The adverse effects of tungsten carbide grinding on the strength of dental zirconia

Yiru Wang; Walter Y H Lam; Henry W K Luk; Marit Øilo; Kaimin Shih; Michael G Botelho

doi:10.1016/j.dental.2020.02.002

The adverse effects of tungsten carbide grinding on the strength of dental zirconia

Dent Mater. 2020 Apr;36(4):560-569. doi: 10.1016/j.dental.2020.02.002. Epub 2020 Feb 13.

Authors

Yiru Wang¹, Walter Y H Lam², Henry W K Luk², Marit Øilo³, Kaimin Shih⁴, Michael G Botelho⁵

Affiliations

¹ Prosthodontics, Faculty of Dentistry, The University of Hong Kong, Hong Kong SAR, China; The Affiliated Stomatology Hospital and School of Stomatology, School of Medicine and Key Laboratory of Oral Biomedical Research of Zhejiang Province, Zhejiang University, Hangzhou, China.
² Prosthodontics, Faculty of Dentistry, The University of Hong Kong, Hong Kong SAR, China.
³ Department of Clinical Dentistry, Faculty of Medicine, University of Bergen, Bergen, Norway.
⁴ Department of Civil Engineering, Faculty of Engineering, The University of Hong Kong, Hong Kong SAR, China.
⁵ Prosthodontics, Faculty of Dentistry, The University of Hong Kong, Hong Kong SAR, China. Electronic address: botelho@hku.hk.

PMID: 32063392
DOI: 10.1016/j.dental.2020.02.002

Abstract

Objectives: This study investigated the effects of tungsten-carbide grinding on the surface characteristics and mechanical strength of dental 3 mol% yttria-stabilized zirconia (3Y-TZP).

Methods: Two types of tungsten-carbide burs (TC), 6-blade (TC₁) and 8-blade (TC₂) were used to grind 3Y-TZP, in a dental air-turbine handpiece with water-cooling and were also subjected to air-particle abrasion (APA): TC₁ + APA and TC₂ + APA; and rubber polishing (RP): TC₁ + RP and TC₂ + RP; one group received only rubber-polishing RP. The control group received no treatment. Surface characterization was examined by surface roughness (R_a) and atomic force microscopy. Specimens were also observed with scanning electron microscopy (SEM) and X-ray-diffraction (XRD) for microstructure and crystalline phases. A piston-on-three-balls biaxial-flexural strength (BFS) test was performed with 15 samples-per-group and the broken specimen were observed under SEM to investigate the fracture origin pattern. One-way ANOVA, Kruskal-Wallis test and Weibull analysis were performed at α = 0.05.

Results: Groups TC₁ and TC₂ had the lowest mean BFS (p < 0.05) with up to 74 % reduction in strength. APA and RP both significantly increased the mean BFS after tungsten-carbide grinding but was still less than the control (p < 0.05). Compared to the control, the mean BFS was significantly reduced for all groups except for the RP group (p < 0.05). APA and rubber-polishing following TC₂ grinding had significant higher mean BFS than those following TC₁ grinding respectively (p < 0.05). SEM revealed distinct micro-cracks after tungsten-carbide grinding.

Significance: Tungsten-carbide burs (6- and 8-blade) are not recommended for zirconia grinding due to the significant reduction of biaxial-flexural strength and observed micro-structural surface and subsurface damage.

Keywords: Dental ceramics; Fractographic analysis; Grinding; Phase transformation; Polishing; Surface roughness; Tungsten carbide; Zirconia.

MeSH terms

Ceramics
Dental Materials
Dental Polishing*
Materials Testing
Microscopy, Electron, Scanning
Surface Properties
Tungsten Compounds
Yttrium
Zirconium*

Substances

Dental Materials
Tungsten Compounds
tungsten carbide
Yttrium
Zirconium
zirconium oxide