Fracture toughness of yttria-stabilized zirconia sintered in conventional and microwave ovens

Statement of problem The fabrication of zirconium dioxide (ZrO2 ) dental prosthetic substructures requires an extended sintering process (8 to 10 hours) in a conventional oven. Microwave sintering is a shorter process (2 hours) than conventional sintering. Purpose The purpose of this study was to compare the fracture toughness of 3 mol % Y2 O3 -stabilized ZrO2 sintered in a conventional or microwave oven. Material and methods Partially sintered ZrO2 specimens from 3 manufacturers, KaVo, Lava 3M, and Crystal HS were milled (KaVo Everest engine) and randomly divided into 2 groups: conventional sintering and microwave sintering (n=16 per group). The specimens were sintered according to the manufacturers’ recommendations and stored in artificial saliva for 10 days. Fracture toughness was determined by using a 4-point bend test, and load to fracture was recorded. Mean fracture toughness for each material was calculated. A 2-way ANOVA followed by the Tukey HDS post hoc test was used to assess the significance of sintering and material effects on fracture toughness, including an interaction between the 2 factors (α=.05). Results The 2-way ANOVA suggested a significant main effect for ZrO2 manufacturer ( P