Bonding between layering materials and zirconia frameworks

Japanese Dental Science Review (2012) 48, 153—161

Available online at www.sciencedirect.com

journal homepage: www.elsevier.com/locate/jdsr

Review Article

Bonding between layering materials and zirconia frameworks ¨rg R. Strub b, Hideo Matsumura a Futoshi Komine a,*, Jo a

Department of Fixed Prosthodontics, Nihon University School of Dentistry, 1-8-13, Kanda-Surugadai, Chiyoda-Ku, Tokyo 101-8310, Japan b Department of Prosthodontics, Albert-Ludwigs University, Hugstetter Strasse 55, 79106 Freiburg, Germany Received 14 December 2011; received in revised form 30 May 2012; accepted 3 June 2012

KEYWORDS Bond strength; Indirect composite; Layering; Porcelain; Zirconia

Summary The availability of zirconium dioxide (zirconia) ceramics in dentistry has expanded the range of designs and applications for all-ceramic restorations and increased its popularity. This article reviews the literature on the bond strength between layering materials and zirconia frameworks used in dental restorations. Database searches were conducted for in vitro studies of bond strength between layering materials and zirconia frameworks. The search was carried out in different electronic databases, supplemented by handsearch in dental journals and by examination of the bibliographies of the retrieved articles. A variety of studies on bond strength was identified, including comparisons with metal—ceramic systems and studies on mismatched coefficients of thermal expansion, the use of press-on ceramics or liner materials, and the effect of cooling time after firing. The available data provide considerable information on achieving stable layering of material/zirconia composites. However, only a few in vitro studies on bond strength between indirect composites and zirconia were identified. Such studies and additional controlled clinical trials are needed. # 2012 Japanese Association for Dental Science. Published by Elsevier Ltd. All rights reserved.

Contents 1. 2. 3. 4.

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bond strength between layering porcelain and zirconia ceramics. . . . . . . . . Bond strength between indirect composite materials and zirconia ceramics Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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* Corresponding author. Tel.: +81 3 3219 8145; fax: +81 3 3219 8351. E-mail address: [email protected] (F. Komine). 1882-7616/$ — see front matter # 2012 Japanese Association for Dental Science. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jdsr.2012.06.001

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154

1. Introduction During the past decade, zirconium dioxide (zirconia) ceramics have seen increasing usage as a framework material for all-ceramic restorations. Their use in dentistry was made possible by the CAD/CAM technology [1]. Clinical studies of zirconia-based all-ceramic restorations have shown promising clinical results and high survival rates [2—19]. However, chipping and fracturing of layering porcelains applied to zirconia frameworks continue to be a problem, with a reported incidence between 0 and 30% [2—18]. Porcelain chipping and fracture can be disappointing for clinicians and patients, and should be regarded as a serious problem. Although simple polishing of the rough margins or repair of the fracture with composite material may suffice in some cases, patients occasionally require total replacement of the restoration. Several causes of porcelain chipping and fracture have been proposed, including mechanical insufficiency of the layering porcelain, inappropriate framework support for the layering porcelain, coefficient of thermal expansion (CTE) mismatch, and unfavorable shear forces between the zirconia framework and layering materials [19]. Studies have indicated that the mechanical integrity and bonding of the layering porcelain to the framework material are key factors in the successful performance of veneer/ framework bilayered restorations [3,20]. This article reviews the literature on the bonding potential between layering materials and the zirconia framework of zirconia-based restorations. A search of electronic databases such as PubMed was conducted, involving in vitro studies that were published between 1966 and the present date. The reference lists of retrieved articles were screened for additional candidate publications. In addition to the database searches, relevant articles, abstracts, and proceedings were handsearched through 1990.

2. Bond strength between layering porcelain and zirconia ceramics Feldspathic porcelain is generally used for veneering zirconia frameworks in all-ceramic restorations. Numerous in vitro studies of the bond strength between layering porcelain and zirconia ceramics have been published in the last decade (Table 1). Metal—ceramic systems have proven to be a reliable option for fixed prosthodontics and remain the gold standard [21,22]. In metal—ceramic restorations, a bond strength greater than 25 MPa between the layering porcelain and metal is believed to be adequate according to the International Standards Organization (ISO) [23]; however, no such estimate for adequate bond strength in all-ceramic materials has been determined. Several test methods namely, shear bond, three- and fourpoint flexure, tensile, and microtensile bond tests have been suggested for bond strength evaluation of veneering porcelain to frameworks. It is important that the bonding interface between veneering porcelain and frameworks should be the stressed region, regardless of the test method being employed. Shear bond tests have been reported as one of the most prevalent bond strength tests in the literature [24— 34]. On the other hand, other articles recommended the use of tensile or microtensile tests to eliminate the occurrence of

F. Komine et al. non-uniform interface stresses [20,35]. Each test method has its advantages and disadvantages, but a common limitation of the most test methods is the difficulty to determine the bond strength from the applied force at failure on the specimen in the specific test setup [32,36]. Shear bond test has been criticized for the development of non-homogeneous stress distributions in the bonding surface [37]. In addition, the elastic modulus of bonding can affect the results of shear bond tests. Increasing the elastic modulus will result in a more uniform distribution of stress over the bonded area, and avoid a concentration of stress at the point of load application. Three and four-point flexure tests have been criticized since maximal tensile stresses were created at the surface of porcelain and resulted in predictable tensile failures [38]. Tensile tests also present some limitations such as difficulty with specimen geometry and a tendency for non-homogeneous stress distribution at the adhesive interfaces with tensile or microtensile test alone [37,39]. Moreover, a possibility of notching on the external surface of porcelain could result in irregular stress distribution with cohesive failures within the porcelain. Failure mode of specimens after bond tests is often cohesive within the ceramic base rather than at the adhesive interface [37,40]. As bonding materials and techniques improved, the bond strengths became high enough to cause cohesive failures in ceramic base. When the fracture initiates away from the interface, the bond strength exceeds the cohesive strength of the porcelain. This can ignore the nature of the stresses generated and their distribution within the interface between materials. Therefore, a careful examination of bond strength tests should be needed for correct interpretation of the bond strength data. A review article [41] regarding the dentin bonding recommended adhesive failures or mixed failures with small (<10%) in the composite specimens should be considered for the bond strength calculation. All broken specimens that show cohesive failure in dentin or resin composite should be discarded as these data are not representative of interface bond strength. Thus, microscopic evaluation of the fractured surfaced should be necessary. In addition, Scherrer et al. [41] recommended a fracture mechanics approach for interfacial bond assessment between the materials. Fracture toughness (KIc), which is the material’s resistance to crack propagation, or the strain energy release rate (GIc) is a test that true interfacial failure within minimal cohesive failures in dentin or resin. Thus, these tests are conceived more beneficial to measure the energy or work to separate the adhesive material for its bond to ceramics [41]. A number of studies compared zirconia-based and metal— ceramic restorations with respect to the bond strength between layering porcelain and the framework material, but the findings are conflicting [32,33,42—44]. Three articles verified that the shear bond strength of layering porcelain to zirconia and metal frameworks was similar [32,43,44]. In the study, the shear bond strength was dependent on the shear strength of the layering porcelain [43]. However, other studies reported that the bond strength in patients with zirconia-based restorations was greater than in those with metal—ceramic restorations [33,42]. These contradictory findings might be due to differences in testing methods, study design, and the properties of the different materials used [42,43].

Studies of bond strength values between layering porcelain and zirconia frameworks.

Study

Ref.

Zirconia material

Manufacturer

Layering porcelain

Manufacturer

Bond strength values [MPa]

Test method

Al-Dohan et al. (2004)

[32]

Procera AllZircon DC-Zirkon Lodestar

Nobel Biocare DCS Dental Ivoclar Vivadent

Cerabien CZR VITA D Noritake

Noritake VITA Noritake

28.03 27.90 30.16

Shear bond test

Aboushelib et al. (2006)

[46]

Cercon Base

DeguDent

Cercon Ceram S Cercon Ceram Express Nobel Rondo Zirconia Lava Ceram Sakura Interaction

DeguDent DeguDent Nobel Biocare 3M ESPE Elephant Dental

17.2 38.6 41.1 30.9 19.9

Microtensile bond test

Aboushelib et al. (2008)

[35]

Cercon Base

DeguDent

Cercon ceramkiss Nobel Rondo Zirconia None

DeguDent Nobel Biocare

36.6 (with press-on ceramics) 36.7 (with press-on ceramics) 34.4 (with press-on ceramics)

Microtensile bond test

Aboushelib et al. (2008)

[60]

Cercon Base white Cercon Base yellow Lava Ceram white Lava Ceram yellow Procera Zirconia

DeguDent DeguDent 3M ESPE 3M ESPE Nobel Biocare

Microtensile bond test

Nobel Biocare

42.4 24.3 29.7 20.8 49.8

Cercon Base white Cercon Base yellow Lava Ceram white Lava Ceram yellow Procera Zirconia

DeguDent DeguDent 3M ESPE 3M ESPE Nobel Biocare

Cercon Ceram S

DeguDent

37.9 17.2 36.1 16.8 39.1

Lava Frame

3M ESPE

Lava Ceram

3M ESPE

Olympia

Jelenko

IPS d.SIGN

Ivoclar Vivadent

Cercon Base

DeguDent

Cercon Ceram S

DeguDent

Ashkanani et al. (2008)

Guess et al. (2008)

Fischer et al. (2009)

[42]

[33]

[34]

Nobel Rondo

VITA In-Ceram YZ Cubes DC-Zirkon

VITA

VITA VM9

VITA

DCS Dental

IPS e.max Ceram

Ivoclar Vivadent

DeguDent U94

DeguDent

VM13

VITA

VITA In-Ceram YZ Cubes

VITA

Wieland Noritake Metalordental

Shear bond test

9.4 9.6 12.8 9.7 11.5 11.5 27.6 26.4

Shear bond test

27.7 27.6 24.4

(after 20,000 thermocycles) (after 20,000 thermocycles) (after 20,000 thermocycles) (after 20,000 thermocycles)

Shear bond test

155

Allux Cerabien ZR Creation ZI

42.45 52.76 (after 5,000 thermocycles) 91.91 82.00 (after 5,000 thermocycles)

Bonding between layering materials and zirconia frameworks

Table 1

156

Table 1 (Continued )

Study

Nakamura et al. (2009)

Ref.

[74]

Zirconia material

Lava Frame

Manufacturer

3M ESPE

Layering porcelain

Manufacturer

Bond strength values [MPa]

Reflex IPS e.max Ceram Initial ZR Lava Ceram Rondo Zirconia Triceram Vintage ZR VITA VM9 Zirox

Wieland Ivoclar Vivadent GC 3M ESPE Nobel Biocare Dentaurum Shofu VITA Wieland

0.0 23.5 25.3 24.2 21.9 31.0 23.7 30.8 22.6

Vintage ZR

Shofu

Cerabien ZR Cercon Ceram S

Noritake DeguDent

22.0 27.8 44.3 40.2 37.8 49.5

(no sandblasting) (0.2 MPa) (0.4 MPa) (0.6 MPa) (0.4 MPa) (0.4 MPa)

Test method

Tensile bond test

[75]

Zirconzahn Cercon Base Lava Frame DC-Zirkon

Steger DeguDent 3M ESPE DCS Dental

Ice Keramik Cercon Ceram S Lava Ceram TriCeram

Steger DeguDent 3M ESPE Esprident

24.46 20.19 27.11 40.49

Shear bond test

Saito et al. (2010)

[43]

Katana Zirconia

Noritake

DeguDent

Noritake DeguDent Ivoclar Vivadent Shofu VITA Noritake

27.0 22.0 22.1 24.8 30.9 25.2

Shear bond test

DeguDent U

Cerabien ZR Cercon ceramkiss IPS e.max Ceram Vintage ZR VITA VM9 Super Porcelain AAA

Katana Zirconia

Noritake

Cerabien ZR

Noritake Ivoclar Vivadent

(cooling (cooling (cooling (cooling

time time time time

0 min) 4 min) 0 min) 4 min)

Shear bond test

IPS e.max Ceram

27.5 27.0 22.1 27.5

Lava Ceram

3M ESPE Dentaurum

VITA VM9

VITA

Zirox

Wieland

(cooling (cooling (cooling (cooling (cooling (cooling (cooling (cooling

time time time time time time time time

0 min) 5 min) 0 min) 5 min) 0 min) 5 min) 0 min) 5 min)

Four-point bending test

Triceram

8.2 7.5 13.3 9.8 17.1 13.0 12.8 11.6

Cerabien ZR

Noritake

Komine et al. (2010)

Go ¨stemeyer et al. (2010)

Suese (2010)

[58]

[57]

[44]

Lava Frame

3-Y Zirconia

3M ESPE

Japan Fine Ceramics

31.5 (sandblasted with 50 mm Al2O3)

Shear bond test

F. Komine et al.

¨ zkurt et al. (2010) O

Shear bond test 28.8 Ivoclar Vivadent IPS e.max Ceram Ivoclar Vivadent [76] Ereifej et al. (2011)

IPS e.max ZirCAD

Shear bond test 36.63 (airborne-particle abrasion) 27.87 (application of liner porcelain) Noritake Cerabien ZR KaVo [52] Kim et al. (2011)

Kavo Everest ZS

40.41 30.03 21.34 47.18 Ivoclar Vivadent Ivoclar Vivadent VITA VITA IPS e.max ZirPress IPS e.max Ceram VITA PM9 VITA VM9 3M ESPE [49] Ishibe et al. (2011)

Lava Frame

27.1 (sandblasted with 100 mm Al2O3) 32.1 24.5 Noritake Shofu DeguDent Shofu DeguDent U Uni-metal EZ

Super Porcelain AAA Vintage Hallow

Manufacturer Zirconia material Ref. Study

Table 1 (Continued )

Layering porcelain

Manufacturer

Bond strength values [MPa]

Test method

Shear bond test

Bonding between layering materials and zirconia frameworks

157 To achieve a strong bond, the CTE of the framework material and layering porcelain should closely match. In metal— ceramic systems, a layering porcelain with a slightly lower CTE than that of the framework material is recommended [24,45]. The use of a framework material with a slightly higher CTE results in a desirable residual compressive stress in the layering porcelain. To prevent chipping and cracking of the layering porcelain, manufacturers have developed specific products that have CTEs slightly lower than or identical to those of zirconia ceramics [46]. The use of a layering porcelain with a higher CTE than that of the zirconia framework results in veneer delamination and extensive microcrack formation [20,43]. A CTE mismatch of approximately 2.0  10 6/8C between the zirconia framework and layering material resulted in spontaneous debonding of the layering porcelain after firing [20,34,43]. However, the shear bond strength of zirconia/veneer composites did not differ with a CTE mismatch from 0.75 to 1.7  10 6/8C [33]. Furthermore, other studies found no correlation between shear bond strength and CTE mismatch of zirconia and layering porcelain [34,43]. Although the ideal CTE between the zirconia framework and layering porcelain has not been established, the layering porcelain must have a slightly lower CTE than that of the zirconia framework to ensure a sufficient bond. The pressing technique used for layering ceramics allows for the creation of the desired tooth anatomy and minimizes firing shrinkage associated with manual layering [47]. In addition, using the pressing technique can prevent porcelain chipping due to the higher tensile strength of press-on veneers and the superior quality of the interface [46]. Several studies compared the bond strength of press-on and layering porcelain to zirconia frameworks [46,48,49]. The application of press-on veneer ceramics directly onto airborne-particle—abraded surfaces is recommended and reduces the chances of chipping and fracture [46,48]. In addition, one study showed that the shear bond strength between layering porcelain and zirconia was equivalent to that between press-on ceramics and zirconia frameworks [49]. However, excellent esthetic outcomes are more difficult to achieve with the pressing technique, because appearance depends on precolored ceramic ingots. To resolve these shortcomings, a double-veneer technique was introduced for single restorations. Here, a layering porcelain is applied over a previously pressed-on veneer [35]. The microtensile bond strength of zirconia and press-on veneer ceramic doublelayered porcelain was comparable to that of zirconia veneered with the press-on ceramic alone. The doubleveneer technique combines the high bond strength and superior interface quality of press-on ceramics with the excellent esthetics of layering porcelain [35]. A ceramic liner material is frequently used to mask the white color of zirconia frameworks and improve the bonding between the framework and layering porcelain. There are some reports of negative effects on bond strength due to the use of such liner materials [50—52]. In addition, they should not be used in combination with press-on ceramics, as this will decrease the bond strength [46]. These results might be due to the generally lower strength of liners as compared to dentin ceramics. However, there is also evidence to the contrary: a few studies showed that the application of a liner material instead enhances the bond strength between some layering porcelains and a zirconia framework [20,46].

158

Table 2

Studies of bond strength values between layering indirect composite materials and zirconia frameworks.

Study

Ref.

Zirconia material

Layering indirect composite material

Surface treatment

Bond strength values [MPa]

Test method

Kobayashi et al. (2009)

[61]

Katana Zirconia (Noritake)

Estenia C&B (Kuraray Medical)

No treatment All Bond 2 Primer B (Bisco) Alloy primer (Kuraray Medical) Clearfil Ceramic Primer (Kuraray Medical) Clearfil Photo Bond (Kuraray Medical) Clearfil Photo Bond + Activator (Kuraray Medical) Estenia Opaque Primer (Kuraray Medical) Porcelain Liner M Liquid A (Sun Medical) V-Primer (Sun Medical)

0.2 10.1 15.6 19.8 21.6 24.2 14.7 11.9 0.1

Shear bond test

Komine et al. (2009)

[62]

Katana Zirconia (Noritake)

Estenia C&B (Kuraray Medical)

All Bond 2 Primer B (Bisco) Alloy primer (Kuraray Medical) AZ Primer (Shofu Inc.) Estenia Opaque Primer (Kuraray Medical) Porcelain Liner M Liquid A (Sun Medical)

4.3 17.6 17.3 15.5 12.2

Chihaya et al. (2010)

[63]

Procera Zirconia (Nobel Biocare) Procera Alumina (Nobel Biocare) Titan 100 (Shofu)

(Kuraray

Add-on primer + Modeling liquid (Kuraray Medical)

22

(Kuraray

Add-on primer + modeling liquid (Kuraray Medical)

28

(Kuraray

Estenia Opaque Primer (Kuraray Medical)

36

Casting gold M. C. Type IV (GC)

Estenia C&B Medical) Estenia C&B Medical) Estenia C&B Medical) Estenia C&B Medical)

(Kuraray

Alloy primer (Kuraray Medical)

22

(5000 (5000 (5000 (5000 (5000

thermocycles) thermocycles) thermocycles) thermocycles) thermocycles)

Shear bond test

Tensile bond test

Miyaji K et al. (2010)

[64]

Aadva Zr (GC)

Gradia (GC)

No treatment Espe Sil (3M ESPE) Rocatec + Espe Sil (3M ESPE)

2.3 8.9 15.7

Shear bond test

Hatta et al. (2011)

[65]

YTZ (Nikkato)

Estenia C&B (Kuraray Medical)

S3 Bond (Kuraray Medical) Rocatec + Espe Sil (3M ESPE)

10.7 12.5

Shear bond test

Fushiki et al. (2011)

[66]

Katana Zirconia (Noritake)

Estenia C&B (Kuraray Medical)

Zirconia coated with porcelain No treatment Clearfil Photo Bond (Kuraray Medical) Clearfil Photo Bond + Activator (Kuraray Medical) Estenia Opaque Primer (Kuraray Medical) Porcelain Liner M Liquid B (Sun Medical) Clearfil Photo Bond (Kuraray Medical) Clearfil Photo Bond + Activator (Kuraray Medical) Estenia Opaque Primer (Kuraray Medical) Porcelain Liner M Liquid B (Sun Medical)

13.8 14.6 18.2 14.5 17.3 15.8 23.2 16.2 21.0

Shear bond test

thermocycles) thermocycles) thermocycles) thermocycles)

F. Komine et al.

(20,000 (20,000 (20,000 (20,000

Bonding between layering materials and zirconia frameworks Thermocycling did not affect shear bond strength in studies on the durability of the bond between layering porcelain and zirconia ceramics [33,42]. This stability of the bond strength is consistent with the findings of previous studies of the bonding of porcelain to metal frameworks [42,53]. Zirconia has lower thermal conductivity than other framework materials used for fixed dental restorations. Excessive tempering tensile stresses might develop within the layering porcelain due to an increased thermal gradient during the cooling process [54]. In metal—ceramic restorations, the degree of residual stress at the interface between the layering porcelain and metal framework depends on the thermal history of the porcelain firing [55]. Thus, the bond strength between the layering porcelain and metal framework might be more stable if controlled cooling rates are used after firing procedures [24,56]. Two in vitro studies assessed the effect of different cooling rates (rapid and slow) on the bond strength between layering porcelain and zirconia ceramics [57,58]. Go ¨stemeyer et al. showed that the bond strength after slow cooling (5 min cooling inside the furnace) was lower than that after rapid cooling (immediate removal from the furnace) [57]. However, a separate study showed that the shear bond strength was greater after slow cooling (4 min cooling outside the furnace) than after rapid cooling (immediate removal from the furnace) [58]. These conflicting findings are probably due to the different cooling and testing methods used in the two studies. Regarding the esthetic outcome, zirconia ceramics have the considerable drawback of being essentially white and opaque. To resolve this issue, the use of mashing liner materials or an increase in veneer thickness was recommended. Colored zirconia frameworks have been introduced for better overall color matching of restorations. To color zirconia frameworks, specific pigments can be added to the initial zirconia ceramics, milled zirconia can be dipped in dissolved coloring agents, or liner material can be applied to the sintered zirconia framework [20,59]. One study investigated the effect of white and colored zirconia, and the surface treatment of the zirconia, on the bond strength to two layering porcelains [60]. The bond strength of airborneparticle—abraded white zirconia was significantly higher for both veneering materials compared to airborne-particle— abraded, colored zirconia. The effects of different surface treatments (as-milled, airborne-particle—abrasion, and liner application) on bond strength varied between white and colored zirconia [60].

3. Bond strength between indirect composite materials and zirconia ceramics

159 be achieved by using an acidic functional monomer containing carboxylic anhydride, phosphonic acid, or phosphate monomer [62]. On the other hand, one study revealed that there were no significant differences between surface treatments for shear bond strength of layering hybrid resin to zirconia ceramics [65]. The authors recommended adequate silane coupling treatment and bonding are needed when using hybrid composite as a veneering material. To fuse a feldspathic porcelain to the zirconia framework and then apply an indirect composite material with the respective silanization and bonding protocols might be advantageous for the durable bonds of indirect composite to zirconia ceramics [70,71]. Fushiki et al. [66] evaluated the effect of both feldspathic porcelain coating of zirconia frameworks and priming agents on the shear bond strength of an indirect composite material to zirconia ceramic frameworks, and the effect of artificial aging with thermocycling. The results suggested that feldspathic porcelain coating of zirconia frameworks is an effective method to obtain clinically acceptable bond strengths of a layering indirect composite material to a zirconia framework. Furthermore, the use of a silane coupling agent and opaque material yielded durable bond strength between the indirect composite and feldspathic-porcelain-coated zirconia. These results show that indirect composite application is a promising alternative to the layering techniqued for tooth- or implant-supported restorations [61]. However, several disadvantages of composite materials have been reported in the literature, including insufficient wear resistance [72], increased plaque accumulation [73], and surface degradation. Therefore, further laboratory studies and clinical trials are necessary before the clinical use of composite-layered zirconia restorations can be recommended. At present, compositelayered zirconia restorations are suitable for long-term provisional restorations of tooth- or implant-supported restorations.

4. Conclusion Numerous in vitro studies regarding the bond strength between layering materials and zirconia frameworks have been conducted for overcoming the chipping of layering porcelain of zirconia-based restorations. Various approaches to obtain the stable bond strengths are currently being developed. In addition, the development and testing of new materials and techniques are required to minimize chipping and fracturing of layering porcelain. Further studies should be needed to validate these protocols and to provide additional information of long-term clinical performance.

Conflict of interest statement An interesting method of layering an indirect composite material onto a zirconia framework was described in some recent studies [61—66] (Table 2). Dental composites exhibit plastic and viscoelastic effects, as well as susceptibility to creep and recovery [67,68]. These features of composite materials can provide functional advantages, especially in areas of high occlusal stress, such as implant-supported fixed restorations [69]. In a short-term in vitro study using a priming agent containing the functional monomer MDP, a superior bond strength between the indirect composite and zirconia framework was found [61]. Additionally, a durable bond strength can

The authors declare no conflict of interest.

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