Strength and Translucency of Four Commercial Chairside Zirconias

Objectives: To examine the strength and translucency of four zirconia materials used in the CEREC^® milling unit
Methods: Four groups (N=10) of zirconias discs (14 mm diameter x 1 mm thick - post-firing) were milled using as Cerec^® InLab: Group 1: Katana^TMSTML (Kuraray Noritake Dental, Inc); Group 2: e.max^®ZirCAD MT Multi (Ivoclar Vivadent Inc.); Group 3: Lava^TM Esthetic (3M^TM ESPE) and Grou p4: e.max^®ZirCAD LT (Ivoclar Vivadent Inc.).
The un-sintered discs were polished through 1200 grit SiC. Materials were sintered according to the manufacturers' schedule.

Specimens were measured using a Hunter Lab UltraScanVIS Spectrophotometer with standardized white and black backgrounds using glycerin. Yxy values were obtained for each disc specimen. The contrast ratio was calculated by CR= Y_black/Y_white.

The disc specimens were loaded in a piston-on-three ball fixture detailed in ISO 6872 and loaded at a rate of 0.5 mm/minute. The strength values were calculated by:

σ = -0.2387 P(X-Y)/b²

where σ is strength (MPa); P is fracture load (N), X and Y are loading constants derived from loading configuration and Poison’s ratio and b is thickness of specimen.
Results: The flexure strengths and contrast ratios are given in Table 1.
Conclusions: Within the bounds of this study, Group 1 had the lowest biaxial flexure strength while Group 4 had the highest strength. Group 1 has the lowest contrast ratio while Group 4 had the highest value.