Mechanical Behavior of Lithium Silicate Press-on-metal Restorative System

Objectives: The objective of the study was to compare bilayer biaxial strength and edge strength of two metal-ceramic (MC) restorative systems.
Methods: The two commercially available systems tested were – lithium silicate press-on-metal system (Obsidian, Glidewell Laboratories) (GL) and leucite-reinforced porcelain based MC system (Ceramco3, Dentsply) (CD). Bilayer disc specimens (n=15) were fabricated with non-precious alloy substrate (Argeloy NP Supreme) following manufacturers’ instructions. The specimens were loaded under biaxial flexure using a piston-on-three-balls set-up and at a cross-head speed of 1mm/min with ceramic under tension. The load required for failure (P_f) was recorded. Bilayer rectangular beam specimens (n=10) were made and loaded with Vickers indenter secured in a custom-made fixture attached to a mechanical testing machine (Instron). The load was applied with a cross-head speed of 0.5 mm/min at 1mm distance from edge of the specimen. The load required to initiate edge chipping (Edge strength, E_s) was recorded. The data were analyzed using Mann-Whitney rank sum test (α=0.05).
Results: The means and standard deviations of strength values are summarized in the table below. GL system showed significantly higher (p<0.001) bilayer failure load and edge strength than CD system.
Conclusions: Lithium silicate press-on-metal restorative system showed superior mechanical behavior in terms of fracture strength and edge chipping resistance than leucite porcelain based MC system. This behavior might be attributed to nano and micron-sized crystals of lithium silicate glass-ceramic and less porosity of pressed ceramic compared to powder porcelain.