IADR Abstract Archives
Reliability of Ultrathin Milled Lithium Disilicate Full Coverage Molar Restorations
Objectives: The present study sought to evaluate the reliability and failure modes of ultrathin (0.5 mm thickness) milled monolithic lithium disilicate full coverage molar restorations.
Methods: Twenty one milled lithium disilicate full coverage restorations (IPS e.max CAD, Ivoclar Vivadent, Schaan, Liechtenstein) were resin-bonded onto composite resin first mandibular molar replicas (Z-100, 3M Oral Care, St. Paul. MN, USA). Three samples were subjected to uni-axial compressive maximum load to failure (1 mm/min), and the mean values used to establish the loading profiles for step-stress accelerated life testing (SSALT). The remaining eighteen samples were subjected to SSALT in water and assigned to three profiles: mild (n=9), moderate (n=6), and aggressive (n=3). Weibull distribution was used and the probability of survival calculated for missions of 100,000 and 200,000 cycles at 100, 200, 300 and 400 N. Samples were inspected under polarized light microscopy for characterization of failure mode. The most representative samples were subjected to fractographic analysis using scanning electron microscopy (SEM).
Results: Following Weibull distribution analysis, the calculated beta (β) was 0.027. This value suggests that failures were dictated by material intrinsic flaws rather than damage accumulation. The calculated characteristic strength was 497.38 N and the Weibull modulus 3.76. The probability of survival was ~99% at 100 N, ~95% at 200 N and ~82% at 300 N. A significant decrease in probability of survival was observed when loads were increased to 400 N (~59%). Sixty-one percent of the restoration fractures were classified as non-reparable.
Conclusions: Within the limitations of this in vitro study, a thickness of 0.5 mm for lithium disilicate milled full coverage restorations is considered insuficient for the rehabilitation of molar teeth.
Methods: Twenty one milled lithium disilicate full coverage restorations (IPS e.max CAD, Ivoclar Vivadent, Schaan, Liechtenstein) were resin-bonded onto composite resin first mandibular molar replicas (Z-100, 3M Oral Care, St. Paul. MN, USA). Three samples were subjected to uni-axial compressive maximum load to failure (1 mm/min), and the mean values used to establish the loading profiles for step-stress accelerated life testing (SSALT). The remaining eighteen samples were subjected to SSALT in water and assigned to three profiles: mild (n=9), moderate (n=6), and aggressive (n=3). Weibull distribution was used and the probability of survival calculated for missions of 100,000 and 200,000 cycles at 100, 200, 300 and 400 N. Samples were inspected under polarized light microscopy for characterization of failure mode. The most representative samples were subjected to fractographic analysis using scanning electron microscopy (SEM).
Results: Following Weibull distribution analysis, the calculated beta (β) was 0.027. This value suggests that failures were dictated by material intrinsic flaws rather than damage accumulation. The calculated characteristic strength was 497.38 N and the Weibull modulus 3.76. The probability of survival was ~99% at 100 N, ~95% at 200 N and ~82% at 300 N. A significant decrease in probability of survival was observed when loads were increased to 400 N (~59%). Sixty-one percent of the restoration fractures were classified as non-reparable.
Conclusions: Within the limitations of this in vitro study, a thickness of 0.5 mm for lithium disilicate milled full coverage restorations is considered insuficient for the rehabilitation of molar teeth.