Fracture load of two thicknesses of different zirconia types after fatiguing and thermocycling

Islam Abd Alraheam; Terry Donovan; Lee Boushell; Ryan Cook; André V Ritter; Taiseer A Sulaiman

doi:10.1016/j.prosdent.2019.05.012

Fracture load of two thicknesses of different zirconia types after fatiguing and thermocycling

J Prosthet Dent. 2020 Apr;123(4):635-640. doi: 10.1016/j.prosdent.2019.05.012. Epub 2019 Aug 2.

Authors

Islam Abd Alraheam¹, Terry Donovan², Lee Boushell³, Ryan Cook⁴, André V Ritter⁵, Taiseer A Sulaiman⁶

Affiliations

¹ Adjunct Faculty, Division of Operative Dentistry and Biomaterials, Department of Restorative Sciences, University of North Carolina, Chapel Hill, NC; Assistant Professor, Department of Conservative Dentistry, University of Jordan, Amman, Jordan.
² Professor, Division of Operative Dentistry and Biomaterials, Department of Restorative Sciences, University of North Carolina, Chapel Hill, NC.
³ Associate Professor, Division of Operative Dentistry and Biomaterials, Department of Restorative Sciences, University of North Carolina, Chapel Hill, NC.
⁴ Associate Professor and Chair, Department of Restorative Sciences, University of North Carolina, Chapel Hill, NC.
⁵ Professor, Executive Dean and COO, School of Dentistry, University of North Carolina, Chapel Hill, NC.
⁶ Assistant Professor and Division Director, Division of Operative Dentistry and Biomaterials, Department of Restorative Sciences, University of North Carolina, Chapel Hill, NC. Electronic address: sulaiman@unc.edu.

PMID: 31383533
DOI: 10.1016/j.prosdent.2019.05.012

Abstract

Statement of problem: A direct relationship has been reported between yttria concentration and translucency in zirconia restorations. However, increased yttria concentration also increases the cubic phase of the zirconia, which reduces its strength. The effect of increased yttria content on the fracture resistance of zirconia as a function of material thickness after fatigue testing requires evaluation.

Purpose: The purpose of this in vitro study was to use the biaxial flexural test to evaluate the effect of yttria concentration on the mean fracture load (N) before and after fatiguing and thermocycling as a function of zirconia thickness.

Material and methods: Disk-shaped specimens of 5 mol% yttria partially stabilized zirconia (5Y-PSZ, BruxZir Anterior Solid Zirconia) and 3 mol% yttria partially stabilized zirconia (3Y-PSZ, BruxZir Shaded Zirconia) were prepared to thicknesses of 1.2 and 0.7 mm. For each thickness, the biaxial flexural test was used to measure the fracture load (N) before and after fatigue testing, with 1.2 million cycles at a 110-N load and simultaneous thermocycling at 5 °C to 55 °C (n=20). The data were analyzed by repeated-measures ANOVA (α=.05).

Results: Yttria concentration, thickness, and exposure to fatiguing had a statistically significant effect on the mean biaxial flexural load (yttria concentration: P<.001; thickness: P<.001; fatiguing: P=.004 for the 3Y-PSZ). One of the major findings in this study was that 30% of the 1.2-mm-thick 5Y-PSZ specimens and 80% of the 0.7-mm-thick 5Y-PSZ specimens fractured during fatiguing. All specimens of the 3Y-PSZ groups survived the fatiguing protocol. The 3Y-PSZ groups had statistically significant higher flexural loads than the 5Y-PSZ groups. The 1.2-mm thickness groups had statistically significant higher flexural loads than the 0.7-mm thickness groups.

Conclusions: Yttria concentration had a significant effect on the strength of zirconia. 5Y-PSZ was considerably less resistant to fracture before and after fatigue testing than 3Y-PSZ. Decreasing the thickness of zirconia reduces its fracture resistance, regardless of the zirconia type.

MeSH terms

Dental Materials*
Dental Stress Analysis
Materials Testing
Surface Properties
Zirconium*

Substances

Dental Materials
Zirconium
zirconium oxide