Reactivity of zirconia with phosphate-bonded investments for hot-pressing

PurposeThe aim of the present study was to investigate the reactivity of zirconia to phosphate-bonded investment on the process of hot-pressing technique.MethodsDisc-shaped specimens, 16 mm diameter and 0.4 mm thick were prepared by cutting and grinding. These specimens were finally sintered. Half of them were sandblasted. The non-sandblasted specimens were used for controls. Both of zirconia discs with and without sandblasting were invested into the three kinds of phosphate-bonded investment. The investments were fired and broken to take out specimens. The biaxial strengths were measured in the way of the biaxial flexural tests according to ISO-6872.ResultsThe biaxial strengths were ranged 762–1200 MPa at the average. The biaxial strengths of sandblasted zirconia discs heated with phosphate-bonded investment were decreased significantly (p < 0.01). SEM and EPMA revealed that the various compounds were observed on the sandblasted specimens. XRD revealed that surfaces of specimens heated with the phosphate-bonded investment showed the formation of phosphate compounds.ConclusionsThe phosphate compounds inhibit stress-induction phase transformation of zirconia and decrease the biaxial strength.