6.

Inert strength of zirconia after occlusal damage from cyclic contacts with hard sphere of radius r = 3.18 mm, in water. (a) Axial loading of 3Y-TZP bars (Prozyr Y-TZP, Norton, East Granby, CT) with tungsten carbide indenter at two loads shown [55]. (b) Sliding loading on 3Y-TZP discs (Zpex, Heany Dental, Scottsville, NY) with zirconia sphere in mouth-motion machine at relatively low load (data courtesy Marcia Borba and Tomoyuki Okamoto). Data points for specimens on the lower solid lines are failures are from contact sites. Boxes at left axis are strengths of unindented specimens (standard deviation bounds). Abrupt drops in strength after cycling correspond to initiation of cone or other macroscopic cracks from quasiplastic zone.