Comparative Study of the Effects of Artificial Aging on Monolayer and Bilayer Zirconia Restorations

Abstract

background and objectives:  observing the effect of low crown thickness on the mechanical properties of monolithic zirconia crowns, then compare them with bilayer zirconia crowns after artificial aging.

Materials and Methods: The research sample consisted of 20 Zirconia Brittau Y-TZP crowns on a first upper molar extractd [ 10 monolithic zirconia crowns with a thickness of 0.8 mm + 10 bilayer zirconia crowns with a thickness of 1.5 mm (0.8 mm for the zirconia core and 0.7 mm for the veneer)], all crowns were subjected to artificial aging cycles in the autoclave under a pressure of 2 bar and a temperature of 134 °C over two cycles of one and a half hour each, after that the crowns were divided into four equal groups, G1: n=5 monolithic zirconia crowns exposed to compression test, G2: n=5 bilayer zirconia crowns exposed to compression test, G3: n=5 monolithic zirconia crowns exposed to shear test, G4: n=5 bilayer zirconia crowns subjected to shear test, then the resistance of the crowns to compression and shear tests was evaluated by the Universal Testing Machine, and then the data was collected and analyzed statistically using the statistical package program of science Social (SPSS V20).

The Results: The results of statistical studies showed the superiority of monolithic zirconia crowns with low thickness (0.8 mm) over bilayer zirconia crowns with its greater thickness (1.5 mm) in fracture resistance after  artificial aging.

The Discussion: monolithic zirconia crowns can be used in areas of high occlusal pressures and at low thicknesses, thus preserving as much dental tissue as possible.