Roughness and its effects on flexural strength of dental yttria-stabilized zirconia ceramics

Abstract This study evaluated the effect of the surface roughness parameters on the flexural strength of Yttria-partially stabilized zirconia, Y-TZP ceramics: ZrO 2 (3 mol%) or ZrO 2 (5 mol%), as function of different surface finishing protocols: polishing or alumina (Al 2 O 3 ) blasting. Zirconia discs were manufactured by CAD/CAM prototyping and sintered at different temperatures. The specimens were characterized by X-ray diffraction, scanning electron microscopy, biaxial flexural strength test and 3D profilometry. In all specimens tetragonal Y 2 O 3 -ZrO 2 was observed to be the main crystalline phase. The 3D profilometry indicated that alumina blasting of ZrO 2 (3 mol%) increased the roughness R a around 16–26 times as opposed to the polished surfaces, and approximately 38 times for ZrO 2 (5 mol%) specimens when compared to the polished samples. The results of flexural strength indicate that groups of ZrO 2 (3 mol% Y 2 O 3 ) ceramics present a reduction of 21–23% from polished to alumina blasted specimens. In the group of ZrO 2 (5 mol% Y 2 O 3 ) ceramics, a flexural strength reduction of 37.5% was observed. A correlation between flexural strength, failure size and different roughness parameters: R a (arithmetic average of the absolute values of the profile heights over the evaluation length), R z (measure of the ordinates of the five highest peaks and the five deepest valleys along the specimen's length) and PV ( mean values of peak and valley measured in the specimen space) is proposed and indicates that Rz and PV should not be neglected in a systematic evaluation of the surface roughness effect on the bulk mechanical properties of dental ceramics.