Translucency Parameter and Biaxial Flexural Strength Measurement of Lithium Disilicate Materials.

Objectives: To measure translucency parameter, biaxial flexural strength, and microstructure of various lithium disilicate materials used for dental restorations.
Methods: CAD/CAM lithium disilicate glass-ceramic blocks: IPS e.max CAD (Ivoclar Vivadent), Cerec Tessera (Dentsply Sirona), and Amber Mill (HASS BIO America) were used (shade A2, HT, and MT). Blocks of each material were milled (PrograMill PM7, Ivoclar Vivadent) into cylinders (diameter = 14 mm) and cut using circular sectioning saw (IsoMET 1000 Precision Saw, Buehler) into disc-shaped specimens (thickness = 1.00 ± 0.05 mm) (n=5/group). They were hand polished to 1200 grit with SiC paper under water lubrication. The translucency parameter of uncrystallized (except IPS e.max CAD) and crystallized samples were tested against a white and black background (with glycerin gel) using a spectrophotometer (UltraScan VIS, HunterLab). A biaxial flexural strength test was performed following ISO 6872. Each specimen was placed centrally on three hardened steel balls (with a diameter of 3.2mm, positioned 120° apart on a support circle with a diameter of 10mm). The maximum load to fracture failure of each specimen was recorded using a universal testing machine (Instron, Model #33R4204 Norwood, MA) with a crosshead speed of 1mm/min. SEM analysis was also done.
Results: Data were analyzed using one-way ANOVA and post hoc Tukey’s HSD statistical analysis (p= 0.05). Materials with significantly different values are denoted with different superscripts. Under SEM imaging, IPS e.max CAD demonstrated long spindle shape crystals. Tessera and Amber Mill contained finer platelet-shaped crystals and Tessera contained a virgilite phase.
Conclusions: Once crystallized, all lithium disilicate materials produced similar translucency despite the smaller crystalline microstructure seen in Tessera and Amber Mill. Despite the presence of an additional virgilite phase in Tessera, it did not produce increased biaxial flexural strength.