Effect of crystallization temperature on the flexural strength of lithium disilicate glass ceramics

This pilot study aimed to compare the flexural strength of Amber Mill CAD to IPS e.max CAD and to determine the impact of different crystallization protocols on the flexural strength of Amber Mill CAD ceramics.

Amber Mill CAD ceramic blocks of a known Vita Classic shade were selected for testing against control IPS e.max CAD blocks of the same shade. Four different translucencies were selected for Amber Mill CAD blocks: high translucency (HT), medium translucency (MT), low translucency (LT), and medium opacity (MO). Two different translucencies were selected for IPS e.max CAD blocks: HT and LT. The partially crystallized blocks were sectioned and placed into six groups for each temperature protocol for a total of 36 samples for Amber Mill CAD and 18 samples for IPS e.max CAD. The samples were sectioned at a thickness of 1.5 mm to simulate the material thickness recommended by the manufacturer for posterior lithium disilicate (LD) crowns. Four crystallization protocols, as recommended by the manufacturer, were used with Amber Mill CAD blocks, and one crystallization protocol was used with IPS e.max CAD blocks. The samples from each group were subjected to 3-point bending test. A two-way analysis of variance (ANOVA) and Tukey pairwise comparison tests were used for statistical analysis and interpretation of collected data.

The mean averages of maximum flexural strength for Amber Mill CAD samples were 269.54 MPa, 280.10 MPa, 277.55 MPa, and 254.16 MPa for HT, MT, LT, and MO, respectively. The mean averages of maximum flexural strength for the IPS e.max CAD samples were 302.99 MPa and 283.49 MPa for HT and LT, respectively. No significant differences in the mean average flexural strength were found between the Amber Mill CAD and IPS e.max CAD blocks (p > 0.05). Further, there were no statistical differences in flexural strength between the four crystallization protocols of Amber Mill CAD (p > 0.05).

Amber Mill CAD shows similar flexural strength to IPS e.max CAD. Further, altering crystallization protocols of the same shade to obtain different translucencies did not affect the flexural strength of Amber Mill CAD.