Effect of Spindle Speed on Microstructure and Flexural Strength of Dental Direct Bio Zirconia

Dental direct block are dental mill blanks made from Yttrium stabilised, presintered and zirconium oxide blanks for the manufacture of dental prostheses. Dental direct presintered blocks with disk-shapede were used to machining the specimens at different rotational speed (10000,20000,40000) r.p.m by After that, the specimens were put through a uniaxial flexure test using balls and loaded in a universal testing machine at a cross-head speed of 0.5 mm/min until they failed. Computer Numerical Control machine (CNC) then sintered at 1600℃. The rotating speed affected the flexural strength, microstructure, crystal phase, and grain size of the studied zirconia. The characterization of samples were conducted using field emission scanning electron microscopy (FESEM) and analyzed with X-ray diffraction (XRD). The results XRD analysis showed the presence of a tetragonal phase in all rotational speeds. The differences in morphology and grain size due to different in rotational speed and grain size increase with increasing the rotational speed about 36%. The best flexural strength was observed at low speed, while Hardness showed little varation (decreasing10%) with increasing rotational speed.