ORIGINAL ARTICLE

J Appl Biomater Funct Mater 2015 ; 13 (1): 17 -27 DOI: 10.5301/jabfm.5000195

Effect of surface treatments on the bond strength of veneering ceramic to zirconia Fatih Mehmet Korkmaz1, Bora Bagis2, Sedanur Turgut1, Sabit Melih Ates3, Elif Aydogan Ayaz1 Department of Prosthodontics, Faculty of Dentistry, Karadeniz Technical University, Trabzon - Turkey Department of Prosthodontics, Faculty of Dentistry, Izmir Katip Celebi University, Izmir - Turkey 3 Department of Prosthodontics, Faculty of Dentistry, Recep Tayyip Erdogan University, Rize - Turkey 1 2

ABSTRACT Aim: The purpose of this study was to evaluate the effect of different surface treatments on the bond strength of veneering ceramic to zirconia. Methods: Square (15 mm x 10 mm x 2 mm) zirconia specimens (n=18) received one of the following surface treatments: Group 1, sandblasting; Group 2, Clearfil ceramic primer application; Group 3, grinding; Group 4, alloy primer application; and Group 5, RelyX ceramic primer application. The zirconia core specimens were layered with a veneering porcelain (5 mm x 3 mm x 3 mm). Mean shear bond strength values (MPa) were calculated. Data were analyzed with one-way ANOVA and Tukey’s post hoc pairwise comparisons (α=0.05). Fractured surfaces of the specimens were examined with scanning electron microscope (SEM). Results: This study showed that bond strengths of the metal primer-treated zirconia specimens (Group 4) were significantly higher than those of the other paired groups. The application of metal primer affected the specimens’ failure mode. SEM analysis demonstrated that Group 4 had mainly cohesive fractures, while the other groups showed approximately equal levels of adhesive and mixed fracture types. The mean and SD values for shear bond strengths ranged from 8.90 ± 3.42 MPa (Group 2) to 19.74 ± 4.96 MPa (Group 4). Conclusions: In conclusion, the application of a metal primer to a zirconia core increased the bond strength of veneering ceramics. The use of chemical agents to improve the strength of the zirconia core’s bond to veneering ceramic may have more benefits than the use of mechanical pretreatments. Key words: Bond strength, Ceramic, Surface treatment, Zirconia Accepted: October 11, 2013

INTRODUCTION Interest in zirconium oxide (zirconia) ceramics has shown significant growth in recent times and has the potential to have a major impact on the field of prosthodontics. Zirconia has been used as a metal-free alternative because of its mechanical properties, such as high flexural strength (1.0-1.2 GPa) and toughness (7-8 MPa m0.5), biocompatibility, chemical and structural stability, and optical properties (1-10). In particular, yttrium oxide partially stabilized tetragonal zirconia polycrystalline (Y-TZP) is among the most commonly used all-ceramic core materials, and it can be fabricated using the computer-aided design and computer-aided manufacturing (CAD-CAM) technique (2, 4, 6).

The dental literature contains a wide range of comprehensive systematic reviews focusing on the survival rates of all-ceramic restorations in comparison with metalceramic ones (2, 11). In comparison with all-ceramic restorations, which have a 93.3% survival rate, metal-ceramic prostheses have more favorable survival rates (95.6%) after 5 years of clinical use (2). Among the ceramic prosthesis types, zirconia-based prostheses have reportedly shown the best clinical performance and have been shown to be the most reliable all-ceramic system even after 5 years of observation (2, 11). Although other all-ceramic restorations show some framework fractures, zirconia is affected only by cracking or chipping of the veneering ceramic (2, 11, 12). After 3 and 5 years, 13.0% and 15.2% of patients, respectively, were found to have clinical failures in their

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Shear bond strength between ceramic and zirconia

veneered Y-TZP frameworks (i.e., chipping and/or delamination of veneering ceramic) (8, 13, 14). Hence, sufficient bond strength between the veneering ceramic and the substructure is considered an important factor in the longterm clinical success of zirconia restorations. Fischer et al (10) reported that the bond strength between zirconia and the veneering ceramic is determined by a range of factors, such as chemical bonds, mechanical interlocking, type and concentration of defects at the interface, wetting properties and the degree of compressive stress in the veneering layer because of the significant difference in the exponent factors of thermal expansion between zirconia and the ceramic. Because the adherence rate of the veneering ceramic to the zirconia substrate has proven to be a key factor in the long-term performance of zirconia restorations, the bond strength gained from in vitro investigations can provide useful information about the behavior and predictability of Y-TZP all-ceramic systems in clinical application (15). Many manufacturers and researchers have attempted to modify the surface properties of zirconia mechanically and chemically to improve its bonding via various surface treatments (6, 8, 10, 16-27). Recent studies were summarized in Table I. In several studies of zirconia ceramic bonding, airborne particle abrasion was used to increase the surface roughness and bonding to the veneering ceramic (17, 18, 32); however, the results of these studies are controversial. Teng et al (18) investigated the effects of different surface conditioning techniques on the bond strength and demonstrated that airborne particle abrasion did not create any significant differences in bonding to ceramic compared with other techniques. Kim et al (8) demonstrated that airborne particle abrasion resulted in significantly higher bond strengths than liner application did. Fischer et al (10) showed that increasing the surface roughness of zirconia and applying a liner did not enhance shear strength. Another study by Fischer et al (22) demonstrated that the use of a liner on Y-TZP cores had no significant effect on bond strength. Although Mosharraf et al (21) showed that the type of zirconia did not have any effect on the bond strength between the zirconia core and the veneer ceramic, grinding dramatically decreased the shear bond strength of white zirconia porcelain. To mask the framework and to increase the wetting property of the zirconia surface, liners can be applied as an intermediate layer between the zirconia substrate and the veneering ceramic. Contrary to some studies that showed that liner application improves the bond strength between the zirconia and resin cements (7, 16, 28), other reports have claimed that this application has no effect on the bond strength between the zirconia and the veneering ceramic and may even weaken it (8, 17, 22). In comparison, various adhesive monomers, such as metal primers, have been developed to permit chemical 18

bonding. An alloy primer composed of 10-methacryloyloxydecryl dihydrogen phosphate (MDP) and 6-(4-vinylbenzyl-n-propyl amino)-1,3,5-triazine-2,4-dithione (VBATDT) in acetone improves the bonding to air-abraded oxide ceramics (7, 16, 19). Metal primers usually bond to pure metals and alloys because of their affinity to metal oxides on metal surfaces (29). Some studies have shown that a MDP monomer promotes bonding to air-abraded oxide ceramic (6, 7, 16, 28, 29). Nevertheless, the question of whether MDP monomer–containing primer can advance the bond between ceramic and zirconia remains unresolved. Other commercially available silane coupling agents exist that contain monomers like 3-methacryloxypropil trimethoxy silane, which are capable of bonding to zirconia. Although a previous study showed that the use of this agent without air abrasion did not promote long-term tensile bond strength (16), recent studies have shown that experimental silane monomer primers can significantly increase the bond strengths between resins and a zirconia surface which was coated with glass powder (30), or treated with tribochemical silica (31). Although manufacturers recommend airborne particle abrasion or liner application as surface treatments for zirconia, the effects of these methods have not yet to be clarified. The effect of metal and ceramic primers on the bond strength of zirconia to the veneering ceramic has not been demonstrated. Therefore, the aim of this study was to evaluate the effect of different surface treatments on bond strengths between Y-TZP ceramics and the veneering ceramic. The null hypothesis was that surface treatments might improve the shear bond strength between the zirconia and the ceramic. MATERIALS AND METHODS Preparation of specimens The materials used in this study are presented in Table II. One type of zirconia-based ceramic (Zirkonzahn; Steger, Ahrntal, Italy), 1 type of veneering ceramic (Vita VM9; Vita Zahnfabrik, Bad Sackingen, Germany) and 3 types of primer (Clearfil ceramic primer; Kuraray, Tokyo, Japan; RelyX ceramic primer; 3M ESPE, St. Paul, MN, USA; and alloy primer; Kuraray, Tokyo, Japan) were selected for this study. Pre-sintered Zirkonzahn zirconium oxide blocks were milled according to the manufacturer’s instructions. Sintering was performed at 1500°C in a furnace (Kavo Everest Therm; Kavo Dental GMBH) according to the cycle recommended by the manufacturer. Dense sintered blocks were cut in the green state using a low-speed diamond disc (Izomet 1000; Buehler, Lake Bluff, IL, USA). A total of 90 square zirconia specimens (15×10×2 mm) were produced (n=18). The bonding surfaces of the zirconia core specimens were polished, ground with 1,200-grit silicon

© 2014 Società Italiana Biomateriali - eISSN 2280-8000

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TABLE I - STUDY CHARACTERISTICS AND OUTCOMES OF THE RECENT STUDIES Authors (ref.)

Purpose

Materials & Methods

Results

Kim et al (2011) (8)

To examine the effects of various surface treatments on the shear bond strength of zirconia and ceramic

1. Zirconia surface treatment groups:   -grinding   -sandblasting   -liner application   -sandblasting and liner application 2.  Shear bond strength

Application of a liner increased the possibility of interfacial failure and sandblasting may be more useful for increasing bond strength than liner application

Ashkanani et al (2008) (9)

To evaluate the strength of zirconia and high-noble alloy with corresponding porcelains using flexural and shear tests

1. Specimens were divided into four groups:   -metal ceramic   -metal ceramic (thermal cycling)   -zirconia   -zirconia (thermal cycling) 2.  Shear bond strength

There was a significant difference between the metal ceramic and zirconia in terms of shear bond strength, regardless of thermal cycling. Thermal cycling did not affect the bond strength among the

Fischer et al (2008) (10)

To investigate the effect of polishing, sandblasting, silica coating, liner application, and regeneration firing on the bond strength of zirconia to 5 different ceramic.

1.  Zirconia surface treatment groups:   -polishing   -sandblasting   -silica-coating   -liner application   -regeneration firing 2. Surface roughness and surface morphology 3.  Shear bond strength

Bonding between veneering ceramic and zirconia may be based on chemical bonds. Increased surface roughness of zirconia did not improve bond strength. Sandblasting and liner application did not enhance shear bond strength.

Kern et al (2009) (16)

To evaluate the influence of air-abrasion and primers on the long-term resin bond strength to zirconia ceramic.

1.  Zirconia surface treatment groups:   -No air abrasion   -Air abrasion (0.05 MPa)   -Air abrasion (0.25 MPa) 2. Each group was divided into 4 subgroups:   -no primer   -metal/zirconia primer   -alloy primer   -ceramic primer 3.  Thermal cycling 4.  Tensile bond strength

The combination of air-abrasion and priming is necessary to achieve durable long-term bonding of resin cement to zirconia. Air abrasion at lower pressures with appropriate adhesive primers appears to be an effective method for long-term strong durable bonds.

Harding et al (2012) (17)

To determine the effect of different surface treatments on the interfacial bond strength between the core and veneer of all-ceramic system, with and without cyclic loading.

1.  Zirconia surface treatment groups:   -airborne particle abrasion   -zirliner application   -no surface treatment 2.  Cyclic loading 3.  Micro tensile bond strength

While airborne particle abrasion of zirconia significantly decreased the micro tensile bond strength to ZirPress veneering ceramic when compared with no surface treatment, application of Zirliner does not significantly improve the bond strength. Cyclic loading did not affect bond strengths in any of the groups.

Teng et al (2012) (18)

To evaluate the effect of a simple and novel surface conditioning method on the bond strength of zirconia and veneering porcelain.

1. Specimens were divided into 4 groups:   -metal–ceramic group   -zirconia-ceramic groups   a. polishing   b. airborne particle abrasion   c. zirconia powder coating 2.  Shear bond strength

Zirconia powder coating created a porous zirconia ceramic, which significantly improved the bonding of porcelain to zirconia compared with polished surfaces.

1. Specimens were divided into 2 groups:   -white zirconia   -colored zirconia 2.  Zirconia surface treatment groups:   -no treatment   -sandblasting   -grinding   -sandblasting and liner application 3.  Shear bond strength

Type of zirconia does not have any effect on the bond strength of zirconia to porcelain. Surface treatments have different effects on the bond strength of the different types of zirconia. Grinding dramatically decreases the bond strength of white zirconia to veneering ceramic.

Mosharraf et al (2011) (21) To investigate the effect of different surface treatments and type of zirconia (white or colored) on the shear bond strength of zirconia core and veneering porcelain.

To be continued

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TABLE I - Continued Authors (ref.)

Purpose

Materials & Methods

Results

Fischer et al (2010) (22)

To evaluate the effect of different ceria-stabilized zirconia/alumina (Ce-TZP/A) substrate surface treatments on the bond strength of different veneering ceramic.

1. Ce-TZP/A specimens were layered with porcelain with or without liner application. Subsequently 2 different surface conditions were investigated:   -polishing   -sandblasting 2.  Shear bond strength

Sandblasting is not required to enhance the bond strength of veneering ceramics to Ce-TZP/A. The application of a liner decreases the shear bond strength of veneering ceramic to Ce-TZP/A.

Al-Dohan et al (2004) (25) To investigate the average shear strength of the core– veneer interface in bilayered all-ceramic systems and to compare metal ceramic with all-ceramic systems.

1. Groups:   -IPS-Empress2   -Procera AllCeram   -Procera AllZircon   -DC-Zircon   -metal ceramic 2.  Shear bond strength

The shear bond strength of the tested 3 of all-ceramic materials (IPS-Empress2, Procera AllZircon, DC-Zircon) were similar to that of the metal ceramic control group.

Aboushelib et al (2005) (26)

To evaluate the core-veneer bond strength of layered all-ceramic restorations, the influence of the surface finish of the core.

1.  Three systems:   -Cercon   -Vita Mark II   -IPS Empress 2 2.  Two surface treatments:   -surfaces were fabricated according to the manufacturer’s instructions   -surfaces were polished 3.  Microtensile bond strength 4.  Finite element analysis

Polishing the core surfaces did not have any effect on the core–veneer bond strength. The core–veneer bond strength is one of the weakest links of layered all-ceramic restorations.

Dias de Souza et al (2011) (28)

To examine if the combination of cement systems and metal primers would increase initial and long-term bond strength values.

1. Zirconia specimens were treated with different commercial primers:   -Metaltite   -Metal Primer II   -Alloy Primer   -Totalbond 2.  Two different resin cements:   -Panavia   -RelyXUnicem 3. Aging 4.  Microtensile bond strength

The use of Alloy Primer increased the bond strength of RelyXUnicem to zirconia. Although Panavia showed higher bond strength than RelyXUnicem initially, both resin cements achieved similar results after 5 months.

Yoshida et al (1997) (29)

To evaluate the durability and shear bond strengths of the 2 different adhesive primers and 3 resin cements to 2 types of noble metal alloys.

1.  Resin cements:   -Imperva Dual   -Panavia 21   -Super-Bond C&B 2.  Adhesive primers   -metal primer   -V-Primer 3.  Metal alloys:   -silver-palladium copper-gold   -Type IV gold alloys 4.  Thermal cycling 5.  Shear bond strength

Metal primer and V-Primer are effective for improving the shear bond strength of adhesive resin cements to noble metal alloys.

Aboushelib et al (2008) (30)

To evaluate the MDP resin composite bond strength to zirconia using selective infiltration etching and novel silane-based zirconia primers.

1.  Different surface treatments:   -selective infiltration etching   -as-sintered 2. Five different experimental zirconia primers 3.  Microtensile bond strength

The combination of selective infiltration etching and novel experimental zirconia primers resulted in significant improvement of zirconia–resin bond strength compared with the control. To be continued

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TABLE I - Continued Authors (ref.)

Purpose

Matinlinna et al (2011) (31) To examine the effect of 5 experimental silane monomer primers on the bond strength of a phosphate ester resincomposite cement bonded to a silicatized zirconia

Materials & Methods

Results

1. Zirconia specimens were subjected to tribochemical silica treatment 2.  Different primers   -five different experimental silane monomer primers   -one ceramic primer 3.  Thermal cycling 4.  Shear bond strength

Silanization with experimental silane primers produced significantly higher bond strengths after artificial aging than the ready-to-use control silane.

MDP = 10-methacryloyloxydecryl dihydrogen phosphate.

TABLE II - MATERIALS USED IN THIS STUDY Material name

Material type

Manufacturer

Composition

Clearfil ceramic primer

Silane-coupling agent

Kuraray, Tokyo, Japan

3-Methacryloxypropyl trimethoxysilane, MDP, ethanol

Alloy primer

Metal primer

Kuraray, Tokyo, Japan

VBATDT and MDP in acetone

RelyX ceramic primer

Silane

3M ESPE, St. Paul, MN, USA

3-Methacryloyloxypropyl trimethoxysilane, ethanol, water

Vita VM9

Feldspathic porcelain

Vita Zahnfabrik, Bad Sackingen, Germany

SiO2, Al2O3, Na2O, CaO, K 2O, TiO2, pigments

Zirkonzahn

Yttrium-stabilized zirconia

Steger, Ahrntal, Italy

ZrO2, Y2O3, Al2O3, SiO2, Fe2O3, Na2O

TEC*

9 10.5

MDP = 10-methacryloyloxydecryl dihydrogen phosphate; TEC = thermal expansion coefficient; VBATDT = 6-(4-vinylbenzyl-n-propyl amino)-1,3,5-triazine-2,4-dithione. *TEC in ppm/°C between 25°C and 500°C. ppm = parts-per-million, 10-6.

carbide abrasives under water cooling, and ultrasonically cleaned in distilled water for 5 minutes. Surface conditioning and the bonding procedure The specimens were randomly divided into 5 groups of 18 specimens each (n=18), which received the following treatments for the bonding surfaces: Group 1: The zirconia was sandblasted with 120-μm Al2O3 particles at 3.5 bar pressure for 10 seconds from a distance of 10 mm perpendicular to the surface. Group 2: The zirconia was treated with a single-component adhesive primer (Clearfil ceramic primer). Group 3: The zirconia was ground with a diamond bur with a 100-μm grain size (Bredent, Senden, Germany) at a speed of 20,000 rpm under water cooling. The bars were replaced after the grinding of every fifth specimen to maintain a consistent amount of grit. Group 4: The zirconia was treated with a metal primer (alloy primer).

Group 5: The zirconia was treated with a prehydrolyzed silane-based primer (RelyX ceramic primer). Each primer was applied to the bonding surface according to the manufacturers’ recommendations. The prepared zirconia specimens were placed in a separable stainless steel mold with a 5-mm clearance in the diameter and a 3-mm height above the core material to condense the veneer ceramic. The veneering procedure was performed using the manual layering technique. The intaglio surface of the mold was isolated (Ceramic Separating Stick; Ivoclar Vivadent AG, Schaan, Liechtenstein) to avoid the adhesion of ceramic powder to the mold during layering. The ceramic powder was mixed on a glass slab with an appropriate amount of the respective liquid, as is commonly done in a dental laboratory, and condensed into the mold. Only the dentin porcelain was layered, not the enamel porcelain. The veneering ceramic was fired according to the firing program of the manufacturer (Vita Vacumat 4000 Premium T; Vita Zahnfabrik, Bad Säckingen, Germany). After the first layer was fired, a second layer was applied. To compensate for firing shrinkage,

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the previous step was repeated to produce a final veneer thickness of 3 mm and a diameter of 5 mm. The final dimensions were measured with a digital micrometer (Mitutoyo Digimatic Caliper; Mitutoyo Corp., Kawasaki, Japan).

TABLE III - SHEAR BOND STRENGTH VALUES (IN MPa) AND FAILURE MODES, EXPRESSED AS PERCENTAGES Groups

Shear bond strength (MPa), means ± SD

Failure modes

Shear bond strength test

Group 1

11.64 ± 3.6A

40% adhesive 25% mixed 35% cohesive

Group 2

8.90 ± 3.42A

45% adhesive 20% mixed 35% cohesive

Group 3

11.59 ± 5.1A

45% adhesive 20% mixed 35% cohesive

Group 4

19.74 ± 4.96B

5% adhesive 10% mixed 85% cohesive

Group 5

10.50 ± 3.01A

40% adhesive 25% mixed 35% cohesive

Using acrylic resin (Meliodent; Heraeus Kulzer GmbH, Hanau, Germany), each specimen was embedded at the center of a metal ring holder 13 mm in height and 15 mm in diameter with the core–veneer interface positioned at the top level of the holder. These metal holders were then mounted in the jig of a universal testing machine (Model 4202; Instron Corp., Norwood, MA, USA). All of the specimens were tightened and stabilized to ensure that the edge of the shearing rod was positioned as close to the core–ceramic interface as possible. The load was applied parallel to the long axis of the specimen through a wedge at the core–veneer interface at a crosshead speed of 0.5 mm/min until the veneering ceramic was delaminated. The shear bond strength (S) values (expressed in MPa) were calculated using the formula S=L/A, where L is the load at failure (in N) and A is the adhesive area (in mm2) measured with a digital micrometer. Shear load at failure was recorded. The fractured specimens were examined for surface topography and further failure mode analysis using a scanning electron microscope (SEM; EVO L10; Carl Zeiss, Oberkochen, Germany). Digital pictures of these specimens were taken at various magnifications to evaluate the fracture surfaces and to verify the modes of failure. A failure between the zirconium and veneering ceramic was defined as an adhesive failure. A failure within either the framework or the veneering ceramic material was defined as a cohesive failure. The term mixed failure was used to describe the combination of these 2 failure types. Specific specimens were selected for the chemical surface structure of zirconia using energy-dispersive X-ray spectroscopy (EDS) analysis. Statistical analyses were performed with SPSS for Windows 15.0 (SPSS Inc., Chicago, IL, USA). The bond strength data obtained from the 5 groups were analyzed with a 1-way analysis of variance (ANOVA). Tukey’s post hoc test was used to detect pairwise differences among the groups at the confidence interval of 95%. RESULTS Shear bond strength The mean and standard deviation (SD) shear bond strength values of the test specimens are shown in Table III. The mean and SD values of the shear bond strengths ranged from 8.90 ± 3.42 MPa (group 2) to 19.74 ± 4.96 MPa (group 4). One-way ANOVA showed significant differences among the 5 groups (P group 3> group 5> group 2. The application of a metal primer also resulted in an increase in the bond strength (P

Effect of surface treatments on the bond strength of veneering ceramic to zirconia.

The purpose of this study was to evaluate the effect of different surface treatments on the bond strength of veneering ceramic to zirconia...
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