Bonding Effectiveness to Differently Sandblasted Dental Zirconia Vincent Bielena / Masanao Inokoshib / Jan De Munckc / Fei Zhangd / Kim Vanmeensele / Shunsuke Minakuchif / Jozef Vleugelsg / Ignace Naerth / Bart Van Meerbeeki
Purpose: To evaluate the effect of different mechanical pre-treatments on the bond durability to dental zirconia. Materials and Methods: Fully sintered IPS e.max ZirCAD (Ivoclar Vivadent) blocks were randomly assigned to one of 4 groups: (1) kept as-sintered (control), (2) sandblasted with 50-μm Al2O3 (Danville), or tribochemically silica sandblasted using (3) CoJet (3M ESPE) and (4) SilJet (Danville). The zirconia specimens were additionally pre-treated chemically using a 10-MDP/silane ceramic primer (Clearfil Ceramic Primer, Kuraray Noritake). Two identically pre-treated zirconia blocks were bonded together using resin-composite cement (RelyX Ultimate, 3M ESPE). The specimens were trimmed at the interface to a cylindrical hourglass shape and stored in distilled water (7 days, 37°C), after which they were randomly tested as is or subjected to additional mechanical aging involving cyclic tensile stress (10 N, 10 Hz, 10,000 cycles). Subsequently, the microtensile bond strength was determined and SEM fractographic analysis performed. Results: Weibull analysis revealed the highest Weibull scale and shape parameters when zirconia was tribochemically silica sandblasted using either CoJet or SilJet. The Weibull shape parameter of Al2O3-sandblasted zirconia was significantly reduced upon mechanical aging, but not when zirconia was tribochemically silica sandblasted. Conclusion: The mechanical surface pre-treatment of zirconia using tribochemical silica sandblasting (CoJet, SilJet) resulted in the most favorable bond durability of a resin-composite cement (RelyX Ultimate) to dental zirconia before and after aging. Keywords: zirconia, bond strength, tribochemical silica sandblasting, silane, composite cement, aging. J Adhes Dent 2015; 17: 235–242. doi: 10.3290/j.jad.a34401
Submitted for publication: 03.03.15; accepted for publication: 21.05.15
S
ince their introduction 10 to 15 years ago, all-ceramic restorations have been widely applied in dentistry. Today, thanks to their favorable mechanical properties and biocompatibility, yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) ceramics are used not only as an alternative to conventional porcelain-fused-to-metal
restorations, but also as an implant abutment or even implant.7,8,13 However, one of the major limitations is the difficulty of obtaining durable bonding to zirconia ceramics because of their high chemical inertness.2-4 Different mechanical and chemical surface pre-treatments have therefore been recommended to improve the
a
Master-after-master in Specialized Oral Health Care, BIOMAT, Department of Oral Health Sciences, KU Leuven (University of Leuven) and Dentistry, University Hospitals Leuven, Leuven, Belgium. Performed the experiments, wrote the manuscript.
f
Full Professor, Gerodontology and Oral Rehabilitation, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan. Contributed substantially to discussion, proofread the manuscript.
g
b
PhD Student, BIOMAT, Department of Oral Health Sciences, KU Leuven (University of Leuven) and Dentistry, University Hospitals Leuven, Leuven, Belgium; Assistant Professor, Gerodontology and Oral Rehabilitation, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan. Experimental design, wrote the manuscript, equal first-author contribution.
Professor, Department of Materials Engineering, KU Leuven (University of Leuven), Belgium. Contributed substantially to discussion, proofread the manuscript.
h
Full Professor, BIOMAT, Department of Oral Health Sciences, KU Leuven (University of Leuven) and Dentistry, University Hospitals Leuven, Leuven, Belgium. Contributed substantially to discussion, proofread the manuscript.
I
Full Professor, BIOMAT, Department of Oral Health Sciences, KU Leuven (University of Leuven) and Dentistry, University Hospitals Leuven, Leuven, Belgium. Idea, hypothesis, proofread the manuscript.
c
Postdoctoral Researcher, BIOMAT, Department of Oral Health Sciences, KU Leuven (University of Leuven) and Dentistry, University Hospitals Leuven, Leuven, Belgium. Scientific advisor and performed statistical analysis.
d
PhD Student, Department of Materials Engineering, KU Leuven (University of Leuven), Belgium. Contributed substantially to discussion, proofread the manuscript.
e
Assistant Professor, Department of Materials Engineering, KU Leuven (University of Leuven), Belgium. Contributed substantially to discussion, proofread the manuscript.
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Correspondence: Professor B. Van Meerbeek, BIOMAT, Department of Oral Health Sciences, KU Leuven (University of Leuven) and Dentistry, University Hospitals Leuven, Kapucijnenvoer 7, blok a bus 7001, B-3000 Leuven, Belgium. Tel: +32-16-33-587, Fax: +32-16-332-752. e-mail: [email protected]
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bonding effectiveness of composite cement to zirconia. Former pre-treatments such as surface grinding using diamond burs,9 chemical etching using hydrofluoric acid4,15 and laser irradiation21 were applied to roughen the surface of zirconia ceramics, but none of them resulted in durable bonding to zirconia.1,2,9 It appears essential to create both a (micro-)mechanically prepared and a chemically activated surface. For instance, tribochemical silica sandblasting with 30- and 110-μm silica-coated aluminium-oxide (Al2O3) particles roughens and also to chemically activates zirconia, thus making it more receptive for chemical bonding via silane coupling agents.6 A previous study11 showed that the combination of mechanical pre-treatment using tribochemical silica sandblasting (CoJet, 3M ESPE; Seefeld, Germany) and chemical pre-treatment using a ceramic primer (Clearfil Ceramic Primer, Kuraray Noritake; Tokyo, Japan) provided the highest bonding effectiveness to dental zirconia. Moreover, the resultant bond appeared insensitive to mechanical aging.12 At the moment, however, the difference between conventional Al2O3 sandblasting and tribochemical silica sandblasting (using silica-coated Al2O3 particles) in terms of their efficacy in making zirconia receptive to bonding is still unclear. Therefore, in continuation of our previous studies,11,12 this laboratory study aimed to assess the effect of three different mechanical pre-treatments on the short-term bonding efficacy to zirconia and on the bond strength after subjecting specimens to additional mechanical aging. The null hypotheses tested were (1) that the bonding efficacy of resin-composite cement to zirconia was not different for the three mechanical pre-treatments tested, and (2) that the strength of the tested resin-composite cement/ zirconia bond was not affected by mechanical aging.
MATERIALS AND METHODS The study design is presented schematically in Fig 1. The research protocol and methodology are described in detail elsewhere.12 In brief, fully sintered zirconia specimens (IPS e.max ZirCAD, Ivoclar Vivadent; Schaan, Liechtenstein) with dimensions of 1.6 x 1.6 x 6.0 mm were prepared. The sintered microspecimens were then ultrasonically cleaned in acetone for 10 min, followed by thorough drying with compressed air. The microspecimens were then randomly assigned to one of four groups: (1) kept as-sintered (control), (2) sandblasted with 50-μm Al2O3 (Danville; San Ramon, CA, USA), or tribochemically silica sandblasted using (3) CoJet (3M ESPE) or (4) SilJet (Danville) (Table 1). Only the Al2O3 sandblasted zirconia was ultrasonically cleaned after the mechanical pre-treatment. Next, the 10-MDP/silanebased primer Clearfil Ceramic Primer (Kuraray Noritake; Tokyo, Japan) was applied for 60 s, followed by thorough drying with compressed air. Finally, two identically pre-treated microspecimens were bonded together using a dual-curing composite cement (Table 1: RelyX Ultimate, 3M ESPE; Seefeld, Germany). Each bonded microspecimen assembly was light cured for 20 s from 236
each side using a high-intensity (1000 mW/cm2 output) light-curing unit (Bluephase G2, Ivoclar Vivadent). The total light-curing time was 80 s. Specimens were kept dry for 1 h at room temperature and were subsequently trimmed at the bonded interface to a cylindrical hourglass shape with a diameter of 1.2 to 1.4 mm using a custom-modified computer-controlled Microspecimen Former (The University of Iowa; Iowa City, IA, USA). After 1-week water storage at 37°C, the specimens were randomly subjected either (1) to immediate microtensile bond strength (μTBS) testing or (2) to additional mechanical aging by cyclic tensile stress of 10 N at 10 Hz for 10,000 cycles using a universal testing machine (Instron 5848 Micro Tester, Instron; High Wycombe, UK). Subsequently, the cross-sectional diameter of each specimen was accurately (to 0.5 μm) determined using a high-precision measuring instrument transformed from an x-y multi-purpose modular microscope (Leitz; Wetzlar, Germany). μTBS testing was conducted following the BIOMAT μTBS testing protocol for zirconia.12 When specimens failed before actual testing, which happened mainly during the preparation of the hourglass isthmus, the μTBS was determined from the specimens that survived specimen processing with an explicit note of the number of pre-test failures (PTF). The number of specimens that failed during mechanical aging (MAF) was explicitly noted as well. PTFs were assigned a random value between zero and 10 MPa.12 MAFs were assigned a random value between 10 MPa and the lowest value measured in the respective group.12 The μTBS results were statistically analyzed using Weibull analysis; pivotal confidence bounds were calculated using Monte Carlo simulation.20 For reasons of reliability and reproducibility, the random-value assignment procedure and subsequent Weibull analysis were repeated 1000 times using the software package R3.0 and Abrem (R Foundation for Statistical Computing; Vienna, Austria) following the same research protocol reported previously.12 All tests were performed at a significance level of _ = 0.05 using the software package mentioned above. To determine the mode of failure, all specimens were observed immediately after fracture at a magnification of 50X using a stereomicroscope (Wild M5A; Heerbrugg, Switzerland). Representative specimens were also imaged using SEM (JSM-6610LV, JEOL; Tokyo, Japan).
RESULTS All data of the Weibull analysis are graphically presented in Fig 2. Table 2 summarizes the Weibull analysis for all groups and lists the percentage of adhesive failures as well. Weibull analysis generally revealed the highest Weibull shape and scale parameters for both tribochemical silica sandblasting techniques (CoJet and SilJet) and the 50-μm Al2O3 sandblasted zirconia specimens that were solely stored for 7 days but did not receive further mechanical aging. The as-sintered (control) zirconia showed the lowest Weibull shape and scale parameters. The bonding efficacy was not affected by mechaniThe Journal of Adhesive Dentistry
Bielen et al
2.0 mm 2.0 mm
1.6 mm
Zr 7.5 mm cut
Mechanical pre-treatment
Chemical pre-treatment
Composite Cement
as sintered
Clearfil Ceramic Primer
RelyX Ultimate
1.6 mm Zr 6.0 mm sinter
IPS e.max ZirCAD Partially sintered
IPS e.max ZirCAD Fully sintered
50 μm Al2O3
trim
CoJet SilJet
H2O 7 days 10 specimens per group microtensile bond strength (μTBS) SEM failure analysis mechanical aging 10 Hz, 10 N, 10,000 x Fig 1 Flow chart detailing the study design.
Table 1
Materials employed
Material
Manufacturer
Type of material
Composition
Application procedure
IPS e.max ZirCAD
Ivoclar Vivadent; Schaan, Liechtenstein
Y-TZP
ZrO2, Y2O3, HfO2, Al2O3
Alumina (Al2O3)
Danville; San Ramon, CA, USA
Alumina sandblasting
50-μm Al2O3
1. Blast the surface from a distance of 2 to 10 mm for 2 s at 0.3 MPa pressure; 2. Ultrasonically clean in distilled water for 15 min.
CoJet
3M ESPE; Seefeld, Germany
Tribochemical silica sandblasting
30-μm silica-coated aluminum oxide
1. Blast the surface from a distance of 2 to 10 mm for 2 s at 0.3 MPa pressure; 2. Remove any residual blast-coating agent with a stream of dry, oil-free air.
SilJet
Danville
Tribochemical silica sandblasting
30-μm silica-coated aluminum oxide
1. Blast the surface from a distance of 2 to 10 mm for 2 s at 0.3 MPa pressure; 2. Remove any residual blast-coating agent with a stream of dry, oil-free air.
Clearfil Ceramic Primer
Kuraray Noritake; Tokyo, Japan
Ceramic primer
3-MPS, 10-MDP, ethanol
Apply primer for 60 s, then thoroughly air dry.
RelyX Ultimate
3M ESPE
Composite cement
Base paste: methacrylate monomers, radiopaque silanated fillers, initiator, stabilizer, rheological additives Catalyst paste: methacrylate monomers, radiopaque alkaline (basic) fillers, initiator, stabilizer, pigments, rheological additives, fluorescence dye, dark cure activator for Scotchbond Universal
1. Squeeze Base and Catalyst paste from the dispenser syringe; 2. Apply the mixed RelyX Ultimate to the specimens; 3. Light cure for 20 s from each side.
Abbreviations: 3-MPS: 3-methacryloxypropyltrimethoxysilane; 10-MDP: 10-methacryloyloxydecyl dihydrogen phosphate.
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50
0
B1
2
5
10 20
Probability of failure (%)
50 10 20
0
B1
2
3.
B6
5
2
3.
B6
1
1
2
Probability of failure (%)
90 98
90 98
Bielen et al
0.1
0.5 1
5
10
50 100
0.1 0.5 1 5 10 50 100 Microtensile bond strength after 7-day water storage and additional mechanical ageing (MPa)
Microtensile bond strength after 7-day water storage (MPa) ‘as sintered’ (control) Al2O3 sandblasted SilJet tribochemical silica sandblasted CoJet tribochemical silica sandblasted
as as as as
recorded recorded recorded recorded
replaced (pft) replaced (pft)
replaced (maf) replaced (maf)
Fig 2 Left: Graph showing the Weibull analysis for the different mechanical surface pre-treatments tested when the specimens were stored for 7 days in water but no additional mechanical aging was applied. Higher scale (B63.2) parameters were recorded for 50-μm Al2O3 sandblasted as well as CoJet and SilJet tribochemically silica sandblasted zirconia than for as-sintered (control) zirconia. For the as-sintered specimens, the as-recorded values and the randomly replaced values due to pre-test failures (PTF) were indicated differently. Right: Graph showing the Weibull analysis for the different mechanical surface pre-treatments tested when the specimens were stored for 7 days in water and additionally mechanically aged. Again, higher scale (B63.2) parameters were recorded for 50-μm Al2O3 sandblasted, CoJet and SilJet tribochemically silica sandblasted zirconia than for as-sintered zirconia. The shape modulus of the 50-μm Al2O3 sandblasted zirconia dropped remarkably after the additional mechanical aging. For the assintered specimens, the as-recorded values, the randomly replaced values due to PTF and the randomly replaced values due to MAF were indicated differently. In both graphs, dotted lines represent the 95% confidence interval of the Weibull plot.
Table 2
Results of Weibull analysis and the recorded failure mode
Zirconia pre-treatment
Aging1
n
PTF2
MAF3 Shape (modulus)4
Scale 95% confidence 95% confidence Percentage (B63.2)5 level at B63.26 level at B107 adhesive failure8
As sintered (control)
7d storage
10
3
/
1.43*
14.40*
8.39–26.43b*
0.70–6.71C*
92.0
+ mechanical
10
4
1
1.00*
21.70*
10.28–49.80ab*
0.31–7.53BC*
98.0
7d storage
10
0
/
2.86
42.91
33.46–56.09a
8.67–29.81A
63.0
+ mechanical
10
1
3
1.39*
43.07*
25.10–77.74ab*
1.77–19.97ABC*
90.0
CoJet tribochemically silica sandblasted
7d storage
10
0
/
2.60
56.22
42.52–75.46a
9.71–37.69A
49.0
+ mechanical
10
0
0
2.56
41.79
31.42–56.41a
6.97–27.80AB
48.0
SilJet tribochemically silica sandblasted
7d storage
10
0
/
2.40
49.00
36.18–67.42a
7.30–31.76AB
47.0
+ mechanical
10
0
0
3.11
50.67
40.08–64.84a
11.63–36.23A
32.0
50-μm Al2O3 sandblasted
1Aging protocol with 7d (7-day) storage in 37°C water, and 7-day storage in 37°C in water followed by additional mechanical aging (+ mechanical) using cyclic tensile stress of 10 N at 10 Hz for 10,000 cycles; 2pre-test failure; 3mechanical aging failure; 4the higher the Weibull shape, the more reliable the treatment; 5the higher the Weibull scale, the higher the bonding effectiveness; 6same superscript lower-case letters indicate absence of statistical significance at B63.2; 7same superscript capital letters indicate absence of statistical significance at B10; 8The rest percentage represents the area percentage of cohesive failure in the composite cement; *Calculated mean from random-value trials performed 1000 times.
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Fig 3 SEM photomicrographs illustrating a representatively fractured surface of RelyX Ultimate that was bonded to as-sintered zirconia (IPS e.max ZirCAD. (a) A specimen that was subjected to 7-day water storage showed adhesive failure along the cement/zirconia interface (I); as the sandwich zirconia/cement/zirconia specimens included two cement/zirconia interfaces, failure occurred in this specimen at both interfaces. (b) Higher magnification of the adhesively failed part indicated by the white arrow in (a). Zirconia grains can be observed. (c) Overview photomicrograph of a specimen that was subjected to additional mechanical aging. No difference in fracture mode was observed compared to a specimen that did not undergo mechanical aging. (d) Higher magnification of the adhesively failed part.
cal aging when the zirconia surface was tribochemically silica sandblasted (CoJet or SilJet). However, for 50-μm Al2O3 sandblasted zirconia, several MAFs were recorded. While their μTBS was hardly affected by aging, the Weibull shape parameter of Al2O3 sandblasted zirconia decreased significantly upon mechanical aging. Overall, the B63.2 and B10 Weibull parameters of the as-sintered (control) zirconia (7-day storage) were significantly lower than those of the surface-treated (either Al2O3 sandblasted or tribochemically silica sandblasted) zirconia according to the 95% confidence intervals (except for the Al2O3 sandblasted specimens subjected to additional mechanical aging: +mechanical; Table 2). The bond strength data were in line with the fracture analysis data, represented in Table 2 as the percentage of specimens that failed adhesively. In general, higher bonding efficacy was associated with a lower percentage of adhesive failures at the interface (and vice versa for lower bonding efficacy). Most of the as-sintered zirconia failed adhesively at the interface; in such cases, the zirconia surface was exposed with the zirconia grains observable microscopically (Fig 3). The 50-μm Al2O3 sandblasted zirconia specimens appeared to have failed less adhesively but more cohesively in the resin-composite cement; nevertheless, most of the 50-μm Al2O3 sandblasted zirconia specimens that received additional mechanical aging failed adhesively (Fig 4). Specimens subjected to tribochemical silica sandblasting using CoJet and SilJet selVol 17, No 3, 2015
dom failed entirely adhesively at the interface (Table 2); microscopically, the cohesively failed surface exhibited the filler of the composite cement (Figs 5 and 6).
DISCUSSION Mechanical pre-treatment of the zirconia surface using the three sandblasting techniques employed significantly improved the bonding effectiveness to zirconia; thus, the first null hypothesis was rejected. The second null hypothesis was accepted for the two tribochemically silica sandblasted (CoJet and SilJet) zirconia groups (as well as for the as-sintered group), but was rejected for the Al2O3 sandblasted zirconia group, as mechanical aging did affect its bonding receptiveness. According to a recent systematic literature review, the most commonly applied test method for assessing bonding efficacy to zirconia is a shear bond strength test.10 Most likely, this can be attributed to the fact that there is no need for further specimen preparation prior to the test. The systematic review, however, also demonstrated that a shear bond strength test is less discriminative than a tensile test.10 Therefore, a μTBS test to assess the bonding efficacy to mechanically pre-treated zirconia was used in this study. In order to apply Weibull statistics, a random value between 0 and 10 and between 10 and the lowest value 239
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CoJet tribochemically silica sandblasted
Fig 4 SEM photomicrographs illustrating a representative fractured surface of RelyX Ultimate that was bonded to 50-μm Al2O3 sandblasted zirconia (IPS e.max ZirCAD. (a) Overview photomicrograph of a specimen subjected to 7-day water storage. A relatively small part of the specimen failed at the interface (I), while the main part failed cohesively in the composite cement (C). (b) Higher magnification of the cohesively failed part showing the structure of the composite cement. (c) Overview photomicrograph of a specimen that was subjected to additional mechanical aging, showing that the specimen failed mainly adhesively along the interface (I). (d) Higher magnification of the adhesively failed part, disclosing the Al2O3 sandblasted zirconia surface.
Fig 5 SEM photomicrographs illustrating a representative fractured surface of RelyX Ultimate that was bonded to CoJet tribochemically silica sandblasted zirconia (IPS e.max ZirCAD. (a) Overview photomicrograph of a specimen subjected to 7-day water storage. The major part failed cohesively in the composite cement (C). (b) Higher magnification of the cohesively failed part, disclosing the filler of the composite cement. (c) Overview photomicrograph of a specimen subjected to additional mechanical aging. Nearly half of the specimen failed adhesively at the interface (I), while the other half failed cohesively in the composite cement (C). (d) Higher magnification of the cohesively failed part.
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Fig 6 SEM photomicrographs illustrating a representative fractured surface of RelyX Ultimate that was bonded to SilJet tribochemically silica sandblasted zirconia (IPS e.max ZirCAD). (a) Overview photomicrograph of a specimen that was subjected to 7-day water storage. The specimen failed both cohesively in the composite cement (C) and adhesively at the interface (I). (b) Higher magnification of the cohesively failed part, disclosing the filler of the composite cement. (c) Overview photomicrograph of a specimen that was subjected to additional mechanical aging. Only about 50% of the specimen failed adhesively at the interface (I), while the other part failed cohesively in the composite cement (C). (d) Higher magnification of the cohesively failed part.
measured in the respective experimental group was assigned to each PTF and each MAF, respectively, according to an approach applied successfully in a previous study.12 This random value assignment for PTFs and MAFs was repeated 1000 times, including a Weibull analysis each time, so that any potential bias was largely avoided. Regarding chemical pre-treatment of zirconia, several studies reported the bond-promoting effect of a primer containing 10-MDP.5,23 In a previous study,12 we measured the bonding efficacy of four different 10-MDP basedprimers/adhesives to dental zirconia. That study revealed that the most consistent data were obtained using the combined 10-MDP/silane based-primer Clearfil Ceramic Primer (Kuraray Noritake); thus, in this study, we decided to chemically pre-treat (after the mechanical pre-treatment) zirconia using Clearfil Ceramic Primer (Kuraray Noritake). Fracture analysis revealed that in the experimental groups – ie, the resin-composite cement was bonded to tribochemically silica sandblasted zirconia using either CoJet or SilJet – the specimens failed adhesively at the interface in certain areas and cohesively within the resincomposite cement at others. This observation is in line with the results of the Weibull analysis, as the specimens that showed the most common failure mode (mixed adhesive/cohesive) and also had significantly higher bond strength values. Moreover, the failure mode of those tribochemically silica sandblasted zirconia specimens was not affected by additional mechanical aging, which is a Vol 17, No 3, 2015
clear indication of their bond stability. In contrast, the as-sintered (control) zirconia specimens – which did not receive any mechanical pre-treatment, but solely chemical pre-treatment – mostly failed adhesively at the cement/ zirconia interface. This observation is also in line with the results of the Weibull analysis. Furthermore, the most frequent failure mode of the 50-μm Al2O3 sandblasted zirconia specimens was somewhere between that of the tribochemically silica sandblasted zirconia specimens and that of the as-sintered group. Without mechanical aging, they failed in a mixed mode or cohesively within the resincomposite cement; with additional mechanical aging, they generally failed adhesively at the cement/zirconia interface. This shift in failure mode for the 50-μm Al2O3 sandblasted zirconia upon mechanical aging may thus indicate that the resultant bond was less stable than that to the tribochemically silica sandblasted zirconia surfaces; the latter specimens did not demonstrate such a shift in failure mode. In terms of aging, the systematic review showed that thermocycling or long-term water storage induced only a small effect on the bonding effectiveness to zirconia.10 Even 10,000 thermocycles only resulted in a small effect.16 As in a previous study,12 this study employed additional mechanical aging to challenge the bond durability to zirconia. Under clinical circumstances, the adhesive interface is more heavily subjected to cyclic mechanical loading than to acute catastrophic stress.19 The effect of mechanical aging differed for the different mechanical 241
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pre-treatments tested. For tribochemical silica sandblasting, irrespective of the system applied (CoJet or SilJet), Weibull analysis revealed that mechanical aging did not affect their bonding efficacy. Tribochemical silica sandblasting clearly led to higher shape and scale parameters, and thus a higher and more consistent bonding efficacy than was the case with 50-μm Al2O3 sandblasted zirconia or when zirconia was not mechanically pre-treated (Table 2). It is peculiar that for Al2O3 sandblasted zirconia, mechanical aging did not affect the B63.2 value, but significantly dropped the Weibull modulus. Al2O3 sandblasting is one of the most commonly applied pre-treatment methods for zirconia.14,22 As deduced from the failure analysis, the bond to Al2O3 sandblasted zirconia should be considered as less stable (after mechanical loading) than that to tribochemically silica sandblasted zirconia. The Weibull modulus also dropped for the resin-composite cement bonded to the as-sintered (control) and thus mechanically untreated zirconia. Overall, when zirconia is mechanically pre-treated, tribochemical silica sandblasting should be considered as the method of choice due to its favorable effect on bond durability. However, it is noteworthy that some authors have reported negative effects of sandblasting zirconia;17,18 the reason mentioned was the risk of microcracks and the resultant decrease in longevity of the Y-TZP framework. Those authors recommended applying sandblasting at a low pressure (1 to 2 bars) and using a particle size below 50 μm in order to minimize surface damage of zirconia.
CONCLUSIONS
3.
4. 5.
6. 7. 8. 9. 10.
11.
12.
13. 14. 15. 16.
17.
18.
The mechanical surface pre-treatment of zirconia with tribochemical silica sandblasting (CoJet and SilJet) resulted in the highest bond durability of a resin-composite cement (RelyX Ultimate) to dental zirconia before and after aging.
19.
ACKNOWLEDGMENT
22.
M.I. acknowledges the Flemish scholarship for Japanese students. This work was performed within the framework of the Research Fund of KU Leuven under project OT/10/052 and of the Research Foundation Flanders (FWO-Flanders) under project G.0431.10.
REFERENCES 1.
2.
Atsu SS, Kilicarslan MA, Kucukesmen HC, Aka PS. Effect of zirconiumoxide ceramic surface treatments on the bond strength to adhesive resin. J Prosthet Dent 2006;95:430-436. Blatz MB, Chiche G, Holst S, Sadan A. Influence of surface treatment and simulated aging on bond strengths of luting agents to zirconia. Quintessence Int 2007;38:745-753.
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20.
21.
23.
Blatz MB, Sadan A, Arch GH, Jr., Lang BR. In vitro evaluation of longterm bonding of Procera AllCeram alumina restorations with a modified resin luting agent. J Prosthet Dent 2003;89:381-387. Blatz MB, Sadan A, Kern M. Resin-ceramic bonding: a review of the literature. J Prosthet Dent 2003;89:268-274. Chen L, Suh BI, Brown D, Chen X. Bonding of primed zirconia ceramics: evidence of chemical bonding and improved bond strengths. Am J Dent 2012;25:103-108. Chen L, Suh BI, Kim J, Tay FR. Evaluation of silica-coating techniques for zirconia bonding. Am J Dent 2011;24:79-84. Della Bona A, Kelly JR. The clinical success of all-ceramic restorations. J Am Dent Assoc 2008;139 Suppl:8S-13S. Denry I, Kelly JR. State of the art of zirconia for dental applications. Dent Mater 2008;24:299-307. Derand P, Derand T. Bond strength of luting cements to zirconium oxide ceramics. Int J Prosthodont 2000;13:131-135. Inokoshi M, De Munck J, Minakuchi S, Van Meerbeek B. Meta-analysis of bonding effectiveness to zirconia ceramics. J Dent Res 2014;93: 329-334. Inokoshi M, Kameyama A, De Munck J, Minakuchi S, Van Meerbeek B. Durable bonding to mechanically and/or chemically pre-treated dental zirconia. J Dent 2013;41:170-179. Inokoshi M, Poitevin A, De Munck J, Minakuchi S, Van Meerbeek B. Bonding effectiveness to different chemically pre-treated dental zirconia. Clin Oral Investig 2014;18:1803-1812. Kelly JR, Denry I. Stabilized zirconia as a structural ceramic: an overview. Dent Mater 2008;24:289-298. Kern M, Barloi A, Yang B. Surface conditioning influences zirconia ceramic bonding. J Dent Res 2009;88:817-822. Kern M, Wegner SM. Bonding to zirconia ceramic: adhesion methods and their durability. Dent Mater 1998;14:64-71. Komine F, Kobayashi K, Blatz MB, Fushiki R, Koizuka M, Taguchi K, Matsumura H. Durability of bond between an indirect composite veneering material and zirconium dioxide ceramics. Acta Odontol Scand 2013;71:457-463. Kosmac T, Oblak C, Jevnikar P, Funduk N, Marion L. The effect of surface grinding and sandblasting on flexural strength and reliability of Y-TZP zirconia ceramic. Dent Mater 1999;15:426-433. Kosmac T, Oblak C, Jevnikar P, Funduk N, Marion L. Strength and reliability of surface treated Y-TZP dental ceramics. J Biomed Mater Res 2000;53:304-313. Poitevin A, De Munck J, Cardoso MV, Mine A, Peumans M, Lambrechts P, Van Meerbeek B. Dynamic versus static bond-strength testing of adhesive interfaces. Dent Mater 2010;26:1068-1076. Symynck J, De Bal F. Monte Carlo pivotal confidence bounds for Weibull analysis, with implementations in R. New Technologies and Products in Machine Manufacturing Technologies 2011:43-50. Ural C, Kulunk T, Kulunk S, Kurt M. The effect of laser treatment on bonding between zirconia ceramic surface and resin cement. Acta Odontol Scand 2010;68:354-359. Yang B, Wolfart S, Scharnberg M, Ludwig K, Adelung R, Kern M. Influence of contamination on zirconia ceramic bonding. J Dent Res 2007;86:749-753. Yoshida K, Tsuo Y, Atsuta M. Bonding of dual-cured resin cement to zirconia ceramic using phosphate acid ester monomer and zirconate coupler. J Biomed Mater Res Part B Appl Biomater 2006;77:28-33.
Clinical relevance: To obtain durable bonding to dental zirconia, the application of combined mechanical and chemical pre-treatment, involving tribochemical silica sandblasting followed by a combined 10-MDP/silane ceramic primer, is clinically highly recommended.
The Journal of Adhesive Dentistry
Purpose: To evaluate the effect of different mechanical pre-treatments on the bond durability to dental zirconia. Materials and Methods: Fully sintered IPS e.max ZirCAD (Ivoclar Vivadent) blocks were randomly assigned to one of 4 groups: (1) kept as-sintered (control), (2) sandblasted with 50-μm Al2O3 (Danville), or tribochemically silica sandblasted using (3) CoJet (3M ESPE) and (4) SilJet (Danville). The zirconia specimens were additionally pre-treated chemically using a 10-MDP/silane ceramic primer (Clearfil Ceramic Primer, Kuraray Noritake). Two identically pre-treated zirconia blocks were bonded together using resin-composite cement (RelyX Ultimate, 3M ESPE). The specimens were trimmed at the interface to a cylindrical hourglass shape and stored in distilled water (7 days, 37°C), after which they were randomly tested as is or subjected to additional mechanical aging involving cyclic tensile stress (10 N, 10 Hz, 10,000 cycles). Subsequently, the microtensile bond strength was determined and SEM fractographic analysis performed. Results: Weibull analysis revealed the highest Weibull scale and shape parameters when zirconia was tribochemically silica sandblasted using either CoJet or SilJet. The Weibull shape parameter of Al2O3-sandblasted zirconia was significantly reduced upon mechanical aging, but not when zirconia was tribochemically silica sandblasted. Conclusion: The mechanical surface pre-treatment of zirconia using tribochemical silica sandblasting (CoJet, SilJet) resulted in the most favorable bond durability of a resin-composite cement (RelyX Ultimate) to dental zirconia before and after aging. Keywords: zirconia, bond strength, tribochemical silica sandblasting, silane, composite cement, aging. J Adhes Dent 2015; 17: 235–242. doi: 10.3290/j.jad.a34401
Submitted for publication: 03.03.15; accepted for publication: 21.05.15
S
ince their introduction 10 to 15 years ago, all-ceramic restorations have been widely applied in dentistry. Today, thanks to their favorable mechanical properties and biocompatibility, yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) ceramics are used not only as an alternative to conventional porcelain-fused-to-metal
restorations, but also as an implant abutment or even implant.7,8,13 However, one of the major limitations is the difficulty of obtaining durable bonding to zirconia ceramics because of their high chemical inertness.2-4 Different mechanical and chemical surface pre-treatments have therefore been recommended to improve the
a
Master-after-master in Specialized Oral Health Care, BIOMAT, Department of Oral Health Sciences, KU Leuven (University of Leuven) and Dentistry, University Hospitals Leuven, Leuven, Belgium. Performed the experiments, wrote the manuscript.
f
Full Professor, Gerodontology and Oral Rehabilitation, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan. Contributed substantially to discussion, proofread the manuscript.
g
b
PhD Student, BIOMAT, Department of Oral Health Sciences, KU Leuven (University of Leuven) and Dentistry, University Hospitals Leuven, Leuven, Belgium; Assistant Professor, Gerodontology and Oral Rehabilitation, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan. Experimental design, wrote the manuscript, equal first-author contribution.
Professor, Department of Materials Engineering, KU Leuven (University of Leuven), Belgium. Contributed substantially to discussion, proofread the manuscript.
h
Full Professor, BIOMAT, Department of Oral Health Sciences, KU Leuven (University of Leuven) and Dentistry, University Hospitals Leuven, Leuven, Belgium. Contributed substantially to discussion, proofread the manuscript.
I
Full Professor, BIOMAT, Department of Oral Health Sciences, KU Leuven (University of Leuven) and Dentistry, University Hospitals Leuven, Leuven, Belgium. Idea, hypothesis, proofread the manuscript.
c
Postdoctoral Researcher, BIOMAT, Department of Oral Health Sciences, KU Leuven (University of Leuven) and Dentistry, University Hospitals Leuven, Leuven, Belgium. Scientific advisor and performed statistical analysis.
d
PhD Student, Department of Materials Engineering, KU Leuven (University of Leuven), Belgium. Contributed substantially to discussion, proofread the manuscript.
e
Assistant Professor, Department of Materials Engineering, KU Leuven (University of Leuven), Belgium. Contributed substantially to discussion, proofread the manuscript.
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Correspondence: Professor B. Van Meerbeek, BIOMAT, Department of Oral Health Sciences, KU Leuven (University of Leuven) and Dentistry, University Hospitals Leuven, Kapucijnenvoer 7, blok a bus 7001, B-3000 Leuven, Belgium. Tel: +32-16-33-587, Fax: +32-16-332-752. e-mail: [email protected]
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bonding effectiveness of composite cement to zirconia. Former pre-treatments such as surface grinding using diamond burs,9 chemical etching using hydrofluoric acid4,15 and laser irradiation21 were applied to roughen the surface of zirconia ceramics, but none of them resulted in durable bonding to zirconia.1,2,9 It appears essential to create both a (micro-)mechanically prepared and a chemically activated surface. For instance, tribochemical silica sandblasting with 30- and 110-μm silica-coated aluminium-oxide (Al2O3) particles roughens and also to chemically activates zirconia, thus making it more receptive for chemical bonding via silane coupling agents.6 A previous study11 showed that the combination of mechanical pre-treatment using tribochemical silica sandblasting (CoJet, 3M ESPE; Seefeld, Germany) and chemical pre-treatment using a ceramic primer (Clearfil Ceramic Primer, Kuraray Noritake; Tokyo, Japan) provided the highest bonding effectiveness to dental zirconia. Moreover, the resultant bond appeared insensitive to mechanical aging.12 At the moment, however, the difference between conventional Al2O3 sandblasting and tribochemical silica sandblasting (using silica-coated Al2O3 particles) in terms of their efficacy in making zirconia receptive to bonding is still unclear. Therefore, in continuation of our previous studies,11,12 this laboratory study aimed to assess the effect of three different mechanical pre-treatments on the short-term bonding efficacy to zirconia and on the bond strength after subjecting specimens to additional mechanical aging. The null hypotheses tested were (1) that the bonding efficacy of resin-composite cement to zirconia was not different for the three mechanical pre-treatments tested, and (2) that the strength of the tested resin-composite cement/ zirconia bond was not affected by mechanical aging.
MATERIALS AND METHODS The study design is presented schematically in Fig 1. The research protocol and methodology are described in detail elsewhere.12 In brief, fully sintered zirconia specimens (IPS e.max ZirCAD, Ivoclar Vivadent; Schaan, Liechtenstein) with dimensions of 1.6 x 1.6 x 6.0 mm were prepared. The sintered microspecimens were then ultrasonically cleaned in acetone for 10 min, followed by thorough drying with compressed air. The microspecimens were then randomly assigned to one of four groups: (1) kept as-sintered (control), (2) sandblasted with 50-μm Al2O3 (Danville; San Ramon, CA, USA), or tribochemically silica sandblasted using (3) CoJet (3M ESPE) or (4) SilJet (Danville) (Table 1). Only the Al2O3 sandblasted zirconia was ultrasonically cleaned after the mechanical pre-treatment. Next, the 10-MDP/silanebased primer Clearfil Ceramic Primer (Kuraray Noritake; Tokyo, Japan) was applied for 60 s, followed by thorough drying with compressed air. Finally, two identically pre-treated microspecimens were bonded together using a dual-curing composite cement (Table 1: RelyX Ultimate, 3M ESPE; Seefeld, Germany). Each bonded microspecimen assembly was light cured for 20 s from 236
each side using a high-intensity (1000 mW/cm2 output) light-curing unit (Bluephase G2, Ivoclar Vivadent). The total light-curing time was 80 s. Specimens were kept dry for 1 h at room temperature and were subsequently trimmed at the bonded interface to a cylindrical hourglass shape with a diameter of 1.2 to 1.4 mm using a custom-modified computer-controlled Microspecimen Former (The University of Iowa; Iowa City, IA, USA). After 1-week water storage at 37°C, the specimens were randomly subjected either (1) to immediate microtensile bond strength (μTBS) testing or (2) to additional mechanical aging by cyclic tensile stress of 10 N at 10 Hz for 10,000 cycles using a universal testing machine (Instron 5848 Micro Tester, Instron; High Wycombe, UK). Subsequently, the cross-sectional diameter of each specimen was accurately (to 0.5 μm) determined using a high-precision measuring instrument transformed from an x-y multi-purpose modular microscope (Leitz; Wetzlar, Germany). μTBS testing was conducted following the BIOMAT μTBS testing protocol for zirconia.12 When specimens failed before actual testing, which happened mainly during the preparation of the hourglass isthmus, the μTBS was determined from the specimens that survived specimen processing with an explicit note of the number of pre-test failures (PTF). The number of specimens that failed during mechanical aging (MAF) was explicitly noted as well. PTFs were assigned a random value between zero and 10 MPa.12 MAFs were assigned a random value between 10 MPa and the lowest value measured in the respective group.12 The μTBS results were statistically analyzed using Weibull analysis; pivotal confidence bounds were calculated using Monte Carlo simulation.20 For reasons of reliability and reproducibility, the random-value assignment procedure and subsequent Weibull analysis were repeated 1000 times using the software package R3.0 and Abrem (R Foundation for Statistical Computing; Vienna, Austria) following the same research protocol reported previously.12 All tests were performed at a significance level of _ = 0.05 using the software package mentioned above. To determine the mode of failure, all specimens were observed immediately after fracture at a magnification of 50X using a stereomicroscope (Wild M5A; Heerbrugg, Switzerland). Representative specimens were also imaged using SEM (JSM-6610LV, JEOL; Tokyo, Japan).
RESULTS All data of the Weibull analysis are graphically presented in Fig 2. Table 2 summarizes the Weibull analysis for all groups and lists the percentage of adhesive failures as well. Weibull analysis generally revealed the highest Weibull shape and scale parameters for both tribochemical silica sandblasting techniques (CoJet and SilJet) and the 50-μm Al2O3 sandblasted zirconia specimens that were solely stored for 7 days but did not receive further mechanical aging. The as-sintered (control) zirconia showed the lowest Weibull shape and scale parameters. The bonding efficacy was not affected by mechaniThe Journal of Adhesive Dentistry
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2.0 mm 2.0 mm
1.6 mm
Zr 7.5 mm cut
Mechanical pre-treatment
Chemical pre-treatment
Composite Cement
as sintered
Clearfil Ceramic Primer
RelyX Ultimate
1.6 mm Zr 6.0 mm sinter
IPS e.max ZirCAD Partially sintered
IPS e.max ZirCAD Fully sintered
50 μm Al2O3
trim
CoJet SilJet
H2O 7 days 10 specimens per group microtensile bond strength (μTBS) SEM failure analysis mechanical aging 10 Hz, 10 N, 10,000 x Fig 1 Flow chart detailing the study design.
Table 1
Materials employed
Material
Manufacturer
Type of material
Composition
Application procedure
IPS e.max ZirCAD
Ivoclar Vivadent; Schaan, Liechtenstein
Y-TZP
ZrO2, Y2O3, HfO2, Al2O3
Alumina (Al2O3)
Danville; San Ramon, CA, USA
Alumina sandblasting
50-μm Al2O3
1. Blast the surface from a distance of 2 to 10 mm for 2 s at 0.3 MPa pressure; 2. Ultrasonically clean in distilled water for 15 min.
CoJet
3M ESPE; Seefeld, Germany
Tribochemical silica sandblasting
30-μm silica-coated aluminum oxide
1. Blast the surface from a distance of 2 to 10 mm for 2 s at 0.3 MPa pressure; 2. Remove any residual blast-coating agent with a stream of dry, oil-free air.
SilJet
Danville
Tribochemical silica sandblasting
30-μm silica-coated aluminum oxide
1. Blast the surface from a distance of 2 to 10 mm for 2 s at 0.3 MPa pressure; 2. Remove any residual blast-coating agent with a stream of dry, oil-free air.
Clearfil Ceramic Primer
Kuraray Noritake; Tokyo, Japan
Ceramic primer
3-MPS, 10-MDP, ethanol
Apply primer for 60 s, then thoroughly air dry.
RelyX Ultimate
3M ESPE
Composite cement
Base paste: methacrylate monomers, radiopaque silanated fillers, initiator, stabilizer, rheological additives Catalyst paste: methacrylate monomers, radiopaque alkaline (basic) fillers, initiator, stabilizer, pigments, rheological additives, fluorescence dye, dark cure activator for Scotchbond Universal
1. Squeeze Base and Catalyst paste from the dispenser syringe; 2. Apply the mixed RelyX Ultimate to the specimens; 3. Light cure for 20 s from each side.
Abbreviations: 3-MPS: 3-methacryloxypropyltrimethoxysilane; 10-MDP: 10-methacryloyloxydecyl dihydrogen phosphate.
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50
0
B1
2
5
10 20
Probability of failure (%)
50 10 20
0
B1
2
3.
B6
5
2
3.
B6
1
1
2
Probability of failure (%)
90 98
90 98
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0.1
0.5 1
5
10
50 100
0.1 0.5 1 5 10 50 100 Microtensile bond strength after 7-day water storage and additional mechanical ageing (MPa)
Microtensile bond strength after 7-day water storage (MPa) ‘as sintered’ (control) Al2O3 sandblasted SilJet tribochemical silica sandblasted CoJet tribochemical silica sandblasted
as as as as
recorded recorded recorded recorded
replaced (pft) replaced (pft)
replaced (maf) replaced (maf)
Fig 2 Left: Graph showing the Weibull analysis for the different mechanical surface pre-treatments tested when the specimens were stored for 7 days in water but no additional mechanical aging was applied. Higher scale (B63.2) parameters were recorded for 50-μm Al2O3 sandblasted as well as CoJet and SilJet tribochemically silica sandblasted zirconia than for as-sintered (control) zirconia. For the as-sintered specimens, the as-recorded values and the randomly replaced values due to pre-test failures (PTF) were indicated differently. Right: Graph showing the Weibull analysis for the different mechanical surface pre-treatments tested when the specimens were stored for 7 days in water and additionally mechanically aged. Again, higher scale (B63.2) parameters were recorded for 50-μm Al2O3 sandblasted, CoJet and SilJet tribochemically silica sandblasted zirconia than for as-sintered zirconia. The shape modulus of the 50-μm Al2O3 sandblasted zirconia dropped remarkably after the additional mechanical aging. For the assintered specimens, the as-recorded values, the randomly replaced values due to PTF and the randomly replaced values due to MAF were indicated differently. In both graphs, dotted lines represent the 95% confidence interval of the Weibull plot.
Table 2
Results of Weibull analysis and the recorded failure mode
Zirconia pre-treatment
Aging1
n
PTF2
MAF3 Shape (modulus)4
Scale 95% confidence 95% confidence Percentage (B63.2)5 level at B63.26 level at B107 adhesive failure8
As sintered (control)
7d storage
10
3
/
1.43*
14.40*
8.39–26.43b*
0.70–6.71C*
92.0
+ mechanical
10
4
1
1.00*
21.70*
10.28–49.80ab*
0.31–7.53BC*
98.0
7d storage
10
0
/
2.86
42.91
33.46–56.09a
8.67–29.81A
63.0
+ mechanical
10
1
3
1.39*
43.07*
25.10–77.74ab*
1.77–19.97ABC*
90.0
CoJet tribochemically silica sandblasted
7d storage
10
0
/
2.60
56.22
42.52–75.46a
9.71–37.69A
49.0
+ mechanical
10
0
0
2.56
41.79
31.42–56.41a
6.97–27.80AB
48.0
SilJet tribochemically silica sandblasted
7d storage
10
0
/
2.40
49.00
36.18–67.42a
7.30–31.76AB
47.0
+ mechanical
10
0
0
3.11
50.67
40.08–64.84a
11.63–36.23A
32.0
50-μm Al2O3 sandblasted
1Aging protocol with 7d (7-day) storage in 37°C water, and 7-day storage in 37°C in water followed by additional mechanical aging (+ mechanical) using cyclic tensile stress of 10 N at 10 Hz for 10,000 cycles; 2pre-test failure; 3mechanical aging failure; 4the higher the Weibull shape, the more reliable the treatment; 5the higher the Weibull scale, the higher the bonding effectiveness; 6same superscript lower-case letters indicate absence of statistical significance at B63.2; 7same superscript capital letters indicate absence of statistical significance at B10; 8The rest percentage represents the area percentage of cohesive failure in the composite cement; *Calculated mean from random-value trials performed 1000 times.
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Fig 3 SEM photomicrographs illustrating a representatively fractured surface of RelyX Ultimate that was bonded to as-sintered zirconia (IPS e.max ZirCAD. (a) A specimen that was subjected to 7-day water storage showed adhesive failure along the cement/zirconia interface (I); as the sandwich zirconia/cement/zirconia specimens included two cement/zirconia interfaces, failure occurred in this specimen at both interfaces. (b) Higher magnification of the adhesively failed part indicated by the white arrow in (a). Zirconia grains can be observed. (c) Overview photomicrograph of a specimen that was subjected to additional mechanical aging. No difference in fracture mode was observed compared to a specimen that did not undergo mechanical aging. (d) Higher magnification of the adhesively failed part.
cal aging when the zirconia surface was tribochemically silica sandblasted (CoJet or SilJet). However, for 50-μm Al2O3 sandblasted zirconia, several MAFs were recorded. While their μTBS was hardly affected by aging, the Weibull shape parameter of Al2O3 sandblasted zirconia decreased significantly upon mechanical aging. Overall, the B63.2 and B10 Weibull parameters of the as-sintered (control) zirconia (7-day storage) were significantly lower than those of the surface-treated (either Al2O3 sandblasted or tribochemically silica sandblasted) zirconia according to the 95% confidence intervals (except for the Al2O3 sandblasted specimens subjected to additional mechanical aging: +mechanical; Table 2). The bond strength data were in line with the fracture analysis data, represented in Table 2 as the percentage of specimens that failed adhesively. In general, higher bonding efficacy was associated with a lower percentage of adhesive failures at the interface (and vice versa for lower bonding efficacy). Most of the as-sintered zirconia failed adhesively at the interface; in such cases, the zirconia surface was exposed with the zirconia grains observable microscopically (Fig 3). The 50-μm Al2O3 sandblasted zirconia specimens appeared to have failed less adhesively but more cohesively in the resin-composite cement; nevertheless, most of the 50-μm Al2O3 sandblasted zirconia specimens that received additional mechanical aging failed adhesively (Fig 4). Specimens subjected to tribochemical silica sandblasting using CoJet and SilJet selVol 17, No 3, 2015
dom failed entirely adhesively at the interface (Table 2); microscopically, the cohesively failed surface exhibited the filler of the composite cement (Figs 5 and 6).
DISCUSSION Mechanical pre-treatment of the zirconia surface using the three sandblasting techniques employed significantly improved the bonding effectiveness to zirconia; thus, the first null hypothesis was rejected. The second null hypothesis was accepted for the two tribochemically silica sandblasted (CoJet and SilJet) zirconia groups (as well as for the as-sintered group), but was rejected for the Al2O3 sandblasted zirconia group, as mechanical aging did affect its bonding receptiveness. According to a recent systematic literature review, the most commonly applied test method for assessing bonding efficacy to zirconia is a shear bond strength test.10 Most likely, this can be attributed to the fact that there is no need for further specimen preparation prior to the test. The systematic review, however, also demonstrated that a shear bond strength test is less discriminative than a tensile test.10 Therefore, a μTBS test to assess the bonding efficacy to mechanically pre-treated zirconia was used in this study. In order to apply Weibull statistics, a random value between 0 and 10 and between 10 and the lowest value 239
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CoJet tribochemically silica sandblasted
Fig 4 SEM photomicrographs illustrating a representative fractured surface of RelyX Ultimate that was bonded to 50-μm Al2O3 sandblasted zirconia (IPS e.max ZirCAD. (a) Overview photomicrograph of a specimen subjected to 7-day water storage. A relatively small part of the specimen failed at the interface (I), while the main part failed cohesively in the composite cement (C). (b) Higher magnification of the cohesively failed part showing the structure of the composite cement. (c) Overview photomicrograph of a specimen that was subjected to additional mechanical aging, showing that the specimen failed mainly adhesively along the interface (I). (d) Higher magnification of the adhesively failed part, disclosing the Al2O3 sandblasted zirconia surface.
Fig 5 SEM photomicrographs illustrating a representative fractured surface of RelyX Ultimate that was bonded to CoJet tribochemically silica sandblasted zirconia (IPS e.max ZirCAD. (a) Overview photomicrograph of a specimen subjected to 7-day water storage. The major part failed cohesively in the composite cement (C). (b) Higher magnification of the cohesively failed part, disclosing the filler of the composite cement. (c) Overview photomicrograph of a specimen subjected to additional mechanical aging. Nearly half of the specimen failed adhesively at the interface (I), while the other half failed cohesively in the composite cement (C). (d) Higher magnification of the cohesively failed part.
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Fig 6 SEM photomicrographs illustrating a representative fractured surface of RelyX Ultimate that was bonded to SilJet tribochemically silica sandblasted zirconia (IPS e.max ZirCAD). (a) Overview photomicrograph of a specimen that was subjected to 7-day water storage. The specimen failed both cohesively in the composite cement (C) and adhesively at the interface (I). (b) Higher magnification of the cohesively failed part, disclosing the filler of the composite cement. (c) Overview photomicrograph of a specimen that was subjected to additional mechanical aging. Only about 50% of the specimen failed adhesively at the interface (I), while the other part failed cohesively in the composite cement (C). (d) Higher magnification of the cohesively failed part.
measured in the respective experimental group was assigned to each PTF and each MAF, respectively, according to an approach applied successfully in a previous study.12 This random value assignment for PTFs and MAFs was repeated 1000 times, including a Weibull analysis each time, so that any potential bias was largely avoided. Regarding chemical pre-treatment of zirconia, several studies reported the bond-promoting effect of a primer containing 10-MDP.5,23 In a previous study,12 we measured the bonding efficacy of four different 10-MDP basedprimers/adhesives to dental zirconia. That study revealed that the most consistent data were obtained using the combined 10-MDP/silane based-primer Clearfil Ceramic Primer (Kuraray Noritake); thus, in this study, we decided to chemically pre-treat (after the mechanical pre-treatment) zirconia using Clearfil Ceramic Primer (Kuraray Noritake). Fracture analysis revealed that in the experimental groups – ie, the resin-composite cement was bonded to tribochemically silica sandblasted zirconia using either CoJet or SilJet – the specimens failed adhesively at the interface in certain areas and cohesively within the resincomposite cement at others. This observation is in line with the results of the Weibull analysis, as the specimens that showed the most common failure mode (mixed adhesive/cohesive) and also had significantly higher bond strength values. Moreover, the failure mode of those tribochemically silica sandblasted zirconia specimens was not affected by additional mechanical aging, which is a Vol 17, No 3, 2015
clear indication of their bond stability. In contrast, the as-sintered (control) zirconia specimens – which did not receive any mechanical pre-treatment, but solely chemical pre-treatment – mostly failed adhesively at the cement/ zirconia interface. This observation is also in line with the results of the Weibull analysis. Furthermore, the most frequent failure mode of the 50-μm Al2O3 sandblasted zirconia specimens was somewhere between that of the tribochemically silica sandblasted zirconia specimens and that of the as-sintered group. Without mechanical aging, they failed in a mixed mode or cohesively within the resincomposite cement; with additional mechanical aging, they generally failed adhesively at the cement/zirconia interface. This shift in failure mode for the 50-μm Al2O3 sandblasted zirconia upon mechanical aging may thus indicate that the resultant bond was less stable than that to the tribochemically silica sandblasted zirconia surfaces; the latter specimens did not demonstrate such a shift in failure mode. In terms of aging, the systematic review showed that thermocycling or long-term water storage induced only a small effect on the bonding effectiveness to zirconia.10 Even 10,000 thermocycles only resulted in a small effect.16 As in a previous study,12 this study employed additional mechanical aging to challenge the bond durability to zirconia. Under clinical circumstances, the adhesive interface is more heavily subjected to cyclic mechanical loading than to acute catastrophic stress.19 The effect of mechanical aging differed for the different mechanical 241
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pre-treatments tested. For tribochemical silica sandblasting, irrespective of the system applied (CoJet or SilJet), Weibull analysis revealed that mechanical aging did not affect their bonding efficacy. Tribochemical silica sandblasting clearly led to higher shape and scale parameters, and thus a higher and more consistent bonding efficacy than was the case with 50-μm Al2O3 sandblasted zirconia or when zirconia was not mechanically pre-treated (Table 2). It is peculiar that for Al2O3 sandblasted zirconia, mechanical aging did not affect the B63.2 value, but significantly dropped the Weibull modulus. Al2O3 sandblasting is one of the most commonly applied pre-treatment methods for zirconia.14,22 As deduced from the failure analysis, the bond to Al2O3 sandblasted zirconia should be considered as less stable (after mechanical loading) than that to tribochemically silica sandblasted zirconia. The Weibull modulus also dropped for the resin-composite cement bonded to the as-sintered (control) and thus mechanically untreated zirconia. Overall, when zirconia is mechanically pre-treated, tribochemical silica sandblasting should be considered as the method of choice due to its favorable effect on bond durability. However, it is noteworthy that some authors have reported negative effects of sandblasting zirconia;17,18 the reason mentioned was the risk of microcracks and the resultant decrease in longevity of the Y-TZP framework. Those authors recommended applying sandblasting at a low pressure (1 to 2 bars) and using a particle size below 50 μm in order to minimize surface damage of zirconia.
CONCLUSIONS
3.
4. 5.
6. 7. 8. 9. 10.
11.
12.
13. 14. 15. 16.
17.
18.
The mechanical surface pre-treatment of zirconia with tribochemical silica sandblasting (CoJet and SilJet) resulted in the highest bond durability of a resin-composite cement (RelyX Ultimate) to dental zirconia before and after aging.
19.
ACKNOWLEDGMENT
22.
M.I. acknowledges the Flemish scholarship for Japanese students. This work was performed within the framework of the Research Fund of KU Leuven under project OT/10/052 and of the Research Foundation Flanders (FWO-Flanders) under project G.0431.10.
REFERENCES 1.
2.
Atsu SS, Kilicarslan MA, Kucukesmen HC, Aka PS. Effect of zirconiumoxide ceramic surface treatments on the bond strength to adhesive resin. J Prosthet Dent 2006;95:430-436. Blatz MB, Chiche G, Holst S, Sadan A. Influence of surface treatment and simulated aging on bond strengths of luting agents to zirconia. Quintessence Int 2007;38:745-753.
242
20.
21.
23.
Blatz MB, Sadan A, Arch GH, Jr., Lang BR. In vitro evaluation of longterm bonding of Procera AllCeram alumina restorations with a modified resin luting agent. J Prosthet Dent 2003;89:381-387. Blatz MB, Sadan A, Kern M. Resin-ceramic bonding: a review of the literature. J Prosthet Dent 2003;89:268-274. Chen L, Suh BI, Brown D, Chen X. Bonding of primed zirconia ceramics: evidence of chemical bonding and improved bond strengths. Am J Dent 2012;25:103-108. Chen L, Suh BI, Kim J, Tay FR. Evaluation of silica-coating techniques for zirconia bonding. Am J Dent 2011;24:79-84. Della Bona A, Kelly JR. The clinical success of all-ceramic restorations. J Am Dent Assoc 2008;139 Suppl:8S-13S. Denry I, Kelly JR. State of the art of zirconia for dental applications. Dent Mater 2008;24:299-307. Derand P, Derand T. Bond strength of luting cements to zirconium oxide ceramics. Int J Prosthodont 2000;13:131-135. Inokoshi M, De Munck J, Minakuchi S, Van Meerbeek B. Meta-analysis of bonding effectiveness to zirconia ceramics. J Dent Res 2014;93: 329-334. Inokoshi M, Kameyama A, De Munck J, Minakuchi S, Van Meerbeek B. Durable bonding to mechanically and/or chemically pre-treated dental zirconia. J Dent 2013;41:170-179. Inokoshi M, Poitevin A, De Munck J, Minakuchi S, Van Meerbeek B. Bonding effectiveness to different chemically pre-treated dental zirconia. Clin Oral Investig 2014;18:1803-1812. Kelly JR, Denry I. Stabilized zirconia as a structural ceramic: an overview. Dent Mater 2008;24:289-298. Kern M, Barloi A, Yang B. Surface conditioning influences zirconia ceramic bonding. J Dent Res 2009;88:817-822. Kern M, Wegner SM. Bonding to zirconia ceramic: adhesion methods and their durability. Dent Mater 1998;14:64-71. Komine F, Kobayashi K, Blatz MB, Fushiki R, Koizuka M, Taguchi K, Matsumura H. Durability of bond between an indirect composite veneering material and zirconium dioxide ceramics. Acta Odontol Scand 2013;71:457-463. Kosmac T, Oblak C, Jevnikar P, Funduk N, Marion L. The effect of surface grinding and sandblasting on flexural strength and reliability of Y-TZP zirconia ceramic. Dent Mater 1999;15:426-433. Kosmac T, Oblak C, Jevnikar P, Funduk N, Marion L. Strength and reliability of surface treated Y-TZP dental ceramics. J Biomed Mater Res 2000;53:304-313. Poitevin A, De Munck J, Cardoso MV, Mine A, Peumans M, Lambrechts P, Van Meerbeek B. Dynamic versus static bond-strength testing of adhesive interfaces. Dent Mater 2010;26:1068-1076. Symynck J, De Bal F. Monte Carlo pivotal confidence bounds for Weibull analysis, with implementations in R. New Technologies and Products in Machine Manufacturing Technologies 2011:43-50. Ural C, Kulunk T, Kulunk S, Kurt M. The effect of laser treatment on bonding between zirconia ceramic surface and resin cement. Acta Odontol Scand 2010;68:354-359. Yang B, Wolfart S, Scharnberg M, Ludwig K, Adelung R, Kern M. Influence of contamination on zirconia ceramic bonding. J Dent Res 2007;86:749-753. Yoshida K, Tsuo Y, Atsuta M. Bonding of dual-cured resin cement to zirconia ceramic using phosphate acid ester monomer and zirconate coupler. J Biomed Mater Res Part B Appl Biomater 2006;77:28-33.
Clinical relevance: To obtain durable bonding to dental zirconia, the application of combined mechanical and chemical pre-treatment, involving tribochemical silica sandblasting followed by a combined 10-MDP/silane ceramic primer, is clinically highly recommended.
The Journal of Adhesive Dentistry
