Influence of Specimen Preparation and Test Methods on the Flexural Strength Results of Monolithic Zirconia Materials.

Marlis Eichberger,Monika Strickstrock,Bogna Stawarczyk,Isabella-Maria Zylla,Daniel Edelhoff,Malgorzata Roos,Christine Schatz

doi:10.3390/ma9030180

Marlis Eichberger, Monika Strickstrock + Show 5 more

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https://doi.org/10.3390/ma9030180

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Abstract

The aim of this work was to evaluate the influence of specimen preparation and test method on the flexural strength results of monolithic zirconia. Different monolithic zirconia materials (Ceramill Zolid (Amann Girrbach, Koblach, Austria), Zenostar ZrTranslucent (Wieland Dental, Pforzheim, Germany), and DD Bio zx2 (Dental Direkt, Spenge, Germany)) were tested with three different methods: 3-point, 4-point, and biaxial flexural strength. Additionally, different specimen preparation methods were applied: either dry polishing before sintering or wet polishing after sintering. Each subgroup included 40 specimens. The surface roughness was assessed using scanning electron microscopy (SEM) and a profilometer whereas monoclinic phase transformation was investigated with X-ray diffraction. The data were analyzed using a three-way Analysis of Variance (ANOVA) with respect to the three factors: zirconia, specimen preparation, and test method. One-way ANOVA was conducted for the test method and zirconia factors within the combination of two other factors. A 2-parameter Weibull distribution assumption was applied to analyze the reliability under different testing conditions. In general, values measured using the 4-point test method presented the lowest flexural strength values. The flexural strength findings can be grouped in the following order: 4-point < 3-point < biaxial. Specimens prepared after sintering showed significantly higher flexural strength values than prepared before sintering. The Weibull moduli ranged from 5.1 to 16.5. Specimens polished before sintering showed higher surface roughness values than specimens polished after sintering. In contrast, no strong impact of the polishing procedures on the monoclinic surface layer was observed. No impact of zirconia material on flexural strength was found. The test method and the preparation method significantly influenced the flexural strength values.

Highlights

Y-TZP (Yttria partially stabilized tetragonal zirconia) Zirconia has become of interest in dentistry, because of its high flexural strength [1] and its well-known transformation toughening ability [2].Materials 2016, 9, 180; doi:10.3390/ma9030180 www.mdpi.com/journal/materialsConventional zirconia (3Y-TZP: Yttrium-cation-doped tetragonal zirconia polycrystals, typically2–3 mol% Y2 O3 ) shows translucency on human dentin level and is not suitable for monolithic tooth restorations from the esthetic point of view [3].Modifications of the microstructure and composition were conducted in recent years to accomplish an adequate esthetic appearance for full anatomical zirconia restorations
The survival time of all-ceramic systems is strongly related to the flexural strengths of the restoration, which is the result of the flexural strength of core and veneering material, and the bond strength between both materials [4,5]
Excellent strengths were reported for the zirconia core material, many studies indicate fractures in the veneering ceramic [6,7]

Summary

Introduction

Y-TZP (Yttria partially stabilized tetragonal zirconia) Zirconia has become of interest in dentistry, because of its high flexural strength [1] and its well-known transformation toughening ability [2].Materials 2016, 9, 180; doi:10.3390/ma9030180 www.mdpi.com/journal/materialsConventional zirconia (3Y-TZP: Yttrium-cation-doped tetragonal zirconia polycrystals, typically2–3 mol% Y2 O3 ) shows translucency on human dentin level and is not suitable for monolithic tooth restorations from the esthetic point of view [3].Modifications of the microstructure and composition were conducted in recent years to accomplish an adequate esthetic appearance for full anatomical zirconia restorations. The survival time of all-ceramic systems is strongly related to the flexural strengths of the restoration, which is the result of the flexural strength of core and veneering material, and the bond strength between both materials [4,5]. Excellent strengths were reported for the zirconia core material, many studies indicate fractures in the veneering ceramic [6,7]. To avoid this problem and to facilitate the fabrication process, the demand for zirconia restorations in a monolithic design without veneering has increased [8]. Different studies reported on a higher fracture resistance of monolithic zirconia crowns compared to conventional veneered versions [8,9]

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