Evaluation of Microshear Bond Strength of Orthodontic Resin Cement to Monolithic Zirconium Oxide as a Function of Surface Conditioning Method Nehir Canigur Bavbeka / Jean-François Rouletb / Mutlu Özcanc
Purpose: To evaluate the microshear bond strength (μSBS) of orthodontic resin cement to monolithic zirconium oxide ceramic (MZ) after different surface conditioning methods. Materials and Methods: Two types of MZ (BruxZir Solid Zirconia, n = 60; Prettau-Zirkon, n = 60) with two types of surface finish (glazed, n = 30 per group; polished, n = 30 per group) were tested after two surface conditioning methods: 1. air abrasion with 30-μm silica coated aluminum oxide (Al2O3) particles (CoJet), or 2. air abrasion with 50-μm Al2O3 particles. The non-conditioned group acted as the control. A universal primer (Monobond-Plus) and an orthodontic primer (Transbond-XT Primer) were applied to all specimen surfaces. Orthodontic resin composite (Transbond-XT) was bonded using a mold and photopolymerized. The bonded specimens were subjected to μSBS testing (0.5 mm/min). Data were analyzed statistically using three-way ANOVA and the Sidac adjustment post-hoc test (α = 0.05). Failure modes were analyzed using a stereomicroscope (30X). Results: Mean μSBS values (MPa) did not show a significant difference between the two brands of MZ (p > 0.05). In both glazed (44 ± 6.4) and polished (45.9 ± 4.8) groups, CoJet application showed the highest μSBS values (p < 0.001). The control group (34.4 ± 6) presented significantly better results compared to that of Al2O3 (30 ± 3.8) (p < 0.05) on glazed surfaces, but it was the opposite in the polished groups (control: 20.3 ± 4.7; Al2O3: 33.8 ± 4.7; p < 0.001). Adhesive failure was the dominant type in all groups. Conditioning MZs with Al2O3 and CoJet increased the percentage of mixed failure type. Conclusion: Air abrasion with CoJet followed by the application of universal primer improved the μSBS of orthodontic resin to both the polished and glazed monolithic zirconium oxide materials tested. Key words: air abrasion, monolithic zirconium oxide, zirconia, microshear bond strength, orthodontic bonding, surface conditioning method. J Adhes Dent 2014; 16: 473–480. doi: 10.3290/j.jad.a32812
T
oday, technological developments in dental materials allow clinicians to offer oral rehabilitations with more esthetic outcomes using fixed dental prostheses (FDP)
a
Research Assistant, Department of Orthodontics, Faculty of Dentistry, Gazi University, Ankara, Turkey. Idea, prepared the specimens, performed the experiments, wrote the manuscript, discussed the results and commented on the manuscript at all stages.
b
Professor, Department of Restorative Dental Sciences, College of Dentistry, University of Florida, Gainesville, FL, USA. Contributed to the hypothesis, experimental design, monitored specimen preparation and experiments, proofread the manuscript, discussed the results and commented on the manuscript at all stages.
c
Professor, Clinic for Fixed and Removable Prosthodontics and Dental Materials Science, Center for Dental and Oral Medicine, Dental Materials Unit, University of Zürich, Zürich, Switzerland. Contributed to the experimental design, consulted on statistical evaluation, contributed to writing the manuscript, discussed the results and commented on the manuscript at all stages.
Correspondence: Nehir Canigur Bavbek, Gazi University, Faculty of Dentistry, Department of Orthodontics, 8. Cadde, 82. Sokak, 06510 Emek, Ankara, Turkey. Tel: +90-505-4282674; Fax: +90-312-2239226. e-mail: [email protected]
Vol 16, No 5, 2014
Submitted for publication: 22.01.14; accepted for publication: 12.08.14
without compromising strength and durability. Due to the increased esthetic demands of the patients, porcelain-fused-to-metal (PFM) FDPs are often replaced with all-ceramic FDPs5 that are optically appealing, biocompatible, color stable, and resistant to wear.40 Despite these advantages, their brittle nature has restricted their use.44 The efforts to develop a new FDP material with a strong framework similar to PFM FDPs but at the same time being as esthetic as glassy-matrix ceramics resulted in the introduction of zirconium oxide. In particular, 2 to 3% mol yttria (Y2O3) containing the tetragonal zirconia polycrystalline (Y-TZP) form of zirconium oxide has become prevalent. Currently, this material is widely used for frameworks of all-ceramic FDPs due to its biocompatibility, high flexural strength, wear resistance, and fracture toughness.11,24,39 Previous studies reported service-life expectations of Y-TZP zirconium oxide core that were comparable to PFM FDPs for posterior indications.16,39,40 However, after routine clinical use, reported disadvantages such as chipping or delamina473
Canigur Bavbek et al
tion of veneering ceramic5,16 posed a clinical challenge. In order to overcome this problem, monolithic zirconium oxide (MZ) was introduced on the dental market. Fabrication of FDPs from MZ is a new technology which is expected to gain substantial interest as it provides high strength, esthetics, and easy fabrication at lower costs.19 Full-contour MZ FDPs are milled from blocks using CAD/ CAM technologies and can be used either polished or glazed for improved optical results.38 Although polishing decreases the surface roughness and may provide sufficient esthetics, many MZ FDPs are glazed superficially during laboratory procedures to improve their optical properties. In addition, glass particles infiltrated into zirconium oxide surfaces such as in glazing could enhance the adhesive bonding, as it can be etched and silanized with silane coupling agents.49 Despite its advantages, the chemical or mechanical bond between the adhesive resins and oxide ceramics is still inferior to that between adhesive resins and glassy matrix ceramics.2,41 Unlike porcelain surfaces, oxide ceramics are not etchable and their glass-free nature reduces favorable silane reaction.2,5,20 Alternative conditioning methods have been discussed in the literature for resin bonding to zirconium oxide. Some authors reported that roughening the surface for mechanical interlocking and using a composite resin containing phosphate monomer showed promising in vitro bond strength values45 and clinical survival rates.36 Others proposed tribochemically silica coating the surface with silica-coated alumina particles, followed by silane application for effective bonding.2,26 However, relying on aggressive abrasion methods for successful mechanical bonding may initiate surface flaws in the material and diminish its strength.47,48 The increased awareness of adult patients of dental esthetics has resulted in more adults seeking orthodontic treatment.21 Consequently, orthodontists started facing substrates other than enamel onto which orthodontic appliances must be bonded.32 Potentially, a lack of bonding protocols in orthodontics for such new materials may yield early debonding of fixed appliances. To date, several studies have addressed different surface conditioning protocols for orthodontic bonding to porcelain materials that are widely used for fabrication of FDPs. These approaches vary from mechanical roughening of the surface using airborne particle abrasion,14,22,35 tribochemical silica coating,35 chemical conditioning with hydrofluoric acid etching or application of silane coupling agents,8,20 or a combination of both mechanical and chemical methods.4,35,42 However, to the authors’ best knowledge, no information is available on how to bond onto MZ for orthodontic procedures. Considering the popularity and increasing demand for MZ crowns in general dental practice, bonding brackets to this material in its polished or glazed form necessitates the development of a protocol for bonding procedures for orthodontic applications. The objectives of this study therefore were to evaluate the effects of different surface conditioning methods on the microshear bond strength of an orthodontic resin composite to polished or glazed MZ materials and to analyze the failure types after debonding. The following null 474
hypotheses were tested: 1) Surface conditioning methods would not improve adhesion compared to the control group, 2) adhesion on polished or glazed MZ would not differ, 3) adhesion to high purity MZ would not differ from that to yttria-stabilized MZ.
MATERIALS AND METHODS The types, brands, manufacturers, chemical compositions, and batch numbers of the materials used in this study are listed in Table 1. Specimen Preparation Two different monolithic zirconium oxide (MZ) materials were tested in this study, MZ1 (BruxZir Solid Zirconia, Glidewell Dental Laboratories; Newport Beach, CA, USA) and MZ2 (Prettau-Zirkon, Zirkonzahn; Neuler, Germany). While MZ1 specimens were obtained from the manufacturer already sintered and polished (5 mm × 5 mm), MZ2 specimens were received in nonsintered in blocks. They were cut into squares (6 mm × 6 mm) approximately 20% greater than the size of sintered MZ1 specimens in order to compensate for the sintering shrinkage. They were then sintered in a furnace at 1500°C (Sintramat High Temperature Furnace, Ivoclar Vivadent; Buffalo, NY, USA) with a heating rate of 8°C/min and a holding time of two hours. After sintering, they were polished with rubber disks (Shofu Dental; San Marcos, CA, USA). Square-shaped (5 mm × 5 mm) MZ1 and MZ2 specimens were polished under water using 600-, 800and 1200-grit silicon carbide abrasive papers in sequence and ultrasonically cleaned in distilled water for 1 min. Specimens (N = 120, n = 60 per brand) from each MZ brand were randomly divided into two subgroups. Half of the specimens were polished and the other half were glazed. The first group of specimens from each product (n = 30) was left as polished, whereas the second group (n = 30) was glazed (Gl) after polishing. Glazing was performed using a spray glaze (Prismatik Universal Low Fusing Spray Glaze, Glidewell Direct; Irvine CA, USA) according to the manufacturer’s recommendations. The specimens were then fired in a furnace at 870˚C for 90 s holding time without vacuum (Jelrus International Wizard Dental Porcelain Oven Furnace, Jelrus; Melville, NY, USA). All specimens were then embedded in autopolymerizing acrylic resin (powder and liquid, Acratray Blue, Henry Schein; Melville NY, USA) with their glazed and polished surfaces exposed. First, the specimens were held in place on a smooth surface with a piece of two-sided adhesive tape. Then, powder and liquid of acrylic resin was mixed (1:3) and poured into the molds to produce cylinders measuring 2.54 cm in diameter and 2.54 cm in length (Ultradent Products; South Jordan, UT, USA). After auto-polymerization started, the mold was placed in a container in cold water to decrease the polymerization temperature. After polymerization, the cylinders were removed from the mold and the twosided adhesive tape was removed. The specimen surfaces were then cleaned with ethanol. The acrylic bottom of the cylinders was ground with 120-grit silicon carbide abrasive The Journal of Adhesive Dentistry
Canigur Bavbek et al
Table 1 Types, brands, manufacturers, chemical compositions, and batch numbers of the materials used in this study Type and brand
Manufacturer
Chemical composition
Batch number
BruxZir Solid Zirconia
Glidewell Dental Laboratories; Newport Beach, CA, USA
High purity ZrO2
NA*
Prettau-Zirkon
Zirkonzahn; Neuler, Germany
ZrO2 (70-97%), Y2O3 (
Purpose: To evaluate the microshear bond strength (μSBS) of orthodontic resin cement to monolithic zirconium oxide ceramic (MZ) after different surface conditioning methods. Materials and Methods: Two types of MZ (BruxZir Solid Zirconia, n = 60; Prettau-Zirkon, n = 60) with two types of surface finish (glazed, n = 30 per group; polished, n = 30 per group) were tested after two surface conditioning methods: 1. air abrasion with 30-μm silica coated aluminum oxide (Al2O3) particles (CoJet), or 2. air abrasion with 50-μm Al2O3 particles. The non-conditioned group acted as the control. A universal primer (Monobond-Plus) and an orthodontic primer (Transbond-XT Primer) were applied to all specimen surfaces. Orthodontic resin composite (Transbond-XT) was bonded using a mold and photopolymerized. The bonded specimens were subjected to μSBS testing (0.5 mm/min). Data were analyzed statistically using three-way ANOVA and the Sidac adjustment post-hoc test (α = 0.05). Failure modes were analyzed using a stereomicroscope (30X). Results: Mean μSBS values (MPa) did not show a significant difference between the two brands of MZ (p > 0.05). In both glazed (44 ± 6.4) and polished (45.9 ± 4.8) groups, CoJet application showed the highest μSBS values (p < 0.001). The control group (34.4 ± 6) presented significantly better results compared to that of Al2O3 (30 ± 3.8) (p < 0.05) on glazed surfaces, but it was the opposite in the polished groups (control: 20.3 ± 4.7; Al2O3: 33.8 ± 4.7; p < 0.001). Adhesive failure was the dominant type in all groups. Conditioning MZs with Al2O3 and CoJet increased the percentage of mixed failure type. Conclusion: Air abrasion with CoJet followed by the application of universal primer improved the μSBS of orthodontic resin to both the polished and glazed monolithic zirconium oxide materials tested. Key words: air abrasion, monolithic zirconium oxide, zirconia, microshear bond strength, orthodontic bonding, surface conditioning method. J Adhes Dent 2014; 16: 473–480. doi: 10.3290/j.jad.a32812
T
oday, technological developments in dental materials allow clinicians to offer oral rehabilitations with more esthetic outcomes using fixed dental prostheses (FDP)
a
Research Assistant, Department of Orthodontics, Faculty of Dentistry, Gazi University, Ankara, Turkey. Idea, prepared the specimens, performed the experiments, wrote the manuscript, discussed the results and commented on the manuscript at all stages.
b
Professor, Department of Restorative Dental Sciences, College of Dentistry, University of Florida, Gainesville, FL, USA. Contributed to the hypothesis, experimental design, monitored specimen preparation and experiments, proofread the manuscript, discussed the results and commented on the manuscript at all stages.
c
Professor, Clinic for Fixed and Removable Prosthodontics and Dental Materials Science, Center for Dental and Oral Medicine, Dental Materials Unit, University of Zürich, Zürich, Switzerland. Contributed to the experimental design, consulted on statistical evaluation, contributed to writing the manuscript, discussed the results and commented on the manuscript at all stages.
Correspondence: Nehir Canigur Bavbek, Gazi University, Faculty of Dentistry, Department of Orthodontics, 8. Cadde, 82. Sokak, 06510 Emek, Ankara, Turkey. Tel: +90-505-4282674; Fax: +90-312-2239226. e-mail: [email protected]
Vol 16, No 5, 2014
Submitted for publication: 22.01.14; accepted for publication: 12.08.14
without compromising strength and durability. Due to the increased esthetic demands of the patients, porcelain-fused-to-metal (PFM) FDPs are often replaced with all-ceramic FDPs5 that are optically appealing, biocompatible, color stable, and resistant to wear.40 Despite these advantages, their brittle nature has restricted their use.44 The efforts to develop a new FDP material with a strong framework similar to PFM FDPs but at the same time being as esthetic as glassy-matrix ceramics resulted in the introduction of zirconium oxide. In particular, 2 to 3% mol yttria (Y2O3) containing the tetragonal zirconia polycrystalline (Y-TZP) form of zirconium oxide has become prevalent. Currently, this material is widely used for frameworks of all-ceramic FDPs due to its biocompatibility, high flexural strength, wear resistance, and fracture toughness.11,24,39 Previous studies reported service-life expectations of Y-TZP zirconium oxide core that were comparable to PFM FDPs for posterior indications.16,39,40 However, after routine clinical use, reported disadvantages such as chipping or delamina473
Canigur Bavbek et al
tion of veneering ceramic5,16 posed a clinical challenge. In order to overcome this problem, monolithic zirconium oxide (MZ) was introduced on the dental market. Fabrication of FDPs from MZ is a new technology which is expected to gain substantial interest as it provides high strength, esthetics, and easy fabrication at lower costs.19 Full-contour MZ FDPs are milled from blocks using CAD/ CAM technologies and can be used either polished or glazed for improved optical results.38 Although polishing decreases the surface roughness and may provide sufficient esthetics, many MZ FDPs are glazed superficially during laboratory procedures to improve their optical properties. In addition, glass particles infiltrated into zirconium oxide surfaces such as in glazing could enhance the adhesive bonding, as it can be etched and silanized with silane coupling agents.49 Despite its advantages, the chemical or mechanical bond between the adhesive resins and oxide ceramics is still inferior to that between adhesive resins and glassy matrix ceramics.2,41 Unlike porcelain surfaces, oxide ceramics are not etchable and their glass-free nature reduces favorable silane reaction.2,5,20 Alternative conditioning methods have been discussed in the literature for resin bonding to zirconium oxide. Some authors reported that roughening the surface for mechanical interlocking and using a composite resin containing phosphate monomer showed promising in vitro bond strength values45 and clinical survival rates.36 Others proposed tribochemically silica coating the surface with silica-coated alumina particles, followed by silane application for effective bonding.2,26 However, relying on aggressive abrasion methods for successful mechanical bonding may initiate surface flaws in the material and diminish its strength.47,48 The increased awareness of adult patients of dental esthetics has resulted in more adults seeking orthodontic treatment.21 Consequently, orthodontists started facing substrates other than enamel onto which orthodontic appliances must be bonded.32 Potentially, a lack of bonding protocols in orthodontics for such new materials may yield early debonding of fixed appliances. To date, several studies have addressed different surface conditioning protocols for orthodontic bonding to porcelain materials that are widely used for fabrication of FDPs. These approaches vary from mechanical roughening of the surface using airborne particle abrasion,14,22,35 tribochemical silica coating,35 chemical conditioning with hydrofluoric acid etching or application of silane coupling agents,8,20 or a combination of both mechanical and chemical methods.4,35,42 However, to the authors’ best knowledge, no information is available on how to bond onto MZ for orthodontic procedures. Considering the popularity and increasing demand for MZ crowns in general dental practice, bonding brackets to this material in its polished or glazed form necessitates the development of a protocol for bonding procedures for orthodontic applications. The objectives of this study therefore were to evaluate the effects of different surface conditioning methods on the microshear bond strength of an orthodontic resin composite to polished or glazed MZ materials and to analyze the failure types after debonding. The following null 474
hypotheses were tested: 1) Surface conditioning methods would not improve adhesion compared to the control group, 2) adhesion on polished or glazed MZ would not differ, 3) adhesion to high purity MZ would not differ from that to yttria-stabilized MZ.
MATERIALS AND METHODS The types, brands, manufacturers, chemical compositions, and batch numbers of the materials used in this study are listed in Table 1. Specimen Preparation Two different monolithic zirconium oxide (MZ) materials were tested in this study, MZ1 (BruxZir Solid Zirconia, Glidewell Dental Laboratories; Newport Beach, CA, USA) and MZ2 (Prettau-Zirkon, Zirkonzahn; Neuler, Germany). While MZ1 specimens were obtained from the manufacturer already sintered and polished (5 mm × 5 mm), MZ2 specimens were received in nonsintered in blocks. They were cut into squares (6 mm × 6 mm) approximately 20% greater than the size of sintered MZ1 specimens in order to compensate for the sintering shrinkage. They were then sintered in a furnace at 1500°C (Sintramat High Temperature Furnace, Ivoclar Vivadent; Buffalo, NY, USA) with a heating rate of 8°C/min and a holding time of two hours. After sintering, they were polished with rubber disks (Shofu Dental; San Marcos, CA, USA). Square-shaped (5 mm × 5 mm) MZ1 and MZ2 specimens were polished under water using 600-, 800and 1200-grit silicon carbide abrasive papers in sequence and ultrasonically cleaned in distilled water for 1 min. Specimens (N = 120, n = 60 per brand) from each MZ brand were randomly divided into two subgroups. Half of the specimens were polished and the other half were glazed. The first group of specimens from each product (n = 30) was left as polished, whereas the second group (n = 30) was glazed (Gl) after polishing. Glazing was performed using a spray glaze (Prismatik Universal Low Fusing Spray Glaze, Glidewell Direct; Irvine CA, USA) according to the manufacturer’s recommendations. The specimens were then fired in a furnace at 870˚C for 90 s holding time without vacuum (Jelrus International Wizard Dental Porcelain Oven Furnace, Jelrus; Melville, NY, USA). All specimens were then embedded in autopolymerizing acrylic resin (powder and liquid, Acratray Blue, Henry Schein; Melville NY, USA) with their glazed and polished surfaces exposed. First, the specimens were held in place on a smooth surface with a piece of two-sided adhesive tape. Then, powder and liquid of acrylic resin was mixed (1:3) and poured into the molds to produce cylinders measuring 2.54 cm in diameter and 2.54 cm in length (Ultradent Products; South Jordan, UT, USA). After auto-polymerization started, the mold was placed in a container in cold water to decrease the polymerization temperature. After polymerization, the cylinders were removed from the mold and the twosided adhesive tape was removed. The specimen surfaces were then cleaned with ethanol. The acrylic bottom of the cylinders was ground with 120-grit silicon carbide abrasive The Journal of Adhesive Dentistry
Canigur Bavbek et al
Table 1 Types, brands, manufacturers, chemical compositions, and batch numbers of the materials used in this study Type and brand
Manufacturer
Chemical composition
Batch number
BruxZir Solid Zirconia
Glidewell Dental Laboratories; Newport Beach, CA, USA
High purity ZrO2
NA*
Prettau-Zirkon
Zirkonzahn; Neuler, Germany
ZrO2 (70-97%), Y2O3 (
