Effect of cooling rate on shear bond strength of veneering porcelain to a zirconia ceramic material

The purpose of the present study was to evaluate the effect of cooling rates after firing procedures of veneering porcelain on shear bond strength between veneering porcelain and a zirconium dioxide (zirconia; ZrO?) ceramic material. A total of 48 ZrO? disks were divided equally into three groups. Two veneering porcelains that are recommended for ZrO? material - Cerabien ZR (CZR), IPS e.max Ceram (EMX) - and one that is recommended for metal ceramics - Super Porcelain AAA (AAA) were assessed. Each group was then further divided into two subgroups (n = 8) according to cooling time (0 or 4 min) after porcelain firing. Specimens were fabricated by veneering the porcelain on the ZrO? disks, after which shear bond testing was conducted. Bond strength differed significantly by cooling time in ZrO?-AAA (P < 0.001) and ZrO?-EMX (P = 0.001) specimens. There was no significant difference in shear bond strength with respect to cooling time in ZrO?-CZR specimens (P = 0.382). The duration of cooling from firing temperature to room temperature may affect the shear bond strength of veneering porcelain to a zirconia material depending on porcelain material used.