Surface Treatments for Zirconia Bonding: A Clinical Perspective
Surface Treatments for Zirconia Bonding: A Clinical Perspective Surface Treatments for Zirconia Bonding: A Clinical Perspective
SURFACE TREATMENTS FOR ZIRCONIA BONDING: A CLINICAL PERSPECTIVEABSTRACTThere has been a monumental shift in the use of zirconia in esthetic/restorative dentistry.Zirconia-based restorative materials exhibit improved strength, versatility of clinicalindications, and the ability to be CAD/CAM milled. They are also an alternative to theincreasingly higher cost of precious metals. As well, the creation of surface adhesiveprimers that create covalent bonding to zirconia will only help to propagate zirconia’s usein clinical dentistry.RÉSUMÉIl y a eu un changement monumental dans l’utilisation de la zircone (oxyde de zirconium)en dentisterie esthétique ou de restauration. Les matériaux de restauration à base dezircone possèdent une résistance améliorée et une versatilité des indications cliniques etpeuvent être utilisés avec la technologie CAO/FAO. Ce sont également une solution derechange aux métaux précieux dont le prix ne cesse d’augmenter. De plus, la création decouches adhésives superficielles favorisant une fixation par liaison covalente à la zirconepermettra de propager l’utilisation de la zircone en dentisterie clinique.Zirconia (ZrO 2 ) is a silica-free, acidresistant,polycrystalline ceramic thatdoes not contain amorphous silica (SiO 2 )glass. Traditional ceramic surface treatments(such as hydrofluoric acid [HF] etchingand/or silane primer application) areineffective on the silica-free surfaces ofzirconia, alumina, and metal. New researchhas shown phosphate monomers to have asignificant affinity for non-silica-based oxidessuch as zirconia. Research has shown that thecombination of light air abrasion andmethacryloyloxydecyl dihydrogen phosphate(MDP)-based zirconia primers is necessary toachieve long-term durable bonding tozirconia. It is imperative for the clinician tooptimize adhesive performance in less-thanretentivepreparation designs with the use ofetch-and-rinse (total etch) or etch-and-dry(self-etch) adhesives onto dentin, such as AllBond 3 or All Bond SE (Bisco, Schaumburg,IL); MDP-containing primers onto thezirconia indirect substrate, such as Z-PRIMEPLUS (Bisco); and dual-cure resin cementssuch as DuoLink or DuoLink SE (Bisco).When preparation designs are fully retentive(and strong adhesion is not critical),organophosphate-containing, self-adhesive,dual-cured resin cements, such as BisCem(Bisco), Maxcem Elite (Kerr, Orange, CA),and RelyX Unicem (3M ESPE, St. Paul, MN),can be used.The incorporation of proven monomers intonew product innovation aimed at addressingclinical challenges is exciting. The use ofprimers to enhance bonding to zirconia hasled to the development of improved materialalternatives in metal-free esthetic restorativedentistry.Treating the Zirconia Surface: Low-Pressure Al2O3 and Zirconia PrimersThe goal of replicating the cohesivehydrophobic interface (dentin-enameljunction, or DEJ) with the use of resin lutingcements is first dependent upon the clinicianaddressing the individual needs of the toothsubstrates (dentin, enamel) and the indirectsubstrates (zirconia, alumina, ceramic,metal). Adhesive bonding agents onto thetooth substrate and primers onto the indirectsubstrate are critical in optimizing thiscohesion.Zirconia has been used in clinical dentistryfor several years with much success. 1–8Creating adhesion to non-silica-based oxideceramics such as zirconia, alumina, and metalwas the challenge that limited their use. 9–14This is changing with our currentunderstanding of zirconia. Zirconia is a silicafree,acid-resistant, polycrystalline ceramic. Itdoes not contain amorphous silica glass (likefeldspathic porcelain, leucite-reinforcedceramics, and lithium disilicate ceramics);thus, traditional ceramic surface treatmentssuch as HF etching followed by silaneapplication are ineffective. 9–14It is now understood that the combination oflow-pressure Al2O3 with primers specific tozirconia may contribute to long-term stabilityof its bonding. The use of pyro-chemical(Pyrosil, Sura Instruments, Jena,Germany) 15,16 or tribo-chemical treatments(Cojet/Rocatec, 3M ESPE) 12,14,17–22 to create apseudo-silane attached surface is analternative method. Internal research at BiscoDental Products with tribo-chemical bonding(Cojet/Rocatec) showed that it did not offerimproved bonding and could be prone todegradation. Other research has shown thattribo-chemical bonding improved bonding24 Journal canadien de dentisterie restauratrice et de prosthodontie Hiver 2010
GRIFFIN ET AL.Strong Bond Strength to Different Substratewith Z-Prime PlusZirconiawith no primer4 MPaCement-Self Cured23 MPaAlumina3 MPa18 MPaTitaniumOptionStainless SteelGold22 MPa23 MPa24 MPa20 MPaFigure 1. Shear bond strengths (SBSs) of different primers on etched lithiumdisilicates before and after accelerated aging (internal Bisco data).Composite27 MPaFigure 2. Bond strengths of Z-PRIME PLUS to varioussubstrates.with the use of primers. 19 Internal studies atBisco have shown Z-PRIME PLUS adhesiondoes not require mechanical altering of thezirconia surface.Phosphate Monomers Specific toZirconiaThere are five commercial ceramic primersystems intended for use with zirconia: AZPrimer (Shofu Dental Corporation, SanMarcos, CA), Clearfil Ceramic Primer(Kuraray America, Houston, TX),Metal/Zirconia Primer (Ivoclar Vivadent,Amherst, NY), Monobond Plus (IvoclarVivadent), and Z-PRIME PLUS. Theseproducts differ in the type and concentrationof phosphate monomers used, clinicaltechnique for use, time of application, andproprietary formulas. Phosphate monomersform chemical bonds with the zirconiasurface and have resin terminal ends thatbond to the resin cements. MDP is the mosttime-tested of the commonly used phosphatemonomers and has been shown to have aspecial affinity for non-glass-based substratesof zirconia, alumina, and metal. MDP is arelatively hydrophobic monomer due to its10-carbon chain and contains both ahydrophilic phosphate terminal end thatchemically adheres to zirconia and apolymerizable methacrylate terminal end thatadheres to resin.Bond strengths are a function of the mode ofcuring, stability of the resin chemistry,compatibility of primer to cement, andcontamination potential dependent uponclinical application times. The acidic natureof phosphate monomers does pose a chemicalchallenge with creating formulas that are bothdurable and stable. Monobond Plus andClearfil Ceramic Primer incorporate silanewith the intended additional use on silicabasedsurfaces. Silane is known to beunstable in acidic environments (Figure 1).The acidic nature of organophosphates(phosphate/phosphonate monomers) placedin products such as Monobond Plus andClearfil Ceramic Primer may lead toinstability of the silane component of theseindividual formulas. Z-PRIME PLUS doesnot contain silane.Z-PRIME PLUS contains a propriety formulaof concentrated MDP and carboxylicmonomers formulated specific to zirconia,alumina, and metal. The versatility of theseprimers is a compelling feature for use onmany different indirect substrates (Figure 2).Adherence of Resin Cements toZirconia: The SciencePhosphate monomers in self-adhesivecements are proven to be effective in adheringto non-silica-based polycrystalline materialsof zirconia, alumina, and metal. 17–20 It is withthis information that primers specific tozirconia, alumina, and metal were created.Numerous research studies have shown thatphosphate /phosphonate monomers are veryeffective in improving zirconia bonding. Intheory, phosphate monomers form chemicalbonds with the zirconia, alumina, and metaloxide surfaces and have resin terminal endgroups, which enable cohesive bonding toappropriate resin cements (Figure 3). 22,23Figure 3. Demonstration of how the hydrogen (-H)group of a phosphate monomer interacts with theZr-O group of zirconia to form a phosphatemonolayer on the zirconia surface.Bonding Zirconia to Preparations withRetention/Resistance FormSelf-adhesive resin cements, such as BisCem,Maxcem Elite, and RelyX Unicem, are dualcured,contain organophosphate monomers,and can be used when preparation designs arefully retentive; however, these cements arehydrophilic due to the acidic resincomponents and have lower physical andmechanical properties than resin cements.Self-adhesive resin cements differ in viscosityWinter 2010 Canadian Journal of Restorative Dentistry and Prosthodontics 25
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SURFACE TREATMENTS FOR ZIRCONIA BONDING: A CLINICAL PERSPECTIVEABSTRACTThere has been a monumental shift in the use of zirconia in esthetic/restorative dentistry.<strong>Zirconia</strong>-based restorative materials exhibit improved strength, versatility of clinicalindications, and the ability to be CAD/CAM milled. They are also an alternative to theincreasingly higher cost of precious metals. As well, the creation of surface adhesiveprimers that create covalent bonding to zirconia will only help to propagate zirconia’s usein clinical dentistry.RÉSUMÉIl y a eu un changement monumental dans l’utilisation de la zircone (oxyde de zirconium)en dentisterie esthétique ou de restauration. Les matériaux de restauration à base dezircone possèdent une résistance améliorée et une versatilité des indications cliniques etpeuvent être utilisés avec la technologie CAO/FAO. Ce sont également une solution derechange aux métaux précieux dont le prix ne cesse d’augmenter. De plus, la création decouches adhésives superficielles favorisant une fixation par liaison covalente à la zirconepermettra de propager l’utilisation de la zircone en dentisterie clinique.<strong>Zirconia</strong> (ZrO 2 ) is a silica-free, acidresistant,polycrystalline ceramic thatdoes not contain amorphous silica (SiO 2 )glass. Traditional ceramic surface treatments(such as hydrofluoric acid [HF] etchingand/or silane primer application) areineffective on the silica-free surfaces ofzirconia, alumina, and metal. New researchhas shown phosphate monomers to have asignificant affinity <strong>for</strong> non-silica-based oxidessuch as zirconia. Research has shown that thecombination of light air abrasion andmethacryloyloxydecyl dihydrogen phosphate(MDP)-based zirconia primers is necessary toachieve long-term durable bonding tozirconia. It is imperative <strong>for</strong> the clinician tooptimize adhesive per<strong>for</strong>mance in less-thanretentivepreparation designs with the use ofetch-and-rinse (total etch) or etch-and-dry(self-etch) adhesives onto dentin, such as AllBond 3 or All Bond SE (Bisco, Schaumburg,IL); MDP-containing primers onto thezirconia indirect substrate, such as Z-PRIMEPLUS (Bisco); and dual-cure resin cementssuch as DuoLink or DuoLink SE (Bisco).When preparation designs are fully retentive(and strong adhesion is not critical),organophosphate-containing, self-adhesive,dual-cured resin cements, such as BisCem(Bisco), Maxcem Elite (Kerr, Orange, CA),and RelyX Unicem (3M ESPE, St. Paul, MN),can be used.The incorporation of proven monomers intonew product innovation aimed at addressingclinical challenges is exciting. The use ofprimers to enhance bonding to zirconia hasled to the development of improved materialalternatives in metal-free esthetic restorativedentistry.Treating the <strong>Zirconia</strong> <strong>Surface</strong>: Low-Pressure Al2O3 and <strong>Zirconia</strong> PrimersThe goal of replicating the cohesivehydrophobic interface (dentin-enameljunction, or DEJ) with the use of resin lutingcements is first dependent upon the clinicianaddressing the individual needs of the toothsubstrates (dentin, enamel) and the indirectsubstrates (zirconia, alumina, ceramic,metal). Adhesive bonding agents onto thetooth substrate and primers onto the indirectsubstrate are critical in optimizing thiscohesion.<strong>Zirconia</strong> has been used in clinical dentistry<strong>for</strong> several years with much success. 1–8Creating adhesion to non-silica-based oxideceramics such as zirconia, alumina, and metalwas the challenge that limited their use. 9–14This is changing with our currentunderstanding of zirconia. <strong>Zirconia</strong> is a silicafree,acid-resistant, polycrystalline ceramic. Itdoes not contain amorphous silica glass (likefeldspathic porcelain, leucite-rein<strong>for</strong>cedceramics, and lithium disilicate ceramics);thus, traditional ceramic surface treatmentssuch as HF etching followed by silaneapplication are ineffective. 9–14It is now understood that the combination oflow-pressure Al2O3 with primers specific tozirconia may contribute to long-term stabilityof its bonding. The use of pyro-chemical(Pyrosil, Sura Instruments, Jena,Germany) 15,16 or tribo-chemical treatments(Cojet/Rocatec, 3M ESPE) 12,14,17–22 to create apseudo-silane attached surface is analternative method. Internal research at BiscoDental Products with tribo-chemical bonding(Cojet/Rocatec) showed that it did not offerimproved bonding and could be prone todegradation. Other research has shown thattribo-chemical bonding improved bonding24 Journal canadien de dentisterie restauratrice et de prosthodontie Hiver 2010
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