Effect of ion exchange on strength and slow crack growth of a dental porcelain

Rosa, Vinicius; Yoshimura, Humberto N.; Pinto, Marcelo M.; Fredericci, Catia; Cesar, Paulo F.

doi:10.1016/j.dental.2008.12.009

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Volume 25, Issue 6 , Pages 736-743, June 2009

Effect of ion exchange on strength and slow crack growth of a dental porcelain

Vinicius Rosa
- Department of Biomaterials and Oral Biochemistry, School of Dentistry, University of São Paulo, São Paulo, Brazil
Humberto N. Yoshimura
- Laboratory of Metallurgy and Ceramic Materials, Institute for Technological Research of the State of São Paulo, São Paulo, Brazil
Marcelo M. Pinto
- Department of Biomaterials and Oral Biochemistry, School of Dentistry, University of São Paulo, São Paulo, Brazil
Catia Fredericci
- Laboratory of Metallurgy and Ceramic Materials, Institute for Technological Research of the State of São Paulo, São Paulo, Brazil
Paulo F. Cesar
- Department of Biomaterials and Oral Biochemistry, School of Dentistry, University of São Paulo, São Paulo, Brazil
- Corresponding author. Departamento de Biomateriais e Bioquímica Oral – Faculdade de Odontologia – Universidade de São Paulo, Av. Prof. Lineu Prestes, 2227 – Cidade Universitária “Armando Salles de Oliveira”, São Paulo – SP – Brasil. Tel.: +55 11 55613042; fax: +55 11 55613042.

Received 2 July 2008; received in revised form 19 September 2008; accepted 17 December 2008.

Abstract

Objectives

To determine the effect of ion exchange on slow crack growth (SCG) parameters (n, stress corrosion susceptibility coefficient, and σ_f0, scaling parameter) and Weibull parameters (m, Weibull modulus, and σ₀, characteristic strength) of a dental porcelain.

Methods

160 porcelain discs were fabricated according to manufacturer's instructions, polished through 1μm and divided into two groups: GC (control) and GI (submitted to an ion exchange procedure using a KNO₃ paste at 470°C for 15min). SCG parameters were determined by biaxial flexural strength test in artificial saliva at 37°C using five constant stress rates (n=10). 20 specimens of each group were tested at 1MPa/s to determine Weibull parameters. The SPT diagram was constructed using the least-squares fit of the strength data versus probability of failure.

Results

Mean values of m and σ₀ (95% confidence interval), n and σ_f0 (standard deviation) were, respectively: 13.8 (10.1−18.8) and 60.4 (58.5−62.2), 24.1 (2.5) and 58.1 (0.01) for GC and 7.4 (5.3−10.0) and 136.8 (129.1−144.7), 36.7 (7.3) and 127.9 (0.01) for GI. Fracture stresses (MPa) calculated using the SPT diagram for lifetimes of 1 day, 1 year and 10 years (at a 5% failure probability) were, respectively, 31.8, 24.9 and 22.7 for GC and 71.2, 60.6 and 56.9 for GI.

Significance

For the porcelain tested, the ion exchange process improved strength and resistance to SCG, however, the material's reliability decreased. The predicted fracture stress at 5% failure probability for a lifetime of 10 years was also higher for the ion treated group.

Keywords: Dental porcelain, Ion exchange, Strength, Slow crack growth, Saliva