Fatigue failure of lithium disilicate and translucent zirconia crowns with different occlusal thicknesses

Objectives: To assess the probability of survival of crowns made of high translucent 3 rd generation zirconia (Prettau Anterior - PA), 2 nd generation zirconia (Prettau - P), and the glass-ceramic lithium disilicate (IPS e.max CAD - EM). Materials: and Methods: CAD-CAM premolar crowns were fabricated with occlusal thicknesses of 1.0 mm or 1.5 mm and cemented on a metal dye. Step-stress accelerated life testing (SSALT) was performed using 3 profiles: mild (n=9), moderate (n=6), and aggressive (n=3). The use-level probability Weibull curves and reliability were calculated for completion of a mission of 100,000 cycles at 300, 600, 900, and 1200 N. Results: : A high probability of survival was found for all ceramics (87-99%) at 300 N, irrespective of thickness. There was no significant decrease in the probability of survival for all P crowns up to 1200 N (83-96%). EM crowns presented lower reliability than P or PA crowns under the 600-900 N mission. PA crowns showed lower reliability than P crowns at higher loads of 1200 N. There was no significant difference in the Weibull modulus (3.23-7.12). P demonstrated the highest characteristic strength (2483-2972 N), followed by PA (1512-1547 N) and EM (971-1154 N). Conclusion: High translucent 3 rd generation zirconia has a high probability of survival (up to 900 N-load), while lithium disilicate survives up to 300 N load only, irrespective of thickness (1.0 mm or 1.5 mm). Clinical Relevance: The probability of survival of posterior crowns made with zirconia ceramics has sufficient strength for parafunctional loads, while glass ceramics resist normal chewing loads only.