Relationship of Flexural Strength and Translucency of Different Ceramics

Objectives: To measure the translucency and biaxial flexural strength of zirconia and lithium disilicate ceramics
Methods: An STL file was designed to prepare twelve specimens of milled ceramic or wax disks, 15.5mm diameter x 1.0mm thick, for four zirconia ceramics: high strength (BruxZir 16 shaded), high translucent (BruxZir Anterior shaded, Katana UTML and STML) and two lithium disilicates (IPS e.max Press HT and LT). Disks were milled, finished and glazed according to manufacturers’ instructions. Translucency parameter (TP) was calculated using a spectrophotometer on black and white backgrounds (B/W) and white and stump shade ND4 backgrounds (S/W). Biaxial flexural strength (BFS) was tested using three-point loading at a crosshead speed of 0.5 mm/min until failure. TP and BFS data were analyzed by ANOVA between materials and Tukey HSD multiple comparison to determine significant differences at p<0.05.
Results: For TP, IPS e.max HT was more translucent using both backgrounds (32.85 for B/W, 15.34 for S/W), while BruxZir 16 was least translucent (19.78 for B/W, 8.83 for S/W). Translucency was similar for BruxZir Anterior and Katana STML. For BFS, BruxZir 16 had the highest strength (995.44 MPa) and e.max HT the lowest (186.75 MPa). No significant differences were found between BruxZir anterior and Katana STML, Katana UTML and IPS e.max LT or IPS e.max LT and IPS e.max HT. TP using both backgrounds was strongly correlated (r=0.99). BFS was inversely corelated with TP using both backgrounds (r=-0.777 B/W and -0.756 S/W).
Conclusions: Lithium disilicate was the most translucent but weakest material, whereas high-strength zirconia was the most opaque and strongest. High-translucent zirconia was more translucent than high strength but less than lithium disilicate. Katana STML and BruxZir anterior had significantly greater strength but lower translucency than Katana UTML. Translucency was negatively correlated with biaxial flexural strength.