Abstract
Reliability of four groups of ceramic indenter/disc systems was tested using a step-stress accelerated life-testing model. Specimens were fatigued to failure according to three step-stress profiles: light, moderate and aggressive. Group LGC/PFM [heat-pressed leucite glass-ceramic on metal (LGC)/porcelain-fused-to-metal (PFM), disc 1.5-mm thickness] exhibited a lowest reliability and mean-time-to-failure (MTTF), and highest failure rate. At 320-N load, Group Y-TZP/Y-TZP [3 mol-% yttria-stabilised tetragonal zirconia polycrystal (Y-TZP)/Y-TZP, disc 0.6-mm thickness] exhibited a significantly longer MTTF than Group LD/LD [heat-pressed lithium disilicate (LD)/LD, disc 1.5-mm thickness] both at 50,000 and 100,000 cycles, at 90% confidence bounds. Y-TZP indenter and disc of 1.2 mm thickness were used as a control and resulted in no fracture at 320-N load and 150,000 cycles. Zirconia specimens at 0.6-mm thickness performed comparably to 1.5-mm LD and better than 1.5-mm layered PFM specimens in terms of reliability (fracture resistance), MTTF and failure rate.
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