- Email: [email protected]
Durability of the resin bond strength to zirconia ceramic after using different surface conditioning methods
d e n t a l m a t e r i a l s 2 3 ( 2 0 0 7 ) 45–50
available at www.sciencedirect.com
journal homepage: www.intl.elsevierhealth.com/journals/dema
Durability of the resin bond strength to zirconia ceramic after using different surface conditioning methods Mona Wolfart ∗ , Frank Lehmann, Stefan Wolfart, Matthias Kern Department of Prosthodontics, Propaedeutics and Dental Materials, Dental School, Christian-Albrechts-University at Kiel, Germany
a r t i c l e
i n f o
a b s t r a c t
Article history:
Objectives. The purpose of this in vitro study was the evaluation of the bond strength and
Received 14 July 2005
its durability of two composite resins to zirconia ceramic after using different surface con-
Accepted 30 November 2005
ditioning methods. Methods. Plexiglas tubes filled with composite resin were bonded to zirconia ceramic discs (Cercon) which were either in their original state as supplied by the manufacturer only
Keywords:
cleaned in isopropanol or were cleaned with an air–powder–water spray with sodium
Cercon
hydrocarbonate solution or were air abraded (50 m Al2 O3 ). Groups of 20 specimens each
Zirconia ceramic
were bonded either with a conventional composite resin (Variolink II) or with a phosphate
Composite resin
monomer (MDP)-containing resin (Panavia F) to the ceramic discs. Subgroups of 10 bonded
Tensile bond strength
specimens were stored in distilled water (37 ◦ C) for either 3 days or for 150 days. Addition-
Surface conditions
ally, the 150 days specimens were thermal cycled 37,500 times. Statistical analyses were conducted with the Wilcoxon rank sum test adjusted by Bonferroni–Holm. Results. The initial tensile bond strength (TBS) for Variolink II ranged from 9.0 to 16.6 MPa and were significantly lower (p ≤ 0.05) than for Panavia F ranging from 18.7 to 45.0 MPa. Air abrasion resulted in significantly higher TBS (p ≤ 0.01) than the two other surface conditioning methods. After 150 days storage, only the air abraded specimens bonded with Panavia F showed high bond strengths of 39.2 MPa, whereas most other specimens debonded spontaneously or showed very low bond strengths. Significance. The use of the MDP-containing composite resin Panavia F on air abraded zirconia ceramic can be recommended as promising bonding method. © 2005 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
1.
Introduction
In recent years, the increasing demand for all-ceramic restorations led to the development of ceramic materials with optimized mechanical properties like densely sintered aluminum oxide and zirconium oxide ceramics [1,2]. These high-strength ceramics offer a wide variety of clinical applications, e.g. posts, fixed partial dentures, implant abutments and even Maryland type resin-bonded fixed partial dentures. Although adhesive cementation is recommended for all-ceramic restorations
[3], especially for the latter application, a long-term durable bond to these ceramics is indispensable for a successful restoration. Several studies investigated the bond strength and the durability of various bonding methods to high-strength oxide ceramics. It has been shown that air abrasion, which is a common method to condition the ceramic surface, and the use of phosphate monomer (MDP)-containing luting agents resulted in high and durable bond strengths [4–12]. However, it has to be taken into consideration that air abrasion might affect
∗ Corresponding author at: Department of Prosthodontics, Propaedeutics and Dental Materials, University Hospital Schleswig-HolsteinCampus Kiel, Arnold-Heller-Str. 16,24105 Kiel, Germany. Tel.: +49 431 597 2874; fax: +49 431 587 2860. E-mail address: [email protected] (M. Wolfart). 0109-5641/$ – see front matter © 2005 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.dental.2005.11.040
46
d e n t a l m a t e r i a l s 2 3 ( 2 0 0 7 ) 45–50
the ceramic surface by creating microcracks which might reduce the fracture strength of the ceramic [13]. The question arises whether this surface conditioning method could be omitted for conditioning to avoid weakening of the ceramic. On the other hand, several authors suggest that resin luting agents providing durable resin bonds significantly strengthen ceramic materials by “healing” minor surface defects caused by air abrasion [14,15]. The bond strength to alumina ceramic has been shown to be relatively low and not stable over time when the bonding agents are applied to the original ceramic surface after cleaning in 96% isopropanol [5,6]. An explanation for the low bond strength to untreated ceramic surfaces might be a certain contamination of the surface during the manufacturing process which influences the bonding mechanism but cannot be eliminated by cleaning in 96% isopropanol. Additional cleaning methods like the use of an air–powder–water spray might be more effective in cleaning the surface than isopropanol alone and might lead to higher bond strengths of composite resins to zirconia ceramic without affecting the ceramic surface adversely. The purpose of this in vitro study was to evaluate the influence of different surface conditioning methods on the bond strength of two composite resins to zirconia ceramic. Furthermore, the durability of the bond strength over 150 days storage time with additional 37,500 thermal cycles should be investigated. The null hypothesis to be tested was that bond strength is influenced by different surface conditioning methods and storage conditions.
2.
Materials and methods
Industrially manufactured discs from the densely sintered zirconia ceramic Cercon (94% ZrO2 stabilized by 5% Y2 O3 ; Cercon; Degudent, Hanau, Germany) were used in this study. The discs had a diameter of 6.4 mm and a thickness of 3.4 mm.
The materials utilized and their characteristics are listed in Table 1. Specimens were assigned to the following six groups consisting of 20 specimens each depending on the surface conditioning method and the luting resin used. After surface conditioning by the described methods, all specimens were ultrasonically cleaned in 96% isopropanol for 3 min prior to bonding. ORG-V: Heliobond followed by Variolink II were applied to the machined original ceramic surface as supplied by the manufacturer. APW-V: The ceramic surface was cleaned for 15 s with an air–powder–water spray with sodium hydrocarbonate solution (Prophy Jet; Dentsply DeTrey, Constance, Germany) prior to the application of Heliobond and Variolink II. ABR-V: The ceramic surface was air abraded with 50 m Al2 O3 at 2.5 bar pressure for 15 s at a distance of 10 mm prior to the application of Heliobond followed by Variolink II. ORG-P: Panavia F was applied to the machined original ceramic surface as supplied by the manufacturer. APW-P: The ceramic surface was cleaned for 15 s with an air–powder–water spray with sodium hydrocarbonate solution prior to the application of Panavia F. ABR-P: Panavia F was applied to the air abraded ceramic surface. Plexiglas tubes with an inner diameter of 3.3 mm were filled with self-curing composite resin Clearfil F2 (Kuraray, Osaka, Japan). After 8 min from the start of mixing, the composite tubes were bonded with the given resins to the ceramic discs using an alignment apparatus. The alignment apparatus consisted of two parallel guides, a tube holder, a silicon pad and an added weight of 750 g. The apparatus ensured that the tube axis was perpendicular to the bonding surface. The bonding method has been described in detail previously [5,16].
Table 1 – List of used materials and their characteristics System Clearfil F2
Variolink II
Panavia F
a
Component
Batch no.
Main compositiona
Manufacturer
BisGMA/TEGDMA/DMA/barium sulfate/silica cont. composite resin
Kuraray, Osaka Japan
Ivoclar Vivadent Schaan, Lichtenstein
Base paste
41148
Catalyst paste
41148
Heliobond
C50463
BisGMA/TEGDMA cont. resin
Base paste
C50466
Catalyst paste Airblock
C55106 0102001080
BisGMA/UDMA/TEGDMA/DMA/barium sulfate/Ba-Al-F-Si-glass/silica cont. composite resin Benzoylperoxide Glycerol
Paste A
00087A
Paste B Oxyguard II
00037B 00315A
BPEDMA/MDP/DMA/silica/barium sulfate/dibenzoylperoxide N,N-diethanol-p-toluidine/silica sodiumfluoride Polyethyleneglycol/glycerine/sodium benzenesulfinate cont. gel
Dentsply DeTrey, Constance, Germany Kuraray, Osaka Japan
According to the information provided by the manufacturers: BisGMA: bisphenol-A-diglycidylmethacrylate; BPEDMA: bisphenol-A-polyethoxy dimethacrylate; DMA: aliphatic dimethacrylate; MDP: 10-methacryloxydecyl dihydrogen phosphate; TEGDMA: triethyleneglycol dimethacrylate; Al: aluminium; Ba: barium; F: fluorine; Si: silicon; cont.: containing.
47
d e n t a l m a t e r i a l s 2 3 ( 2 0 0 7 ) 45–50
Excess cement was removed from the bonding margin using foam pellets and then an oxygen blocking gel was applied with a syringe (Oxyguard II for Panavia F and Airblock for Variolink II). After 5 min, the specimens were light-cured from two opposite sides for 20 s at a distance of 5 mm with a dental curing light (Optilux 500; Demetron company, Danbury, USA), after three more minutes, they were further cured in a xenon strobe light-curing unit (Dentacolor XS; HeraeusKulzer, Wehrheim, Germany) for an additional 90 s. Each bonding group was divided into two subgroups of 10 specimens each and stored in distilled water at 37 ◦ C either for 3 days without thermal cycling (TC) or for 150 days with additional 37,500 thermal cycles between 5 and 55 ◦ C (dwell time 30 s). Following the different storage times, the tensile bond strength test was performed at a crosshead speed of 2 mm/min in a universal testing machine (Zwick Z 010/TN2A; Ulm, Germany) using a special test configuration, which provided a moment-free axial force application. A collet held the tube while an alignment jig allowed self-centering of the specimens. The jig was attached to the load cell and crosshead by upper and lower chains, allowing the whole system to be selfaligning. Statistical analyses of the test results were performed using the Kruskal–Wallis test followed by multiple pair-wise comparisons of groups using the Wilcoxon rank sum test. Significance levels were adjusted with the Bonferroni–Holm correction for multiple testing. The fractured interfaces of the zirconia ceramic specimens were examined with a light microscope (Wild Makroskop M 420; Heerbrugg, Germany) at 30× magnification to calculate the debonded area which was assigned to adhesive or cohesive failure modes. After sputtering using a gold-alloy conductive layer of approximately 30 nm, representative specimens were examined using a scanning electron microscope (SEM; XL 30 CP; Philips, Eindhoven, Netherlands) with an acceleration voltage of 15 keV and a working distance of 10 mm.
age conditions. Statistically significant differences between the groups and between the storage conditions are indicated in the same table. The use of the MDP-containing composite resin on air abraded ceramic surfaces (group ABR-P) resulted in the highest bond strength values after 3 and 150 days (medians 45.0 and 39.2 MPa, respectively). The initial bond strengths (3 days storage) for the groups with original surfaces and surfaces cleaned with air–powder–water spray were significantly lower (p ≤ 0.01) than for the groups with air abraded surfaces for both the MDPcontaining composite resin and the conventional composite resin. Specimens bonded with the MDP-containing composite resin showed significantly higher bond strengths than specimens bonded with the conventional composite resin for all three surface conditioning methods (p ≤ 0.05). During the 150 days storage time and 37,500 TC, all specimens of the groups ORG-P, ORG-V, APW-V and ABR-V debonded spontaneously. In the group APW-P, only three of the ten specimens did not debond. These three specimens showed low bond strengths of 4.4, 9.0 and 10.7 MPa, respectively. Although the bond strengths for the specimens of group ABR-P decreased slightly over 150 days storage and TC, this decrease was not statistically significant (p > 0.05). The distribution of the failure modes for all groups is shown in Fig. 1. For all groups bonded with the conventional composite resin, the failure modes were completely adhesive. For the air abraded specimens bonded with the MDP-containing composite resin, the failure mode was completely cohesive after 3 days and mostly cohesive (98%) after 150 days, whereas the specimens with original surface and the specimens cleaned with air–powder–water spray showed a predominantly cohesive failure mode after 3 days, but a nearly 100% adhesive failure mode after 150 days. Representative SEM photographs of the fracture interfaces after tensile testing are shown in Figs. 2–4.
3.
4.
Results
The tensile bond strength (TBS) values are summarized in Table 2 for the six bonding groups and the two different stor-
Discussion
The results of the present study show that the bond strength was influenced by both, the different surface conditioning
Table 2 – Tensile bond strength to zirconia ceramic with different surface conditioning methods Groups
Storage time 3 days/0 TC Median
ORG-V APW-V ABR-V ORG-P APW-P ABR-P
11.0A a 9.0A a 16.6B,E a 18.7C,E a 32.1C a 45.0D a
25th/75th percentile 9.7/12.2 7.4/10.3 15.5/20.7 16.8/25.8 17.7/34.2 43.9/45.8
150 days/37,500 TC Median 0.0A b 0.0A b 0.0A b 0.0A b 0.0A b 39.2B a
25th/75th percentile 0.0/0.0 0.0/0.0 0.0/0.0 0.0/0.0 0.0/4.4 34.4/46.2
Median: 25th and 75th in MPa (n = 10). TC: thermal cycles. Within the same column: median values with the same upper case superscript letters (A–E) are not statistically different (p > 0.05). Within the same row, median values with the same lower case subscript letters (a and b) are not statistically different (p > 0.05). Global Kruskal–Wallis test followed by pair-wise comparison using the Wilcoxon test adjusted by Bonferroni–Holm.
48
d e n t a l m a t e r i a l s 2 3 ( 2 0 0 7 ) 45–50
Fig. 1 – Mean percentages of areas assigned to the failure modes observed in the six bonding groups after different storage times.
Fig. 2 – SEM photograph of a sample from group ABR-V after 150 days storage. The failure mode was completely adhesive.
Fig. 3 – SEM photograph of a sample from group ABR-P after 150 days storage. The failure mode was completely cohesive.
d e n t a l m a t e r i a l s 2 3 ( 2 0 0 7 ) 45–50
49
Fig. 4 – SEM photograph of a sample from group APW-P with mixed failure mode after 150 days storage.
methods and the storage conditions. Air abraded specimens bonded with the MDP-containing composite resin showed the highest bond strengths. A slight decrease in bond strength was observed over 150 days storage time with TC which, however, was not statistically significant. This decrease might be due to a certain degeneration of the resin itself, which has already been shown for other resins [17]. This is supported by the fact that for both the 3 and 150 days specimens a completely or nearly completely cohesive failure mode was found in this group as indicated by light microscope (Fig. 1) and confirmed by SEM (Fig. 3). Several studies investigated different bonding methods for example different silicoating methods, silanization, acrylization or the use of different bonding agents to alumina and zirconia ceramic. However, a high and durable bond strength was only achieved on air abraded surfaces with the use of a MDPcontaining primer [5] or a MDP-containing composite resin [5,6,8,10]. These findings confirm the results of the present study as the group of the air abraded specimens bonded with the MDP-containing composite resin showed a durable bond strength over 150 days, while the specimens bonded with the conventional composite resin debonded spontaneously during this period. The phosphate ester group of the adhesive monomer MDP bonds directly to metal oxides [18], therefore, the above cited studies and the present results suggest a chemical bond between MDP and both aluminum and zirconium oxides. The application of the two composite resins Panavia F and Variolink II to the original surface of the zirconia ceramic discs resulted in low initial bond strengths as it was already shown for densely sintered alumina ceramics [5,6]. Furthermore, the bond was not stable over time as all specimens with original surface conditions debonded spontaneously during 150 days storage and TC. Similar results were found in the present study after cleaning the ceramic surface by air–powder–water spray which did not result in higher bond strengths than bonding to the original surface independent from the bonding resin used. After long-term storage and TC, only three specimens of the APW-P group (which showed significantly lower bond strengths) had not debonded spontaneously. It can be
assumed that the monomer MDP was not able to create a stable bond neither to the machined surface nor to the surface cleaned by air–powder–water spray. Presumably, cleaning the ceramic surface by air–powder–water spray does not result in structural changes on the ceramic surface as they occur after air abrasion. Nevertheless, these changes seem to be necessary to achieve a stable bond to zirconia ceramic. Although there are studies indicating that air abrasion affects the surface of zirconia ceramic which leads to a reduction of the flexural strength of these ceramics [13], there are other authors who showed that air abrasion might even strengthen zirconia ceramics [19,20]. Furthermore, a negative effect of the microcracks on the ceramic surface caused by air abrasion on the clinical performance of resin-bonded allceramic restorations is questionable. In a long-term clinical study with two- and single-retainer all-ceramic (In-Ceram alumina and In-Ceram zirconia) resin-bonded fixed partial dentures fractures occurred at the connector sites which were not air abraded, but never at the retainer wings which were air abraded prior to bonding [21].
5.
Conclusions
Under the limitations of this study, these findings indicate that not only cleaning, but roughening and activating the surface by air abrasion with Al2 O3 particles prior to adhesive bonding and the use of a MDP-containing resin composite is necessary to achieve durable bond to densely sintered zirconia ceramics.
references
[1] Komine F, Tomic M, Gerds T, Strub JR. Influence of different adhesive resin cements on the fracture strength of aluminum oxide ceramic posterior crowns. J Prosthet Dent 2004;92:359–64. [2] Piconi C, Maccauro G. Zirconia as a ceramic biomaterial. Biomaterials 1999;20:1–25. [3] Burke FJ, Fleming GJ, Nathanson D, Marquis PM. Are adhesive technologies needed to support ceramics? An
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[4]
[5]
[6] [7]
[8] [9] [10] [11]
[12]
[13]
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assessment of the current evidence. J Adhes Dent 2002;4:7–22. Blatz MB, Sadan A, Martin J, Lang B. In vitro evaluation of shear bond strengths of resin to densely-sintered high-purity zirconium-oxide ceramic after long-term storage and thermal cycling. J Prosthet Dent 2004;91:356–62. Hummel M, Kern M. Durability of the resin bond strength to the alumina ceramic procera. Dent Mater 2004;20: 498–508. Friederich R, Kern M. Resin bond strength to densely sintered alumina ceramic. Int J Prosthodont 2002;15:333–8. Wegner S, Gerdes W, Kern M. Influence of storage conditions on the resin bond strength to zirconia ceramic. J Dent Res 2001;80:790 [Abstract No. 2111]. Wegner S, Kern M. Long-term resin bond strength to zirconia ceramic. J Adhes Dent 2000;2:139–45. Vogel K, Salz U. Factors influencing adhesion to Al2 O3 - and ZrO2 -ceramic. J Dent Res 1998;77:941 [Abstract No. 2475]. Kern M, Wegner SM. Bonding to zirconia ceramic: adhesion methods and their durability. Dent Mater 1998;14:64–71. ¨ Schonbrodt M, Schmage P, Nergiz I, Platzer U. Haftfestigkeit ¨ zahnfarbener Wurzelstifte in Abhangigkeit von der ¨ Oberflachenbehandlung und dem Befestigungskomposit. ¨ Dtsch Zahnarztl Z 2003;58:55–9. Blatz MB, Sadan A, Soignet D, Blatz U, Mercante D, Chiche G. Long-term resin bond to densely sintered aluminum oxide ceramic. J Esthet Restor Dent 2003;15:362–8. Discussion 9. Zhang Y, Lawn BR, Rekow ED, Thompson VP. Effect of sandblasting on the long-term performance of dental
[14]
[15]
[16]
[17]
[18]
[19]
[20]
[21]
ceramics. J Biomed Mater Res 2004;71B:381– 6. Fleming GJ, Jandu HS, Nolan L, Shaini FJ. The influence of alumina abrasion and cement lute on the strength of a porcelain laminate veneering material. J Dent 2004;32:67–74. Addison O, Fleming GJ. The influence of cement lute, thermocycling and surface preparation on the strength of a porcelain laminate veneering material. Dent Mater 2004;20:286–92. Kern M, Thompson VP. Bonding to a glass infiltrated alumina ceramic: adhesion methods and their durability. J Prosthet Dent 1995;73:240–9. ¨ Soderholm K-JM, Roberts MJ. Influence of water exposure on the tensile strength of composites. J Dent Res 1990;69:1812–6. Wada T. Development of a new adhesive material and its properties. In: Gettleman L, Vrijhoef MMA, Uchiyama Y, editors. Proceedings of the international symposium on adhesive prosthodontics. June 24, 1986. p. 9–18. Kosmac T, Oblak C, Jevnikar P, Funduk N, Marion L. Strength and reliability of surface treated Y-TZP dental ceramics. J Biomed Mater Res 2000;53:304–13. Kosmac T, Oblak C, Jevnikar P, Funduk N, Marion L. The effect of surface grinding and sandblasting on flexural strength and reliability of Y-TZP zirconia ceramic. Dent Mater 1999;15:426–33. Kern M. Clinical long-term survival of two-retainer and single-retainer all-ceramic resin-bonded fixed partial dentures. Quintessence Int 2005;36:141–7.
available at www.sciencedirect.com
journal homepage: www.intl.elsevierhealth.com/journals/dema
Durability of the resin bond strength to zirconia ceramic after using different surface conditioning methods Mona Wolfart ∗ , Frank Lehmann, Stefan Wolfart, Matthias Kern Department of Prosthodontics, Propaedeutics and Dental Materials, Dental School, Christian-Albrechts-University at Kiel, Germany
a r t i c l e
i n f o
a b s t r a c t
Article history:
Objectives. The purpose of this in vitro study was the evaluation of the bond strength and
Received 14 July 2005
its durability of two composite resins to zirconia ceramic after using different surface con-
Accepted 30 November 2005
ditioning methods. Methods. Plexiglas tubes filled with composite resin were bonded to zirconia ceramic discs (Cercon) which were either in their original state as supplied by the manufacturer only
Keywords:
cleaned in isopropanol or were cleaned with an air–powder–water spray with sodium
Cercon
hydrocarbonate solution or were air abraded (50 m Al2 O3 ). Groups of 20 specimens each
Zirconia ceramic
were bonded either with a conventional composite resin (Variolink II) or with a phosphate
Composite resin
monomer (MDP)-containing resin (Panavia F) to the ceramic discs. Subgroups of 10 bonded
Tensile bond strength
specimens were stored in distilled water (37 ◦ C) for either 3 days or for 150 days. Addition-
Surface conditions
ally, the 150 days specimens were thermal cycled 37,500 times. Statistical analyses were conducted with the Wilcoxon rank sum test adjusted by Bonferroni–Holm. Results. The initial tensile bond strength (TBS) for Variolink II ranged from 9.0 to 16.6 MPa and were significantly lower (p ≤ 0.05) than for Panavia F ranging from 18.7 to 45.0 MPa. Air abrasion resulted in significantly higher TBS (p ≤ 0.01) than the two other surface conditioning methods. After 150 days storage, only the air abraded specimens bonded with Panavia F showed high bond strengths of 39.2 MPa, whereas most other specimens debonded spontaneously or showed very low bond strengths. Significance. The use of the MDP-containing composite resin Panavia F on air abraded zirconia ceramic can be recommended as promising bonding method. © 2005 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
1.
Introduction
In recent years, the increasing demand for all-ceramic restorations led to the development of ceramic materials with optimized mechanical properties like densely sintered aluminum oxide and zirconium oxide ceramics [1,2]. These high-strength ceramics offer a wide variety of clinical applications, e.g. posts, fixed partial dentures, implant abutments and even Maryland type resin-bonded fixed partial dentures. Although adhesive cementation is recommended for all-ceramic restorations
[3], especially for the latter application, a long-term durable bond to these ceramics is indispensable for a successful restoration. Several studies investigated the bond strength and the durability of various bonding methods to high-strength oxide ceramics. It has been shown that air abrasion, which is a common method to condition the ceramic surface, and the use of phosphate monomer (MDP)-containing luting agents resulted in high and durable bond strengths [4–12]. However, it has to be taken into consideration that air abrasion might affect
∗ Corresponding author at: Department of Prosthodontics, Propaedeutics and Dental Materials, University Hospital Schleswig-HolsteinCampus Kiel, Arnold-Heller-Str. 16,24105 Kiel, Germany. Tel.: +49 431 597 2874; fax: +49 431 587 2860. E-mail address: [email protected] (M. Wolfart). 0109-5641/$ – see front matter © 2005 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.dental.2005.11.040
46
d e n t a l m a t e r i a l s 2 3 ( 2 0 0 7 ) 45–50
the ceramic surface by creating microcracks which might reduce the fracture strength of the ceramic [13]. The question arises whether this surface conditioning method could be omitted for conditioning to avoid weakening of the ceramic. On the other hand, several authors suggest that resin luting agents providing durable resin bonds significantly strengthen ceramic materials by “healing” minor surface defects caused by air abrasion [14,15]. The bond strength to alumina ceramic has been shown to be relatively low and not stable over time when the bonding agents are applied to the original ceramic surface after cleaning in 96% isopropanol [5,6]. An explanation for the low bond strength to untreated ceramic surfaces might be a certain contamination of the surface during the manufacturing process which influences the bonding mechanism but cannot be eliminated by cleaning in 96% isopropanol. Additional cleaning methods like the use of an air–powder–water spray might be more effective in cleaning the surface than isopropanol alone and might lead to higher bond strengths of composite resins to zirconia ceramic without affecting the ceramic surface adversely. The purpose of this in vitro study was to evaluate the influence of different surface conditioning methods on the bond strength of two composite resins to zirconia ceramic. Furthermore, the durability of the bond strength over 150 days storage time with additional 37,500 thermal cycles should be investigated. The null hypothesis to be tested was that bond strength is influenced by different surface conditioning methods and storage conditions.
2.
Materials and methods
Industrially manufactured discs from the densely sintered zirconia ceramic Cercon (94% ZrO2 stabilized by 5% Y2 O3 ; Cercon; Degudent, Hanau, Germany) were used in this study. The discs had a diameter of 6.4 mm and a thickness of 3.4 mm.
The materials utilized and their characteristics are listed in Table 1. Specimens were assigned to the following six groups consisting of 20 specimens each depending on the surface conditioning method and the luting resin used. After surface conditioning by the described methods, all specimens were ultrasonically cleaned in 96% isopropanol for 3 min prior to bonding. ORG-V: Heliobond followed by Variolink II were applied to the machined original ceramic surface as supplied by the manufacturer. APW-V: The ceramic surface was cleaned for 15 s with an air–powder–water spray with sodium hydrocarbonate solution (Prophy Jet; Dentsply DeTrey, Constance, Germany) prior to the application of Heliobond and Variolink II. ABR-V: The ceramic surface was air abraded with 50 m Al2 O3 at 2.5 bar pressure for 15 s at a distance of 10 mm prior to the application of Heliobond followed by Variolink II. ORG-P: Panavia F was applied to the machined original ceramic surface as supplied by the manufacturer. APW-P: The ceramic surface was cleaned for 15 s with an air–powder–water spray with sodium hydrocarbonate solution prior to the application of Panavia F. ABR-P: Panavia F was applied to the air abraded ceramic surface. Plexiglas tubes with an inner diameter of 3.3 mm were filled with self-curing composite resin Clearfil F2 (Kuraray, Osaka, Japan). After 8 min from the start of mixing, the composite tubes were bonded with the given resins to the ceramic discs using an alignment apparatus. The alignment apparatus consisted of two parallel guides, a tube holder, a silicon pad and an added weight of 750 g. The apparatus ensured that the tube axis was perpendicular to the bonding surface. The bonding method has been described in detail previously [5,16].
Table 1 – List of used materials and their characteristics System Clearfil F2
Variolink II
Panavia F
a
Component
Batch no.
Main compositiona
Manufacturer
BisGMA/TEGDMA/DMA/barium sulfate/silica cont. composite resin
Kuraray, Osaka Japan
Ivoclar Vivadent Schaan, Lichtenstein
Base paste
41148
Catalyst paste
41148
Heliobond
C50463
BisGMA/TEGDMA cont. resin
Base paste
C50466
Catalyst paste Airblock
C55106 0102001080
BisGMA/UDMA/TEGDMA/DMA/barium sulfate/Ba-Al-F-Si-glass/silica cont. composite resin Benzoylperoxide Glycerol
Paste A
00087A
Paste B Oxyguard II
00037B 00315A
BPEDMA/MDP/DMA/silica/barium sulfate/dibenzoylperoxide N,N-diethanol-p-toluidine/silica sodiumfluoride Polyethyleneglycol/glycerine/sodium benzenesulfinate cont. gel
Dentsply DeTrey, Constance, Germany Kuraray, Osaka Japan
According to the information provided by the manufacturers: BisGMA: bisphenol-A-diglycidylmethacrylate; BPEDMA: bisphenol-A-polyethoxy dimethacrylate; DMA: aliphatic dimethacrylate; MDP: 10-methacryloxydecyl dihydrogen phosphate; TEGDMA: triethyleneglycol dimethacrylate; Al: aluminium; Ba: barium; F: fluorine; Si: silicon; cont.: containing.
47
d e n t a l m a t e r i a l s 2 3 ( 2 0 0 7 ) 45–50
Excess cement was removed from the bonding margin using foam pellets and then an oxygen blocking gel was applied with a syringe (Oxyguard II for Panavia F and Airblock for Variolink II). After 5 min, the specimens were light-cured from two opposite sides for 20 s at a distance of 5 mm with a dental curing light (Optilux 500; Demetron company, Danbury, USA), after three more minutes, they were further cured in a xenon strobe light-curing unit (Dentacolor XS; HeraeusKulzer, Wehrheim, Germany) for an additional 90 s. Each bonding group was divided into two subgroups of 10 specimens each and stored in distilled water at 37 ◦ C either for 3 days without thermal cycling (TC) or for 150 days with additional 37,500 thermal cycles between 5 and 55 ◦ C (dwell time 30 s). Following the different storage times, the tensile bond strength test was performed at a crosshead speed of 2 mm/min in a universal testing machine (Zwick Z 010/TN2A; Ulm, Germany) using a special test configuration, which provided a moment-free axial force application. A collet held the tube while an alignment jig allowed self-centering of the specimens. The jig was attached to the load cell and crosshead by upper and lower chains, allowing the whole system to be selfaligning. Statistical analyses of the test results were performed using the Kruskal–Wallis test followed by multiple pair-wise comparisons of groups using the Wilcoxon rank sum test. Significance levels were adjusted with the Bonferroni–Holm correction for multiple testing. The fractured interfaces of the zirconia ceramic specimens were examined with a light microscope (Wild Makroskop M 420; Heerbrugg, Germany) at 30× magnification to calculate the debonded area which was assigned to adhesive or cohesive failure modes. After sputtering using a gold-alloy conductive layer of approximately 30 nm, representative specimens were examined using a scanning electron microscope (SEM; XL 30 CP; Philips, Eindhoven, Netherlands) with an acceleration voltage of 15 keV and a working distance of 10 mm.
age conditions. Statistically significant differences between the groups and between the storage conditions are indicated in the same table. The use of the MDP-containing composite resin on air abraded ceramic surfaces (group ABR-P) resulted in the highest bond strength values after 3 and 150 days (medians 45.0 and 39.2 MPa, respectively). The initial bond strengths (3 days storage) for the groups with original surfaces and surfaces cleaned with air–powder–water spray were significantly lower (p ≤ 0.01) than for the groups with air abraded surfaces for both the MDPcontaining composite resin and the conventional composite resin. Specimens bonded with the MDP-containing composite resin showed significantly higher bond strengths than specimens bonded with the conventional composite resin for all three surface conditioning methods (p ≤ 0.05). During the 150 days storage time and 37,500 TC, all specimens of the groups ORG-P, ORG-V, APW-V and ABR-V debonded spontaneously. In the group APW-P, only three of the ten specimens did not debond. These three specimens showed low bond strengths of 4.4, 9.0 and 10.7 MPa, respectively. Although the bond strengths for the specimens of group ABR-P decreased slightly over 150 days storage and TC, this decrease was not statistically significant (p > 0.05). The distribution of the failure modes for all groups is shown in Fig. 1. For all groups bonded with the conventional composite resin, the failure modes were completely adhesive. For the air abraded specimens bonded with the MDP-containing composite resin, the failure mode was completely cohesive after 3 days and mostly cohesive (98%) after 150 days, whereas the specimens with original surface and the specimens cleaned with air–powder–water spray showed a predominantly cohesive failure mode after 3 days, but a nearly 100% adhesive failure mode after 150 days. Representative SEM photographs of the fracture interfaces after tensile testing are shown in Figs. 2–4.
3.
4.
Results
The tensile bond strength (TBS) values are summarized in Table 2 for the six bonding groups and the two different stor-
Discussion
The results of the present study show that the bond strength was influenced by both, the different surface conditioning
Table 2 – Tensile bond strength to zirconia ceramic with different surface conditioning methods Groups
Storage time 3 days/0 TC Median
ORG-V APW-V ABR-V ORG-P APW-P ABR-P
11.0A a 9.0A a 16.6B,E a 18.7C,E a 32.1C a 45.0D a
25th/75th percentile 9.7/12.2 7.4/10.3 15.5/20.7 16.8/25.8 17.7/34.2 43.9/45.8
150 days/37,500 TC Median 0.0A b 0.0A b 0.0A b 0.0A b 0.0A b 39.2B a
25th/75th percentile 0.0/0.0 0.0/0.0 0.0/0.0 0.0/0.0 0.0/4.4 34.4/46.2
Median: 25th and 75th in MPa (n = 10). TC: thermal cycles. Within the same column: median values with the same upper case superscript letters (A–E) are not statistically different (p > 0.05). Within the same row, median values with the same lower case subscript letters (a and b) are not statistically different (p > 0.05). Global Kruskal–Wallis test followed by pair-wise comparison using the Wilcoxon test adjusted by Bonferroni–Holm.
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Fig. 1 – Mean percentages of areas assigned to the failure modes observed in the six bonding groups after different storage times.
Fig. 2 – SEM photograph of a sample from group ABR-V after 150 days storage. The failure mode was completely adhesive.
Fig. 3 – SEM photograph of a sample from group ABR-P after 150 days storage. The failure mode was completely cohesive.
d e n t a l m a t e r i a l s 2 3 ( 2 0 0 7 ) 45–50
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Fig. 4 – SEM photograph of a sample from group APW-P with mixed failure mode after 150 days storage.
methods and the storage conditions. Air abraded specimens bonded with the MDP-containing composite resin showed the highest bond strengths. A slight decrease in bond strength was observed over 150 days storage time with TC which, however, was not statistically significant. This decrease might be due to a certain degeneration of the resin itself, which has already been shown for other resins [17]. This is supported by the fact that for both the 3 and 150 days specimens a completely or nearly completely cohesive failure mode was found in this group as indicated by light microscope (Fig. 1) and confirmed by SEM (Fig. 3). Several studies investigated different bonding methods for example different silicoating methods, silanization, acrylization or the use of different bonding agents to alumina and zirconia ceramic. However, a high and durable bond strength was only achieved on air abraded surfaces with the use of a MDPcontaining primer [5] or a MDP-containing composite resin [5,6,8,10]. These findings confirm the results of the present study as the group of the air abraded specimens bonded with the MDP-containing composite resin showed a durable bond strength over 150 days, while the specimens bonded with the conventional composite resin debonded spontaneously during this period. The phosphate ester group of the adhesive monomer MDP bonds directly to metal oxides [18], therefore, the above cited studies and the present results suggest a chemical bond between MDP and both aluminum and zirconium oxides. The application of the two composite resins Panavia F and Variolink II to the original surface of the zirconia ceramic discs resulted in low initial bond strengths as it was already shown for densely sintered alumina ceramics [5,6]. Furthermore, the bond was not stable over time as all specimens with original surface conditions debonded spontaneously during 150 days storage and TC. Similar results were found in the present study after cleaning the ceramic surface by air–powder–water spray which did not result in higher bond strengths than bonding to the original surface independent from the bonding resin used. After long-term storage and TC, only three specimens of the APW-P group (which showed significantly lower bond strengths) had not debonded spontaneously. It can be
assumed that the monomer MDP was not able to create a stable bond neither to the machined surface nor to the surface cleaned by air–powder–water spray. Presumably, cleaning the ceramic surface by air–powder–water spray does not result in structural changes on the ceramic surface as they occur after air abrasion. Nevertheless, these changes seem to be necessary to achieve a stable bond to zirconia ceramic. Although there are studies indicating that air abrasion affects the surface of zirconia ceramic which leads to a reduction of the flexural strength of these ceramics [13], there are other authors who showed that air abrasion might even strengthen zirconia ceramics [19,20]. Furthermore, a negative effect of the microcracks on the ceramic surface caused by air abrasion on the clinical performance of resin-bonded allceramic restorations is questionable. In a long-term clinical study with two- and single-retainer all-ceramic (In-Ceram alumina and In-Ceram zirconia) resin-bonded fixed partial dentures fractures occurred at the connector sites which were not air abraded, but never at the retainer wings which were air abraded prior to bonding [21].
5.
Conclusions
Under the limitations of this study, these findings indicate that not only cleaning, but roughening and activating the surface by air abrasion with Al2 O3 particles prior to adhesive bonding and the use of a MDP-containing resin composite is necessary to achieve durable bond to densely sintered zirconia ceramics.
references
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