Clin Oral Invest DOI 10.1007/s00784-013-1152-7
ORIGINAL ARTICLE
Bonding effectiveness to different chemically pre-treated dental zirconia Masanao Inokoshi & André Poitevin & Jan De Munck & Shunsuke Minakuchi & Bart Van Meerbeek
Received: 27 August 2013 / Accepted: 17 November 2013 # Springer-Verlag Berlin Heidelberg 2013
Abstract Objective The objective of this study was to evaluate the effect of different chemical pre-treatments on the bond durability to dental zirconia. Methods Fully sintered IPS e.max ZirCAD (Ivoclar Vivadent) blocks were subjected to tribochemical silica sandblasting (CoJet, 3M ESPE). The zirconia samples were additionally pre-treated using one of four zirconia primers/adhesives (Clearfil Ceramic Primer, Kuraray Noritake; Monobond Plus, Ivoclar Vivadent; Scotchbond Universal, 3M ESPE; ZPRIME Plus, Bisco). Finally, two identically pre-treated zirconia blocks were bonded together using composite cement (RelyX Ultimate, 3M ESPE). The specimens were trimmed at the interface to a cylindrical hourglass and stored in distilled water (7 days, 37 °C), after which they were randomly tested as is or subjected to mechanical ageing involving cyclic tensile stress (10 N, 10 Hz, 10,000 cycles). Subsequently, the micro-tensile bond strength was determined, and SEM fractographic analysis performed. Results Weibull analysis revealed the highest Weibull scale and shape parameters for the ‘Clearfil Ceramic Primer/ mechanical ageing’ combination. Chemical pre-treatment of CoJet (3M ESPE) sandblasted zirconia using Clearfil Ceramic Primer (Kuraray Noritake) and Monobond Plus (Ivoclar M. Inokoshi : A. Poitevin : J. De Munck : B. Van Meerbeek (*) KU Leuven BIOMAT, Department of Oral Health Sciences, KU Leuven (University of Leuven) & Dentistry, University Hospitals Leuven, Kapucijnenvoer 7, Blok a Bus 7001, 3000 Leuven, Belgium e-mail: [email protected] S. Minakuchi Gerodontology and Oral Rehabilitation, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo, Tokyo 113-8549, Japan
Vivadent) revealed a significantly higher bond strength than when Scotchbond Universal (3M ESPE) and Z-PRIME Plus (Bisco) were used. After ageing, Clearfil Ceramic Primer (Kuraray Noritake) revealed the most stable bond durability. Conclusion Combined mechanical/chemical pre-treatment, the latter with either Clearfil Ceramic Primer (Kuraray Noritake) or Monobond Plus (Ivoclar Vivadent), resulted in the most durable bond to zirconia. Clinical relevance As a standard procedure to durably bond zirconia to tooth tissue, the application of a combined 10methacryloyloxydecyl dihydrogen phosphate/silane ceramic primer to zirconia is clinically highly recommended. Keywords Zirconia . Bond strength . Tribochemical silica sandblasting . Silane . Composite cement . Ageing
Introduction All-ceramic restorations are widely applied for medium-tolarge tooth reconstructions in recent years. Thanks to their superb biocompatibility and favourable mechanical properties, yttria-stabilized tetragonal zirconia polycrystalline (YTZP) ceramics can be used as alternative for conventional metal frameworks. However, due to their chemical inertness, one of the major limitations is the difficulty to adhere zirconia to the tooth preparation [1]. As such, zirconia can today not be employed to truly minimal invasively restore severely destructed teeth, since it still requires macro-retention to hold the restoration in place. Different mechanical and chemical surface pre-treatments have been recommended to improve the bonding effectiveness of composite cement to zirconia. For instance,
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tribochemical silica sandblasting with 30- and 110-μm silicacoated aluminium oxide (Al2O3) particles has been shown not only to roughen but also to chemically activate zirconia, thus making it more receptive for chemical bonding via silane (3methacryloxypropyltrimethoxysilane, 3-MPS) coupling agents. To avoid the well-documented subsurface damage and transformation induced by high pressure and big particle size, one should apply air abrasion at lower pressure (1–2 bars) using particles up to 50 μm in size [2, 3]. The sole application of traditional ceramic (silane) primers appeared not very effective on zirconia [4–6], while the application of 10methacryloyloxydecyl dihydrogen phosphate (10-MDP) containing primers has been documented to chemically bond to zirconia, especially when applied on previously air-abraded zirconia using 50- to 110-μm alumina particles or 110-μm silica-coated alumina sand [2, 7–9]. Recently, several manufacturers have introduced a kind of ‘universal’ primer that is claimed to improve bond durability to the different kinds of etchable (glass-containing) and unetchable (glass-free/poor, polycrystalline) dental ceramics. Several studies have reported on the effectiveness of such ceramic primers [2, 3, 10–19]. From a previous study [20], it was concluded that mechanical pre-treatment, using tribochemical silica sandblasting (CoJet; 3M ESPE, Seefeld, Germany), in combination with chemical pre-treatment, using a ceramic primer (Clearfil Ceramic Primer, Kuraray Noritake, Tokyo, Japan; Monobond Plus, Ivoclar Vivadent, Schaan, Liechtenstein), provided the highest bonding effectiveness to dental zirconia. Moreover, none of these bonds appeared sensitive to thermocycling. Therefore, in continuation of our previous study, this laboratory study aimed to assess the effect of four different primers/adhesives that are indicated for bonding to zirconia, on the short-term bonding effectiveness and on the bonding effectiveness after the specimens have been exposed to additional ageing. Bonding effectiveness was assessed using a micro-tensile bond strength (μTBS) approach and ultramorphological analysis of the fractured surfaces. Resistance against mechanical ageing was assessed by subjecting the micro-specimens to cyclic tensile stress. The null hypotheses tested were (1) that the bonding effectiveness of composite cement to zirconia ceramics was not different for the four zirconia primers/adhesives tested and (2) that the strength of the tested composite cement–zirconia bond was not affected by mechanical ageing.
Materials and methods The study design is schematically explained in Fig. 1. Presintered CAD/CAM blocks (IPS e.max ZirCAD, Ivoclar Vivadent) were sectioned by means of an automated water-
cooled diamond saw (Accutom 50, Struers, Copenhagen, Denmark) to obtain micro-specimens with a dimension of 2×2×7.5 mm. Next, the micro-specimens were sintered by the manufacturer using the proprietary sintering program (Ivoclar Vivadent). The micro-specimen size after sintering was 1.6×1.6×6.0 mm. The sintered micro-specimens were then ultrasonically cleaned in acetone for 10 min, followed by thorough drying with compressed air. Next, the microspecimens were subjected to tribochemical silica sandblasting (Table 1; CoJet, 3M ESPE), as the latter appeared the most effective bonding-receptive mechanical pre-treatment of zirconia, this is based on own previously unpublished data and a performed, yet unpublished, systematic literature review on bonding effectiveness to zirconia. Each micro-specimen was then assigned randomly to one of four groups, according to the four different primer/adhesive protocols (Table 1). Finally, two identically pre-treated micro-specimens were bonded together using a dual-cure composite cement (Table 1; RelyX Ultimate, 3M ESPE); they were stabilized in a precisely fitting silicone mould (Extrude Medium, Kerr, Orange, CA, USA), thereby standardizing the cement thickness. Each bonded micro-specimen assembly was light-cured for 20 s from each side using a high-intensity (output of 1,000 mW/cm2) lightcuring unit (Bluephase G2, Ivoclar Vivadent). The total lightcuring 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 with a diameter of 1.2– 1.4 mm using a custom-modified computer-controlled MicroSpecimen Former (The University of Iowa, Iowa City, IA, USA), equipped with a regular-grit cylindrical diamond bur (Komet 842 314 014, Komet, Lemgo, Germany). After 1week water storage at 37 °C, the specimens were randomly subjected either (1) to immediate μTBS testing (see below) or (2) to additional mechanical ageing using a cyclic tensile stress of 10 N at 10 Hz for 10,000 cycles with a universal testing machine (Instron 5848 MicroTester, Instron, Bucks, UK) prior to μTBS testing. Subsequently, the cross-sectional diameter of each specimen was accurately (accuracy=0.5 μm) determined using a high-precision measuring instrument transformed from an x– y multipurpose modular microscope (Leitz, Wetzlar, Germany). Specimens were then fixed to a modified notched BIOMAT jig (fixation height=4–6 mm) with cyanoacrylate glue (Model Repair II Blue, Dentsply-Sankin, Ōtawara, Japan). They were loaded at a crosshead speed of 1 mm/min until failure in the universal testing machine. The μTBS was expressed in megapascals, as derived from dividing the imposed surface (newtons) at the time of fracture by the bond area (square millimetres). When specimens failed before actual testing, which happened mainly during the preparation of the circular constriction, the μTBS was determined from the specimens that survived specimen processing with an explicit note of the number of pretesting failures (‘ptf’). The number
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Fig. 1 Flow chart detailing the study set-up
of specimens that failed during the mechanical ageing (mechanical ageing failures or ‘maf’) was explicitly noted as well. For the former ptf failures, a random value between 0 and 10 MPa was assigned. Since the latter maf failures did have some bond strength, a random value between 10 MPa and the lowest value measured in the respective group was assigned. The μTBS results were statistically analysed using Weibull analysis; pivotal confidence bounds were calculated using Monte Carlo simulation [21]. For reasons of reliability and reproducibility, we repeated the random-value assignment procedure and subsequent Weibull analysis 1,000 times using the software package R3.0 and Abrem (R Foundation for Statistical Computing, Vienna, Austria) and a custom-made script for this software. From these 1,000 simulations, the mean Weibull module and characteristic strength were calculated. Different groups were compared at the B63.2 unreliability level, being considered as the actual bonding effectiveness. All tests were performed at a significance level of α = 0.05 using the abovementioned software package. To determine the mode of failure, all specimens were observed immediately after fracture at a magnification of ×50 using a stereomicroscope (Wild M5A, Heerbrugg, Switzerland). The fractured surfaces were classified according to one of the following failure modes: A = ‘Adhesive’ failure
at the cement–zirconia interface, C = ‘Cohesive’ failure in cement and Z = ‘Cohesive’ failure in zirconia. Representative specimens were also imaged using a scanning electron microscope (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. The highest Weibull ‘shape’ (5.17) and ‘scale’ (51.29) were observed when zirconia was chemically pre-treated using the 10MDP/silane-based ceramic primer, Clearfil Ceramic Primer (Kuraray Noritake), and the micro-specimens were subjected to additional mechanical ageing. While the two ceramic primers, Clearfil Ceramic Primer (Kuraray Noritake) and Monobond Plus (Ivoclar Vivadent), showed equally high bonding effectiveness to zirconia, the universal adhesive Scotchbond Universal (3M ESPE) and the primer Z-PRIME Plus (Bisco) revealed significantly lower bonding effectiveness to zirconia (Table 2). After additional mechanical ageing, Weibull analysis could not be performed for Z-PRIME Plus (Bisco), because only one specimen survived the mechanical
Y-TZP
Tribochemical coating
Silane coupling agent Silane coupling agent
One-step self-etch adhesive containing silane
Zirconia-alumina-metal primer Composite cement
IPS e.max ZirCAD
CoJet
Clearfil Ceramic Primer Monobond Plus
Scotchbond Universal
Z-PRIME Plus RelyX Ultimate
Bisco, Schaumburg, IL, USA 3M ESPE
3M ESPE
Kuraray Noritake, Tokyo, Japan Ivoclar Vivadent
Ivoclar Vivadent, Schaan, Liechtenstein 3M ESPE, Seefeld, Germany
Manufacturer
3-MPS, 10-MDP, ethanol Phosphoric acid methacrylate, silane methacrylate, disulfide methacrylate, ethanol 10-MDP, dimethacrylate resins, HEMA, Vitrebond copolymer, filler, ethanol, water, initiators, silane 10-MDP, BPDM, HEMA, ethanol 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
30 μm silica-coated aluminium oxide
ZrO2, Y2O3, HfO2, Al2O3, other oxide ceramics
Composition
Apply 1–2 coats of primer, then air-dry for 3–5 s (1) Squeeze base and catalyst paste from the dispenser syringe; (2) apply the mixed RelyX Ultimate to specimens; and (3) light-cure for 20 s from each side
Apply primer for 20 s, then gently air-dry
(1) Blast the surface from a distance of 2–10 mm for 2 s at 0.3-MPa pressure; (2) remove any residual blast-coating agent with a stream of dry, oil-free air Apply primer for 60 s, then thoroughly air-dry Apply primer for 60 s, then thoroughly air-dry
Application procedure
3-MPS 3-methacryloxypropyltrimethoxysilane, 10-MDP 10-methacryloyloxydecyl dihydrogen phosphate, HEMA hydroxyethylmethacrylate, BPDM biphenyl dimethacrylate
Type of material
Material
Table 1 Overview of the different materials employed
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Fig. 2 a Graph showing the Weibull analysis for the different zirconia primers/adhesives tested when no additional mechanical ageing was applied. Higher scale parameters were recorded for Clearfil Ceramic Primer (Kuraray Noritake) and Monobond Plus (Ivoclar Vivadent) than for Scotchbond Universal (3M ESPE) and Z-PRIME Plus (Bisco). For Scotchbond Universal (3M ESPE) and Z-PRIME Plus (Bisco), the actually measured values and those replaced by a random value were marked differently. b Graph showing the Weibull analysis for the different
zirconia primers/adhesives tested when additional mechanical ageing was applied. Higher scale parameters were recorded for Clearfil Ceramic Primer (Kuraray Noritake) than for Monobond Plus (Ivoclar Vivadent) and Scotchbond Universal (3M ESPE). For Monobond Plus (Ivoclar Vivadent) and Scotchbond Universal (3M ESPE), the actually measured values and those replaced by a random value were marked differently. Weibull analysis was not possible for Z-PRIME Plus (Bisco), because only few specimens survived the mechanical loading
ageing (Table 2). The bonding effectiveness was not affected by mechanical ageing when Clearfil Ceramic Primer (Kuraray
Noritake) was used. However, for Monobond Plus (Ivoclar Vivadent), the range of the recorded bond strengths was
Table 2 The results of Weibull analysis and the recorded failure mode Zirconia pre-treatment
Ageinga
Sample Size ptf maf Shape Scale 95 % confidence (modulus)b (B63.2)c level at B63.2d
Clearfil Ceramic Primer
7d mechanical 7d mechanical 7d mechanical 7d mechanical
10 10 10 10 10 10 10 10
Monobond Plus Scotchbond Universal Z-PRIME Plus
0 0 0 1 1 5 3 7
– 0 – 1 – 1 – 2
2.03 5.17 3.95 1.26f 1.40f 1.33f 1.51f –g
49.09 51.29 42.79 38.93f 18.22f 14.28f 13.21f –g
33.16–72.26 (a) 44.63–59.24 (a) 35.84–51.68 (a) 21.53–73.83 (ab)f 10.69–32.47 (b)f 7.30–30.38 (b)f 7.86–23.82 (b)f –g
95 % confidence Percentage level at B10 ‘adhesive’ failuree 5.05–28.8 20.3–41.6 13.5–32.5 1.14–16.82f 0.74–8.53f 0.34–5.53f 0.75–6.36f –g
57 67 69 56 96.5 98 98 99
ptf pretesting failure, maf mechanical ageing failure Ageing protocol with ‘7d’ referring to 7-day storage in 37 °C water; mechanical = cyclic tensile stress of 10 N at 10 Hz for 10,000 cycles in addition to 7-day storage in 37 °C water
a
b
The higher the Weibull shape, the more reliable the treatment
c
The higher the Weibull scale, the higher the bonding effectiveness
d
Same letters within brackets indicate statistical non-significance at B63.2
e
The rest percentage represents the area percentage of ‘cohesive’ failure in the composite cement
f
Calculated mean from the 1,000 times random-value replacement assignments
g
Weibull analysis could not be performed due to lack of sufficient specimens that survived the mechanical ageing
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broadened. When Scotchbond Universal (3M ESPE) or ZPRIME Plus (Bisco) were used, the bond strength dropped upon ageing. The bond-strength data were in line with the fracture analysis data. Specimens subjected to chemical pre-treatment using the ceramic primers Clearfil Ceramic Primer (Kuraray Noritake) and Monobond Plus (Ivoclar Vivadent), which seldom failed entirely ‘adhesively’ at the interface (Table 2); at microscopic level, many composite remnants were still found to be attached to the surface (Figs. 3 and 4). Most of the specimens that were chemically pre-treated using Scotchbond Universal (3M ESPE) or Z-PRIME Plus (Bisco), on the other hand, failed ‘adhesively’ at the interface (Table 2). Then, the zirconia surface was exposed without much surface alterations observable at microscopic level (Figs. 5 and 6), which is suggestive of a rather weak interaction with zirconia.
Discussion Chemical pre-treatment of the zirconia surface using primers significantly influenced the bonding effectiveness to zirconia, by which the null hypothesis (1) was rejected. The null hypothesis (2) was also rejected, as mechanical ageing did also affect the bonding effectiveness to zirconia. The most common test method to assess bonding effectiveness to zirconia is the shear bond-strength test [22], most likely because it requires nearly no further specimen processing of the fully sintered zirconia, once the bonding procedure is completed. However, the shear bond-strength test has repeatedly been documented to result in inhomogeneous stress distribution along the interface, for instance, often leading Fig. 3 SEM photomicrographs illustrating a representatively fractured surface of RelyX Ultimate (3M ESPE) bonded to zirconia (IPS e.max ZirCAD, Ivoclar Vivadent) using Clearfil Ceramic Primer (Kuraray Noritake). a Overview of a specimen that was subjected to 7day water storage. The major part failed cohesively in the composite cement (C). b Higher magnification of the cohesive failure part, disclosing the filler of the composite cement. c Overview of a specimen that was subjected to additional mechanical ageing. Nearly half of the specimen failed at the interface (I), while the other half failed cohesively in the composite cement (C). d Higher magnification of the cohesive failure part
rather to ‘cohesive’ failure in the substrate than to ‘adhesive’ failure at the actual interface [22–25]. In addition, the discriminative power of a shear bond-strength test is much lower than that of a μTBS test [26], because of which the latter μTBS approach was employed in this study. Also, our previous study confirmed that a μTBS protocol can be used to evaluate bonding effectiveness to zirconia ceramics [20]. Nevertheless, it can be expected that the micro-specimen trimming procedure applied may have stressed the cement– zirconia interface and thus affected the interfacial strength. We however standardized the trimming procedure using the custom-modified computer-controlled MicroSpecimen Former (The University of Iowa), so that one may expect that all specimens should have received a nearly equal trimming load before being pulled apart, thereby not having introduced another test variable. In this study, we opted for tribochemical silica sandblasting of zirconia prior to additional chemical pre-treatment, since this form of ‘active’ sandblasting (versus ‘conventional’ sandblasting using alumina powder) appeared, as mentioned above, as the most effective mechanical pre-treatment of zirconia with regard to bonding receptiveness. It is however noteworthy that some authors reported that sandblasting may negatively influence the properties of Y-TZP ceramics [27, 28]. According to those authors, sandblasting can produce micro-cracks and thus decrease the strength and longevity of Y-TZP. Some more recent own (unpublished) data demonstrated that the mechanical pre-treatment also influenced the resistance of zirconia against low-temperature degradation but that this depended largely on the kind of zirconia grade tested. The Literature has nevertheless recommended that zirconia should be sandblasted at low pressure (1–2 bars) and using
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Fig. 4 SEM photomicrographs illustrating a representatively fractured surface of RelyX Ultimate (3M ESPE) bonded to zirconia (IPS e.max ZirCAD, Ivoclar Vivadent) using Monobond Plus (Ivoclar Vivadent). a Overview of a specimen that was subjected to 7-day water storage. Nearly half of the specimen failed at the interface (I), while the other half failed cohesively in the composite cement (C). b Higher magnification of the
cohesive failure part. c Overview of a specimen that was subjected to additional mechanical ageing. The major part failed cohesively in the composite cement (C). No difference in fracture mode was observed when compared to a specimen that did not undergo mechanical ageing. d Higher magnification of the transition zone between the interfacially failed part and the cohesive failure part
powder with a particle size below 50 μm to avoid surface damage [2, 3].
The μTBS data were analysed using Weibull statistics. The Weibull distribution is a continuous probability distribution;
Fig. 5 SEM photomicrographs illustrating a representatively fractured surface of RelyX Ultimate (3M ESPE) bonded to zirconia (IPS e.max ZirCAD, Ivoclar Vivadent) using Scotchbond Universal (3M ESPE). a Overview of a specimen that was subjected to 7-day water storage, showing that the specimen failed mainly ‘adhesively’ along the interface (I). b Higher magnification of the interfacially failed part, disclosing the
CoJet (3M ESPE)-pre-treated zirconia surface. c Overview of a specimen that was subjected to additional mechanical ageing. No difference in fracture mode was observed when compared to a specimen that did not undergo mechanical ageing. d Higher magnification of the transition zone between the two interfacially failed parts
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Fig. 6 SEM photomicrographs illustrating a representatively fractured surface of RelyX Ultimate (3M ESPE) bonded to zirconia (IPS e.max ZirCAD, Ivoclar Vivadent) using Z-PRIME Plus (Bisco). a A specimen that was subjected to 7-day water storage showed that the specimen failed interfacially along the interface (I). No difference in fracture mode was observed when compared to a specimen, for which Scotchbond Universal
(3M ESPE) was used. b Higher magnification of the interfacially failed part, disclosing the CoJet (3M ESPE)-pre-treated zirconia surface. c Overview of a specimen that was subjected to additional mechanical ageing. No difference in fracture mode was observed when compared to a specimen that did not undergo mechanical ageing. d Higher magnification of the transition zone between the two interfacially failed parts
Weibull survival analysis has been developed as, among others, an engineering design method for reliability analysis and prediction of components, often being referred to as ‘reliability engineering’ [29–31]. Up to now, it has been used a few times in projects assessing the bonding effectiveness to zirconia [32–35]. In our experiments, some specimens failed prior to the actual bond-strength test, either during specimen preparation, recorded as ptf, or during mechanical ageing, recorded as mechanical ageing failure or maf. Excluding these specimens from our analysis would positively bias our results and result in apparent higher bond strengths. Assigning all pretesting failures a zero value would also bias the results, as some bond strength was present, but not enough to survive specimen processing. Moreover, Weibull analysis cannot deal with zero values. Therefore, we opted to assign to the specimens that failed prior to testing (ptf and maf) a random value in the respective group. Since we applied 10 N for mechanical ageing, we replaced ptf with random values between 0 and 10 MPa. For maf, on the other hand, we replaced them with random values between 10 MPa and the lowest value observed in the respective group. We performed this replacement simulation, including the Weibull analysis, 1,000 times and thereby thought to have avoided bias. The Weibull analysis revealed that the chemical surface pre-treatment of zirconia using a combined 10-MDP/silanebased primer (Clearfil Ceramic Primer, Kuraray Noritake; Monobond Plus, Ivoclar Vivadent) clearly led to higher shape
and scale parameters, and thus, a higher and more consistent bonding effectiveness than when the universal adhesive Scotchbond Universal (3M ESPE) or the zirconia primer ZPRIME Plus (Bisco) was used (Table 2). Regarding the latter, when the micro-specimens were additionally subjected to mechanical loading, only one specimen survived, by which this group was excluded from the Weibull analysis. Overall, the use of the ceramic primers Clearfil Ceramic Primer (Kuraray Noritake) and Monobond Plus (Ivoclar Vivadent) appeared most reliable to bond to zirconia. It would be interesting to investigate if there exist potential synergistic (or perhaps antagonistic) effects regarding the chemical interaction of the phosphate (10-MDP) and silanol (3-MPS) functional groups with the tribochemical silica sandblasted zirconia surface. Fractographic analysis revealed that the experimental groups, following which zirconia, was pre-treated with the ceramic primers Clearfil Ceramic Primer (Kuraray Noritake) and Monobond Plus (Ivoclar Vivadent) caused the specimens to fail more in a ‘mixed’ mode, also often including ‘cohesive’ failure within the composite cement. This observation agrees well with the results of the Weibull analysis, as the samples that typically failed in a ‘mixed’ failure mode also presented with significantly higher bond-strength values. The failure mode was, however, not affected by additional mechanical ageing. Also noteworthy is that all groups exhibiting relatively low bond strengths, in particular the groups chemically pre-
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treated with Scotchbond Universal (3M ESPE) or Z-PRIME Plus (Bisco), typically failed entirely at the cement–zirconia interface. SEM failure analysis did almost not reveal adhesive remnants on the fractured surfaces. Chemically, the best adhesion to zirconia can be obtained using a phosphate-based functional monomer; in particular, 10-MDP is known for its favourable chemical bonding capabilities to diverse substrates, among which is dental zirconia [36, 37]. All the products tested do contain 10-MDP, but appeared not equally effective. Therefore, other factors must explain the differences in the μTBS measured. Besides the actual concentration of 10-MDP in the different primer/ adhesives tested, also the purity of the functional monomer may affect its performance. Information on both concentration and purity is commonly not released by the manufacturer. A commercially available 10-MDP (PCM Products, Krefeld, Germany) was for instance documented to have a purity of about 80 %. Both formulations that did perform most effectively contain also silane methacrylate (3-MPS), though this was intentionally added to chemically bond to glass ceramics. Nevertheless, this silane methacrylate might also be beneficial for adhesion to zirconia, thanks to its efficient wetting capabilities and, in particular, its reaction with the CoJet (3M ESPE) silica sandblasted zirconia surface. CoJet (3M ESPE) sandblasting coats the zirconia surface with a silica layer, thanks to the high-speed surface impaction of alumina particles modified with silica. This silica layer helps forming a chemical bond of the silane agent with the zirconia surface [38]. The ‘universal’ adhesive Scotchbond Universal (3M ESPE) contains both 10-MDP and silane and many other ingredients, among which is water, to enable efficient adhesion in the first place to the tooth substrate. Having many ingredients mixed into one adhesive solution, they all may mutually compete to contact the zirconia surface, thus preventing the actual functional monomers (10-MDP, silane) from effectively interacting. The low bonding effectiveness recorded for Z-PRIME Plus (Bisco) was somewhat unexpected, as it was proven to chemically interact with zirconia [36], and as this is in contrast to the more favourable bond strengths (though measured mostly in shear) by other authors [3, 12, 18]. Overall, the dedicated ceramic primers (Clearfil Ceramic Primer, Kuraray Noritake; Monobond Plus, Ivoclar Vivadent), both containing 10-MDP and silane, resulted in the best bonding effectiveness of the composite cement RelyX Ultimate (3M ESPE), to tribochemical silica sandblasted (CoJet, 3M ESPE) zirconia. Regarding the ageing protocol, several researchers reported that thermo-cycling or long-term water storage did not affect the bonding effectiveness to zirconia [20, 34, 39]. Therefore, in this study, we applied mechanical ageing to assess the bond durability to zirconia. Intuitively, this may also be more clinically relevant, as under clinical circumstances, the adhesive interface is more subjected to cyclic stress than to acute
catastrophic stress [40]. The effect of mechanical loading differed for the different primers/adhesives tested. For Clearfil Ceramic Primer (Kuraray Noritake), the bond strength even slightly increased after mechanical ageing. Noteworthy is that the B63.2 value did not change but that the B10 value and shape increased. Much less ‘low’ values were observed, suggesting that the high frequency of the applied mechanical ageing may have induced additional curing of the composite cement. For Monobond Plus (Ivoclar Vivadent), the mechanical ageing broadened the range of the recorded bond-strength values. In contrast to Clearfil Ceramic Primer (Kuraray Noritake), more ‘low’ bond-strength values were recorded after mechanical ageing. These may be related to small flaws generated during mechanical loading. For Scotchbond Universal (3M ESPE) and Z-PRIME Plus (Bisco), the mechanical ageing even resulted in some premature failures (maf), while some other specimens revealed a bond strength similar to the control value. This suggests that they were cyclically loaded close to the fatigue limit, probably a little above the limit for Scotchbond Universal (3M ESPE) and a little below for Z-Prime Plus (Bisco). Further studies are now needed to investigate other parameters (frequency, applied mechanical stress, application time, etc.) on the bond durability to zirconia.
Conclusion The chemical surface pre-treatment of zirconia with a dedicated ceramic primer (Clearfil Ceramic Primer, Kuraray Noritake; Monobond Plus, Ivoclar Vivadent) resulted in the most favourable bond durability of composite cement (RelyX Ultimate, 3M ESPE) to dental zirconia.
Conflict of interest The authors declare that they have no conflict of interest.
References 1. Thompson JY, Stoner BR, Piascik JR, Smith R (2011) Adhesion/ cementation to zirconia and other non-silicate ceramics: where are we now? Dent Mater 27(1):71–82. doi:10.1016/j.dental.2010.10.022 2. Kern M, Barloi A, Yang B (2009) Surface conditioning influences zirconia ceramic bonding. J Dent Res 88(9):817–822. doi:10.1177/ 0022034509340881 3. Magne P, Paranhos MP, Burnett LH Jr (2010) New zirconia primer improves bond strength of resin-based cements. Dent Mater 26(4): 345–352. doi:10.1016/j.dental.2009.12.005 4. Derand T, Molin M, Kvam K (2005) Bond strength of composite luting cement to zirconia ceramic surfaces. Dent Mater 21(12):1158– 1162. doi:10.1016/j.dental.2005.02.005 5. Friederich R, Kern M (2002) Resin bond strength to densely sintered alumina ceramic. Int J Prosthodont 15(4):333–338
Clin Oral Invest 6. Kern M, Wegner SM (1998) Bonding to zirconia ceramic: adhesion methods and their durability. Dent Mater 14(1):64–71 7. Ozcan M, Nijhuis H, Valandro LF (2008) Effect of various surface conditioning methods on the adhesion of dual-cure resin cement with MDP functional monomer to zirconia after thermal aging. Dent Mater J 27(1):99–104 8. Yang B, Barloi A, Kern M (2010) Influence of air-abrasion on zirconia ceramic bonding using an adhesive composite resin. Dent Mater 26(1):44–50. doi:10.1016/j.dental.2009.08.008 9. Yoshida K, Tsuo Y, Meng X, Atsuta M (2007) Mechanical properties of dual-cured resin luting agents for ceramic restoration. J Prosthodont 16(5):370–376. doi:10.1111/j.1532-849X.2007.00221.x 10. Akyil MS, Uzun IH, Bayindir F (2010) Bond strength of resin cement to yttrium-stabilized tetragonal zirconia ceramic treated with air abrasion, silica coating, and laser irradiation. Photomed Laser Surg 28(6):801–808. doi:10.1089/pho.2009.2697 11. Azimian F, Klosa K, Kern M (2012) Evaluation of a new universal primer for ceramics and alloys. J Adhes Dent 14(3):275–282. doi:10. 3290/j.jad.a22193 12. Chen L, Suh BI, Kim J, Tay FR (2011) Evaluation of silica-coating techniques for zirconia bonding. Am J Dent 24(2):79–84 13. de Oyague RC, Monticelli F, Toledano M, Osorio E, Ferrari M, Osorio R (2009) Influence of surface treatments and resin cement selection on bonding to densely-sintered zirconium-oxide ceramic. Dent Mater 25(2):172–179. doi:10.1016/j.dental.2008.05.012 14. Foxton RM, Cavalcanti AN, Nakajima M, Pilecki P, Sherriff M, Melo L, Watson TF (2011) Durability of resin cement bond to aluminium oxide and zirconia ceramics after air abrasion and laser treatment. J Prosthodont 20(2):84–92. doi:10.1111/j.1532-849X.2010.00678.x 15. Koizumi H, Nakayama D, Komine F, Blatz MB, Matsumura H (2012) Bonding of resin-based luting cements to zirconia with and without the use of ceramic priming agents. J Adhes Dent 14(4):385– 392. doi:10.3290/j.jad.a22711 16. Lin J, Shinya A, Gomi H (2010) Effect of self-adhesive resin cement and tribochemical treatment on bond strength to zirconia. Int J Oral Sci 2(1):28–34 17. Phark JH, Duarte S Jr, Hernandez A, Blatz MB, Sadan A (2009) In vitro shear bond strength of dual-curing resin cements to two different high-strength ceramic materials with different surface texture. Acta Odontol Scand 67(6):346–354. doi:10.1080/00016350903074525 18. Piascik JR, Swift EJ, Braswell K, Stoner BR (2012) Surface fluorination of zirconia: adhesive bond strength comparison to commercial primers. Dent Mater 28(6):604–608. doi:10.1016/j.dental.2012.01. 008 19. Yoshida T, Ito M, Platt JA (2012) Mechanical properties and resin bond strength of surface-treated zirconia. Dent Mater 28 (Supplement 1):e38. doi:10.1016/j.dental.2012.07.092 20. Inokoshi M, Kameyama A, De Munck J, Minakuchi S, Van Meerbeek B (2013) Durable bonding to mechanically and/or chemically pre-treated dental zirconia. J Dent 41(2):170–179. doi:10. 1016/j.jdent.2012.10.017 21. Symynck J, De Bal F (2011) Monte Carlo pivotal confidence bounds for Weibull analysis, with implementations in R. New Technologies and Products in Machine Manufacturing Technologies 18(1):43–50 22. Blatz MB, Sadan A, Kern M (2003) Resin-ceramic bonding: a review of the literature. J Prosthet Dent 89(3):268–274. doi:10.1067/mpr. 2003.50
23. Della Bona A, van Noort R (1995) Shear vs. tensile bond strength of resin composite bonded to ceramic. J Dent Res 74(9):1591–1596 24. Denry I, Kelly JR (2008) State of the art of zirconia for dental applications. Dent Mater 24(3):299–307. doi:10.1016/j.dental.2007. 05.007 25. El Zohairy AA, De Gee AJ, Mohsen MM, Feilzer AJ (2003) Microtensile bond strength testing of luting cements to prefabricated CAD/CAM ceramic and composite blocks. Dent Mater 19(7):575–583 26. De Munck J, Mine A, Poitevin A, Van Ende A, Cardoso MV, Van Landuyt KL, Peumans M, Van Meerbeek B (2012) Meta-analytical review of parameters involved in dentin bonding. J Dent Res 91(4): 351–357. doi:10.1177/0022034511431251 27. Kosmac T, Oblak C, Jevnikar P, Funduk N, Marion L (2000) Strength and reliability of surface treated Y-TZP dental ceramics. J Biomed Mater Res 53(4):304–313 28. Zhang Y, Lawn BR, Rekow ED, Thompson VP (2004) Effect of sandblasting on the long-term performance of dental ceramics. J Biomed Mater Res B 71(2):381–386. doi:10.1002/jbm.b.30097 29. Basu B, Tiwari D, Kundu D, Prasad R (2009) Is Weibull distribution the most appropriate statistical strength distribution for brittle materials? Ceram Int 35(1):237–246. doi:10.1016/j.ceramint.2007.10.003 30. Quinn JB, Quinn GD (2010) A practical and systematic review of Weibull statistics for reporting strengths of dental materials. Dent Mater 26(2):135–147. doi:10.1016/j.dental.2009.09.006 31. Weibull W (1951) A statistical distribution function of wide applicability. J Appl Mec 18:293–297 32. Heikkinen TT, Lassila LV, Matinlinna JP, Vallittu PK (2007) Effect of operating air pressure on tribochemical silica-coating. Acta Odontol Scand 65(4):241–248. doi:10.1080/00016350701459753 33. Heikkinen TT, Matinlinna JP, Vallittu PK, Lassila LVJ (2010) Effect of primers and resins on the shear bond strength of resin composite to zirconia. SRX Dentistry 2010:1–8. doi:10.3814/2010/295137 34. Kumbuloglu O, Lassila LV, User A, Vallittu PK (2006) Bonding of resin composite luting cements to zirconium oxide by two air-particle abrasion methods. Oper Dent 31(2):248–255. doi:10.2341/05-22 35. Xie ZG, Meng XF, Xu LN, Yoshida K, Luo XP, Gu N (2011) Effect of air abrasion and dye on the surface element ratio and resin bond of zirconia ceramic. Biomed Mater 6(6):065004. doi:10.1088/17486041/6/6/065004 36. Chen L, Suh BI, Brown D, Chen X (2012) Bonding of primed zirconia ceramics: evidence of chemical bonding and improved bond strengths. Am J Dent 25(2):103–108 37. Yoshida K, Tsuo Y, Atsuta M (2006) Bonding of dual-cured resin cement to zirconia ceramic using phosphate acid ester monomer and zirconate coupler. J Biomed Mater Res B 77(1):28–33. doi:10.1002/ jbm.b.30424 38. Atsu SS, Kilicarslan MA, Kucukesmen HC, Aka PS (2006) Effect of zirconium-oxide ceramic surface treatments on the bond strength to adhesive resin. J Prosthet Dent 95(6):430–436. doi:10.1016/j. prosdent.2006.03.016 39. Tanaka R, Fujishima A, Shibata Y, Manabe A, Miyazaki T (2008) Cooperation of phosphate monomer and silica modification on zirconia. J Dent Res 87(7):666–670 40. Poitevin A, De Munck J, Cardoso MV, Mine A, Peumans M, Lambrechts P, Van Meerbeek B (2010) Dynamic versus static bond-strength testing of adhesive interfaces. Dent Mater 26(11): 1068–1076. doi:10.1016/j.dental.2010.07.007
ORIGINAL ARTICLE
Bonding effectiveness to different chemically pre-treated dental zirconia Masanao Inokoshi & André Poitevin & Jan De Munck & Shunsuke Minakuchi & Bart Van Meerbeek
Received: 27 August 2013 / Accepted: 17 November 2013 # Springer-Verlag Berlin Heidelberg 2013
Abstract Objective The objective of this study was to evaluate the effect of different chemical pre-treatments on the bond durability to dental zirconia. Methods Fully sintered IPS e.max ZirCAD (Ivoclar Vivadent) blocks were subjected to tribochemical silica sandblasting (CoJet, 3M ESPE). The zirconia samples were additionally pre-treated using one of four zirconia primers/adhesives (Clearfil Ceramic Primer, Kuraray Noritake; Monobond Plus, Ivoclar Vivadent; Scotchbond Universal, 3M ESPE; ZPRIME Plus, Bisco). Finally, two identically pre-treated zirconia blocks were bonded together using composite cement (RelyX Ultimate, 3M ESPE). The specimens were trimmed at the interface to a cylindrical hourglass and stored in distilled water (7 days, 37 °C), after which they were randomly tested as is or subjected to mechanical ageing involving cyclic tensile stress (10 N, 10 Hz, 10,000 cycles). Subsequently, the micro-tensile bond strength was determined, and SEM fractographic analysis performed. Results Weibull analysis revealed the highest Weibull scale and shape parameters for the ‘Clearfil Ceramic Primer/ mechanical ageing’ combination. Chemical pre-treatment of CoJet (3M ESPE) sandblasted zirconia using Clearfil Ceramic Primer (Kuraray Noritake) and Monobond Plus (Ivoclar M. Inokoshi : A. Poitevin : J. De Munck : B. Van Meerbeek (*) KU Leuven BIOMAT, Department of Oral Health Sciences, KU Leuven (University of Leuven) & Dentistry, University Hospitals Leuven, Kapucijnenvoer 7, Blok a Bus 7001, 3000 Leuven, Belgium e-mail: [email protected] S. Minakuchi Gerodontology and Oral Rehabilitation, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo, Tokyo 113-8549, Japan
Vivadent) revealed a significantly higher bond strength than when Scotchbond Universal (3M ESPE) and Z-PRIME Plus (Bisco) were used. After ageing, Clearfil Ceramic Primer (Kuraray Noritake) revealed the most stable bond durability. Conclusion Combined mechanical/chemical pre-treatment, the latter with either Clearfil Ceramic Primer (Kuraray Noritake) or Monobond Plus (Ivoclar Vivadent), resulted in the most durable bond to zirconia. Clinical relevance As a standard procedure to durably bond zirconia to tooth tissue, the application of a combined 10methacryloyloxydecyl dihydrogen phosphate/silane ceramic primer to zirconia is clinically highly recommended. Keywords Zirconia . Bond strength . Tribochemical silica sandblasting . Silane . Composite cement . Ageing
Introduction All-ceramic restorations are widely applied for medium-tolarge tooth reconstructions in recent years. Thanks to their superb biocompatibility and favourable mechanical properties, yttria-stabilized tetragonal zirconia polycrystalline (YTZP) ceramics can be used as alternative for conventional metal frameworks. However, due to their chemical inertness, one of the major limitations is the difficulty to adhere zirconia to the tooth preparation [1]. As such, zirconia can today not be employed to truly minimal invasively restore severely destructed teeth, since it still requires macro-retention to hold the restoration in place. Different mechanical and chemical surface pre-treatments have been recommended to improve the bonding effectiveness of composite cement to zirconia. For instance,
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tribochemical silica sandblasting with 30- and 110-μm silicacoated aluminium oxide (Al2O3) particles has been shown not only to roughen but also to chemically activate zirconia, thus making it more receptive for chemical bonding via silane (3methacryloxypropyltrimethoxysilane, 3-MPS) coupling agents. To avoid the well-documented subsurface damage and transformation induced by high pressure and big particle size, one should apply air abrasion at lower pressure (1–2 bars) using particles up to 50 μm in size [2, 3]. The sole application of traditional ceramic (silane) primers appeared not very effective on zirconia [4–6], while the application of 10methacryloyloxydecyl dihydrogen phosphate (10-MDP) containing primers has been documented to chemically bond to zirconia, especially when applied on previously air-abraded zirconia using 50- to 110-μm alumina particles or 110-μm silica-coated alumina sand [2, 7–9]. Recently, several manufacturers have introduced a kind of ‘universal’ primer that is claimed to improve bond durability to the different kinds of etchable (glass-containing) and unetchable (glass-free/poor, polycrystalline) dental ceramics. Several studies have reported on the effectiveness of such ceramic primers [2, 3, 10–19]. From a previous study [20], it was concluded that mechanical pre-treatment, using tribochemical silica sandblasting (CoJet; 3M ESPE, Seefeld, Germany), in combination with chemical pre-treatment, using a ceramic primer (Clearfil Ceramic Primer, Kuraray Noritake, Tokyo, Japan; Monobond Plus, Ivoclar Vivadent, Schaan, Liechtenstein), provided the highest bonding effectiveness to dental zirconia. Moreover, none of these bonds appeared sensitive to thermocycling. Therefore, in continuation of our previous study, this laboratory study aimed to assess the effect of four different primers/adhesives that are indicated for bonding to zirconia, on the short-term bonding effectiveness and on the bonding effectiveness after the specimens have been exposed to additional ageing. Bonding effectiveness was assessed using a micro-tensile bond strength (μTBS) approach and ultramorphological analysis of the fractured surfaces. Resistance against mechanical ageing was assessed by subjecting the micro-specimens to cyclic tensile stress. The null hypotheses tested were (1) that the bonding effectiveness of composite cement to zirconia ceramics was not different for the four zirconia primers/adhesives tested and (2) that the strength of the tested composite cement–zirconia bond was not affected by mechanical ageing.
Materials and methods The study design is schematically explained in Fig. 1. Presintered CAD/CAM blocks (IPS e.max ZirCAD, Ivoclar Vivadent) were sectioned by means of an automated water-
cooled diamond saw (Accutom 50, Struers, Copenhagen, Denmark) to obtain micro-specimens with a dimension of 2×2×7.5 mm. Next, the micro-specimens were sintered by the manufacturer using the proprietary sintering program (Ivoclar Vivadent). The micro-specimen size after sintering was 1.6×1.6×6.0 mm. The sintered micro-specimens were then ultrasonically cleaned in acetone for 10 min, followed by thorough drying with compressed air. Next, the microspecimens were subjected to tribochemical silica sandblasting (Table 1; CoJet, 3M ESPE), as the latter appeared the most effective bonding-receptive mechanical pre-treatment of zirconia, this is based on own previously unpublished data and a performed, yet unpublished, systematic literature review on bonding effectiveness to zirconia. Each micro-specimen was then assigned randomly to one of four groups, according to the four different primer/adhesive protocols (Table 1). Finally, two identically pre-treated micro-specimens were bonded together using a dual-cure composite cement (Table 1; RelyX Ultimate, 3M ESPE); they were stabilized in a precisely fitting silicone mould (Extrude Medium, Kerr, Orange, CA, USA), thereby standardizing the cement thickness. Each bonded micro-specimen assembly was light-cured for 20 s from each side using a high-intensity (output of 1,000 mW/cm2) lightcuring unit (Bluephase G2, Ivoclar Vivadent). The total lightcuring 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 with a diameter of 1.2– 1.4 mm using a custom-modified computer-controlled MicroSpecimen Former (The University of Iowa, Iowa City, IA, USA), equipped with a regular-grit cylindrical diamond bur (Komet 842 314 014, Komet, Lemgo, Germany). After 1week water storage at 37 °C, the specimens were randomly subjected either (1) to immediate μTBS testing (see below) or (2) to additional mechanical ageing using a cyclic tensile stress of 10 N at 10 Hz for 10,000 cycles with a universal testing machine (Instron 5848 MicroTester, Instron, Bucks, UK) prior to μTBS testing. Subsequently, the cross-sectional diameter of each specimen was accurately (accuracy=0.5 μm) determined using a high-precision measuring instrument transformed from an x– y multipurpose modular microscope (Leitz, Wetzlar, Germany). Specimens were then fixed to a modified notched BIOMAT jig (fixation height=4–6 mm) with cyanoacrylate glue (Model Repair II Blue, Dentsply-Sankin, Ōtawara, Japan). They were loaded at a crosshead speed of 1 mm/min until failure in the universal testing machine. The μTBS was expressed in megapascals, as derived from dividing the imposed surface (newtons) at the time of fracture by the bond area (square millimetres). When specimens failed before actual testing, which happened mainly during the preparation of the circular constriction, the μTBS was determined from the specimens that survived specimen processing with an explicit note of the number of pretesting failures (‘ptf’). The number
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Fig. 1 Flow chart detailing the study set-up
of specimens that failed during the mechanical ageing (mechanical ageing failures or ‘maf’) was explicitly noted as well. For the former ptf failures, a random value between 0 and 10 MPa was assigned. Since the latter maf failures did have some bond strength, a random value between 10 MPa and the lowest value measured in the respective group was assigned. The μTBS results were statistically analysed using Weibull analysis; pivotal confidence bounds were calculated using Monte Carlo simulation [21]. For reasons of reliability and reproducibility, we repeated the random-value assignment procedure and subsequent Weibull analysis 1,000 times using the software package R3.0 and Abrem (R Foundation for Statistical Computing, Vienna, Austria) and a custom-made script for this software. From these 1,000 simulations, the mean Weibull module and characteristic strength were calculated. Different groups were compared at the B63.2 unreliability level, being considered as the actual bonding effectiveness. All tests were performed at a significance level of α = 0.05 using the abovementioned software package. To determine the mode of failure, all specimens were observed immediately after fracture at a magnification of ×50 using a stereomicroscope (Wild M5A, Heerbrugg, Switzerland). The fractured surfaces were classified according to one of the following failure modes: A = ‘Adhesive’ failure
at the cement–zirconia interface, C = ‘Cohesive’ failure in cement and Z = ‘Cohesive’ failure in zirconia. Representative specimens were also imaged using a scanning electron microscope (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. The highest Weibull ‘shape’ (5.17) and ‘scale’ (51.29) were observed when zirconia was chemically pre-treated using the 10MDP/silane-based ceramic primer, Clearfil Ceramic Primer (Kuraray Noritake), and the micro-specimens were subjected to additional mechanical ageing. While the two ceramic primers, Clearfil Ceramic Primer (Kuraray Noritake) and Monobond Plus (Ivoclar Vivadent), showed equally high bonding effectiveness to zirconia, the universal adhesive Scotchbond Universal (3M ESPE) and the primer Z-PRIME Plus (Bisco) revealed significantly lower bonding effectiveness to zirconia (Table 2). After additional mechanical ageing, Weibull analysis could not be performed for Z-PRIME Plus (Bisco), because only one specimen survived the mechanical
Y-TZP
Tribochemical coating
Silane coupling agent Silane coupling agent
One-step self-etch adhesive containing silane
Zirconia-alumina-metal primer Composite cement
IPS e.max ZirCAD
CoJet
Clearfil Ceramic Primer Monobond Plus
Scotchbond Universal
Z-PRIME Plus RelyX Ultimate
Bisco, Schaumburg, IL, USA 3M ESPE
3M ESPE
Kuraray Noritake, Tokyo, Japan Ivoclar Vivadent
Ivoclar Vivadent, Schaan, Liechtenstein 3M ESPE, Seefeld, Germany
Manufacturer
3-MPS, 10-MDP, ethanol Phosphoric acid methacrylate, silane methacrylate, disulfide methacrylate, ethanol 10-MDP, dimethacrylate resins, HEMA, Vitrebond copolymer, filler, ethanol, water, initiators, silane 10-MDP, BPDM, HEMA, ethanol 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
30 μm silica-coated aluminium oxide
ZrO2, Y2O3, HfO2, Al2O3, other oxide ceramics
Composition
Apply 1–2 coats of primer, then air-dry for 3–5 s (1) Squeeze base and catalyst paste from the dispenser syringe; (2) apply the mixed RelyX Ultimate to specimens; and (3) light-cure for 20 s from each side
Apply primer for 20 s, then gently air-dry
(1) Blast the surface from a distance of 2–10 mm for 2 s at 0.3-MPa pressure; (2) remove any residual blast-coating agent with a stream of dry, oil-free air Apply primer for 60 s, then thoroughly air-dry Apply primer for 60 s, then thoroughly air-dry
Application procedure
3-MPS 3-methacryloxypropyltrimethoxysilane, 10-MDP 10-methacryloyloxydecyl dihydrogen phosphate, HEMA hydroxyethylmethacrylate, BPDM biphenyl dimethacrylate
Type of material
Material
Table 1 Overview of the different materials employed
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Fig. 2 a Graph showing the Weibull analysis for the different zirconia primers/adhesives tested when no additional mechanical ageing was applied. Higher scale parameters were recorded for Clearfil Ceramic Primer (Kuraray Noritake) and Monobond Plus (Ivoclar Vivadent) than for Scotchbond Universal (3M ESPE) and Z-PRIME Plus (Bisco). For Scotchbond Universal (3M ESPE) and Z-PRIME Plus (Bisco), the actually measured values and those replaced by a random value were marked differently. b Graph showing the Weibull analysis for the different
zirconia primers/adhesives tested when additional mechanical ageing was applied. Higher scale parameters were recorded for Clearfil Ceramic Primer (Kuraray Noritake) than for Monobond Plus (Ivoclar Vivadent) and Scotchbond Universal (3M ESPE). For Monobond Plus (Ivoclar Vivadent) and Scotchbond Universal (3M ESPE), the actually measured values and those replaced by a random value were marked differently. Weibull analysis was not possible for Z-PRIME Plus (Bisco), because only few specimens survived the mechanical loading
ageing (Table 2). The bonding effectiveness was not affected by mechanical ageing when Clearfil Ceramic Primer (Kuraray
Noritake) was used. However, for Monobond Plus (Ivoclar Vivadent), the range of the recorded bond strengths was
Table 2 The results of Weibull analysis and the recorded failure mode Zirconia pre-treatment
Ageinga
Sample Size ptf maf Shape Scale 95 % confidence (modulus)b (B63.2)c level at B63.2d
Clearfil Ceramic Primer
7d mechanical 7d mechanical 7d mechanical 7d mechanical
10 10 10 10 10 10 10 10
Monobond Plus Scotchbond Universal Z-PRIME Plus
0 0 0 1 1 5 3 7
– 0 – 1 – 1 – 2
2.03 5.17 3.95 1.26f 1.40f 1.33f 1.51f –g
49.09 51.29 42.79 38.93f 18.22f 14.28f 13.21f –g
33.16–72.26 (a) 44.63–59.24 (a) 35.84–51.68 (a) 21.53–73.83 (ab)f 10.69–32.47 (b)f 7.30–30.38 (b)f 7.86–23.82 (b)f –g
95 % confidence Percentage level at B10 ‘adhesive’ failuree 5.05–28.8 20.3–41.6 13.5–32.5 1.14–16.82f 0.74–8.53f 0.34–5.53f 0.75–6.36f –g
57 67 69 56 96.5 98 98 99
ptf pretesting failure, maf mechanical ageing failure Ageing protocol with ‘7d’ referring to 7-day storage in 37 °C water; mechanical = cyclic tensile stress of 10 N at 10 Hz for 10,000 cycles in addition to 7-day storage in 37 °C water
a
b
The higher the Weibull shape, the more reliable the treatment
c
The higher the Weibull scale, the higher the bonding effectiveness
d
Same letters within brackets indicate statistical non-significance at B63.2
e
The rest percentage represents the area percentage of ‘cohesive’ failure in the composite cement
f
Calculated mean from the 1,000 times random-value replacement assignments
g
Weibull analysis could not be performed due to lack of sufficient specimens that survived the mechanical ageing
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broadened. When Scotchbond Universal (3M ESPE) or ZPRIME Plus (Bisco) were used, the bond strength dropped upon ageing. The bond-strength data were in line with the fracture analysis data. Specimens subjected to chemical pre-treatment using the ceramic primers Clearfil Ceramic Primer (Kuraray Noritake) and Monobond Plus (Ivoclar Vivadent), which seldom failed entirely ‘adhesively’ at the interface (Table 2); at microscopic level, many composite remnants were still found to be attached to the surface (Figs. 3 and 4). Most of the specimens that were chemically pre-treated using Scotchbond Universal (3M ESPE) or Z-PRIME Plus (Bisco), on the other hand, failed ‘adhesively’ at the interface (Table 2). Then, the zirconia surface was exposed without much surface alterations observable at microscopic level (Figs. 5 and 6), which is suggestive of a rather weak interaction with zirconia.
Discussion Chemical pre-treatment of the zirconia surface using primers significantly influenced the bonding effectiveness to zirconia, by which the null hypothesis (1) was rejected. The null hypothesis (2) was also rejected, as mechanical ageing did also affect the bonding effectiveness to zirconia. The most common test method to assess bonding effectiveness to zirconia is the shear bond-strength test [22], most likely because it requires nearly no further specimen processing of the fully sintered zirconia, once the bonding procedure is completed. However, the shear bond-strength test has repeatedly been documented to result in inhomogeneous stress distribution along the interface, for instance, often leading Fig. 3 SEM photomicrographs illustrating a representatively fractured surface of RelyX Ultimate (3M ESPE) bonded to zirconia (IPS e.max ZirCAD, Ivoclar Vivadent) using Clearfil Ceramic Primer (Kuraray Noritake). a Overview of a specimen that was subjected to 7day water storage. The major part failed cohesively in the composite cement (C). b Higher magnification of the cohesive failure part, disclosing the filler of the composite cement. c Overview of a specimen that was subjected to additional mechanical ageing. Nearly half of the specimen failed at the interface (I), while the other half failed cohesively in the composite cement (C). d Higher magnification of the cohesive failure part
rather to ‘cohesive’ failure in the substrate than to ‘adhesive’ failure at the actual interface [22–25]. In addition, the discriminative power of a shear bond-strength test is much lower than that of a μTBS test [26], because of which the latter μTBS approach was employed in this study. Also, our previous study confirmed that a μTBS protocol can be used to evaluate bonding effectiveness to zirconia ceramics [20]. Nevertheless, it can be expected that the micro-specimen trimming procedure applied may have stressed the cement– zirconia interface and thus affected the interfacial strength. We however standardized the trimming procedure using the custom-modified computer-controlled MicroSpecimen Former (The University of Iowa), so that one may expect that all specimens should have received a nearly equal trimming load before being pulled apart, thereby not having introduced another test variable. In this study, we opted for tribochemical silica sandblasting of zirconia prior to additional chemical pre-treatment, since this form of ‘active’ sandblasting (versus ‘conventional’ sandblasting using alumina powder) appeared, as mentioned above, as the most effective mechanical pre-treatment of zirconia with regard to bonding receptiveness. It is however noteworthy that some authors reported that sandblasting may negatively influence the properties of Y-TZP ceramics [27, 28]. According to those authors, sandblasting can produce micro-cracks and thus decrease the strength and longevity of Y-TZP. Some more recent own (unpublished) data demonstrated that the mechanical pre-treatment also influenced the resistance of zirconia against low-temperature degradation but that this depended largely on the kind of zirconia grade tested. The Literature has nevertheless recommended that zirconia should be sandblasted at low pressure (1–2 bars) and using
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Fig. 4 SEM photomicrographs illustrating a representatively fractured surface of RelyX Ultimate (3M ESPE) bonded to zirconia (IPS e.max ZirCAD, Ivoclar Vivadent) using Monobond Plus (Ivoclar Vivadent). a Overview of a specimen that was subjected to 7-day water storage. Nearly half of the specimen failed at the interface (I), while the other half failed cohesively in the composite cement (C). b Higher magnification of the
cohesive failure part. c Overview of a specimen that was subjected to additional mechanical ageing. The major part failed cohesively in the composite cement (C). No difference in fracture mode was observed when compared to a specimen that did not undergo mechanical ageing. d Higher magnification of the transition zone between the interfacially failed part and the cohesive failure part
powder with a particle size below 50 μm to avoid surface damage [2, 3].
The μTBS data were analysed using Weibull statistics. The Weibull distribution is a continuous probability distribution;
Fig. 5 SEM photomicrographs illustrating a representatively fractured surface of RelyX Ultimate (3M ESPE) bonded to zirconia (IPS e.max ZirCAD, Ivoclar Vivadent) using Scotchbond Universal (3M ESPE). a Overview of a specimen that was subjected to 7-day water storage, showing that the specimen failed mainly ‘adhesively’ along the interface (I). b Higher magnification of the interfacially failed part, disclosing the
CoJet (3M ESPE)-pre-treated zirconia surface. c Overview of a specimen that was subjected to additional mechanical ageing. No difference in fracture mode was observed when compared to a specimen that did not undergo mechanical ageing. d Higher magnification of the transition zone between the two interfacially failed parts
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Fig. 6 SEM photomicrographs illustrating a representatively fractured surface of RelyX Ultimate (3M ESPE) bonded to zirconia (IPS e.max ZirCAD, Ivoclar Vivadent) using Z-PRIME Plus (Bisco). a A specimen that was subjected to 7-day water storage showed that the specimen failed interfacially along the interface (I). No difference in fracture mode was observed when compared to a specimen, for which Scotchbond Universal
(3M ESPE) was used. b Higher magnification of the interfacially failed part, disclosing the CoJet (3M ESPE)-pre-treated zirconia surface. c Overview of a specimen that was subjected to additional mechanical ageing. No difference in fracture mode was observed when compared to a specimen that did not undergo mechanical ageing. d Higher magnification of the transition zone between the two interfacially failed parts
Weibull survival analysis has been developed as, among others, an engineering design method for reliability analysis and prediction of components, often being referred to as ‘reliability engineering’ [29–31]. Up to now, it has been used a few times in projects assessing the bonding effectiveness to zirconia [32–35]. In our experiments, some specimens failed prior to the actual bond-strength test, either during specimen preparation, recorded as ptf, or during mechanical ageing, recorded as mechanical ageing failure or maf. Excluding these specimens from our analysis would positively bias our results and result in apparent higher bond strengths. Assigning all pretesting failures a zero value would also bias the results, as some bond strength was present, but not enough to survive specimen processing. Moreover, Weibull analysis cannot deal with zero values. Therefore, we opted to assign to the specimens that failed prior to testing (ptf and maf) a random value in the respective group. Since we applied 10 N for mechanical ageing, we replaced ptf with random values between 0 and 10 MPa. For maf, on the other hand, we replaced them with random values between 10 MPa and the lowest value observed in the respective group. We performed this replacement simulation, including the Weibull analysis, 1,000 times and thereby thought to have avoided bias. The Weibull analysis revealed that the chemical surface pre-treatment of zirconia using a combined 10-MDP/silanebased primer (Clearfil Ceramic Primer, Kuraray Noritake; Monobond Plus, Ivoclar Vivadent) clearly led to higher shape
and scale parameters, and thus, a higher and more consistent bonding effectiveness than when the universal adhesive Scotchbond Universal (3M ESPE) or the zirconia primer ZPRIME Plus (Bisco) was used (Table 2). Regarding the latter, when the micro-specimens were additionally subjected to mechanical loading, only one specimen survived, by which this group was excluded from the Weibull analysis. Overall, the use of the ceramic primers Clearfil Ceramic Primer (Kuraray Noritake) and Monobond Plus (Ivoclar Vivadent) appeared most reliable to bond to zirconia. It would be interesting to investigate if there exist potential synergistic (or perhaps antagonistic) effects regarding the chemical interaction of the phosphate (10-MDP) and silanol (3-MPS) functional groups with the tribochemical silica sandblasted zirconia surface. Fractographic analysis revealed that the experimental groups, following which zirconia, was pre-treated with the ceramic primers Clearfil Ceramic Primer (Kuraray Noritake) and Monobond Plus (Ivoclar Vivadent) caused the specimens to fail more in a ‘mixed’ mode, also often including ‘cohesive’ failure within the composite cement. This observation agrees well with the results of the Weibull analysis, as the samples that typically failed in a ‘mixed’ failure mode also presented with significantly higher bond-strength values. The failure mode was, however, not affected by additional mechanical ageing. Also noteworthy is that all groups exhibiting relatively low bond strengths, in particular the groups chemically pre-
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treated with Scotchbond Universal (3M ESPE) or Z-PRIME Plus (Bisco), typically failed entirely at the cement–zirconia interface. SEM failure analysis did almost not reveal adhesive remnants on the fractured surfaces. Chemically, the best adhesion to zirconia can be obtained using a phosphate-based functional monomer; in particular, 10-MDP is known for its favourable chemical bonding capabilities to diverse substrates, among which is dental zirconia [36, 37]. All the products tested do contain 10-MDP, but appeared not equally effective. Therefore, other factors must explain the differences in the μTBS measured. Besides the actual concentration of 10-MDP in the different primer/ adhesives tested, also the purity of the functional monomer may affect its performance. Information on both concentration and purity is commonly not released by the manufacturer. A commercially available 10-MDP (PCM Products, Krefeld, Germany) was for instance documented to have a purity of about 80 %. Both formulations that did perform most effectively contain also silane methacrylate (3-MPS), though this was intentionally added to chemically bond to glass ceramics. Nevertheless, this silane methacrylate might also be beneficial for adhesion to zirconia, thanks to its efficient wetting capabilities and, in particular, its reaction with the CoJet (3M ESPE) silica sandblasted zirconia surface. CoJet (3M ESPE) sandblasting coats the zirconia surface with a silica layer, thanks to the high-speed surface impaction of alumina particles modified with silica. This silica layer helps forming a chemical bond of the silane agent with the zirconia surface [38]. The ‘universal’ adhesive Scotchbond Universal (3M ESPE) contains both 10-MDP and silane and many other ingredients, among which is water, to enable efficient adhesion in the first place to the tooth substrate. Having many ingredients mixed into one adhesive solution, they all may mutually compete to contact the zirconia surface, thus preventing the actual functional monomers (10-MDP, silane) from effectively interacting. The low bonding effectiveness recorded for Z-PRIME Plus (Bisco) was somewhat unexpected, as it was proven to chemically interact with zirconia [36], and as this is in contrast to the more favourable bond strengths (though measured mostly in shear) by other authors [3, 12, 18]. Overall, the dedicated ceramic primers (Clearfil Ceramic Primer, Kuraray Noritake; Monobond Plus, Ivoclar Vivadent), both containing 10-MDP and silane, resulted in the best bonding effectiveness of the composite cement RelyX Ultimate (3M ESPE), to tribochemical silica sandblasted (CoJet, 3M ESPE) zirconia. Regarding the ageing protocol, several researchers reported that thermo-cycling or long-term water storage did not affect the bonding effectiveness to zirconia [20, 34, 39]. Therefore, in this study, we applied mechanical ageing to assess the bond durability to zirconia. Intuitively, this may also be more clinically relevant, as under clinical circumstances, the adhesive interface is more subjected to cyclic stress than to acute
catastrophic stress [40]. The effect of mechanical loading differed for the different primers/adhesives tested. For Clearfil Ceramic Primer (Kuraray Noritake), the bond strength even slightly increased after mechanical ageing. Noteworthy is that the B63.2 value did not change but that the B10 value and shape increased. Much less ‘low’ values were observed, suggesting that the high frequency of the applied mechanical ageing may have induced additional curing of the composite cement. For Monobond Plus (Ivoclar Vivadent), the mechanical ageing broadened the range of the recorded bond-strength values. In contrast to Clearfil Ceramic Primer (Kuraray Noritake), more ‘low’ bond-strength values were recorded after mechanical ageing. These may be related to small flaws generated during mechanical loading. For Scotchbond Universal (3M ESPE) and Z-PRIME Plus (Bisco), the mechanical ageing even resulted in some premature failures (maf), while some other specimens revealed a bond strength similar to the control value. This suggests that they were cyclically loaded close to the fatigue limit, probably a little above the limit for Scotchbond Universal (3M ESPE) and a little below for Z-Prime Plus (Bisco). Further studies are now needed to investigate other parameters (frequency, applied mechanical stress, application time, etc.) on the bond durability to zirconia.
Conclusion The chemical surface pre-treatment of zirconia with a dedicated ceramic primer (Clearfil Ceramic Primer, Kuraray Noritake; Monobond Plus, Ivoclar Vivadent) resulted in the most favourable bond durability of composite cement (RelyX Ultimate, 3M ESPE) to dental zirconia.
Conflict of interest The authors declare that they have no conflict of interest.
References 1. Thompson JY, Stoner BR, Piascik JR, Smith R (2011) Adhesion/ cementation to zirconia and other non-silicate ceramics: where are we now? Dent Mater 27(1):71–82. doi:10.1016/j.dental.2010.10.022 2. Kern M, Barloi A, Yang B (2009) Surface conditioning influences zirconia ceramic bonding. J Dent Res 88(9):817–822. doi:10.1177/ 0022034509340881 3. Magne P, Paranhos MP, Burnett LH Jr (2010) New zirconia primer improves bond strength of resin-based cements. Dent Mater 26(4): 345–352. doi:10.1016/j.dental.2009.12.005 4. Derand T, Molin M, Kvam K (2005) Bond strength of composite luting cement to zirconia ceramic surfaces. Dent Mater 21(12):1158– 1162. doi:10.1016/j.dental.2005.02.005 5. Friederich R, Kern M (2002) Resin bond strength to densely sintered alumina ceramic. Int J Prosthodont 15(4):333–338
Clin Oral Invest 6. Kern M, Wegner SM (1998) Bonding to zirconia ceramic: adhesion methods and their durability. Dent Mater 14(1):64–71 7. Ozcan M, Nijhuis H, Valandro LF (2008) Effect of various surface conditioning methods on the adhesion of dual-cure resin cement with MDP functional monomer to zirconia after thermal aging. Dent Mater J 27(1):99–104 8. Yang B, Barloi A, Kern M (2010) Influence of air-abrasion on zirconia ceramic bonding using an adhesive composite resin. Dent Mater 26(1):44–50. doi:10.1016/j.dental.2009.08.008 9. Yoshida K, Tsuo Y, Meng X, Atsuta M (2007) Mechanical properties of dual-cured resin luting agents for ceramic restoration. J Prosthodont 16(5):370–376. doi:10.1111/j.1532-849X.2007.00221.x 10. Akyil MS, Uzun IH, Bayindir F (2010) Bond strength of resin cement to yttrium-stabilized tetragonal zirconia ceramic treated with air abrasion, silica coating, and laser irradiation. Photomed Laser Surg 28(6):801–808. doi:10.1089/pho.2009.2697 11. Azimian F, Klosa K, Kern M (2012) Evaluation of a new universal primer for ceramics and alloys. J Adhes Dent 14(3):275–282. doi:10. 3290/j.jad.a22193 12. Chen L, Suh BI, Kim J, Tay FR (2011) Evaluation of silica-coating techniques for zirconia bonding. Am J Dent 24(2):79–84 13. de Oyague RC, Monticelli F, Toledano M, Osorio E, Ferrari M, Osorio R (2009) Influence of surface treatments and resin cement selection on bonding to densely-sintered zirconium-oxide ceramic. Dent Mater 25(2):172–179. doi:10.1016/j.dental.2008.05.012 14. Foxton RM, Cavalcanti AN, Nakajima M, Pilecki P, Sherriff M, Melo L, Watson TF (2011) Durability of resin cement bond to aluminium oxide and zirconia ceramics after air abrasion and laser treatment. J Prosthodont 20(2):84–92. doi:10.1111/j.1532-849X.2010.00678.x 15. Koizumi H, Nakayama D, Komine F, Blatz MB, Matsumura H (2012) Bonding of resin-based luting cements to zirconia with and without the use of ceramic priming agents. J Adhes Dent 14(4):385– 392. doi:10.3290/j.jad.a22711 16. Lin J, Shinya A, Gomi H (2010) Effect of self-adhesive resin cement and tribochemical treatment on bond strength to zirconia. Int J Oral Sci 2(1):28–34 17. Phark JH, Duarte S Jr, Hernandez A, Blatz MB, Sadan A (2009) In vitro shear bond strength of dual-curing resin cements to two different high-strength ceramic materials with different surface texture. Acta Odontol Scand 67(6):346–354. doi:10.1080/00016350903074525 18. Piascik JR, Swift EJ, Braswell K, Stoner BR (2012) Surface fluorination of zirconia: adhesive bond strength comparison to commercial primers. Dent Mater 28(6):604–608. doi:10.1016/j.dental.2012.01. 008 19. Yoshida T, Ito M, Platt JA (2012) Mechanical properties and resin bond strength of surface-treated zirconia. Dent Mater 28 (Supplement 1):e38. doi:10.1016/j.dental.2012.07.092 20. Inokoshi M, Kameyama A, De Munck J, Minakuchi S, Van Meerbeek B (2013) Durable bonding to mechanically and/or chemically pre-treated dental zirconia. J Dent 41(2):170–179. doi:10. 1016/j.jdent.2012.10.017 21. Symynck J, De Bal F (2011) Monte Carlo pivotal confidence bounds for Weibull analysis, with implementations in R. New Technologies and Products in Machine Manufacturing Technologies 18(1):43–50 22. Blatz MB, Sadan A, Kern M (2003) Resin-ceramic bonding: a review of the literature. J Prosthet Dent 89(3):268–274. doi:10.1067/mpr. 2003.50
23. Della Bona A, van Noort R (1995) Shear vs. tensile bond strength of resin composite bonded to ceramic. J Dent Res 74(9):1591–1596 24. Denry I, Kelly JR (2008) State of the art of zirconia for dental applications. Dent Mater 24(3):299–307. doi:10.1016/j.dental.2007. 05.007 25. El Zohairy AA, De Gee AJ, Mohsen MM, Feilzer AJ (2003) Microtensile bond strength testing of luting cements to prefabricated CAD/CAM ceramic and composite blocks. Dent Mater 19(7):575–583 26. De Munck J, Mine A, Poitevin A, Van Ende A, Cardoso MV, Van Landuyt KL, Peumans M, Van Meerbeek B (2012) Meta-analytical review of parameters involved in dentin bonding. J Dent Res 91(4): 351–357. doi:10.1177/0022034511431251 27. Kosmac T, Oblak C, Jevnikar P, Funduk N, Marion L (2000) Strength and reliability of surface treated Y-TZP dental ceramics. J Biomed Mater Res 53(4):304–313 28. Zhang Y, Lawn BR, Rekow ED, Thompson VP (2004) Effect of sandblasting on the long-term performance of dental ceramics. J Biomed Mater Res B 71(2):381–386. doi:10.1002/jbm.b.30097 29. Basu B, Tiwari D, Kundu D, Prasad R (2009) Is Weibull distribution the most appropriate statistical strength distribution for brittle materials? Ceram Int 35(1):237–246. doi:10.1016/j.ceramint.2007.10.003 30. Quinn JB, Quinn GD (2010) A practical and systematic review of Weibull statistics for reporting strengths of dental materials. Dent Mater 26(2):135–147. doi:10.1016/j.dental.2009.09.006 31. Weibull W (1951) A statistical distribution function of wide applicability. J Appl Mec 18:293–297 32. Heikkinen TT, Lassila LV, Matinlinna JP, Vallittu PK (2007) Effect of operating air pressure on tribochemical silica-coating. Acta Odontol Scand 65(4):241–248. doi:10.1080/00016350701459753 33. Heikkinen TT, Matinlinna JP, Vallittu PK, Lassila LVJ (2010) Effect of primers and resins on the shear bond strength of resin composite to zirconia. SRX Dentistry 2010:1–8. doi:10.3814/2010/295137 34. Kumbuloglu O, Lassila LV, User A, Vallittu PK (2006) Bonding of resin composite luting cements to zirconium oxide by two air-particle abrasion methods. Oper Dent 31(2):248–255. doi:10.2341/05-22 35. Xie ZG, Meng XF, Xu LN, Yoshida K, Luo XP, Gu N (2011) Effect of air abrasion and dye on the surface element ratio and resin bond of zirconia ceramic. Biomed Mater 6(6):065004. doi:10.1088/17486041/6/6/065004 36. Chen L, Suh BI, Brown D, Chen X (2012) Bonding of primed zirconia ceramics: evidence of chemical bonding and improved bond strengths. Am J Dent 25(2):103–108 37. Yoshida K, Tsuo Y, Atsuta M (2006) Bonding of dual-cured resin cement to zirconia ceramic using phosphate acid ester monomer and zirconate coupler. J Biomed Mater Res B 77(1):28–33. doi:10.1002/ jbm.b.30424 38. Atsu SS, Kilicarslan MA, Kucukesmen HC, Aka PS (2006) Effect of zirconium-oxide ceramic surface treatments on the bond strength to adhesive resin. J Prosthet Dent 95(6):430–436. doi:10.1016/j. prosdent.2006.03.016 39. Tanaka R, Fujishima A, Shibata Y, Manabe A, Miyazaki T (2008) Cooperation of phosphate monomer and silica modification on zirconia. J Dent Res 87(7):666–670 40. Poitevin A, De Munck J, Cardoso MV, Mine A, Peumans M, Lambrechts P, Van Meerbeek B (2010) Dynamic versus static bond-strength testing of adhesive interfaces. Dent Mater 26(11): 1068–1076. doi:10.1016/j.dental.2010.07.007
