Effect of Different Etching Periods on Fracture Strength of Machinable Lithium Disilicate

The aim of our study was to evaluate the effect of different etching times of hydrofluoric acid on the fracture strength of machinable lithium disilicate glass-ceramic (IPS e.max CAD). 80 IPS e.max CAD (5×5×2mm) specimens were divided into 5 groups (15 specimens in each group), using 5% Hydrofluoric acid (HF) to etch the groups (0 s, 20 s, 60 s, 120 s, 180 s). Then for 7 specimens of each group, silane was applied on the etched surface followed by a thin layer (0.1 mm) of resin cement. Fracture load was determined for all specimens using a universal testing machine with the use of a specially designed metal plate to hold the specimen during testing. All data were statistically analyzed using one-way ANOVA and paired t-test with a confidence interval of 95%. Etching IPS e.max CAD for 20 seconds did not decrease the fracture strength. While the other etching times showed a significant decrease in fracture strength with an increase in etching time. Resin cement significantly increased the fracture strength of each group.