The effect of zirconia sintering temperature on flexural strength, grain size, and contrast ratio. Stawarczyk B(1), Ozcan M, Hallmann L, Ender A, Mehl A, Haemmerlet HÃ¤MMERLET. chhe effect of zirconia sintering temperature on flexural strength, grain size, and contrast ratio. Stawarczyk B(1), Ozcan M, Hallmann L, Ender A, Mehl A, Haemmerlet HÃ¤MMERLET. ch