Fracture strength of low translucent and high translucent monolithic zirconia crowns with different thicknesses

Objective. The aim of the study was to examine the fracture strength of fully anatomical monolithic high translucent Y-TZP, yttria-stabilized tetragonal zirconia polycrystal, crowns and to compare them with monolithic low translucent Y-TZP crowns in different thicknesses. Materials and methods. 80 standardized crowns were made out of a master model resembling a first mandibular molar made in composite material; 40 crowns made of Lava Zirconia by 3M ESPE, a monolithic low translucent Y-TZP material, and 40 crowns made of Lava Plus by 3M ESPE, a monolithic high translucent Y-TZP material. In each group ten crowns of the thicknesses 1.0 mm, 0.7 mm, 0.5 mm and 0.3 mm were made. All crowns underwent thermocycling and preload to simulate aging and normal wear. Finally the specimens were placed in a testing jig and underwent load to fracture. Results. No significant difference was found when comparing the two materials. When comparing the materials in each thickness a significant difference was found in the 0.5 mm group where the high translucent YTZ-P had a higher mean fracture strength value. A significant difference was seen between the different thicknesses within both groups. The strength increased with added thicknesses. Conclusions. The low translucent and high translucent monolithic YTZ-P perform equally well. The use of high translucent monolithic Y-TZP could result in more aesthetic results and the minimal invasive preparation could lead to a reduction in biological complications. This could be beneficial for the patient since the results suggest that even a thin restoration sustains reasonable load in an in vitro environment. Clinical studies are needed to confirm this suggestion