Long-term Storage Affects Adhesion Between Titanium and Zirconia Using Resin Cements Barbara Cvikla / Mirza Dragicb / Alexander Franzc / Modesto Raabeb / Reinhard Gruberd / Andreas Moritze
Purpose: To determine the impact of long-term storage on adhesion between titanium and zirconia using resin cements. Materials and Methods: Titanium grade 4 blocks were adhesively fixed onto zirconia disks with four resin cements: Panavia F 2.0 (Kuraray Europe), GC G-Cem (GC Europe), RelyX Unicem (3M ESPE), and SmartCem 2 (Dentsply DeguDent). Shear bond strength was determined after storage in a water bath for 24 h, 16, 90, and 150 days at 37°C, and after 6000 cycles between 5°C and 55°C. Fracture behavior was evaluated using scanning electron microscopy. Results: After storage for at least 90 days and after thermocycling, GC G-Cem (16.9 MPa and 15.1 MPa, respectively) and RelyX Unicem (10.8 MPa and 15.7 MPa, respectively) achieved higher shear bond strength compared to SmartCem 2 (7.1 MPa and 4.0 MPa, respectively) and Panavia F2 (4.1 MPa and 7.4 MPa, respectively). At day 150, GC G-Cem and RelyX Unicem caused exclusively mixed fractures. SmartCem 2 and Panavia F2 showed adhesive fractures in one-third of the cases; all other fractures were of mixed type. After 24 h (GC G-Cem: 26.0, RelyX Unicem: 20.5 MPa, SmartCem 2: 16.1 MPa, Panavia F2: 23.6 MPa) and 16 days (GC G-Cem: 12.8, RelyX Unicem: 14.2 MPa, SmartCem 2: 9.8 MPa, Panavia F2: 14.7 MPa) of storage, shear bond strength was similar among the four cements. Conclusion: Long-term storage and thermocycling differentially affects the bonding of resin cement between titanium and zirconia. Key words: titanium, zirconia, long-term storage, thermocycling, shear bond strength. J Adhes Dent 2014; 16: 459–464. doi: 10.3290/j.jad.a32809
D
ental implants have become an established treatment of tooth loss,18 and titanium has often been used as an abutment material to connect the implant with the prosthetic suprastructures.33 However, as esthetic demands have increased, ceramic abutments
a
Assistant Professor, Department of Conservative Dentistry and Periodontology, Medical University of Vienna, Vienna, Austria; Department of Preventive, Restorative and Pediatric Dentistry, University of Bern, Bern, Switzerland. Experimental design, performed the experiments, wrote the manuscript.
b
Dentist, Department of Conservative Dentistry and Periodontology, Medical University of Vienna, Vienna, Austria. Performed the experiments.
c
Researcher, Department of Conservative Dentistry and Periodontology, Medical University of Vienna, Vienna, Austria. Proofread manuscript, performed statistical evaluation.
d
Professor, Department of Oral Surgery, Medical University of Vienna, Vienna, Austria; Laboratory for Oral Cell Biology, University of Bern, Bern, Switzerland. Wrote the manuscript, contributed substantially to discussion.
e
Professor, Department of Conservative Dentistry and Periodontology, Medical University of Vienna, Vienna, Austria. Contributed substantially to discussion.
Correspondence: Reinhard Gruber, Department of Oral Surgery, Medical University of Vienna and Laboratory of Oral Cell Biology, School of Dental Medicine, University of Bern, Freiburgstrasse 7, CH-3010 Bern, Switzerland. Tel: +41-31632-8622. e-mail: [email protected]
Vol 16, No 5, 2014
Submitted for publication: 18.06.13; accepted for publication: 10.07.14
have been introduced.33 To combine the benefits of both materials, titanium is bonded to the ceramic part, with the latter typically being made of zirconia.4,38 Resin cements can provide an adhesive bond between titanium and ceramics,1,32 but if this bond fails, there is a risk of aspiration of the ceramic, bone loss, prosthetic fractures, and microbiological complications.26 Thus, longterm adhesion between titanium and ceramic is required for the preservation of the implant-abutment bond. The selection of the appropriate resin cement is of critical importance for the long-term prognosis of implants and prosthetic restorations.19,29 Resin cements were originally developed to provide adhesion not only between dental materials (eg, ceramics or composites) and dental hard tissue16 but also between dental materials.9,12,23 Cements based on polymers and fillers are available for the long-term fixation of prosthetic suprastructures27 and abutments24 in implant dentistry. Therefore, research on the long-term bond strength between titanium and zirconia and the influcence of different resin cements is clinically relevant. To predict the long-term bond strength of cemented joints, mechanical testing with resin cements has been 459
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Table 1
Cement materials, chemical compositions, and application mode
Material
Composition
Application mode
GC G-Cem (GC Europe; Leuven, Belgium)
4-methacryloxyethyltrimellitate anhydride (4-META), urethane dimethacrylate (UDMA), aluminosilicate glass, pigment, dimethacrylate, distilled water, phosphoric ester monomer, initiator, camphorquinone
GC G-Cem capsules were mixed in a high-frequency mixing device. Afterwards, the mixture was applied on surfaces, remaining excess was removed, and light curing was performed for 10 s using bluephase 20i.
Panavia F 2.0 (Kuraray Europe; Hattersheim am Main, Germany)
Paste A: 10-methacryloyloxydecyl dihydrogen phosphate, hydrophobic aromatic dimethacrylate, hydrophobic aliphatic methacrylate, hydrophilic aliphatic dimethacrylate, silanated silica filler, silanated colloidal silica, dl-camphorquinone, catalysts, initiators Paste B: Sodium fluoride, hydrophobic aromatic dimethacrylate, hydrophobic aliphatic methacrylate, hydrophilic aliphatic dimethacrylate, silanated barium glass filler, catalysts, accelerators, pigments ED Primer A: 2-hydroxyethyl methacrylate, 10-methacryloyloxydecyl dihydrogen phosphate, N-methacryloyl-5-aminosalicylic acid, water, accelerators ED Primer B: N-methacryloyl-5-aminosalicylic acid, water, catalysts, accelerators
Panavia F 2.0 pastes A & B were mixed for 20 s. Afterwards, it was applied onto surfaces previously treated with ceramic primer or ED Primer A and B. The remaining excess was removed, and light curing was performed for 20 s using bluephase 20i.
RelyX Unicem (3M ESPE; Seefeld, Germany)
Methacrylate monomers containing phosphoric acid groups, methacrylate monomers, initiator components, stabilizers, alkaline (basic) fillers, silanated fillers, initiator components, pigments
RelyX Unicem capsules were mixed in a high-frequency mixing device. Then the mixture was applied on surfaces, the remaining excess was removed, and light curing was performed for 40 s using bluephase 20i.
SmartCem 2 (Dentsply DeguDent; Hanau, Germany)
Urethane dimethacrylate, di- and tri-methacrylate resins, phosphoric acid modified acrylate resin, barium boron fluoroaluminosilicate glass, organic peroxide initiator, camphorquinone, photoinitiator, phosphene oxide photoinitiator, accelerators, butylated hydroxy toluene, UV stabilizer, titanium dioxide, iron oxide, hydrophobic amorphous silicon dioxide
SmartCem 2 cement was directly dispensed through a mixing tip. Then it was applied on surfaces, the remaining excess was removed, and light curing was performed for 40 s (bluephase 20i).
performed. For example, the bond strength of Panavia F 2.0 and RelyX Unicem on zirconia decreased after artificial aging.10,30 Moreover, GC G-Cem, RelyX Unicem, Panavia 21, and SmartCem 2 showed a distinct response to thermocycling when bonded to glass ceramics.20 The longterm bond to human hard dental tissue is influenced by various properties of resin cements, eg, water absorption, shrinkage behavior, physical properties, pH values, and film thickness.20,31 In addition, the effect of long-term water storage and thermocycling of cement bonded to laserprepared dentin has been examined.11 Overall, the data suggest that resin cements can affect the long-term bond strength between different dental materials. To our knowledge, however, no information is available on long-term bond strength between titanium and zirconia taking the influence of different resin cements into consideration. The purpose of the present study was to use the shear bond strength test to evaluate the influence of four resin cements on the bond strength between titanium and zirconia following long-term in vitro storage and thermocycling. Based on the current knowledge on long-term bond strength of cemented joints, the following hypothesis was posed: Different resin cements mediate different bond strengths between titanium and zirconia after long-term in vitro storage. 460
MATERIALS AND METHODS Sample Preparation Titanium grade 4 blocks (10 mm × 4 mm × 4 mm) and disks (diameter 3 mm, height 2 mm) made from zirconium dioxide (zirconia) were manufactured from the same materials that are clinically used in implant dentistry (Dentsply DeguDent; Hanau, Germany). A sample size calculation based on α = 0.05 and a power of 0.80 indicated that 300 samples were required. All samples were airborne-particle abraded with aluminum oxide particles with a diameter of 110 μm at 3 bar pressure from a distance of 10 mm. Four different resin cements were investigated (Table 1). Titanium blocks and zirconia disks were divided into four groups of 75 specimens each according to the resin cements (Panavia F 2.0, GC G-Cem, RelyX Unicem, and SmartCem 2). Resin cements were prepared and the bonding procedures between the titanium blocks and zirconia disks were performed following the respective manufacturer’s instructions. Storage and Thermocycling Specimens were subdivided into 5 groups (n = 15) for different storage conditions: water bath for 24 h at 37°C; water bath for 16 days at 37°C; water bath for The Journal of Adhesive Dentistry
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300 titanium blocks and 300 zirconium dioxide disks
airborn-particle abraded
75 samples
75 samples
75 samples
75 samples
Panavia F2.0
GC-G-CEM
RelyX Unicem
SmartCem 2
a b c d e
a b c d e
a b c d e
a b c d e
a
n = 15
37° 24h water bath
b
n = 15
c
n = 15
37°
d
37°
16d water bath
n = 15
37°
90d water bath
150d water bath
e
n = 15
5°
55°
6000 cycles thermocycling
Shear bond test Scanning electron microscopy Fig 1 Experimental procedure. Titanium blocks (n = 300) and zirconia disks (n = 300) were airborne-particle abraded and divided into four groups for the resin cements (Panavia F 2.0, GC G-Cem, RelyX Unicem, and SmartCem 2). After adhesively bonding the titanium blocks to the zirconia disks, the specimens were subdivided into 5 groups (n = 15) for different storage conditions (water bath for 24 h at 37°C; water bath for 16 days at 37°C; water bath for 90 days at 37°C; water bath for 150 days at 37°C and thermocycling for 6000 cycles at 5°C and 55°C). Shear bond strength testing and SEM evaluation of fracture behavior were performed.
90 days at 37°C; water bath for 150 days at 37°C and thermocycling for 6000 cycles at 5°C to 55°C. Mechanical Testing A universal testing machine (Zwick Roell; Ulm, Germany) with a crosshead speed of 1 mm/min was used to determine stress at failure. Force (in Newtons) at failure was divided by the bond area (mm2) yielding data in MPa. Since titanium and zirconia are both artificial Vol 16, No 5, 2014
and replicable materials, this study setting warrants a macroshear bond strength test.7,34 A flow chart of the experimental procedure is given in Fig 1. Evaluation of Fracture Behavior Adhesive surfaces were analyzed after debonding to identify failure mechanisms. Cement residues could be located on the titanium or zirconia surface (cohesive fracture behavior), on both surfaces (mixed fracture behavior), 461
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Table 2 Shear bond strength values (means ± standard deviations) of four different cements in different short- and long-term storage conditions Material
Storage conditions 24 h
16 days
90 days
150 days
Thermocycling
RelyX Unicem
20.5 ± 6.2
12.8 ± 2.9
10.8 ± 5.4
10.9 ± 5.8
15.7 ± 7.3
GC G-Cem
26.0 ± 5.6
14.2 ± 5.6
16.9 ± 4.9
12.7 ± 2.9
15.1 ± 7.3
Panavia F 2.0
23.6 ± 5.7
14.7 ± 6.2
4.1 ± 1.7
4.1 ± 2.2
7.4 ± 6.7
SmartCem 2
16.1 ± 4.9
9.8 ± 5.2
7.1 ± 3.8
5.9 ± 2.9
4.0 ± 2.5
40
**
** **
**
**
GC-G-CEM
**
RelyX Unicem Panavia F2.0
30
MPa
SmartCem 2 20
10
0 24 h
16 d
90 d
150 d
Fig 2 Mechanical testing after short- and long-term water storage. The shear bond strength of the samples cemented with GC G-Cem and RelyX Unicem was generally higher than that of the other samples. All cements showed their highest shear bond values after 24 h of water storage, which decreased significantly during longer storage (** p < 0.01).
40
** **
GC-G-CEM RelyX Unicem Panavia F2.0
30
MPa
SmartCem 2
20
or on neither surface (adhesive fracture behavior). Randomly selected samples of each group were qualitatively topographically examined with a scanning electron microscope (Hitachi 1000, Hitachi High-Technologies Europe; Krefeld, Germany) at 300X and 100X magnifications. Statistical Analysis Data were analyzed using the Kruskal-Wallis test and the Mann-Whitney U-Test (SPSS version 19.0; Chicago, IL, USA). A significant difference was defined as p < 0.05. No statistical analysis of the surface examination was performed.
10
RESULTS 0 TC
Fig 3 Mechanical testing after thermocycling representing simulated long-term storage. The shear bond strengths of GC G-Cem and RelyX Unicem after thermocycling for 6000 cycles were significantly higher than that of Panavia F 2.0 and SmartCem 2 (** p < 0.01).
462
Mechanical Testing All specimens remained bonded after aging through water storage or thermocycling. The mean shear bond strength in MPa and the standard deviation of the tested cements are shown in Table 2. The shear bond values of all resin cements tested decreased when stored for 16 days. Importantly, GC G-Cem and RelyX The Journal of Adhesive Dentistry
Cvikl et al GC-G-CEM
RelyX Unicem 93%
100%
Panavia F2.0 67%
SmartCem 2 67%
Fig 4 SEM images (300X magnification) of fracture behavior, which showed predominantly mixed fracture mode with GC G-Cem and RelyX Unicem when used as adhesive materials. In contrast, cohesive fracture was also observed in one-third of the samples of Panavia F 2.0 and SmartCem2. Arrows point to the fracture region in cement.
Unicem reached a plateau at day 90, whereas the shear bond values of Panavia F 2.0 and SmartCem 2 further decreased over time (Fig 2). After thermocycling, GC G-Cem and RelyX Unicem showed significantly higher shear bond strength between titanium and zirconia compared to Panavia F 2.0 and SmartCem 2 (Fig 3). Evaluation of Fracture Behavior Mixed fracture behavior with cement remaining on titanium and zirconia occurred in 93% of RelyX Unicem samples, in 100% of the GC G-Cem samples, in 67% of the Panavia F 2.0 samples, and in 67% of the SmartCem 2 samples. Adhesive fracture behavior with no cement remaining on either part was observed in 7% of the RelyX Unicem samples, 33% of the Panavia F 2.0 samples, and 33% of the SmartCem 2 samples (Fig 4).
DISCUSSION Resin cements can affect the long-term prognosis of the bond between titanium implants and zirconia abutments.1 It is thus relevant to use resin cements that provide a long-term, stable bond between titanium and zirconia. However, to our knowledge, no information about resin cements connecting titanium and zirconia after prolonged storage and thermocycling is available to date. We therefore posed the hypothesis that different resin cements have different properties in terms of bond strength between titanium and zirconia after long-term in vitro storage. The results of this study support this hypothesis: GC G-Cem and RelyX Unicem exhibited higher shear bond values between titanium and zirconia compared to Panavia F 2.0 and SmartCem 2 after prolonged storage and thermocycling. The data support existing knowledge that longterm storage shows differences in resin cements’ abilities to bond dental tissues and materials. The present short-term storage data are consistent with the work on adhesive bonding between ceramics and dentin. For example, GC G-Cem, RelyX Unicem, and Panavia,35 as well as GC G-Cem, RelyX Unicem, and SmartCem 220,37 achieved similar adhesion between ceramics and dentin. Moreover, adhesion between titanium and ceramics was similar for RelyX Unicem and Panavia F 2.0 after shortterm storage.8,14 Thus, when using short-term protocols, Vol 16, No 5, 2014
resin cements have only a moderate impact on adhesion. Prosthetic restorations, however, should remain in situ for decades. We therefore used long-term storage and thermocycling protocols the better to address this clinical demand. Long-term storage in water has a consistent effect on shear bond strength. For example, shear bond strength of RelyX Unicem and Panavia F to zirconia significantly decreased after 180 days,5 which is in line with the current findings. A study on the shear bond strength of Panavia F and RelyX ARC on zirconia after 180 days storage also corroborates the present results.6 Overall, artificial aging reduced bond strength; however, most studies were conducted with thermocycling. Thermocycling reduced shear bond strength between RelyX Unicem and zirconia,3,13 which supports the present findings. Thermocycling also reduced the bond strength between SmartCem 2 and dentin.20 On glass ceramic, thermocycling even increased the bond strength with RelyX Unicem, SmartCem 2, and GC G-Cem.20 In the present study with titanium and zirconia, GC G-Cem and RelyX Unicem achieved higher shear bond strengths than did Panavia F 2.0 and SmartCem 2. The higher number of mixed fractures with GC G-Cem and RelyX Unicem compared to Panavia F 2.0 and SmartCem 2 basically support data obtained from mechanical testing. Overall, the results of this study confirm the existing knowledge that a correlation exists between “bondstrength difference” and storage time and between “bond-strength difference” and thermocycling.21 Interestingly, the cements react similarly to long-term storage conditions, independent of the materials they connect. The influence of the chemical conversion of the resin cements on the bond strength also requires long-term investigations, since differences in their shrinkage behavior,22 physical properties, pH values, film thickness, viscosity, weight percentage,17,36 and water absorption25 have been demonstrated. These studies, however, were all conducted within a maximum of four weeks.
CONCLUSION In general, long-term storage and thermocycling differentially affect the bonding of resin cement and materials; hence, no general conclusions on resin 463
Cvikl et al
cements can be drawn. However, the results of this study suggest that that GC G-Cem and RelyX Unicem provide stronger long-term bonding between titanium and zirconia than do Panavia F 2.0 and SmartCem 2. Advanced experimental conditions (eg, simulation of mastication cycles and bonding in a climatic chamber, long-term storage in artificial saliva), including their impact on the chemical composition of the cements, will add to our general understanding of the impact of resin cements on shear bond strength between titanium and zirconia.
ACKNOWLEDGMENTS We thank DeguDent GmbH (Germany) for providing the material.
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18. Henry PJ. Oral implant restoration for enhanced oral function. Clin Experiment Pharmacol Physiol 2005;32:123-127. 19. Hill EE, Lott J. A clinically focused discussion of luting materials. Austral Dent J 2011;56(suppl 1):67-76. 20. Hitz T, Stawarczyk B, Fischer J, Hämmerle CH, Sailer I. Are selfadhesive resin cements a valid alternative to conventional resin cements? A laboratory study of the long-term bond strength. Dent Mater 2012;28:1183-1190. 21. Inokoshi M, De Munck J, Minakuchi S, Van Meerbeek B. Meta-analysis of bonding effectiveness to zirconia ceramics. J Dent Res 2014;93: 329-334. 22. Kitzmuller K, Graf A, Watts D, Schedle A. Setting kinetics and shrinkage of self-adhesive resin cements depend on cure-mode and temperature. Dent Mater 2011;27:544-551. 23. Maeda FA, Bello-Silva MS, Eduardo CD, Miranda Junior WG, Cesar PF. Association of different primers and resin cements for adhesive bonding to zirconia ceramics. J Adhes Dent 2014;16:261-265. 24. Mehl C, Harder S, Shahriari A, Steiner M, Kern M. Influence of abutment height and thermocycling on retrievability of cemented implantsupported crowns. Int J Oral Maxillofacial Impl 2012;27:1106-1115. 25. Nakamura T, Wakabayashi K, Kinuta S, Nishida H, Miyamae M, Yatani H. Mechanical properties of new self-adhesive resin-based cement. J Prosthodon Res 2010;54:59-64. 26. Nejatidanesh F, Savabi O, Ebrahimi M, Savabi G. Retentiveness of implant-supported metal copings using different luting agents. Dent Res J 2012;9:13-18. 27. Nejatidanesh F, Savabi O, Shahtoosi M. Retention of implant-supported zirconium oxide ceramic restorations using different luting agents. Clin Oral Implant Res 2011;24(suppl A100):20-24. 28. Özcan M, Pekkan G, Khan A. Does rinsing following particle deposition methods have a negative effect on adhesion to titanium? J Adhes Dent 2013;15:307-310. 29. Pameijer CH. A review of luting agents. Int J Dent 2012;752861:1-7. 30. Phark JH, Duarte S Jr, Blatz M, Sadan A. An in vitro evaluation of the long-term resin bond to a new densely sintered high-purity zirconiumoxide ceramic surface. J Prosthet Dent 2009;101:29-38. 31. Piwowarczyk A, Bender R, Ottl P, Lauer HC. Long-term bond between dual-polymerizing cementing agents and human hard dental tissue. Dent Mater 2007;23:211-217. 32. Radovic I, Monticelli F, Goracci C, Vulicevic ZR, Ferrari M. Self-adhesive resin cements: a literature review. J Adhes Dent 2008;10:251-258. 33. Sailer I, Philipp A, Zembic A, Pjetursson BE, Hämmerle CH, Zwahlen M. A systematic review of the performance of ceramic and metal implant abutments supporting fixed implant reconstructions. Clin Oral Implant Res 2009;20(suppl 4):4-31. 34. Sano H, Shono T, Sonoda H, Takatsu T, Ciucchi B, Carvalho R, et al. Relationship between surface area for adhesion and tensile bond strength – evaluation of a micro-tensile bond test. Dent Mater 1994;10: 236-240. 35. Sarr M, Mine A, De Munck J, Cardoso MV, Kane AW, Vreven J, Van Meerbeek B, Van Landuyt KL. Immediate bonding effectiveness of contemporary composite cements to dentin. Clin Oral Invest 2010;14: 569-577. 36. Saskalauskaite E, Tam LE, McComb D. Flexural strength, elastic modulus, and pH profile of self-etch resin luting cements. J Prosthodont 2008;17:262-268. 37. Simon JF, de Rijk WG, Hill J, Hill N. Tensile bond strength of ceramic crowns to dentin using resin cements. Int J Computer Dent 2011;14:309-319. 38. Watkin A, Kerstein RB. Improving darkened anterior peri-implant tissue color with zirconia custom implant abutments. Compend Contin Educ Dent 2008;29:238-240, 242.
Clinical relevance: Considering that in-vitro settings only partially reflect a clinical situation, the data suggest that GC G-Cem and RelyX Unicem provide stronger long-term bonding between titanium and zirconia than do Panavia F 2.0 and SmartCem 2.
The Journal of Adhesive Dentistry
Purpose: To determine the impact of long-term storage on adhesion between titanium and zirconia using resin cements. Materials and Methods: Titanium grade 4 blocks were adhesively fixed onto zirconia disks with four resin cements: Panavia F 2.0 (Kuraray Europe), GC G-Cem (GC Europe), RelyX Unicem (3M ESPE), and SmartCem 2 (Dentsply DeguDent). Shear bond strength was determined after storage in a water bath for 24 h, 16, 90, and 150 days at 37°C, and after 6000 cycles between 5°C and 55°C. Fracture behavior was evaluated using scanning electron microscopy. Results: After storage for at least 90 days and after thermocycling, GC G-Cem (16.9 MPa and 15.1 MPa, respectively) and RelyX Unicem (10.8 MPa and 15.7 MPa, respectively) achieved higher shear bond strength compared to SmartCem 2 (7.1 MPa and 4.0 MPa, respectively) and Panavia F2 (4.1 MPa and 7.4 MPa, respectively). At day 150, GC G-Cem and RelyX Unicem caused exclusively mixed fractures. SmartCem 2 and Panavia F2 showed adhesive fractures in one-third of the cases; all other fractures were of mixed type. After 24 h (GC G-Cem: 26.0, RelyX Unicem: 20.5 MPa, SmartCem 2: 16.1 MPa, Panavia F2: 23.6 MPa) and 16 days (GC G-Cem: 12.8, RelyX Unicem: 14.2 MPa, SmartCem 2: 9.8 MPa, Panavia F2: 14.7 MPa) of storage, shear bond strength was similar among the four cements. Conclusion: Long-term storage and thermocycling differentially affects the bonding of resin cement between titanium and zirconia. Key words: titanium, zirconia, long-term storage, thermocycling, shear bond strength. J Adhes Dent 2014; 16: 459–464. doi: 10.3290/j.jad.a32809
D
ental implants have become an established treatment of tooth loss,18 and titanium has often been used as an abutment material to connect the implant with the prosthetic suprastructures.33 However, as esthetic demands have increased, ceramic abutments
a
Assistant Professor, Department of Conservative Dentistry and Periodontology, Medical University of Vienna, Vienna, Austria; Department of Preventive, Restorative and Pediatric Dentistry, University of Bern, Bern, Switzerland. Experimental design, performed the experiments, wrote the manuscript.
b
Dentist, Department of Conservative Dentistry and Periodontology, Medical University of Vienna, Vienna, Austria. Performed the experiments.
c
Researcher, Department of Conservative Dentistry and Periodontology, Medical University of Vienna, Vienna, Austria. Proofread manuscript, performed statistical evaluation.
d
Professor, Department of Oral Surgery, Medical University of Vienna, Vienna, Austria; Laboratory for Oral Cell Biology, University of Bern, Bern, Switzerland. Wrote the manuscript, contributed substantially to discussion.
e
Professor, Department of Conservative Dentistry and Periodontology, Medical University of Vienna, Vienna, Austria. Contributed substantially to discussion.
Correspondence: Reinhard Gruber, Department of Oral Surgery, Medical University of Vienna and Laboratory of Oral Cell Biology, School of Dental Medicine, University of Bern, Freiburgstrasse 7, CH-3010 Bern, Switzerland. Tel: +41-31632-8622. e-mail: [email protected]
Vol 16, No 5, 2014
Submitted for publication: 18.06.13; accepted for publication: 10.07.14
have been introduced.33 To combine the benefits of both materials, titanium is bonded to the ceramic part, with the latter typically being made of zirconia.4,38 Resin cements can provide an adhesive bond between titanium and ceramics,1,32 but if this bond fails, there is a risk of aspiration of the ceramic, bone loss, prosthetic fractures, and microbiological complications.26 Thus, longterm adhesion between titanium and ceramic is required for the preservation of the implant-abutment bond. The selection of the appropriate resin cement is of critical importance for the long-term prognosis of implants and prosthetic restorations.19,29 Resin cements were originally developed to provide adhesion not only between dental materials (eg, ceramics or composites) and dental hard tissue16 but also between dental materials.9,12,23 Cements based on polymers and fillers are available for the long-term fixation of prosthetic suprastructures27 and abutments24 in implant dentistry. Therefore, research on the long-term bond strength between titanium and zirconia and the influcence of different resin cements is clinically relevant. To predict the long-term bond strength of cemented joints, mechanical testing with resin cements has been 459
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Table 1
Cement materials, chemical compositions, and application mode
Material
Composition
Application mode
GC G-Cem (GC Europe; Leuven, Belgium)
4-methacryloxyethyltrimellitate anhydride (4-META), urethane dimethacrylate (UDMA), aluminosilicate glass, pigment, dimethacrylate, distilled water, phosphoric ester monomer, initiator, camphorquinone
GC G-Cem capsules were mixed in a high-frequency mixing device. Afterwards, the mixture was applied on surfaces, remaining excess was removed, and light curing was performed for 10 s using bluephase 20i.
Panavia F 2.0 (Kuraray Europe; Hattersheim am Main, Germany)
Paste A: 10-methacryloyloxydecyl dihydrogen phosphate, hydrophobic aromatic dimethacrylate, hydrophobic aliphatic methacrylate, hydrophilic aliphatic dimethacrylate, silanated silica filler, silanated colloidal silica, dl-camphorquinone, catalysts, initiators Paste B: Sodium fluoride, hydrophobic aromatic dimethacrylate, hydrophobic aliphatic methacrylate, hydrophilic aliphatic dimethacrylate, silanated barium glass filler, catalysts, accelerators, pigments ED Primer A: 2-hydroxyethyl methacrylate, 10-methacryloyloxydecyl dihydrogen phosphate, N-methacryloyl-5-aminosalicylic acid, water, accelerators ED Primer B: N-methacryloyl-5-aminosalicylic acid, water, catalysts, accelerators
Panavia F 2.0 pastes A & B were mixed for 20 s. Afterwards, it was applied onto surfaces previously treated with ceramic primer or ED Primer A and B. The remaining excess was removed, and light curing was performed for 20 s using bluephase 20i.
RelyX Unicem (3M ESPE; Seefeld, Germany)
Methacrylate monomers containing phosphoric acid groups, methacrylate monomers, initiator components, stabilizers, alkaline (basic) fillers, silanated fillers, initiator components, pigments
RelyX Unicem capsules were mixed in a high-frequency mixing device. Then the mixture was applied on surfaces, the remaining excess was removed, and light curing was performed for 40 s using bluephase 20i.
SmartCem 2 (Dentsply DeguDent; Hanau, Germany)
Urethane dimethacrylate, di- and tri-methacrylate resins, phosphoric acid modified acrylate resin, barium boron fluoroaluminosilicate glass, organic peroxide initiator, camphorquinone, photoinitiator, phosphene oxide photoinitiator, accelerators, butylated hydroxy toluene, UV stabilizer, titanium dioxide, iron oxide, hydrophobic amorphous silicon dioxide
SmartCem 2 cement was directly dispensed through a mixing tip. Then it was applied on surfaces, the remaining excess was removed, and light curing was performed for 40 s (bluephase 20i).
performed. For example, the bond strength of Panavia F 2.0 and RelyX Unicem on zirconia decreased after artificial aging.10,30 Moreover, GC G-Cem, RelyX Unicem, Panavia 21, and SmartCem 2 showed a distinct response to thermocycling when bonded to glass ceramics.20 The longterm bond to human hard dental tissue is influenced by various properties of resin cements, eg, water absorption, shrinkage behavior, physical properties, pH values, and film thickness.20,31 In addition, the effect of long-term water storage and thermocycling of cement bonded to laserprepared dentin has been examined.11 Overall, the data suggest that resin cements can affect the long-term bond strength between different dental materials. To our knowledge, however, no information is available on long-term bond strength between titanium and zirconia taking the influence of different resin cements into consideration. The purpose of the present study was to use the shear bond strength test to evaluate the influence of four resin cements on the bond strength between titanium and zirconia following long-term in vitro storage and thermocycling. Based on the current knowledge on long-term bond strength of cemented joints, the following hypothesis was posed: Different resin cements mediate different bond strengths between titanium and zirconia after long-term in vitro storage. 460
MATERIALS AND METHODS Sample Preparation Titanium grade 4 blocks (10 mm × 4 mm × 4 mm) and disks (diameter 3 mm, height 2 mm) made from zirconium dioxide (zirconia) were manufactured from the same materials that are clinically used in implant dentistry (Dentsply DeguDent; Hanau, Germany). A sample size calculation based on α = 0.05 and a power of 0.80 indicated that 300 samples were required. All samples were airborne-particle abraded with aluminum oxide particles with a diameter of 110 μm at 3 bar pressure from a distance of 10 mm. Four different resin cements were investigated (Table 1). Titanium blocks and zirconia disks were divided into four groups of 75 specimens each according to the resin cements (Panavia F 2.0, GC G-Cem, RelyX Unicem, and SmartCem 2). Resin cements were prepared and the bonding procedures between the titanium blocks and zirconia disks were performed following the respective manufacturer’s instructions. Storage and Thermocycling Specimens were subdivided into 5 groups (n = 15) for different storage conditions: water bath for 24 h at 37°C; water bath for 16 days at 37°C; water bath for The Journal of Adhesive Dentistry
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300 titanium blocks and 300 zirconium dioxide disks
airborn-particle abraded
75 samples
75 samples
75 samples
75 samples
Panavia F2.0
GC-G-CEM
RelyX Unicem
SmartCem 2
a b c d e
a b c d e
a b c d e
a b c d e
a
n = 15
37° 24h water bath
b
n = 15
c
n = 15
37°
d
37°
16d water bath
n = 15
37°
90d water bath
150d water bath
e
n = 15
5°
55°
6000 cycles thermocycling
Shear bond test Scanning electron microscopy Fig 1 Experimental procedure. Titanium blocks (n = 300) and zirconia disks (n = 300) were airborne-particle abraded and divided into four groups for the resin cements (Panavia F 2.0, GC G-Cem, RelyX Unicem, and SmartCem 2). After adhesively bonding the titanium blocks to the zirconia disks, the specimens were subdivided into 5 groups (n = 15) for different storage conditions (water bath for 24 h at 37°C; water bath for 16 days at 37°C; water bath for 90 days at 37°C; water bath for 150 days at 37°C and thermocycling for 6000 cycles at 5°C and 55°C). Shear bond strength testing and SEM evaluation of fracture behavior were performed.
90 days at 37°C; water bath for 150 days at 37°C and thermocycling for 6000 cycles at 5°C to 55°C. Mechanical Testing A universal testing machine (Zwick Roell; Ulm, Germany) with a crosshead speed of 1 mm/min was used to determine stress at failure. Force (in Newtons) at failure was divided by the bond area (mm2) yielding data in MPa. Since titanium and zirconia are both artificial Vol 16, No 5, 2014
and replicable materials, this study setting warrants a macroshear bond strength test.7,34 A flow chart of the experimental procedure is given in Fig 1. Evaluation of Fracture Behavior Adhesive surfaces were analyzed after debonding to identify failure mechanisms. Cement residues could be located on the titanium or zirconia surface (cohesive fracture behavior), on both surfaces (mixed fracture behavior), 461
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Table 2 Shear bond strength values (means ± standard deviations) of four different cements in different short- and long-term storage conditions Material
Storage conditions 24 h
16 days
90 days
150 days
Thermocycling
RelyX Unicem
20.5 ± 6.2
12.8 ± 2.9
10.8 ± 5.4
10.9 ± 5.8
15.7 ± 7.3
GC G-Cem
26.0 ± 5.6
14.2 ± 5.6
16.9 ± 4.9
12.7 ± 2.9
15.1 ± 7.3
Panavia F 2.0
23.6 ± 5.7
14.7 ± 6.2
4.1 ± 1.7
4.1 ± 2.2
7.4 ± 6.7
SmartCem 2
16.1 ± 4.9
9.8 ± 5.2
7.1 ± 3.8
5.9 ± 2.9
4.0 ± 2.5
40
**
** **
**
**
GC-G-CEM
**
RelyX Unicem Panavia F2.0
30
MPa
SmartCem 2 20
10
0 24 h
16 d
90 d
150 d
Fig 2 Mechanical testing after short- and long-term water storage. The shear bond strength of the samples cemented with GC G-Cem and RelyX Unicem was generally higher than that of the other samples. All cements showed their highest shear bond values after 24 h of water storage, which decreased significantly during longer storage (** p < 0.01).
40
** **
GC-G-CEM RelyX Unicem Panavia F2.0
30
MPa
SmartCem 2
20
or on neither surface (adhesive fracture behavior). Randomly selected samples of each group were qualitatively topographically examined with a scanning electron microscope (Hitachi 1000, Hitachi High-Technologies Europe; Krefeld, Germany) at 300X and 100X magnifications. Statistical Analysis Data were analyzed using the Kruskal-Wallis test and the Mann-Whitney U-Test (SPSS version 19.0; Chicago, IL, USA). A significant difference was defined as p < 0.05. No statistical analysis of the surface examination was performed.
10
RESULTS 0 TC
Fig 3 Mechanical testing after thermocycling representing simulated long-term storage. The shear bond strengths of GC G-Cem and RelyX Unicem after thermocycling for 6000 cycles were significantly higher than that of Panavia F 2.0 and SmartCem 2 (** p < 0.01).
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Mechanical Testing All specimens remained bonded after aging through water storage or thermocycling. The mean shear bond strength in MPa and the standard deviation of the tested cements are shown in Table 2. The shear bond values of all resin cements tested decreased when stored for 16 days. Importantly, GC G-Cem and RelyX The Journal of Adhesive Dentistry
Cvikl et al GC-G-CEM
RelyX Unicem 93%
100%
Panavia F2.0 67%
SmartCem 2 67%
Fig 4 SEM images (300X magnification) of fracture behavior, which showed predominantly mixed fracture mode with GC G-Cem and RelyX Unicem when used as adhesive materials. In contrast, cohesive fracture was also observed in one-third of the samples of Panavia F 2.0 and SmartCem2. Arrows point to the fracture region in cement.
Unicem reached a plateau at day 90, whereas the shear bond values of Panavia F 2.0 and SmartCem 2 further decreased over time (Fig 2). After thermocycling, GC G-Cem and RelyX Unicem showed significantly higher shear bond strength between titanium and zirconia compared to Panavia F 2.0 and SmartCem 2 (Fig 3). Evaluation of Fracture Behavior Mixed fracture behavior with cement remaining on titanium and zirconia occurred in 93% of RelyX Unicem samples, in 100% of the GC G-Cem samples, in 67% of the Panavia F 2.0 samples, and in 67% of the SmartCem 2 samples. Adhesive fracture behavior with no cement remaining on either part was observed in 7% of the RelyX Unicem samples, 33% of the Panavia F 2.0 samples, and 33% of the SmartCem 2 samples (Fig 4).
DISCUSSION Resin cements can affect the long-term prognosis of the bond between titanium implants and zirconia abutments.1 It is thus relevant to use resin cements that provide a long-term, stable bond between titanium and zirconia. However, to our knowledge, no information about resin cements connecting titanium and zirconia after prolonged storage and thermocycling is available to date. We therefore posed the hypothesis that different resin cements have different properties in terms of bond strength between titanium and zirconia after long-term in vitro storage. The results of this study support this hypothesis: GC G-Cem and RelyX Unicem exhibited higher shear bond values between titanium and zirconia compared to Panavia F 2.0 and SmartCem 2 after prolonged storage and thermocycling. The data support existing knowledge that longterm storage shows differences in resin cements’ abilities to bond dental tissues and materials. The present short-term storage data are consistent with the work on adhesive bonding between ceramics and dentin. For example, GC G-Cem, RelyX Unicem, and Panavia,35 as well as GC G-Cem, RelyX Unicem, and SmartCem 220,37 achieved similar adhesion between ceramics and dentin. Moreover, adhesion between titanium and ceramics was similar for RelyX Unicem and Panavia F 2.0 after shortterm storage.8,14 Thus, when using short-term protocols, Vol 16, No 5, 2014
resin cements have only a moderate impact on adhesion. Prosthetic restorations, however, should remain in situ for decades. We therefore used long-term storage and thermocycling protocols the better to address this clinical demand. Long-term storage in water has a consistent effect on shear bond strength. For example, shear bond strength of RelyX Unicem and Panavia F to zirconia significantly decreased after 180 days,5 which is in line with the current findings. A study on the shear bond strength of Panavia F and RelyX ARC on zirconia after 180 days storage also corroborates the present results.6 Overall, artificial aging reduced bond strength; however, most studies were conducted with thermocycling. Thermocycling reduced shear bond strength between RelyX Unicem and zirconia,3,13 which supports the present findings. Thermocycling also reduced the bond strength between SmartCem 2 and dentin.20 On glass ceramic, thermocycling even increased the bond strength with RelyX Unicem, SmartCem 2, and GC G-Cem.20 In the present study with titanium and zirconia, GC G-Cem and RelyX Unicem achieved higher shear bond strengths than did Panavia F 2.0 and SmartCem 2. The higher number of mixed fractures with GC G-Cem and RelyX Unicem compared to Panavia F 2.0 and SmartCem 2 basically support data obtained from mechanical testing. Overall, the results of this study confirm the existing knowledge that a correlation exists between “bondstrength difference” and storage time and between “bond-strength difference” and thermocycling.21 Interestingly, the cements react similarly to long-term storage conditions, independent of the materials they connect. The influence of the chemical conversion of the resin cements on the bond strength also requires long-term investigations, since differences in their shrinkage behavior,22 physical properties, pH values, film thickness, viscosity, weight percentage,17,36 and water absorption25 have been demonstrated. These studies, however, were all conducted within a maximum of four weeks.
CONCLUSION In general, long-term storage and thermocycling differentially affect the bonding of resin cement and materials; hence, no general conclusions on resin 463
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cements can be drawn. However, the results of this study suggest that that GC G-Cem and RelyX Unicem provide stronger long-term bonding between titanium and zirconia than do Panavia F 2.0 and SmartCem 2. Advanced experimental conditions (eg, simulation of mastication cycles and bonding in a climatic chamber, long-term storage in artificial saliva), including their impact on the chemical composition of the cements, will add to our general understanding of the impact of resin cements on shear bond strength between titanium and zirconia.
ACKNOWLEDGMENTS We thank DeguDent GmbH (Germany) for providing the material.
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18. Henry PJ. Oral implant restoration for enhanced oral function. Clin Experiment Pharmacol Physiol 2005;32:123-127. 19. Hill EE, Lott J. A clinically focused discussion of luting materials. Austral Dent J 2011;56(suppl 1):67-76. 20. Hitz T, Stawarczyk B, Fischer J, Hämmerle CH, Sailer I. Are selfadhesive resin cements a valid alternative to conventional resin cements? A laboratory study of the long-term bond strength. Dent Mater 2012;28:1183-1190. 21. Inokoshi M, De Munck J, Minakuchi S, Van Meerbeek B. Meta-analysis of bonding effectiveness to zirconia ceramics. J Dent Res 2014;93: 329-334. 22. Kitzmuller K, Graf A, Watts D, Schedle A. Setting kinetics and shrinkage of self-adhesive resin cements depend on cure-mode and temperature. Dent Mater 2011;27:544-551. 23. Maeda FA, Bello-Silva MS, Eduardo CD, Miranda Junior WG, Cesar PF. Association of different primers and resin cements for adhesive bonding to zirconia ceramics. J Adhes Dent 2014;16:261-265. 24. Mehl C, Harder S, Shahriari A, Steiner M, Kern M. Influence of abutment height and thermocycling on retrievability of cemented implantsupported crowns. Int J Oral Maxillofacial Impl 2012;27:1106-1115. 25. Nakamura T, Wakabayashi K, Kinuta S, Nishida H, Miyamae M, Yatani H. Mechanical properties of new self-adhesive resin-based cement. J Prosthodon Res 2010;54:59-64. 26. Nejatidanesh F, Savabi O, Ebrahimi M, Savabi G. Retentiveness of implant-supported metal copings using different luting agents. Dent Res J 2012;9:13-18. 27. Nejatidanesh F, Savabi O, Shahtoosi M. Retention of implant-supported zirconium oxide ceramic restorations using different luting agents. Clin Oral Implant Res 2011;24(suppl A100):20-24. 28. Özcan M, Pekkan G, Khan A. Does rinsing following particle deposition methods have a negative effect on adhesion to titanium? J Adhes Dent 2013;15:307-310. 29. Pameijer CH. A review of luting agents. Int J Dent 2012;752861:1-7. 30. Phark JH, Duarte S Jr, Blatz M, Sadan A. An in vitro evaluation of the long-term resin bond to a new densely sintered high-purity zirconiumoxide ceramic surface. J Prosthet Dent 2009;101:29-38. 31. Piwowarczyk A, Bender R, Ottl P, Lauer HC. Long-term bond between dual-polymerizing cementing agents and human hard dental tissue. Dent Mater 2007;23:211-217. 32. Radovic I, Monticelli F, Goracci C, Vulicevic ZR, Ferrari M. Self-adhesive resin cements: a literature review. J Adhes Dent 2008;10:251-258. 33. Sailer I, Philipp A, Zembic A, Pjetursson BE, Hämmerle CH, Zwahlen M. A systematic review of the performance of ceramic and metal implant abutments supporting fixed implant reconstructions. Clin Oral Implant Res 2009;20(suppl 4):4-31. 34. Sano H, Shono T, Sonoda H, Takatsu T, Ciucchi B, Carvalho R, et al. Relationship between surface area for adhesion and tensile bond strength – evaluation of a micro-tensile bond test. Dent Mater 1994;10: 236-240. 35. Sarr M, Mine A, De Munck J, Cardoso MV, Kane AW, Vreven J, Van Meerbeek B, Van Landuyt KL. Immediate bonding effectiveness of contemporary composite cements to dentin. Clin Oral Invest 2010;14: 569-577. 36. Saskalauskaite E, Tam LE, McComb D. Flexural strength, elastic modulus, and pH profile of self-etch resin luting cements. J Prosthodont 2008;17:262-268. 37. Simon JF, de Rijk WG, Hill J, Hill N. Tensile bond strength of ceramic crowns to dentin using resin cements. Int J Computer Dent 2011;14:309-319. 38. Watkin A, Kerstein RB. Improving darkened anterior peri-implant tissue color with zirconia custom implant abutments. Compend Contin Educ Dent 2008;29:238-240, 242.
Clinical relevance: Considering that in-vitro settings only partially reflect a clinical situation, the data suggest that GC G-Cem and RelyX Unicem provide stronger long-term bonding between titanium and zirconia than do Panavia F 2.0 and SmartCem 2.
The Journal of Adhesive Dentistry
