Subcritical crack growth behavior and life data analysis of two types of dental Y-TZP ceramics.

OBJECTIVES

The aim of this study was to evaluate the mechanical properties and the subcritical crack growth behavior of a presintered dental Y-TZP (Kavo Everest ZS) and a hot isostatic pressed Y-TZP (Kavo Everest ZH) and to perform life data analysis.

METHODS

For each material 150 bending bars were produced. The initial fracture strength was determined in a four-point bending test. The subcritical crack growth parameters n and A were determined in a dynamic fatigue method at four decreasing loading rates from 110MPa/s to 0.11MPa/s in distilled water at 38°C. For each loading rate Weibull statistics were performed and the Weibull moduli m and characteristic strengths σ(0) were calculated. Using these data, strength-fracture probability-life time (SPT) predictions were derived for 1 day, 1 year, 5 years and 10 years, based on a static crack growth mechanism.

RESULTS

The "hipped" Y-TZP ceramic exhibited a higher initial strength (σ(c)=1618.18), characteristic strength (σ(0)=837.15) and fracture toughness (K(IC)=4.52MPa/m(1/2)) than the pre-sintered ceramic (σ(c)=1431, σ(0)=745.46 and K(IC)=3.17MPa/m(1/2), respectively). Fatigue parameters, n and A, were 28.5 and 7.97×10(-24) for Everest ZH and 30.15 and 5.47×10(-20) for Everest ZS. The predicted fracture stress at 5% failure probability for a lifetime of 10 years was 259.34MPa for Everest ZH and 263.2MPa for Everest ZS.

CONCLUSIONS

Although the "hipped" Y-TZP showed favorable initial mechanical properties, no significant difference could be found in the susceptibility of both ceramics to subcritical crack growth and their long-term strength.