Effect of thickness,yttria and aging on zirconia veneers strength

The aims of this study were to compare and evaluate the effect of two different thicknesses, yttria percentage and artificial aging of laminate veneer zirconia restorations on their fracture resistance. Materials and Methods: Eighty laminate veneer restoration were prepared from partial sintering of zirconia 3Y(yttria),5Y(yttria),combined3Y&5Y(yttria) and lithium disilicate. Specimens were randomly assigned into four main groups according to the percentage of yttria content (n=20) as Group I, II, III and IV for lithium disilicate (control), for 3Y% zirconia, for 5Y% zirconia and for combined 3Y&5Y% zirconia laminate veneer restorations respectively. Each of them were further subdivided into two subgroups (n=10) according to their thickness that in turn were also divided into two subgroups, whether it has undergone artificial aging or not (n=5). Results: o.5 mm thickness the lowest fracture resistance mean value among the tested zirconia ceramic materials and artificial aging significantly reduced the fracture resistance mean value for the laminate veneer restorations except for the combined (3Y&5Y) zirconia and lithium disilicate restorations.