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This study aimed to evaluate the effect of air‐abrasion/sintering order and autoclave aging on the surface roughness (Ra), phase transformation, and biaxial flexural strength (BFS) of monolithic zirconia. A total of 104 monolithic zirconia specimens (Katana ML) were divided into eight groups according to airborne‐particle abrasion protocols and hydrothermal aging: control (non‐aged: C‐, aged: C+), air‐abrasion before sintering (BS‐, BS+), air‐abrasion after sintering (AS‐, AS+), and air‐abrasion before and after sintering (BAS‐, BAS+). A steam autoclave was used for accelerated aging, and Ra values were measured with a surface profilometer. All specimens were analyzed by X‐ray diffraction to determine any phase transformation on the zirconia surface. BFS was measured by using the piston‐on‐three‐balls method. Scanning electron microscopy and atomic force microscopy were performed on one specimen per group. BS and BAS groups showed higher Ra values compared with groups C and AS. The aging process significantly increased the monoclinic phase content of all specimens. Lower monoclinic levels were found in AS+ and BAS+ compared with other aged groups. The AS groups exhibited higher flexural strength values relative to control groups, whereas BS groups exhibited significantly lower flexural strength values (p < .05). There was no reduction in flexural strength by using the BAS protocol. Air‐abrasion of zirconia at the pre‐sintered stage only is not recommended in clinical use because of the remarkable decrease in flexural strength.

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