Does the application of surface treatments in different sintering stages affect flexural strength and optical properties of zirconia?

To investigate the influence of surface treatments conducted in presintering and postsintering stages on flexural strength and optical properties of zirconia. Specimens were milled from partially sintered zirconia blocks in different geometries and divided into three main groups as presintered, postsintered, and control groups. Test groups were further divided into three subgroups (n = 10) according to the surface treatments conducted (grinding, Er,Cr:YSGG laser irradiation, air-borne particle abrasion [APA]). Four-point flexural strength (σ) test and Weibull analysis were conducted. Color differences (ΔE00 ) and translucency parameter (TPab ) were calculated with a spectrophotometer. Surfaces of specimens were scrutinized under FESEM. Data were statistically analyzed. Postsintered groups exhibited higher σ values (P < .05). Within all groups, highest and lowest σ values were detected at postsintered and presintered APA groups, respectively (P < .05). All ΔE00 values were above the perceptibility threshold (ΔE00  > 0.8). Higher TPab values were obtained and deeper scratches were observed in presintered groups. Surface treatments performed at postsintering stage had a favorable effect on the flexural strength of all specimens. Surface treatments performed before sintering increased translucency and caused higher ΔE00 values. Surface treatments performed at different sintering stages can alter mechanical and optical properties of zirconia.