RESEARCH AND EDUCATION

Effect of surface treatments on the properties and morphological change of dental zirconia Lubica Hallmann, PhD,a Peter Ulmer, Prof Dr,b Sebastian Wille, PhD,c Olesandr Polonskyi, PhD,d Stefan Köbel, PhD,e Thomas Trottenberg, PhD,f Sven Bornholdt, PhD,g Fabian Haase, MSc,h Holger Kersten, Prof Dr,i and Matthias Kern, Prof Dr med dent habilj

ABSTRACT Statement of problem. Creating a rough surface for bonding with airborne-particle abrasion with alumina may damage the surface of zirconia. Other treatment methods for creating a bonding surface without causing damage require investigation. Purpose. The purpose of this in vitro study was to find ways of treating the zirconia surface without causing flaws, debris, pits, microcracks, or tetragonal to monoclinic phase transformation. Material and methods. Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramic surfaces were treated with gas plasma, argon-ion bombardment, 150-mm abrasive zirconia particles, and abrasive 150-mm alumina particles; untreated surfaces were used as the control group. X-ray diffraction (XRD) and confocal Raman spectroscopy were used to study the phase transformation. The roughness of specimens was measured with a confocal 3D laser scanning microscope. Modification of surface topography was analyzed with field emission scanning electron microscopy (FESEM), and the flexural strength was measured with a universal testing machine. Statistical analyses were performed with 1-way ANOVA, followed by comparison of means with the Tukey honest significant difference test. The standard deviation was calculated with descriptive statistics. Results. The sintered Y-TZP ceramic used in this study showed 2 phases, tetragonal and cubic. Specimens abraded with 150-mm alumina particles showed a higher monoclinic volume fraction (VmXRD=8.68%) and roughness (Ra=0.91mm) than specimens abraded with 150-mm zirconia particles (VmXRD=1.22%, Ra=0.08mm). One-way ANOVA indicated a significance difference in roughness among groups (P.2). FESEM measurements showed that airborne-particle abrading Y-TZP surfaces with 150-mm alumina particles caused more damage to this area than the other methods. Conclusions. Y-TZP ceramic surfaces treated with zirconia particles, argon-ion bombardment, and gas plasma were damaged less in comparison with surfaces abraded with alumina particles. (J Prosthet Dent 2015;-:---)

Supported by Deutsche Forschungs-Gemeinschaft via SFB TR24 project B13. a Researcher, Department of Prosthodontics, Propaedeutics and Dental Materials, School of Dentistry, Kiel University, Kiel, Germany. b Professor, Institute of Geochemistry and Petrology, Zürich, Switzerland. c Researcher, Department of Prosthodontics, Propaedeutics and Dental Materials, School of Dentistry, Kiel University, Kiel, Germany. d Researcher, Department of Multicomponent Materials, Institute of Materials Science, Faculty of Engineering, Kiel University, Kiel, Germany. e Researcher, Design and Materials Division, Institute of System Engineering, HES-SO Valais Wallis, Sion, Switzerland. f Researcher, Plasma Technology Group, Institute of Experimental and Applied Physics, Kiel University, Kiel, Germany. g Researcher, Plasma Technology Group, Institute of Experimental and Applied Physics, Kiel University, Kiel, Germany. h Researcher, Plasma Technology Group, Institute of Experimental and Applied Physics, Kiel University, Kiel, Germany. i Professor, Plasma Technology Group, Institute of Experimental and Applied Physics, Kiel University, Kiel, Germany. j Professor, Department of Prosthodontics, Propaedeutics and Dental Materials, School of Dentistry, Kiel University, Kiel, Germany.

THE JOURNAL OF PROSTHETIC DENTISTRY

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Table 1. Materials used

Clinical Implication

Materials

Lot No.

In clinical practice, substitution of abrasive alumina particles with zirconia particles may reduce the damage caused to ceramic surfaces by airborne-particle abrasion.

High Translucent (HT) Y-TZP (Katana; Kuraray Noritake Dental)

DDZQJ

150-mm alumina abrasive (Pluradent)

14546

150-mm Y-TZP abrasive (IMERYS Fused Minerals)

HQB 0230

Table 2. Preparation of specimens Group

To improve the esthetic outcome of fixed dental prostheses, metal-free prosthetic restorations have become popular because they preserve the color of the soft tissue.1 Significant progress in dental restoration techniques using ceramic core materials has been made.2 However, although these materials are better than metals because of their biocompatibility, esthetics, lower thermal conductivity, and chemical resistance,3 their fracture toughness (KIc) is relatively low.4 The application of zirconia-based ceramics in dentistry has reduced this problem. Garvie et al5 were the first to discover the increase in flexural strength due to the phase transformation of partially stabilized zirconia. Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) have excellent mechanical properties because of the stress-induced martensitic phase transformation.6,7 However, the traditional adhesive techniques applied to silica-based ceramics cannot be applied to Y-TZP ceramics.8-12 Etching silica-based ceramic surfaces with hydrofluoric acid followed by the silanization of these surfaces improves the durability of the bonding between the ceramic surface and the resin cement13-15 but cannot be used for zirconia ceramics because hydrofluoric acid is incapable of creating adequate roughness and micromechanical interlocking.9 The airborne-particle abrasion of zirconia ceramic surfaces with alumina particles has been found to have a positive effect on the durability of the resin-zirconia bonding7,12,13 by increasing roughness, creating mechanical interlocking, and simultaneously cleaning the surface.12,16-19 However, some studies20-23 have shown that airborne-particle abrasion with alumina can damage Y-TZP ceramic surfaces and can degrade the long-term performance of ceramic crowns. Flaws, debris, pits, microcracks, alumina particles embedded during airborne-particle abrasion might negatively affect the durability of the resin-zirconia bonding.9,20-23 To avoid this damage, some authors have recommended the use of softer, rounder abrasives instead of sharp, hard alumina particles.22 Replacing the alumina airborneparticle abrasion of Y-TZP ceramic surfaces with other more suitable surface modifications may extend the life of zirconia ceramic restorations.23 Attempts have been made to replace airborneparticle abrasion with alumina particles with other methods which do not diminish the excellent mechanical properties of Y-TZP ceramics.24-32 However, the methods

THE JOURNAL OF PROSTHETIC DENTISTRY

Treatments

UNT

Untreated specimens (control)

AAP

Specimens abraded with 150-mm alumina particles

AZP

Specimens abraded with 150-mm zirconia particles

BAI

Specimens bombarded with argon-ion

GPE

Specimens treated with gas plasma (H2:Ar=10:3); specimens were placed directly at electrode

GPOE

Specimens treated with gas plasma (H2:Ar=10:3); specimens were placed 3 cm over electrode

proposed have their shortcomings. Laser treatments and plasma-coating techniques are not practical in many clinics. Following the recommendations of some researchers,23,33,34 in this study, Y-TZP ceramic surfaces were treated with either abrasive 150-mm zirconia particles, argon-ion bombardment, or gas plasma (hydrogen with argon admixture=10:3). The hypothesis was that airborne-particle abrasion with zirconia has a different effect on phase transformation, roughness, flexural strength, and topography of Y-TZP ceramic surfaces compared with that of airborne-particle abrasion with alumina. Additionally, we hypothesized that the treatment of Y-TZP ceramic surfaces with gas plasma and argon-ion bombardment would not damage the ceramic surface. MATERIAL AND METHODS Presintered highly translucent Y-TZP (>91 wt% zirconia, >5 wt% Y2O3, 2 wt% HfO2, 0.1 wt% Al2O3,