Y-TZP CERAMICS ( yttria stabilised tetragonal zirconia polcrystals )

Y-TZP ( yttria stabilized tetragonal zirconia polycrystals )  is  composed of many very small particles (tetragonal crystallites metastable at room temperature <0.5 micrometer,) without any glassy phase at the crystallite border and. In the stress field of propagating cracks the matrix pressure on the tetragonal particles of Y-TZP is reduced by tensile stresses and a tetragonal to monoclinic  phase transformation occurs by a diffusionless shear process at near sonic velocities, similar to those of the martensite formation in quenched steel. The resulting volume expansion (3-5%) and the shear stresses formed in the particles affect martensitic transformation and pressure tensions on the matrix, opposing the opening of the crack and increasing the energy necessary for further crack growth.

Because of its high strength and resistance to crack propagation this can be used as a material of choice for posterior F.P.D s  

REF : Dental Materials (2004) 20, 655-662