Mechanical strength and subcritical crack growth under wet cyclic loading of glass-infiltrated dental ceramics

ObjectivesEvaluate the flexural strength (σ) and subcritical crack growth (SCG) under cyclic loading of glass-infiltrated alumina-based (IA, In-Ceram Alumina) and zirconia-reinforced (IZ, In-Ceram Zirconia) ceramics, testing the hypothesis that wet environment influences the SCG of both ceramics when submitted to cyclic loading.MethodsBar-shaped specimens of IA (n = 45) and IZ (n = 45) were fabricated and loaded in three-point bending (3P) in 37 °C artificial saliva (IA3P and IZ3P) and cyclic fatigued (F) in dry (D) and wet (W) conditions (IAFD, IAFW, IZFD, IZFW). The initial σ and the number of cycles to fracture were obtained from 3P and F tests, respectively. Data was examined using Weibull statistics. The SCG behavior was described in terms of crack velocity as a function of maximum stress intensity factor (KImax).ResultsThe Weibull moduli (m = 8) were similar for both ceramics. The characteristic strength (σ0) of IA and IZ was and 466 MPa 550 MPa, respectively. The wet environment significantly increased the SCG of IZ, whereas a less evident effect was observed for IA. In general, both ceramics were prone to SCG, with crack propagation occurring at KI as low as 43–48% of their critical KI. The highest σ of IZ should lead to longer lifetimes for similar loading conditions.SignificanceWater combined with cyclic loading causes pronounced SCG in IZ and IA materials. The lifetime of dental restorations based on these ceramics is expected to increase by reducing their direct exposure to wet conditions and/or by using high content zirconia ceramics with higher strength.