Analyzing the interfacial strength of multi-layer zirconias

Sonaj J. Vardhaman

Vardhaman, Sonaj J, Lim, ChekHai, Zhang, Yu
University of Pennsylvania School of Dental Medicine, Department of Preventive and Restorative Sciences


The use of multi-layered CAD/CAM zirconia is rapidly increasing in dentistry. Thus, a comprehensive investigation of the effect of multi-layering fabrication techniques and variation in strength between different layers is required. Each of the multi-layer zirconia tested is unique in its composition and properties


Four multi-layer zirconia samples with different compositions were investigated (n = 120). To measure the flexural strength, bar-shaped specimens (16x2x1.5mm) were obtained from enamel, dentin and cross-section layers. The bars were obtained by cutting pre-sintered CAD-CAM zirconia blocks from (1) IPS ZirCAD MULTI (MULTI), (2) Katana Ultra Translucent Multi-Layer (UTML), (3) Super Translucent Multi-Layer (STML), and (4) Multi-Layer (ML). Samples were sintered, and polished to a 1µm finish. Further a four-point flexure test was performed using the universal testing machine (1.0 mm/min). Fractographic-features were analyzed using optical microscope and SEM.


The mean flexural strength significantly varied between layers for MULTI- dentin layer had the highest strength, while enamel and cross-sectional layers exhibited lower but similar strength. There was no difference between the enamel and dentin layers of UTML, STML and ML; however, the strengths of cross-sectional samples were ∼30% lower than enamel and dentin layers. The fracture site for cross-sectional samples were observed mainly in enamel/ transition-1 interface for all groups tested.


The layered manufacturing technique compromises the bulk strength of zirconia, in comparison to individual layer strength. This is consistent with the fact that fracture site in cross-sectional multi-layer beams was located at the interface of enamel/transition-1.