Strength characterization and lifetime prediction of dental ceramic materials

To determine the Weibull modulus m, the characteristic strength σ₀,the subcritical crack growth (SCG) parameters (n &A^*) as well as the lifetime durability of three dental ceramic materials in water: a polycrystalline yttria-stabilized zirconia (Zenostar MT O, YSZ, Ivoclar Vivadent/Wieland, Germany), a lithium disilicate glass ceramic (IPS e.max CAD, LD, Ivoclar Vivadent, Liechtenstein), and a zirconia-containing lithium silicate glass ceramic (Celtra Duo, ZLS, Dentsply Sirona Inc, USA).

30 specimens (Ø12 mm × 0.9 mm thickness) of each material were fabricated. The biaxial ring-on-ring bending tests at four stress rates σ˙ (100, 10, 1, 0.1 MPa/s) were performed in water for all three ceramics. The results were used to determine the Weibull and SCG parameters, and to plot the Strength-Probability-Time (SPT) diagram.

YSZ showed the highest m (12.5) and highest σ₀ (542 MPa), while the values for the glass ceramic materials were lower: for LD m = 4.7, σ₀ = 407 MPa, and for ZLS m = 2.7, σ₀ = 279 MPa. The n for YSZ, LD and ZLS in water were 31.1, 13.7 and 16.6, respectively. The strength of YSZ decreased by 50% within a simulated period of 10 years, and for the glass ceramic materials the decrease was up to 80%.

Determining the Weibull and SCG parameters from the constant stress rate testing is an efficient methodology for ranking materials in terms of durability and longevity.