IADR Abstract Archives
Initial and Fatigue Strength of IPS e.max CAD vs. Press
Objectives: The aim of this research was to elucidate the resistance to fatigue crack growth of IPS e.max (both CAD and Press) using fracture mechanics treatment based on a simple dynamic fatigue test and advanced imaging.
Methods: 80 rectangular IPS e.max lithium disilicate glass-ceramic bars (2x3x25mm3, Ivoclar Vivadent) with surface finished as CAD/CAM (IPS e.max CAD, n=40) and as pressed (IPS e.max Press, n=40) were examined. All samples were polished with edges beveled. Fatigue flexural strengths were determined by four-point-bend dynamic fatigue tests. Initial (fast loading) and fatigue (slow loading) flexural strengths were measured by loading rates of 1, 0.1, 0.01, 0.001, 0.0001mm/min. The velocity exponent N of slow crack growth was determined according to ASTM standard (ASTM C 1368 – 06). Effects of ceramic microstructure (CAD vs. Press) were investigated using scanning electron microscopy (SEM). Failure analysis was conducted on fractured surfaces by optical fractography.
Results: SEM images of polished and chemically etched sections of the pressed and CAD showed that particle size was much larger in Press than in CAD. Flexural strengths in CAD specimens were 345±34N and 201±20N for fast fracture (1mm/min loading rate) and slow fracture (0.0001mm/min loading rate), respectively, which were 56% (221±37) and 40% (143±12) stronger than their pressed counterparts. The velocity exponent N value for the slow crack growth was 17 for e.max CAD and 21 for e.max Press, indicating CAD is more susceptible to slow crack growth relative to the pressed specimens. In fractographic analysis of fast loading rate at 1mm/min, the pressed bar was fractured at a much lower stress level compared to the CAD specimens.
Conclusions: CAD lithium disilicate had higher flexural strength than their pressed counterparts. CAD lithium disilicate was more susceptible to slow crack growth than the pressed counterparts.
Methods: 80 rectangular IPS e.max lithium disilicate glass-ceramic bars (2x3x25mm3, Ivoclar Vivadent) with surface finished as CAD/CAM (IPS e.max CAD, n=40) and as pressed (IPS e.max Press, n=40) were examined. All samples were polished with edges beveled. Fatigue flexural strengths were determined by four-point-bend dynamic fatigue tests. Initial (fast loading) and fatigue (slow loading) flexural strengths were measured by loading rates of 1, 0.1, 0.01, 0.001, 0.0001mm/min. The velocity exponent N of slow crack growth was determined according to ASTM standard (ASTM C 1368 – 06). Effects of ceramic microstructure (CAD vs. Press) were investigated using scanning electron microscopy (SEM). Failure analysis was conducted on fractured surfaces by optical fractography.
Results: SEM images of polished and chemically etched sections of the pressed and CAD showed that particle size was much larger in Press than in CAD. Flexural strengths in CAD specimens were 345±34N and 201±20N for fast fracture (1mm/min loading rate) and slow fracture (0.0001mm/min loading rate), respectively, which were 56% (221±37) and 40% (143±12) stronger than their pressed counterparts. The velocity exponent N value for the slow crack growth was 17 for e.max CAD and 21 for e.max Press, indicating CAD is more susceptible to slow crack growth relative to the pressed specimens. In fractographic analysis of fast loading rate at 1mm/min, the pressed bar was fractured at a much lower stress level compared to the CAD specimens.
Conclusions: CAD lithium disilicate had higher flexural strength than their pressed counterparts. CAD lithium disilicate was more susceptible to slow crack growth than the pressed counterparts.