × 5 × 3 mm3 under cooling, they were then grounded by silicon carbide abrasive paper (Silicium Carbid, Matador, Wasserfest 991A, softflex) under cooling to their final dimension of 8 × 4 × 2 mm3. Afterwards, sample surfaces were polished using a polishing machine with Al2O3 polishing powder (polisher & grinder, Metaserv 2000). Table 1 summarizes the characteristics of surface conditioning methods and ceramic types with codes and manufacturing company names. In order to understand the effects of two major mechanisms on bond strength of zirconia to luting agents, seven experimental groups (n = 7) of specimens with different surface treatment were prepared: 1) zirconia specimens after airborne particle abrasion (SZ), 2) zirconia specimens after etching with 45 vol % HNO3 + 10 vol % HF + 45 vol % H2O solution for 2 min. (ZH), 3) zirconia specimens after airborne particle abrasion and simultaneous etching (HSZ), 4) zirconia specimens coated with a layer of a Fluorapatite-Leucite glaze (GZ), 5) GZ specimens with additional acid etching for 30 s (HGZ), 6) zirconia specimens coated with a layer of salt glaze (SGZ) and 7) SGZ specimens after etching with 2% HCl for 20 s (HSGZ). In four of these groups, specimens were treated by chemical procedures (GZ, HGZ, SGZ and HSGZ) and other three groups underwent micromechanical surface treatments. In GZ specimens, in order to improve the surface condition before sintering process, a layer of Fluorapatite-Leucite glass-ceramic (IPS d.SIGN, Ivoclar, Vivadent, S2, Liechtenstein) was applied to surface of each specimen. The GZ and HGZ specimens were airborne particle abraded (Easy Blast BEGO) with 50-μm aluminum-oxide (Al2O3) particles (at 1.5 bar for 8 s at a distance of 150 mm), before sintering process. This was followed by ultrasonic cleaning (BIOSONIC JR.JELCRAFT TM Vectorss, Pennwalt, JELENKO) with 96% ethanol alcohol for 5 min, and air-drying (Sirona S5, Siemens, model D 3111). The glaze layers were applied on all 49 specimens and were sintered at maximum temperature of 1500 °C for 8 h (Zikon Ofen, Zirkon Zahn). Before testing, all groups with the exception of GZ specimens were airborne particle abraded with 50-μm aluminum-oxide (Al2O3) particles at 4 bar pressure for 8 s at a distance of 10 mm, followed by ultrasonic cleaning in 96% ethanol
alcohol for 5 min and then air-drying. The side view SEM image of a GZ specimen is presented in Fig. 1. Salt glaze for SGZ and HSGZ samples was prepared by addition of 42.12 wt.% potassium carbonate, 15.19 wt.% boric acid and 42.69 wt.% phosphoric acid (Merck, Germany) to distilled water at 60 °C in order to form a thick solution in the K2O–P2O5–B2O3 system. The sandblasted zirconia bars were dipped into this solution for 2 min, cleaned with ultrasonic and steam, and then were air-dried. Subsequently these specimens were heated in a dental furnace (Elephant Hoorn, Holand) at 500–900 °C with a heating rate of 60 °C/min with holding time of 30 min. The specimens were then cooled down for 10 min at the rate of 40 °C/min. Acrylic plastic tubes (3.0 mm in height and 2.0 mm in diameter) were filled with composite (ClearFill AP-X, shadeA2, Kuraray Medical, Japan) to fabricate composite cylinders. The cylinder topsides were light-polymerized (VSI light curing system, ARIALUX Blue Pass+, SN821530) for 40 s. The output power of the light curing system was 450 mW/Cm2. The composite cylinders were bonded to the ceramic specimens 5 min after light polymerization. Resin luting agents (Panavia F2.0, Kuraray Medical INC.1621 Sakazu, Kurashiki, Okayama 710–0801, Japan) were mixed and applied on ceramic surfaces according to the manufacturer's recommendations. Excess resin was removed with foam pellets (Small Sponge Pledgets, Kuraray) and oxygenblocking gel (Oxyguard II; Kuraray) was applied according to manufacturer's instructions. T PANAVIA F 2.0 Paste is a dual-cure (light or self-cure) resin-based cement for ceramics. Clearfil Ceramic Primer is a silane-coupling agent that provides an enhanced adhesive surface to ceramic. The resin luting agents were light-polymerized from four sides, for 20 s each, for a total of 80 s as described above. Shear bond strength was tested with a universal testing machine (Zwick/Roell Z020, Type BDO-FB020TN) at a crosshead speed of 1 mm/min. Loads were converted to stress by dividing the failure load by the bonding area. Statistical analysis was performed by SPSS statistical software using 1-way analysis of variance (ANOVA) and repeated measures approach with shear bond strength as the dependent variable, the surface conditioning methods as the independent factor and the Tukey honestly significant difference (HSD) posthoc pair-wise comparison procedure with a = 0.05.
Table 1 Codes and types of materials studied with manufacturing companies.
IPS d.SIGN Panavia F2.0 ClearFill AP-X Ice Zirconia
Material type
Manufacturer
Fluorapatite Leucite glass – ceramic
Ivoclar Vivadent AG, Liechtenstein
Y-TZP
Kuraray Medical INC.japan Kuraray Medical INC.japan ZirkonZahn, Italy
Fig. 1. SEM side view image of a GZ specimen.
A. Moradabadi et al. / Materials Science and Engineering C 34 (2014) 311–317
313
Table 2 Mean shear strengths and standard deviations for seven experimental groups. Groups
N
Mean (MPa)
Standard deviation
SZ ZH HSZ GZ GZH SGZ HSGZ
7 7 7 7 7 7 7
28.14 21.88 26.95 4.73 19.73 4.27 22.36
7.37 4.54 7.78 1.103 4.21 0.79 2.48
After preparation, specimen surfaces were examined with an optical microscope (Stereo, Carlzeiss, Germany) at 40× magnification to understand the possible mode of failure at the ceramic or at the composite surface. Selected ceramic surfaces and the fracture surfaces of the composite cylinders were analyzed using Scanning Electron Microscopy (SEM) micrographs (SEM Machine, VEGA/TESCAN). The thickness of the applied glaze layers was measured using SEM micrographs. Sample surfaces were also analyzed by atomic force microscopy (AFM) in order to determine the surface topography and its effects on final strength. The AFM machine, a DualScope C-26 DME, was used in a tapping mode. More specifically, for salt-glazed specimens, X-ray diffraction technique (XRD) was used with Cu-kα radiation (λ = 0.154 nm) in order to characterize crystallite phases observed by SEM on the surface of the specimens.
3. Results The shear bond strength (SBS) values are summarized in Table 3 for the seven bonding groups. A one-way ANOVA model and repeated measures approach were performed for data analyzing, statistically. The Tukey HSD post-hoc pair-wise comparison test was conducted on all group data in order to analyze the effects of various surface treatments on average shear strengths. Results show that sandblasting surface treatment had the highest shear bond strength and two glaze layer-coating methods had the lowest shear bond strengths. SZ (28.14 ± 7.37 MPa), HSZ (26.95 ± 7.79 MPa) and ZH (21.88 ± 4.54 MPa) groups had shear strength values significantly higher than of those of either GZ (4.73 ± 1.10 MPa) or SGZ (4.27 ± 0.80 MPa) groups. However, after etching, shear strength values, HGZ (26.95 ± 7.78 MPa) and HSGZ (22.36 ± 2.48 MPa), have significantly increased. The Tukey post-hoc pair-wise comparisons divided samples in all groups into three subsets. The first subset is composed of GZ and SGZ groups. The second subset is consisted of ZH, HSZ, HGZ and HSGZ groups. Finally, the third subset includes SZ, ZH, HSZ and HSGZ groups. This means that there are no significant differences between treatments that are involved in each subset. Failure modes were observed by optical microscopy after shear test. All specimens in SGZ and HSGZ groups failed 100% adhesively. 57.15% of
Table 3 Subsets of homogeneous groups determined by Tukey post-hoc test. Subset Treatment SGZ GZ HGZ ZH HSGZ HSZ SZ Significance
N 7 7 7 7 7 7 7
1 4.27 4.73
2
19.73 21.88 22.36 26.95 1.000
0.097
3
21.88 22.36 26.95 28.14 0.208
Fig. 2. SEM micrographs of different failure modes: (a) a sample from HZ group with mixed, (b) a sample from HSGZ group with adhesive, and (c) a sample from SZ group with cohesive failure mode.
314
A. Moradabadi et al. / Materials Science and Engineering C 34 (2014) 311–317
failure modes in specimens of group GZ were adhesive and 42.85% were mixed. Similar samples after etching showed 42.85% adhesive and 57.15% mixed failure modes in HGZ samples. ZH specimens showed 57.15% adhesive failure mode and 42.85% mixed failure mode. Finally, failure modes in SZ specimens were 42.85% adhesive, 14.30% mixed and 42.85% cohesive. The SEM micrographs of the different failure modes are presented in Fig. 2. 4. Discussion As mentioned earlier, the main goal of this study was to evaluate the effects of two different mechanisms of chemical and micromechanical adhesion on bond strength between dental resin agent, Panavia F2, and zirconia restoration material. In order to investigate the chemical adhesion mechanism, a glaze layer with two different compositions was applied on top of the zirconia bars. The results showed that the polished surfaces of both zirconia and glaze layer resulted in relatively low bond strengths. Hence, the dominant mechanism to obtain adequate bond strength between zirconia dental ceramic and resin agent was micromechanical retention. As each commercial system has special composition and intaglio surface configuration; results of different studies could not be readily compared to the others with a high degree of accuracy. Studies on bond strengths, however, have shown that airborne particle abrasion in combination with MDP-containing resin luting agent, Panavia F2, would provide adequate bond strengths while resin luting agents without such monomers were not able to obtain suitable bonding between densely sintered zirconia and alumina dental ceramics [8,10–14]. Currently in dental applications airborne particle abrasion for densely sintered all-ceramic restorations is a common surface treatment [8,13]. Such methods improve micromechanical retention by means of surface roughening; and, moreover, lead to increasing surface energy and wettability [8,26]. Although such processes would create cracks on restoration surface and decrease its strength to some extent; on the other hand, it has been proven that utilization of resin luting agents could have healing effect and nearly neutralize cracks detriments [8,27,28]. A comparison among shear strengths for different groups (Table 2) shows that applying the glaze layer either in form of salt glaze or Fluorapatite-Leucite glass layer results in similar values to zirconia surface without any treatments (~5–6 MPa) [2], which are significantly lower strengths than micromechanical method strengths (4.45 MPa versus 25.45 MPa). However, the same glazed surfaces after etching process showed significantly higher strengths (~21.5 MPa). Hence, one can conclude that micromechanical retention is a more effective mechanism than chemical adhesion in order to obtain higher bond strengths between zirconia core and resin luting agent; Moreover, low bond strength between densely sintered ceramic materials and resin luting agents can be improved by abrasion surface treatments and creation of bulges and dents on surface to increase roughness. Fig. 3 shows SEM micrographs of GZ and SGZ samples. As shown, glazed samples have smooth surfaces before the etching process. An increase in surface roughness is clearly observable after etching process, which results in an increase in shear bond strength of group GZ from 4.73 MPa to 26.95 MPa. Similarly, the shear strength of SGZ specimens increased from 4.27 MPa to 22.36 MPa before and after etching process, respectively. According to contact mechanics theories [29–31], the remarkable increase in shear bond strengths in these groups after etching process; is caused by the increase in surface roughness, which in turn can be attributed to micromechanical retention mechanism. It was observed that the ratio of adhesive fracture after etching process in GZ specimens decreased which was caused by an increase in micromechanical retention. The specimens in SGZ group presented adhesive mode of fracture before and after etching process. This can be attributed to the presence of glaze layer and surface composition resulted from the etching process. We believe, formation of glass-ceramic
crystallites instead of a uniform layer of salt glaze due to deficiency of peak temperature in sintering process has resulted in a non-uniformity in surface composition and consequently weakened chemical adhesion between glaze layer and MDP-containing resin luting agent. According to SEM micrographs, surface roughness of HSGZ group after etching process is similar to the surface roughness of HGZ group, which is smaller in size and limited to interspaces of crystallites. This can result in a decrease in wettability and therefore debilitation of micromechanical retention. Fig. 4 represents X-ray diffraction (XRD) pattern for zirconia bar on which a layer of salt glaze in the P2O5–B2O3–K2O system was applied and subsequently was heated from 500 to 900 °C at a heating rate of 60 °C/min with holding time of 30 min. The samples were then cooled down for 10 min at a rate of 40 °C/min. As it can be observed from the pattern, main XRD peaks of the specimen occur at diffraction angles (2θ) of 30.60°, 50.50° and 62.20° that correspond to (111), (220) and (222) planes respectively. These planes that are ascribed to tetragonal ZrO2 phase constitute the main part of the zirconia base. Moreover, it can be observed from the XRD pattern that there are several other weak peaks at 2θ of 35.8°, 40.60° and 51.20°, and also at 2θ of 25.20°, 33.00° and 41.40° which are attributed to ZrP and ZrB2 phases, respectively. Hence, there is clear evidence that zirconia base materials reacted with glaze layer and created crystallites that can also be seen in SEM micrograph of this specimen in Fig. 5. Fig. 5 (a) and (b) shows SEM and AFM micrographs of SZ group (A1, B1), ZH group (Fig. A2, B2) and HSZ group (Fig. A3, B3), respectively. The measured mean shear bond strengths for these groups (Table 2) were 28.14 MPa, 21.88 MPa and 26.95 MPa, respectively. These bond strengths are significantly higher than bond strengths for glazed zirconia in GZ, SGZ groups. SEM and AFM micrographs presented in Fig. 5 also demonstrate the surface topographies of the specimens in these groups. According to these micrographs, airborne particle abrasion generated jagged roughness with wide distribution. While, the etching process results in surface roughness in hump and round form with limited distribution on surface. Hence, the jagged roughness led to better micromechanical retention and consequently higher bond strengths [28]. A closer look at the fracture modes for these samples exhibits that 42.85% of SZ specimens fractured cohesively which is resulted from higher bond strengths with dental resin agents. In contrast, HSZ specimens that were exposed to etching process after sandblast just had 57.15% mixed, and 42.85% adhesive modes of fracture, which resulted in their low bond strengths. These low strengths could occur due to destruction and deformation of jagged surface roughness by additional etching process into hump and round surface roughness that would decrease micromechanical retention. In the case of ZH specimens, 57.15% of fracture modes were adhesive and others had mixed modes. This increase in adhesive modes of fracture could also be interpreted by surface roughness topography as was prescribed for GZ and SGZ specimens. The clear presence of zirconia tetragonal grains (Fig. 5-A1) shows that, in contrast to group SZ, etched zirconia specimens had hump and rounded surface topography due to erosion of grain boundary areas with higher surface energies by etching process [28]. Surface topography of ZH samples is not jagged and has smaller amplitude, due to micro-size zirconia tetragonal grains (~1 μm), than SZ specimen surface roughness amplitude, due to Al2O3 sand airborne particle abrasion process (~50 μm). This leads to the decrease in micromechanical retention and consequently the decrease in bond strength between zirconia surface and Panavia F2. Finally, it should be noted that in-vitro studies always have inherent limitations; although, they are effective tools for simulation of the oral environment. Two of the primary objectives of in-vitro studies are elimination of influential parameters and limitation of variables. Whenever in-vitro investigations are used to draw clinically relevant conclusions, care should be taken and materials with different compositions and different manufacturers cannot be recommended without further investigation.
A. Moradabadi et al. / Materials Science and Engineering C 34 (2014) 311–317
315
Fig. 3. SEM micrographs of zirconia ceramic surfaces covered by (a) glass-ceramic layer before (left) and after (right) HF-etching (GZ and HGZ), and (b) salt glaze layer before (left) and after (right) HCL-etching (SGZ and HSGZ).
Fig. 4. XRD pattern of a salt glaze layer that was applied on zirconia substrate.
316
A. Moradabadi et al. / Materials Science and Engineering C 34 (2014) 311–317
Fig. 5. Representative images of the treated zirconia ceramic surface topographies, Left: SEM, and Right: surface roughness from AFM; (a) zirconia surface sandblasted by 50 μm alumina particles (SZ), (b) zirconia ceramic surface treated by HNO3–HF solution (ZH), and (c) zirconia surface treated by both of these methods (SZH).
A. Moradabadi et al. / Materials Science and Engineering C 34 (2014) 311–317
5. Conclusions In this study we have shown that micromechanical retention is the dominant mechanism for zirconia core bonding to Panavia F2 dental resin agent. We have also reported that the weakness in bonding between zirconia all-ceramic restoration and resin luting agents is not due to inadequate chemical adhesion of zirconia base material. This is due to the fact that densely sintered ceramics such as zirconia cores have hard, smooth surfaces that led to diminution in wettability, inadequate micromechanical retention, and lower bond strengths. Among limited methods investigated in this study, airborne particle abrasion obtained highest shear bond strengths. Optimized etching process can also lead to higher bond strengths than what was examined in this study. In consideration of in-vitro study limitations and long-term storage and thermal cycling, more investigations are needed for more precise conclusions. Also, future work is needed to verify the results in oral simulated media e.g. artificial saliva.
[4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23]
Acknowledgments [24]
Authors greatly appreciate the comments and help of Drs. Ghasemi and Eslami from School of Dentistry, Shahid Beheshti University of Medical Sciences.
[25] [26] [27] [28]
References [29] [1] J. Chevalier, L. Gremillard, J. Eur. Ceram. Soc. 29 (7) (2009) 1245–1255. [2] P.F. Manicone, P.R. Iommetti, L. Raffaelli, J. Dent. 35 (2007) 819–826. [3] J.Y. Thompson, B.R. Stoner, J.R. Piascik, Mater. Sci. Eng. C 27 (2007) 565–569.
[30] [31]
317
I. Denry, J.R. Kelly, Dent. Mater. 24 (2008) 299–307. R. Janda, J.F. Roulet, M. Wulf, H.J. Tiller, Dent. Mater. 19 (2003) 567–573. M. Ozcana, P.K. Vallittu, Dent. Mater. 19 (2003) 725–731. M.B. Blatz, A. Sadan, J. Martin, B. Lang, J. Prosthet. Dent. 91 (2004) 356–362. J.R. Kelly, I. Denry, Dent. Mater. 24 (2008) 289–298. M. Kern, S.M. Wegner, Dent. Mater. 14 (1998) 64–71. W.O. Soboyejo, D. Brooks, J. Am. Ceram. Soc. 78 (6) (1995) 1481–1488. R. Van Noort, Introduction to Dental Materials, Second ed. Mosby Co, Hong Kong, 2002. M. Wolfart, F. Lehmann, S. Wolfart, M. Kern, Dent. Mater. 23 (2007) 45–50. M.N. Aboushelib, J.P. Matinlinna, Z. Salameh, H. Ounsi, Dent. Mater. 24 (2008) 1268–1272. Y. Zhang, B.R. Lawn, E.D. Rekow, V.P. Thompson, J. Biomed. Mater. Res. B 71B (2004) 381–386. M.N. Aboushelib, C.J. Kleverlaan, A.J. Feilzer, J. Prosthet. Dent. 98 (2007) 379–388. A.C. Quaas, B. Yang, M. Kernb, Dent. Mater. 23 (2007) 506–512. N. Rahbar, Y. Yang, W.O. Soboyejo, Mater. Sci. Eng. A 488 (2008) 381–388. X. Nui, N. Rahbar, S. Farias, W.O. Soboyejo, J. Mech. Behav. Biomed. 2 (2009) 596–602. M. Huang, N. Rahbar, R. Wang, V.P. Thompson, E.D. Rekow, Mater. Sci. Eng. A 464 (2007) 315–320. N. Rahbar, W.O. Soboyejo, Fatigue Fract. Eng. Mater. 34 (2011) 887–897. J. Du, X. Niu, N. Rahbar, W. Soboyejo, Acta Biomater. 9 (2013) 5273–5279. T. Derand, M. Molin, K. Kvam, Dent. Mater. 21 (2005) 1158–1162. V.E. Annamalai, B.L. Anantharamu, C.V. Gokularathnam, R. Krishnamurthy, J. Mater. Sci. Lett. 10 (1991) 459–460. R.E. Chinn, Ceramography: Preparation and Analysis of Ceramic Microstructures, first ed. Wiley-American Ceramic Society, 2002. T. Sekercioglu, H. Rende, A. Gülsöz, C. Merana, J. Mater. Process. Technol. 142 (2003) 82–86. M.B. Blatz, Quintessence Int. 33 (2002) 415–426. F.J. Burke, G.J. Fleming, J. Adhes. Dent. 4 (2002) 7–22. N. Rahbar, K. Wolf, A. Orana, R. Fennimore, Z. Zong, J. Meng, G. Papandreou, C. Maryanoff, W.O. Soboyejo, J. Appl. Phys. 104 (2008) 103533. J. Meng, A. Orana, T. Tan, K. Wolf, N. Rahbar, H. Li, G. Papandreou, C. Maryanoff, W.O. Soboyejo, J. Mater. Res. 25 (2010) 641–647. R. Melo, N. Rahbar, W.O. Soboyejo, Mater. Sci. Eng. C 31 (4) (2011) 770–774. K. Uehara, M. Sakurai, J. Mater. Process. Technol. 127 (2002) 178–181.
Contents lists available at ScienceDirect
Materials Science and Engineering C journal homepage: www.elsevier.com/locate/msec
Effects of surface treatment on bond strength between dental resin agent and zirconia ceramic Ashkan Moradabadi a, Sareh Esmaeily Sabet Roudsari b, Bijan Eftekhari Yekta d, Nima Rahbar c,⁎ a
Department of Electrochemistry, Universität Ulm, Ulm, Germany Department of Optoelectonics, Universität Ulm, Ulm, Germany Department of Civil and Environmental Engineering, Worcester Polytechnic Institute, Worcester, MA 01609, USA d School of Materials Engineering, Iran University of Science and Technology, Tehran, Iran b c
a r t i c l e
i n f o
Article history: Received 19 February 2013 Received in revised form 2 August 2013 Accepted 18 September 2013 Available online 26 September 2013 Keywords: Zirconia Dental resin Bond strength Adhesion Micromechanical retention
a b s t r a c t This paper presents the results of an experimental study to understand the dominant mechanism in bond strength between dental resin agent and zirconia ceramic by investigating the effects of different surface treatments. Effects of two major mechanisms of chemical and micromechanical adhesion were evaluated on bond strength of zirconia to luting agent. Specimens of yttrium-oxide-partially-stabilized zirconia blocks were fabricated. Seven groups of specimens with different surface treatment were prepared. 1) zirconia specimens after airborne particle abrasion (SZ), 2) zirconia specimens after etching (ZH), 3) zirconia specimens after airborne particle abrasion and simultaneous etching (HSZ), 4) zirconia specimens coated with a layer of a FluorapatiteLeucite glaze (GZ), 5) GZ specimens with additional acid etching (HGZ), 6) zirconia specimens coated with a layer of salt glaze (SGZ) and 7) SGZ specimens after etching with 2% HCl (HSGZ). Composite cylinders were bonded to airborne-particle-abraded surfaces of ZirkonZahn specimens with Panavia F2 resin luting agent. Failure modes were examined under 30× magnification and the effect of surface treatments was analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). SZ and HSZ groups had the highest and GZ and SGZ groups had the lowest mean shear bond strengths among all groups. Mean shear bond strengths were significantly decreased by applying a glaze layer on zirconia surfaces in GZ and SGZ groups. However, bond strengths were improved after etching process. Airborne particle abrasion resulted in higher shear bond strengths compared to etching treatment. Modes of failure varied among different groups. Finally, it is concluded that micromechanical adhesion was a more effective mechanism than chemical adhesion and airborne particle abrasion significantly increased mean shear bond strengths compared with another surface treatments. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Demands for densely sintered ceramics as dental restorative materials have recently increased because of their outstanding properties. These oxide materials have optimized properties such as: biocompatibility [1–3] and favorable optical properties [2–7] as well as high mechanical strengths [8]. These high strength ceramics are used in dental restorations as all-ceramic crowns and bridges and in various all-ceramic core and post systems [2–4,6]. Zirconium oxide, currently the material of choice for dental application, is typically used in Yttria partially stabilized Tetragonal Zirconia Polycrystal (Y-TZP) [9]. Y-TZP has a unique toughening mechanism called “transformation toughening.” Crack propagation in Y-TZP is resisted by transformation from tetragonal to monoclinic phase through a substantial increase in volume (~4.5%) that induces compressive stresses over the crack tip [2,4,9–11]. Ceramics generally bond to resin by formation of chemical bonds and micromechanical interlocking [8,12]. Hence, long-term performance of ⁎ Corresponding author. Tel.: +1 508 831 6567; fax: +1 508 831 5808. E-mail address: [email protected] (N. Rahbar). 0928-4931/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.msec.2013.09.015
dental restoration is heavily dependent on bond durability [13]. Since, reliable chemical bonds to zirconia-based materials cannot be easily established [8,14], many studies have been focused on various surface treatments to improve bonding between zirconia and dental resin agents. Various chemical or mechanical treatments have been suggested to improve bond strength such as Silicoater [6,12], Pyrosilpen [6], tribochemical silica coating [7,11,12], Kevloc [11], sputtering [3], sandblasting [8,10,15], grinding [6], selective infiltration-etching [12,16], and additional cleaning procedures [17–22]. One of the most successful coatings with adequate values of adhesion is resin cementation [7]. Panavia F (Kuraray) is a dual-polymerizing, fluoride-releasing resin luting agent that also contains the adhesive monomer Methanediphosphonic acid (MDP) [12]. While, some researchers have suggested that high and durable bond strength was achieved on airabraded surfaces with the use of a MDP-containing composite resin, others claimed that airborne particle abrasion or chemical surface treatments such as silanization could not significantly improve bond strength. Some even claimed no surface treatment is required to achieve a durable bonding between the zirconia and dental resin [2,8,10,13,14]. Another method that has been used to establish a stronger bonding
312
A. Moradabadi et al. / Materials Science and Engineering C 34 (2014) 311–317
between the zirconia surface and the resin luting material is to fuse a thin layer of glass (porcelain) pearls to zirconia [23]. Acid etching has also been utilized to enhance the bonding between zirconia and cement by increasing micromechanical retention. While application of acidic agents, such as phosphoric and hydrofluoric acid for zirconia etching will not create the needed roughened surface for strong bonding [6,8], a solution of HF and HNO3 is reported to be more effective for etching of zirconia surface [24,25]. Hence, a correlation between different zirconia restoration surface treatments and adhesion to dental luting cements is clearly missing. The aim of this study was to improve the bond strength of MDP resin composite to zirconia ceramic using a novel chemical surface treatment by applying a thin layer of two different glaze layers on zirconia surface. The results were compared with traditional micromechanical treatments such as airborne particle abrasion and acid etching. 2. Material and methods Forty-nine square-shaped specimens of high-purity zirconiumoxide ceramic were cut from a pre-sintered ZirkonZahn zirconia block. The samples were cut by a cutting machine (Buehler, ISOMET 2000) with a diamond blade into square-shaped bars with the initial dimension of 9 × 5 × 3 mm3 under cooling, they were then grounded by silicon carbide abrasive paper (Silicium Carbid, Matador, Wasserfest 991A, softflex) under cooling to their final dimension of 8 × 4 × 2 mm3. Afterwards, sample surfaces were polished using a polishing machine with Al2O3 polishing powder (polisher & grinder, Metaserv 2000). Table 1 summarizes the characteristics of surface conditioning methods and ceramic types with codes and manufacturing company names. In order to understand the effects of two major mechanisms on bond strength of zirconia to luting agents, seven experimental groups (n = 7) of specimens with different surface treatment were prepared: 1) zirconia specimens after airborne particle abrasion (SZ), 2) zirconia specimens after etching with 45 vol % HNO3 + 10 vol % HF + 45 vol % H2O solution for 2 min. (ZH), 3) zirconia specimens after airborne particle abrasion and simultaneous etching (HSZ), 4) zirconia specimens coated with a layer of a Fluorapatite-Leucite glaze (GZ), 5) GZ specimens with additional acid etching for 30 s (HGZ), 6) zirconia specimens coated with a layer of salt glaze (SGZ) and 7) SGZ specimens after etching with 2% HCl for 20 s (HSGZ). In four of these groups, specimens were treated by chemical procedures (GZ, HGZ, SGZ and HSGZ) and other three groups underwent micromechanical surface treatments. In GZ specimens, in order to improve the surface condition before sintering process, a layer of Fluorapatite-Leucite glass-ceramic (IPS d.SIGN, Ivoclar, Vivadent, S2, Liechtenstein) was applied to surface of each specimen. The GZ and HGZ specimens were airborne particle abraded (Easy Blast BEGO) with 50-μm aluminum-oxide (Al2O3) particles (at 1.5 bar for 8 s at a distance of 150 mm), before sintering process. This was followed by ultrasonic cleaning (BIOSONIC JR.JELCRAFT TM Vectorss, Pennwalt, JELENKO) with 96% ethanol alcohol for 5 min, and air-drying (Sirona S5, Siemens, model D 3111). The glaze layers were applied on all 49 specimens and were sintered at maximum temperature of 1500 °C for 8 h (Zikon Ofen, Zirkon Zahn). Before testing, all groups with the exception of GZ specimens were airborne particle abraded with 50-μm aluminum-oxide (Al2O3) particles at 4 bar pressure for 8 s at a distance of 10 mm, followed by ultrasonic cleaning in 96% ethanol
alcohol for 5 min and then air-drying. The side view SEM image of a GZ specimen is presented in Fig. 1. Salt glaze for SGZ and HSGZ samples was prepared by addition of 42.12 wt.% potassium carbonate, 15.19 wt.% boric acid and 42.69 wt.% phosphoric acid (Merck, Germany) to distilled water at 60 °C in order to form a thick solution in the K2O–P2O5–B2O3 system. The sandblasted zirconia bars were dipped into this solution for 2 min, cleaned with ultrasonic and steam, and then were air-dried. Subsequently these specimens were heated in a dental furnace (Elephant Hoorn, Holand) at 500–900 °C with a heating rate of 60 °C/min with holding time of 30 min. The specimens were then cooled down for 10 min at the rate of 40 °C/min. Acrylic plastic tubes (3.0 mm in height and 2.0 mm in diameter) were filled with composite (ClearFill AP-X, shadeA2, Kuraray Medical, Japan) to fabricate composite cylinders. The cylinder topsides were light-polymerized (VSI light curing system, ARIALUX Blue Pass+, SN821530) for 40 s. The output power of the light curing system was 450 mW/Cm2. The composite cylinders were bonded to the ceramic specimens 5 min after light polymerization. Resin luting agents (Panavia F2.0, Kuraray Medical INC.1621 Sakazu, Kurashiki, Okayama 710–0801, Japan) were mixed and applied on ceramic surfaces according to the manufacturer's recommendations. Excess resin was removed with foam pellets (Small Sponge Pledgets, Kuraray) and oxygenblocking gel (Oxyguard II; Kuraray) was applied according to manufacturer's instructions. T PANAVIA F 2.0 Paste is a dual-cure (light or self-cure) resin-based cement for ceramics. Clearfil Ceramic Primer is a silane-coupling agent that provides an enhanced adhesive surface to ceramic. The resin luting agents were light-polymerized from four sides, for 20 s each, for a total of 80 s as described above. Shear bond strength was tested with a universal testing machine (Zwick/Roell Z020, Type BDO-FB020TN) at a crosshead speed of 1 mm/min. Loads were converted to stress by dividing the failure load by the bonding area. Statistical analysis was performed by SPSS statistical software using 1-way analysis of variance (ANOVA) and repeated measures approach with shear bond strength as the dependent variable, the surface conditioning methods as the independent factor and the Tukey honestly significant difference (HSD) posthoc pair-wise comparison procedure with a = 0.05.
Table 1 Codes and types of materials studied with manufacturing companies.
IPS d.SIGN Panavia F2.0 ClearFill AP-X Ice Zirconia
Material type
Manufacturer
Fluorapatite Leucite glass – ceramic
Ivoclar Vivadent AG, Liechtenstein
Y-TZP
Kuraray Medical INC.japan Kuraray Medical INC.japan ZirkonZahn, Italy
Fig. 1. SEM side view image of a GZ specimen.
A. Moradabadi et al. / Materials Science and Engineering C 34 (2014) 311–317
313
Table 2 Mean shear strengths and standard deviations for seven experimental groups. Groups
N
Mean (MPa)
Standard deviation
SZ ZH HSZ GZ GZH SGZ HSGZ
7 7 7 7 7 7 7
28.14 21.88 26.95 4.73 19.73 4.27 22.36
7.37 4.54 7.78 1.103 4.21 0.79 2.48
After preparation, specimen surfaces were examined with an optical microscope (Stereo, Carlzeiss, Germany) at 40× magnification to understand the possible mode of failure at the ceramic or at the composite surface. Selected ceramic surfaces and the fracture surfaces of the composite cylinders were analyzed using Scanning Electron Microscopy (SEM) micrographs (SEM Machine, VEGA/TESCAN). The thickness of the applied glaze layers was measured using SEM micrographs. Sample surfaces were also analyzed by atomic force microscopy (AFM) in order to determine the surface topography and its effects on final strength. The AFM machine, a DualScope C-26 DME, was used in a tapping mode. More specifically, for salt-glazed specimens, X-ray diffraction technique (XRD) was used with Cu-kα radiation (λ = 0.154 nm) in order to characterize crystallite phases observed by SEM on the surface of the specimens.
3. Results The shear bond strength (SBS) values are summarized in Table 3 for the seven bonding groups. A one-way ANOVA model and repeated measures approach were performed for data analyzing, statistically. The Tukey HSD post-hoc pair-wise comparison test was conducted on all group data in order to analyze the effects of various surface treatments on average shear strengths. Results show that sandblasting surface treatment had the highest shear bond strength and two glaze layer-coating methods had the lowest shear bond strengths. SZ (28.14 ± 7.37 MPa), HSZ (26.95 ± 7.79 MPa) and ZH (21.88 ± 4.54 MPa) groups had shear strength values significantly higher than of those of either GZ (4.73 ± 1.10 MPa) or SGZ (4.27 ± 0.80 MPa) groups. However, after etching, shear strength values, HGZ (26.95 ± 7.78 MPa) and HSGZ (22.36 ± 2.48 MPa), have significantly increased. The Tukey post-hoc pair-wise comparisons divided samples in all groups into three subsets. The first subset is composed of GZ and SGZ groups. The second subset is consisted of ZH, HSZ, HGZ and HSGZ groups. Finally, the third subset includes SZ, ZH, HSZ and HSGZ groups. This means that there are no significant differences between treatments that are involved in each subset. Failure modes were observed by optical microscopy after shear test. All specimens in SGZ and HSGZ groups failed 100% adhesively. 57.15% of
Table 3 Subsets of homogeneous groups determined by Tukey post-hoc test. Subset Treatment SGZ GZ HGZ ZH HSGZ HSZ SZ Significance
N 7 7 7 7 7 7 7
1 4.27 4.73
2
19.73 21.88 22.36 26.95 1.000
0.097
3
21.88 22.36 26.95 28.14 0.208
Fig. 2. SEM micrographs of different failure modes: (a) a sample from HZ group with mixed, (b) a sample from HSGZ group with adhesive, and (c) a sample from SZ group with cohesive failure mode.
314
A. Moradabadi et al. / Materials Science and Engineering C 34 (2014) 311–317
failure modes in specimens of group GZ were adhesive and 42.85% were mixed. Similar samples after etching showed 42.85% adhesive and 57.15% mixed failure modes in HGZ samples. ZH specimens showed 57.15% adhesive failure mode and 42.85% mixed failure mode. Finally, failure modes in SZ specimens were 42.85% adhesive, 14.30% mixed and 42.85% cohesive. The SEM micrographs of the different failure modes are presented in Fig. 2. 4. Discussion As mentioned earlier, the main goal of this study was to evaluate the effects of two different mechanisms of chemical and micromechanical adhesion on bond strength between dental resin agent, Panavia F2, and zirconia restoration material. In order to investigate the chemical adhesion mechanism, a glaze layer with two different compositions was applied on top of the zirconia bars. The results showed that the polished surfaces of both zirconia and glaze layer resulted in relatively low bond strengths. Hence, the dominant mechanism to obtain adequate bond strength between zirconia dental ceramic and resin agent was micromechanical retention. As each commercial system has special composition and intaglio surface configuration; results of different studies could not be readily compared to the others with a high degree of accuracy. Studies on bond strengths, however, have shown that airborne particle abrasion in combination with MDP-containing resin luting agent, Panavia F2, would provide adequate bond strengths while resin luting agents without such monomers were not able to obtain suitable bonding between densely sintered zirconia and alumina dental ceramics [8,10–14]. Currently in dental applications airborne particle abrasion for densely sintered all-ceramic restorations is a common surface treatment [8,13]. Such methods improve micromechanical retention by means of surface roughening; and, moreover, lead to increasing surface energy and wettability [8,26]. Although such processes would create cracks on restoration surface and decrease its strength to some extent; on the other hand, it has been proven that utilization of resin luting agents could have healing effect and nearly neutralize cracks detriments [8,27,28]. A comparison among shear strengths for different groups (Table 2) shows that applying the glaze layer either in form of salt glaze or Fluorapatite-Leucite glass layer results in similar values to zirconia surface without any treatments (~5–6 MPa) [2], which are significantly lower strengths than micromechanical method strengths (4.45 MPa versus 25.45 MPa). However, the same glazed surfaces after etching process showed significantly higher strengths (~21.5 MPa). Hence, one can conclude that micromechanical retention is a more effective mechanism than chemical adhesion in order to obtain higher bond strengths between zirconia core and resin luting agent; Moreover, low bond strength between densely sintered ceramic materials and resin luting agents can be improved by abrasion surface treatments and creation of bulges and dents on surface to increase roughness. Fig. 3 shows SEM micrographs of GZ and SGZ samples. As shown, glazed samples have smooth surfaces before the etching process. An increase in surface roughness is clearly observable after etching process, which results in an increase in shear bond strength of group GZ from 4.73 MPa to 26.95 MPa. Similarly, the shear strength of SGZ specimens increased from 4.27 MPa to 22.36 MPa before and after etching process, respectively. According to contact mechanics theories [29–31], the remarkable increase in shear bond strengths in these groups after etching process; is caused by the increase in surface roughness, which in turn can be attributed to micromechanical retention mechanism. It was observed that the ratio of adhesive fracture after etching process in GZ specimens decreased which was caused by an increase in micromechanical retention. The specimens in SGZ group presented adhesive mode of fracture before and after etching process. This can be attributed to the presence of glaze layer and surface composition resulted from the etching process. We believe, formation of glass-ceramic
crystallites instead of a uniform layer of salt glaze due to deficiency of peak temperature in sintering process has resulted in a non-uniformity in surface composition and consequently weakened chemical adhesion between glaze layer and MDP-containing resin luting agent. According to SEM micrographs, surface roughness of HSGZ group after etching process is similar to the surface roughness of HGZ group, which is smaller in size and limited to interspaces of crystallites. This can result in a decrease in wettability and therefore debilitation of micromechanical retention. Fig. 4 represents X-ray diffraction (XRD) pattern for zirconia bar on which a layer of salt glaze in the P2O5–B2O3–K2O system was applied and subsequently was heated from 500 to 900 °C at a heating rate of 60 °C/min with holding time of 30 min. The samples were then cooled down for 10 min at a rate of 40 °C/min. As it can be observed from the pattern, main XRD peaks of the specimen occur at diffraction angles (2θ) of 30.60°, 50.50° and 62.20° that correspond to (111), (220) and (222) planes respectively. These planes that are ascribed to tetragonal ZrO2 phase constitute the main part of the zirconia base. Moreover, it can be observed from the XRD pattern that there are several other weak peaks at 2θ of 35.8°, 40.60° and 51.20°, and also at 2θ of 25.20°, 33.00° and 41.40° which are attributed to ZrP and ZrB2 phases, respectively. Hence, there is clear evidence that zirconia base materials reacted with glaze layer and created crystallites that can also be seen in SEM micrograph of this specimen in Fig. 5. Fig. 5 (a) and (b) shows SEM and AFM micrographs of SZ group (A1, B1), ZH group (Fig. A2, B2) and HSZ group (Fig. A3, B3), respectively. The measured mean shear bond strengths for these groups (Table 2) were 28.14 MPa, 21.88 MPa and 26.95 MPa, respectively. These bond strengths are significantly higher than bond strengths for glazed zirconia in GZ, SGZ groups. SEM and AFM micrographs presented in Fig. 5 also demonstrate the surface topographies of the specimens in these groups. According to these micrographs, airborne particle abrasion generated jagged roughness with wide distribution. While, the etching process results in surface roughness in hump and round form with limited distribution on surface. Hence, the jagged roughness led to better micromechanical retention and consequently higher bond strengths [28]. A closer look at the fracture modes for these samples exhibits that 42.85% of SZ specimens fractured cohesively which is resulted from higher bond strengths with dental resin agents. In contrast, HSZ specimens that were exposed to etching process after sandblast just had 57.15% mixed, and 42.85% adhesive modes of fracture, which resulted in their low bond strengths. These low strengths could occur due to destruction and deformation of jagged surface roughness by additional etching process into hump and round surface roughness that would decrease micromechanical retention. In the case of ZH specimens, 57.15% of fracture modes were adhesive and others had mixed modes. This increase in adhesive modes of fracture could also be interpreted by surface roughness topography as was prescribed for GZ and SGZ specimens. The clear presence of zirconia tetragonal grains (Fig. 5-A1) shows that, in contrast to group SZ, etched zirconia specimens had hump and rounded surface topography due to erosion of grain boundary areas with higher surface energies by etching process [28]. Surface topography of ZH samples is not jagged and has smaller amplitude, due to micro-size zirconia tetragonal grains (~1 μm), than SZ specimen surface roughness amplitude, due to Al2O3 sand airborne particle abrasion process (~50 μm). This leads to the decrease in micromechanical retention and consequently the decrease in bond strength between zirconia surface and Panavia F2. Finally, it should be noted that in-vitro studies always have inherent limitations; although, they are effective tools for simulation of the oral environment. Two of the primary objectives of in-vitro studies are elimination of influential parameters and limitation of variables. Whenever in-vitro investigations are used to draw clinically relevant conclusions, care should be taken and materials with different compositions and different manufacturers cannot be recommended without further investigation.
A. Moradabadi et al. / Materials Science and Engineering C 34 (2014) 311–317
315
Fig. 3. SEM micrographs of zirconia ceramic surfaces covered by (a) glass-ceramic layer before (left) and after (right) HF-etching (GZ and HGZ), and (b) salt glaze layer before (left) and after (right) HCL-etching (SGZ and HSGZ).
Fig. 4. XRD pattern of a salt glaze layer that was applied on zirconia substrate.
316
A. Moradabadi et al. / Materials Science and Engineering C 34 (2014) 311–317
Fig. 5. Representative images of the treated zirconia ceramic surface topographies, Left: SEM, and Right: surface roughness from AFM; (a) zirconia surface sandblasted by 50 μm alumina particles (SZ), (b) zirconia ceramic surface treated by HNO3–HF solution (ZH), and (c) zirconia surface treated by both of these methods (SZH).
A. Moradabadi et al. / Materials Science and Engineering C 34 (2014) 311–317
5. Conclusions In this study we have shown that micromechanical retention is the dominant mechanism for zirconia core bonding to Panavia F2 dental resin agent. We have also reported that the weakness in bonding between zirconia all-ceramic restoration and resin luting agents is not due to inadequate chemical adhesion of zirconia base material. This is due to the fact that densely sintered ceramics such as zirconia cores have hard, smooth surfaces that led to diminution in wettability, inadequate micromechanical retention, and lower bond strengths. Among limited methods investigated in this study, airborne particle abrasion obtained highest shear bond strengths. Optimized etching process can also lead to higher bond strengths than what was examined in this study. In consideration of in-vitro study limitations and long-term storage and thermal cycling, more investigations are needed for more precise conclusions. Also, future work is needed to verify the results in oral simulated media e.g. artificial saliva.
[4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23]
Acknowledgments [24]
Authors greatly appreciate the comments and help of Drs. Ghasemi and Eslami from School of Dentistry, Shahid Beheshti University of Medical Sciences.
[25] [26] [27] [28]
References [29] [1] J. Chevalier, L. Gremillard, J. Eur. Ceram. Soc. 29 (7) (2009) 1245–1255. [2] P.F. Manicone, P.R. Iommetti, L. Raffaelli, J. Dent. 35 (2007) 819–826. [3] J.Y. Thompson, B.R. Stoner, J.R. Piascik, Mater. Sci. Eng. C 27 (2007) 565–569.
[30] [31]
317
I. Denry, J.R. Kelly, Dent. Mater. 24 (2008) 299–307. R. Janda, J.F. Roulet, M. Wulf, H.J. Tiller, Dent. Mater. 19 (2003) 567–573. M. Ozcana, P.K. Vallittu, Dent. Mater. 19 (2003) 725–731. M.B. Blatz, A. Sadan, J. Martin, B. Lang, J. Prosthet. Dent. 91 (2004) 356–362. J.R. Kelly, I. Denry, Dent. Mater. 24 (2008) 289–298. M. Kern, S.M. Wegner, Dent. Mater. 14 (1998) 64–71. W.O. Soboyejo, D. Brooks, J. Am. Ceram. Soc. 78 (6) (1995) 1481–1488. R. Van Noort, Introduction to Dental Materials, Second ed. Mosby Co, Hong Kong, 2002. M. Wolfart, F. Lehmann, S. Wolfart, M. Kern, Dent. Mater. 23 (2007) 45–50. M.N. Aboushelib, J.P. Matinlinna, Z. Salameh, H. Ounsi, Dent. Mater. 24 (2008) 1268–1272. Y. Zhang, B.R. Lawn, E.D. Rekow, V.P. Thompson, J. Biomed. Mater. Res. B 71B (2004) 381–386. M.N. Aboushelib, C.J. Kleverlaan, A.J. Feilzer, J. Prosthet. Dent. 98 (2007) 379–388. A.C. Quaas, B. Yang, M. Kernb, Dent. Mater. 23 (2007) 506–512. N. Rahbar, Y. Yang, W.O. Soboyejo, Mater. Sci. Eng. A 488 (2008) 381–388. X. Nui, N. Rahbar, S. Farias, W.O. Soboyejo, J. Mech. Behav. Biomed. 2 (2009) 596–602. M. Huang, N. Rahbar, R. Wang, V.P. Thompson, E.D. Rekow, Mater. Sci. Eng. A 464 (2007) 315–320. N. Rahbar, W.O. Soboyejo, Fatigue Fract. Eng. Mater. 34 (2011) 887–897. J. Du, X. Niu, N. Rahbar, W. Soboyejo, Acta Biomater. 9 (2013) 5273–5279. T. Derand, M. Molin, K. Kvam, Dent. Mater. 21 (2005) 1158–1162. V.E. Annamalai, B.L. Anantharamu, C.V. Gokularathnam, R. Krishnamurthy, J. Mater. Sci. Lett. 10 (1991) 459–460. R.E. Chinn, Ceramography: Preparation and Analysis of Ceramic Microstructures, first ed. Wiley-American Ceramic Society, 2002. T. Sekercioglu, H. Rende, A. Gülsöz, C. Merana, J. Mater. Process. Technol. 142 (2003) 82–86. M.B. Blatz, Quintessence Int. 33 (2002) 415–426. F.J. Burke, G.J. Fleming, J. Adhes. Dent. 4 (2002) 7–22. N. Rahbar, K. Wolf, A. Orana, R. Fennimore, Z. Zong, J. Meng, G. Papandreou, C. Maryanoff, W.O. Soboyejo, J. Appl. Phys. 104 (2008) 103533. J. Meng, A. Orana, T. Tan, K. Wolf, N. Rahbar, H. Li, G. Papandreou, C. Maryanoff, W.O. Soboyejo, J. Mater. Res. 25 (2010) 641–647. R. Melo, N. Rahbar, W.O. Soboyejo, Mater. Sci. Eng. C 31 (4) (2011) 770–774. K. Uehara, M. Sakurai, J. Mater. Process. Technol. 127 (2002) 178–181.
