Self-adhesive Resin Cements: Adhesive Performance to Indirect Restorative Ceramics José Zorzina / Renan Bellib / Andrea Wagnerc / Anselm Petscheltd / Ulrich Lohbauere Purpose: To evaluate the bonding performance of self-adhesive resin cements to zirconia and lithium disilicate in self- and dual-curing modes before and after thermocycling. Materials and Methods: Rectangular bars (3 mm high, 3 mm wide, 9 mm long) were manufactured from zirconia (Vita In-Ceram YZ for inLab, VITA) and lithium disilicate blocks (IPS e.max Press, Ivoclar Vivadent) (n = 240 per material). Zirconia bars were sandblasted (35 μm Al2O3, 1.5 bar pressure). Lithium disilicate bars were HF etched (20 s, IPS Ceramic Etching Gel, Ivoclar Vivadent) and silanized with ESPE Sil (3M ESPE). Forty bars of zirconia were luted in twos perpendicular to each other as were 40 bars of lithium disilicate using RelyX Unicem Automix 2 (3M ESPE), G-Cem LinkAce (GC Europe) or Maxcem Elite (Kerr) in self- or dual-curing mode. Half of the specimens from each material were submitted to tensile bond strength (TBS) testing after 24-h storage in distilled water at 37°C, and half underwent TBS testing after thermocycling (5000 cycles, 5°C/55°C, 30-s dwell time). Bond strength values for each bonding substrate were analyzed using one-way ANOVA (Student-NewmanKeuls, α = 0.05). Results: On zirconia, dual-curing resulted in significantly (p < 0.05) higher tensile bond strengths compared to self-curing, with the exception of RelyX Unicem 2 after thermocycling. Thermocycling significantly (p < 0.05) reduced the tensile bond strength of Maxcem Elite to zirconia in both curing modes. The TBS of self-adhesive cements to lithium disilicate showed no significant (p > 0.05) difference between the different curing modes and after thermocycling. Conclusion: For most of the investigated self-adhesive cements, bond strengths to zirconia were increased by dual curing; this was not true for lithium disilicate. For luting on zirconia with self-adhesive cements, dual curing is strongly recommended in clinical situations. Keywords: self-adhesive resin cements, tensile bond strength, zirconia, lithium disilicate, thermocycling J Adhes Dent 2014; 16: 541–546. doi: 10.3290/j.jad.a33201
a
Research Assistant, Dental Clinic 1, Department of Restorative Dentistry and Periodontology, Friedrich Alexander University Erlangen-Nürnberg, Erlangen, Germany. Idea, hypothesis, performed the experiments and statistical evaluation, wrote the manuscript in partial fulfillment of requirements for post-doctoral “Dr. Habil.” degree.
b
Research Associate, Dental Clinic 1, Department of Restorative Dentistry and Periodontology, Friedrich Alexander University Erlangen-Nürnberg, Erlangen, Germany. Idea, hypothesis, proofread the manuscript, contributed substantially to discussion, consulted on statistical evaluation.
c
Research Assistant, Dental Clinic 1, Department of Restorative Dentistry and Periodontology, Friedrich Alexander University Erlangen-Nürnberg, Erlangen, Germany. Idea, hypothesis, performed the experiments.
d
Professor and Department Chair, Dental Clinic 1, Department of Restorative Dentistry and Periodontology, Friedrich Alexander University Erlangen-Nürnberg, Erlangen, Germany. Proofread the manuscript, contributed substantially to discussion.
e
Associate Professor, Dental Clinic 1, Department of Restorative Dentistry and Periodontology, Friedrich Alexander University Erlangen-Nürnberg, Erlangen, Germany. Idea, hypothesis, experimental design, consulted on statistical evaluation, contributed substantially to discussion, proofread the manuscript.
Correspondence: Dr. José Zorzin, Dental Clinic 1, Department of Restorative Dentistry and Periodontology, Friedrich Alexander University Erlangen-Nürnberg, Glückstr. 11, D-91054 Erlangen, Germany. Tel: +49-9131-853-6479, Fax: +49-9131-853-3603. e-mail: [email protected]
Vol 16, No 6, 2014
Submitted for publication: 24.05.14; accepted for publication: 09.10.14
I
n order to achieve bonding to tooth and restoration, self-adhesive cements employ a complex chemistry based on (meth)acrylate monomers containing carboxylic or phosphoric acid groups. These are hydrolyzed and attach to hydroxyapatite via hydrogen bonding, resulting in a complex with low initial pH and high hydrophilicity.10 On the restoration side, chemical bonding is mediated by a silane coupling agent on silica-based ceramics or by directly established phosphate links to zirconia substrates.8 Once the bonding domains are created, the reaction takes the route of pH neutralization, based on the acid-base reaction between acidic groups of functionalized monomers and ions of the acid-soluble glass fillers, calcium hydroxide,14 or the mineralized tooth tissue.10 Significant differences in pH neutralization behavior have been observed among different self-adhesive cements.20 Improper pH neutralization leads to excessive hydrophilicity of the cured cement, subsequent reduction of mechanical properties,14,20 and increased volume expansion15 due to water sorption. The setting mechanism of self-adhesive resin cements follows a typical chemical- and light-curing free-radical po541
Zorzin et al
Table 1
Materials used (information as disclosed by the manufacturers)
Material
Manufacturer, Batch No.
Shade Lot
Contents
Fillers
RelyX Unicem 2 Automix
3M ESPE (Seefeld, Germany) 4955054
A2
Base paste: mono-, di- and triglycerine dimethacrylate ester of phosphoric acid 20-30 wt%, 2,2’-ethylene dioxydiethylmethacrylate 10-20 wt% Catalyst paste: bisphenol A bis3- (methacryloxypropyl) ether substituted dimethacrylate 20-30 wt%, barbituric acid 0.05) differences in the bond strength to lithium disilicate were detected. This was found within each material cement group (ir544
Fig 2 Mean tensile bond strength (MPa) and standard deviation on zirconia for self- and dual-curing modes, before and after thermocycling.
respective of the curing mode or thermocycling status) as well as between the respective groups (eg, within the self-curing groups, etc).
DISCUSSION For TBS testing, the experimental set-up described by Lohbauer12 and Amaral4 was chosen as it eliminates shear stress and provides a purely tensile stress along the interface plane. The low compliance rope (Dyneema SK75, DSM Dyneema) and the pulley to carry the rope ensured balanced force distributions at the two loading points. In contrast to e.max CAD, e.max PRESS ingots are already in the final crystallized state. The e.max PRESS ingots are just made molten again for injection. No changes in crystal structure can be found between the e.max PRESS ingots (before pressing) and the final restoration (after pressing). This can be seen macroscopically when HF-etching the ingot. It will show the same opaque surface as the etched pressed restoration. In SEM images, the same crystals structure can be seen before and after pressing. Thus, the ceramic structure used in the experiment in this study is the same as that used in the oral cavity. The pretreatment protocol used for zirconia in this study involved sandblasting without priming, which leads to tensile bond strengths comparable to those attained for lithium disilicate after HF etching and silanization. Many reports have shown that bond strength to zirconia is improved by airborne particle abrasion, which increases the surface area through roughening.4,5 Besides micromechanical retention, chemical bonding between phosphate monomers and zirconia also takes place.8 The Journal of Adhesive Dentistry
Zorzin et al
Tensile bond-strength [MPa]
40
Fig 3 Mean tensile bond strength (in MPa) and standard deviation on lithium disilicate for self- and dual-curing modes, before and after thermocycling.
35
24 h
30
Thermocycling
25 20 15 10 5 0 Self-curing Dual-curing Self-curing Dual-curing Self-curing Dual-curing RelyX Unicem 2
The first null hypothesis, ie, that the curing mode has no influence on bond strength, must be partially rejected for bonding to zirconia and accepted for the lithium disilicate substrate. The measured TBS values on zirconia were affected most by the selected curing mode. Dualcured specimens had significantly higher bond strength values than those that were only self-cured when zirconia was used as the substrate (Table 2). On lithium disilicate, dual-cured specimens had no statistically significant higher bond strength values than self-cured specimens (Table 3). It is known that dual curing of self-adhesive resin cements results in a higher degree of conversion18 and extent of polymerization.6 Sufficient curing is crucial to achieve adequate physical and mechanical material properties,11 in this case, higher cohesive strength of the self-adhesive luting agents and thus higher bond strength.3 Phosphoric acid-functionalized monomers are suspected to compete for free radicals and interfere with polymerization,1 resulting in a low degree of conversion18 and extent of polymerization.6 For self-adhesive resin cements in self-curing mode, a significantly lower degree of conversion and lower bond strength has been shown in the recent literature,2,3,16 which was confirmed by the results of the present study. On zirconia, the second null hypothesis must be rejected, as significant differences between the bonding ability of the self-adhesive cements were observed. In both the self-curing and dual-curing mode after 24 h, GCem LinkAce achieved 21.45 MPa, the significantly highest mean value compared to RelyX Unicem 2 and Maxcem Elite. The bonding ability of self-adhesive resin cements is mainly based upon phosphoric acid-functionalized monomers.10 Based on the results, it can be presumed that material chemistry plays a central role in the 24-h efficacy of bonding to zirconia. Such differences are difficult to discuss, as the chemical formulations are protected by manufacturers (Table 1). Vol 16, No 6, 2014
G-Cem LinkAce
Maxcem Elite
For cementation to zirconia without separate primer application before luting, bonding efficacy depends entirely on the luting agent and its mechanical stability. In order to challenge the mechanical stability, thermal loading was performed on the adhesive interface. Due to their acid-functionalized monomers, self-adhesive resin cements have a low pH upon mixing, allowing them to demineralize enamel and dentin, attach to the hydroxyapatite calciumions, and create a bond to the tooth via ionized phosphoric-acid methacrylates.10,15 Studies have demonstrated that the long-term mechanical stability of self-adhesive resin cements in self-curing mode is significantly influenced by their pH-neutralization behavior.20 That study showed that materials with insufficient pH neutralization, such as Maxcem Elite, experienced a significant decrease in flexural strength after thermocycling, whereas materials with better pH neutralization, eg, RelyX Unicem 2, showed no decrease in mechanical properties. This correlates with the findings of this study, in which the TBS of Maxcem Elite to zirconia dropped significantly after thermocycling from 14.54 MPa to 3.89 MPa in self-curing mode and from 19.89 MPa to 14.21 MPa in dual-curing mode. In contrast, no significant differences in TBS after thermal loading could be shown for RelyX Unicem 2 and G-Cem LinkAce. Therefore, the null hypothesis that thermocycling has no significant influence on bond strength has to be partially rejected for luting to zirconia. For the lithium disilicate ceramic, thermocycling had no significant influence on bond strength. Luting to lithium-disilicate specimens was performed using a separate ethanol-based 3-methacryloxypropyltrimethoxy silane silane-coupling agent. This methacrylate-free primer was employed to avoid undesirable interactions, such as inhibition of the condensation reaction between the silanol of the primer and the ceramic.7 In this case, the primary link between the bonding substrate and the luting agent is the 545
Zorzin et al
silanized ceramic surface and not the self-adhesive resin, so that the bonding to the ceramic is primarily generated by the silane. Differences in the bonding performance of the different materials and the mechanisms discussed above leading to them are thereby attenuated. This is probably the reason that no significant differences were observed in either curing mode after 24 h or thermocycling among different cements. Therefore, the second null hypothesis that the self-adhesive cement used does not influence bond strength to lithium disilicate is accepted. The statistically nonsignificant decrease in bond strength after thermocycling can be attributed in part to the loss of mechanical stability of the cements discussed above. A degradation of the siloxane network resulting in loss of bond strength13 between the lithium disilicate and the self-adhesive resin cement does not seem likely.
5.
6.
7.
8.
9.
10.
11. 12.
CONCLUSION Within the limits of this study, it can be concluded that self-adhesive resin cements effectively bond to zirconia without the need for a separate priming procedure, making them an attractive alternative for routine luting of zirconia crowns. However, the resulting bond strength to zirconia varies among the different brands of self-adhesive cements. This was not observed for luting to lithium disilicate. As the selected curing mode had the greatest influence on the measured bond strengths to zirconia, light curing of self-adhesive resin cements is strongly recommended whenever it is clinically possible, in order to achieve reliable, stable long-term bonding.
13. 14.
15. 16.
17.
18. 19.
ACKNOWLEDGMENTS The manufacturers supplied the materials examined.
20.
Blatz M, Phark J-H, Özer F, Mante F, Saleh N, Bergler M, Sadan A. In vitro comparative bond strength of contemporary self-adhesive resin cements to zirconium oxide ceramic with and without air-particle abrasion. Clin Oral Investig 2010;14:187-192. Cadenaro M, Navarra CO, Antoniolli F, Mazzoni A, Di Lenarda R, Rueggeberg FA, Breschi L. The effect of curing mode on extent of polymerization and microhardness of dual-cured, self-adhesive resin cements. Am J Dent 2010;23:14-18. Chen L, Shen H, Suh BI. Effect of incorporating BisGMA resin on the bonding properties of silane and zirconia primers. J Prosthet Dent 2013;110:402-407. Chen L, Suh BI, Brown D, Chen X. Bonding of primed zirconia ceramics: evidence of chemical bonding and improved bond strengths. Am J Dent 2012;25:103-108. Ferracane JL, Mitchem JC, Condon JR, Todd R. Wear and marginal breakdown of composites with various degrees of cure. J Dent Res 1997;76:1508-1516. Ferracane JL, Stansbury JW, Burke FJ. Self-adhesive resin cements – chemistry, properties and clinical considerations. J Oral Rehabil 2011;38:295-314. Li J, Li H, Fok AS, Watts DC. Multiple correlations of material parameters of light-cured dental composites. Dent Mater 2009;25:829-836. Lohbauer U, Zipperle M, Rischka K, Petschelt A, Müller FA. Hydroxylation of dental zirconia surfaces: characterization and bonding potential. J Biomed Mater Res B Appl Biomater 2008;87:461-467. Lung CYK, Matinlinna JP. Aspects of silane coupling agents and surface conditioning in dentistry: an overview. Dent Mater 2012;28:467-477. Madruga FC, Ogliari FA, Ramos TS, Bueno M, Moraes RR. Calcium hydroxide, pH-neutralization and formulation of model self-adhesive resin cements. Dent Mater 2013;29:413-418. Park JW, Ferracane JL. Water aging reverses residual stresses in hydrophilic dental composites. J Dent Res 2014;93:195-200. Sabatini C, Patel M, D’Silva E. In vitro shear bond strength of three selfadhesive resin cements and a resin-modified glass ionomer cement to various prosthodontic substrates. Oper Dent 2012;38:186-196. Van Landuyt KL, Nawrot T, Geebelen B, De Munck J, Snauwaert J, Yoshihara K, Scheers H, Godderis L, Hoet P, Van Meerbeek B. How much do resin-based dental materials release? A meta-analytical approach. Dent Mater 2011;27:723-747. Vrochari AD, Eliades G, Hellwig E, Wrbas K-T. Curing efficiency of four selfetching, self-adhesive resin cements. Dent Mater 2009;25:1104-1108. Vrochari AD, Eliades G, Hellwig E, Wrbas KT. Water sorption and solubility of four self-etching, self-adhesive resin luting agents. J Adhes Dent 2010;12:39-43. Zorzin J, Petschelt A, Ebert J, Lohbauer U. pH neutralization and influence on mechanical strength in self-adhesive resin luting agents. Dent Mater 2012;28:672-679.
REFERENCES 1.
2.
3.
4.
Adusei G, Deb S, Nicholson JW, Mou L, Singh G. Polymerization behavior of an organophosphorus monomer for use in dental restorative materials. J Applied Polymer Sci 2003;88:565-569. Aguiar T, Pinto C, Cavalli V, Nobre-Dos-Santos M, Ambrosano G, Mathias P, Gianinni M. Influence of the curing mode on fluoride ion release of self-adhesive resin luting cements in water or during pH-cycling regimen. Oper Dent 2012;37:63-70. Aguiar TR, Di Francescantonio M, Ambrosano GMB, Giannini M. Effect of curing mode on bond strength of self-adhesive resin luting cements to dentin. J Biomed Mater Res B Appl Biomater 2010;93B:122-127. Amaral M, Belli R, Cesar PF, Valandro LF, Petschelt A, Lohbauer U. The potential of novel primers and universal adhesives to bond to zirconia. J Dent 2014;42:90-98.
546
Clinical relevance: As the selected curing mode had the greatest influence on the measured bond strengths to zirconia, light curing of self-adhesive resin cements is strongly recommended whenever it is clinically possible, in order to achieve reliable, stable long-term bonding. Furthermore, clinicians must take into account that bond strength to zirconia varies among the different brands of self-adhesive cements.
The Journal of Adhesive Dentistry
a
Research Assistant, Dental Clinic 1, Department of Restorative Dentistry and Periodontology, Friedrich Alexander University Erlangen-Nürnberg, Erlangen, Germany. Idea, hypothesis, performed the experiments and statistical evaluation, wrote the manuscript in partial fulfillment of requirements for post-doctoral “Dr. Habil.” degree.
b
Research Associate, Dental Clinic 1, Department of Restorative Dentistry and Periodontology, Friedrich Alexander University Erlangen-Nürnberg, Erlangen, Germany. Idea, hypothesis, proofread the manuscript, contributed substantially to discussion, consulted on statistical evaluation.
c
Research Assistant, Dental Clinic 1, Department of Restorative Dentistry and Periodontology, Friedrich Alexander University Erlangen-Nürnberg, Erlangen, Germany. Idea, hypothesis, performed the experiments.
d
Professor and Department Chair, Dental Clinic 1, Department of Restorative Dentistry and Periodontology, Friedrich Alexander University Erlangen-Nürnberg, Erlangen, Germany. Proofread the manuscript, contributed substantially to discussion.
e
Associate Professor, Dental Clinic 1, Department of Restorative Dentistry and Periodontology, Friedrich Alexander University Erlangen-Nürnberg, Erlangen, Germany. Idea, hypothesis, experimental design, consulted on statistical evaluation, contributed substantially to discussion, proofread the manuscript.
Correspondence: Dr. José Zorzin, Dental Clinic 1, Department of Restorative Dentistry and Periodontology, Friedrich Alexander University Erlangen-Nürnberg, Glückstr. 11, D-91054 Erlangen, Germany. Tel: +49-9131-853-6479, Fax: +49-9131-853-3603. e-mail: [email protected]
Vol 16, No 6, 2014
Submitted for publication: 24.05.14; accepted for publication: 09.10.14
I
n order to achieve bonding to tooth and restoration, self-adhesive cements employ a complex chemistry based on (meth)acrylate monomers containing carboxylic or phosphoric acid groups. These are hydrolyzed and attach to hydroxyapatite via hydrogen bonding, resulting in a complex with low initial pH and high hydrophilicity.10 On the restoration side, chemical bonding is mediated by a silane coupling agent on silica-based ceramics or by directly established phosphate links to zirconia substrates.8 Once the bonding domains are created, the reaction takes the route of pH neutralization, based on the acid-base reaction between acidic groups of functionalized monomers and ions of the acid-soluble glass fillers, calcium hydroxide,14 or the mineralized tooth tissue.10 Significant differences in pH neutralization behavior have been observed among different self-adhesive cements.20 Improper pH neutralization leads to excessive hydrophilicity of the cured cement, subsequent reduction of mechanical properties,14,20 and increased volume expansion15 due to water sorption. The setting mechanism of self-adhesive resin cements follows a typical chemical- and light-curing free-radical po541
Zorzin et al
Table 1
Materials used (information as disclosed by the manufacturers)
Material
Manufacturer, Batch No.
Shade Lot
Contents
Fillers
RelyX Unicem 2 Automix
3M ESPE (Seefeld, Germany) 4955054
A2
Base paste: mono-, di- and triglycerine dimethacrylate ester of phosphoric acid 20-30 wt%, 2,2’-ethylene dioxydiethylmethacrylate 10-20 wt% Catalyst paste: bisphenol A bis3- (methacryloxypropyl) ether substituted dimethacrylate 20-30 wt%, barbituric acid 0.05) differences in the bond strength to lithium disilicate were detected. This was found within each material cement group (ir544
Fig 2 Mean tensile bond strength (MPa) and standard deviation on zirconia for self- and dual-curing modes, before and after thermocycling.
respective of the curing mode or thermocycling status) as well as between the respective groups (eg, within the self-curing groups, etc).
DISCUSSION For TBS testing, the experimental set-up described by Lohbauer12 and Amaral4 was chosen as it eliminates shear stress and provides a purely tensile stress along the interface plane. The low compliance rope (Dyneema SK75, DSM Dyneema) and the pulley to carry the rope ensured balanced force distributions at the two loading points. In contrast to e.max CAD, e.max PRESS ingots are already in the final crystallized state. The e.max PRESS ingots are just made molten again for injection. No changes in crystal structure can be found between the e.max PRESS ingots (before pressing) and the final restoration (after pressing). This can be seen macroscopically when HF-etching the ingot. It will show the same opaque surface as the etched pressed restoration. In SEM images, the same crystals structure can be seen before and after pressing. Thus, the ceramic structure used in the experiment in this study is the same as that used in the oral cavity. The pretreatment protocol used for zirconia in this study involved sandblasting without priming, which leads to tensile bond strengths comparable to those attained for lithium disilicate after HF etching and silanization. Many reports have shown that bond strength to zirconia is improved by airborne particle abrasion, which increases the surface area through roughening.4,5 Besides micromechanical retention, chemical bonding between phosphate monomers and zirconia also takes place.8 The Journal of Adhesive Dentistry
Zorzin et al
Tensile bond-strength [MPa]
40
Fig 3 Mean tensile bond strength (in MPa) and standard deviation on lithium disilicate for self- and dual-curing modes, before and after thermocycling.
35
24 h
30
Thermocycling
25 20 15 10 5 0 Self-curing Dual-curing Self-curing Dual-curing Self-curing Dual-curing RelyX Unicem 2
The first null hypothesis, ie, that the curing mode has no influence on bond strength, must be partially rejected for bonding to zirconia and accepted for the lithium disilicate substrate. The measured TBS values on zirconia were affected most by the selected curing mode. Dualcured specimens had significantly higher bond strength values than those that were only self-cured when zirconia was used as the substrate (Table 2). On lithium disilicate, dual-cured specimens had no statistically significant higher bond strength values than self-cured specimens (Table 3). It is known that dual curing of self-adhesive resin cements results in a higher degree of conversion18 and extent of polymerization.6 Sufficient curing is crucial to achieve adequate physical and mechanical material properties,11 in this case, higher cohesive strength of the self-adhesive luting agents and thus higher bond strength.3 Phosphoric acid-functionalized monomers are suspected to compete for free radicals and interfere with polymerization,1 resulting in a low degree of conversion18 and extent of polymerization.6 For self-adhesive resin cements in self-curing mode, a significantly lower degree of conversion and lower bond strength has been shown in the recent literature,2,3,16 which was confirmed by the results of the present study. On zirconia, the second null hypothesis must be rejected, as significant differences between the bonding ability of the self-adhesive cements were observed. In both the self-curing and dual-curing mode after 24 h, GCem LinkAce achieved 21.45 MPa, the significantly highest mean value compared to RelyX Unicem 2 and Maxcem Elite. The bonding ability of self-adhesive resin cements is mainly based upon phosphoric acid-functionalized monomers.10 Based on the results, it can be presumed that material chemistry plays a central role in the 24-h efficacy of bonding to zirconia. Such differences are difficult to discuss, as the chemical formulations are protected by manufacturers (Table 1). Vol 16, No 6, 2014
G-Cem LinkAce
Maxcem Elite
For cementation to zirconia without separate primer application before luting, bonding efficacy depends entirely on the luting agent and its mechanical stability. In order to challenge the mechanical stability, thermal loading was performed on the adhesive interface. Due to their acid-functionalized monomers, self-adhesive resin cements have a low pH upon mixing, allowing them to demineralize enamel and dentin, attach to the hydroxyapatite calciumions, and create a bond to the tooth via ionized phosphoric-acid methacrylates.10,15 Studies have demonstrated that the long-term mechanical stability of self-adhesive resin cements in self-curing mode is significantly influenced by their pH-neutralization behavior.20 That study showed that materials with insufficient pH neutralization, such as Maxcem Elite, experienced a significant decrease in flexural strength after thermocycling, whereas materials with better pH neutralization, eg, RelyX Unicem 2, showed no decrease in mechanical properties. This correlates with the findings of this study, in which the TBS of Maxcem Elite to zirconia dropped significantly after thermocycling from 14.54 MPa to 3.89 MPa in self-curing mode and from 19.89 MPa to 14.21 MPa in dual-curing mode. In contrast, no significant differences in TBS after thermal loading could be shown for RelyX Unicem 2 and G-Cem LinkAce. Therefore, the null hypothesis that thermocycling has no significant influence on bond strength has to be partially rejected for luting to zirconia. For the lithium disilicate ceramic, thermocycling had no significant influence on bond strength. Luting to lithium-disilicate specimens was performed using a separate ethanol-based 3-methacryloxypropyltrimethoxy silane silane-coupling agent. This methacrylate-free primer was employed to avoid undesirable interactions, such as inhibition of the condensation reaction between the silanol of the primer and the ceramic.7 In this case, the primary link between the bonding substrate and the luting agent is the 545
Zorzin et al
silanized ceramic surface and not the self-adhesive resin, so that the bonding to the ceramic is primarily generated by the silane. Differences in the bonding performance of the different materials and the mechanisms discussed above leading to them are thereby attenuated. This is probably the reason that no significant differences were observed in either curing mode after 24 h or thermocycling among different cements. Therefore, the second null hypothesis that the self-adhesive cement used does not influence bond strength to lithium disilicate is accepted. The statistically nonsignificant decrease in bond strength after thermocycling can be attributed in part to the loss of mechanical stability of the cements discussed above. A degradation of the siloxane network resulting in loss of bond strength13 between the lithium disilicate and the self-adhesive resin cement does not seem likely.
5.
6.
7.
8.
9.
10.
11. 12.
CONCLUSION Within the limits of this study, it can be concluded that self-adhesive resin cements effectively bond to zirconia without the need for a separate priming procedure, making them an attractive alternative for routine luting of zirconia crowns. However, the resulting bond strength to zirconia varies among the different brands of self-adhesive cements. This was not observed for luting to lithium disilicate. As the selected curing mode had the greatest influence on the measured bond strengths to zirconia, light curing of self-adhesive resin cements is strongly recommended whenever it is clinically possible, in order to achieve reliable, stable long-term bonding.
13. 14.
15. 16.
17.
18. 19.
ACKNOWLEDGMENTS The manufacturers supplied the materials examined.
20.
Blatz M, Phark J-H, Özer F, Mante F, Saleh N, Bergler M, Sadan A. In vitro comparative bond strength of contemporary self-adhesive resin cements to zirconium oxide ceramic with and without air-particle abrasion. Clin Oral Investig 2010;14:187-192. Cadenaro M, Navarra CO, Antoniolli F, Mazzoni A, Di Lenarda R, Rueggeberg FA, Breschi L. The effect of curing mode on extent of polymerization and microhardness of dual-cured, self-adhesive resin cements. Am J Dent 2010;23:14-18. Chen L, Shen H, Suh BI. Effect of incorporating BisGMA resin on the bonding properties of silane and zirconia primers. J Prosthet Dent 2013;110:402-407. Chen L, Suh BI, Brown D, Chen X. Bonding of primed zirconia ceramics: evidence of chemical bonding and improved bond strengths. Am J Dent 2012;25:103-108. Ferracane JL, Mitchem JC, Condon JR, Todd R. Wear and marginal breakdown of composites with various degrees of cure. J Dent Res 1997;76:1508-1516. Ferracane JL, Stansbury JW, Burke FJ. Self-adhesive resin cements – chemistry, properties and clinical considerations. J Oral Rehabil 2011;38:295-314. Li J, Li H, Fok AS, Watts DC. Multiple correlations of material parameters of light-cured dental composites. Dent Mater 2009;25:829-836. Lohbauer U, Zipperle M, Rischka K, Petschelt A, Müller FA. Hydroxylation of dental zirconia surfaces: characterization and bonding potential. J Biomed Mater Res B Appl Biomater 2008;87:461-467. Lung CYK, Matinlinna JP. Aspects of silane coupling agents and surface conditioning in dentistry: an overview. Dent Mater 2012;28:467-477. Madruga FC, Ogliari FA, Ramos TS, Bueno M, Moraes RR. Calcium hydroxide, pH-neutralization and formulation of model self-adhesive resin cements. Dent Mater 2013;29:413-418. Park JW, Ferracane JL. Water aging reverses residual stresses in hydrophilic dental composites. J Dent Res 2014;93:195-200. Sabatini C, Patel M, D’Silva E. In vitro shear bond strength of three selfadhesive resin cements and a resin-modified glass ionomer cement to various prosthodontic substrates. Oper Dent 2012;38:186-196. Van Landuyt KL, Nawrot T, Geebelen B, De Munck J, Snauwaert J, Yoshihara K, Scheers H, Godderis L, Hoet P, Van Meerbeek B. How much do resin-based dental materials release? A meta-analytical approach. Dent Mater 2011;27:723-747. Vrochari AD, Eliades G, Hellwig E, Wrbas K-T. Curing efficiency of four selfetching, self-adhesive resin cements. Dent Mater 2009;25:1104-1108. Vrochari AD, Eliades G, Hellwig E, Wrbas KT. Water sorption and solubility of four self-etching, self-adhesive resin luting agents. J Adhes Dent 2010;12:39-43. Zorzin J, Petschelt A, Ebert J, Lohbauer U. pH neutralization and influence on mechanical strength in self-adhesive resin luting agents. Dent Mater 2012;28:672-679.
REFERENCES 1.
2.
3.
4.
Adusei G, Deb S, Nicholson JW, Mou L, Singh G. Polymerization behavior of an organophosphorus monomer for use in dental restorative materials. J Applied Polymer Sci 2003;88:565-569. Aguiar T, Pinto C, Cavalli V, Nobre-Dos-Santos M, Ambrosano G, Mathias P, Gianinni M. Influence of the curing mode on fluoride ion release of self-adhesive resin luting cements in water or during pH-cycling regimen. Oper Dent 2012;37:63-70. Aguiar TR, Di Francescantonio M, Ambrosano GMB, Giannini M. Effect of curing mode on bond strength of self-adhesive resin luting cements to dentin. J Biomed Mater Res B Appl Biomater 2010;93B:122-127. Amaral M, Belli R, Cesar PF, Valandro LF, Petschelt A, Lohbauer U. The potential of novel primers and universal adhesives to bond to zirconia. J Dent 2014;42:90-98.
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Clinical relevance: As the selected curing mode had the greatest influence on the measured bond strengths to zirconia, light curing of self-adhesive resin cements is strongly recommended whenever it is clinically possible, in order to achieve reliable, stable long-term bonding. Furthermore, clinicians must take into account that bond strength to zirconia varies among the different brands of self-adhesive cements.
The Journal of Adhesive Dentistry
