FATIGUE RESISTANCE OF MONOLITHIC CAD/CAM ZIRCONIA AND LITHIUM DISILICATE CROWNS
Objectives: Monolithic lithium disilicate (LiDi) and zirconia crowns are restorative dentist’s ceramics of choice for posterior and high occlusal stress regions. This study analyzed the fatigue damage resistance of CAD LiDi and CAD zirconia molar crowns using a step-stress fatigue test on a mouth-motion simulator (ELF 3300). CAD leucite-reinforced glass ceramic (LRGC) crowns were used as control.
Methods: CAD/CAM technology was employed to create standardized anatomical molar crowns; zirconia (Lava™ Plus, n=24), LiDi (IPS e.max CAD, n=24), LRGC (IPS Empress CAD, n=24). Specimens were fabricated by cementing (Multilink Automix) crowns on aged dentin-like resin composite abutments (Filtek Z100). Three step-stress profiles (aggressive, moderate and mild) were used for the accelerated sliding-contact mouth-motion fatigue test. Twenty-one crowns were randomly distributed among the three profiles (1:2:4). For Group II, clinically relevant fatigue, the crowns were subject to 1,250,000 cycles at 200N. All specimens were subjected to post mortem damage examination by optical microscopy and a sectioning technique. Failure was classified as chip-off fracture and/or bulk fracture.
Results: All zirconia and LiDi crowns survived mouth-motion step-stress fatigue loading to 1700 N and 90,000 cycles. Occlusal damage was noted in all specimens. Cross-sectional view revealed that contact-induced cone cracks were the dominant damage modes in all systems. LiDi mean partial cone crack length was 1140±500 microns, while zirconia was 42±30 microns. 2 median and 1 radial cracks seen only in LiDi crowns. All LRGC crowns fractured, at ~450N and 60,000 cycles.
Conclusions: Monolithic zirconia crowns displayed superior fatigue resistance compared to LiDi crowns. Both LiDi and zirconia crowns survived accelerated sliding-contact mouth-motion fatigue test up to extremely high loads, suggesting they are viable options for posterior high-stress applications.