The effect of repeated firing on hardness and elasticity of fully crystallized computer-aided design/computer-aided manufacturing lithium disilicate ceramics.

Abstract

The aim of this study was to evaluate the hardness and elastic properties of various computer-aided design (CAD)/computer-aided manufacturing lithium disilicate ceramics, including IPS e.max CAD, GC Initial LiSi Block and CEREC Tessera and to assess the impact of repeated firings on these characteristics. Sixty fully crystallized square-plate specimens were generated, 20 for each evaluated material (n = 20), and were subjected to two additional firings. Initially and after each additional firing, hardness and modulus values were measured with a nanoindentation tester. Changes in microstructure and elemental composition were analyzed by field emission scanning electron microscopy and energy-dispersive x-ray spectroscopy. Statistical analysis was conducted in RStudio using linear mixed-effects models, with significance set at α = 0.05. Across all firing cycle protocols, CEREC Tessera specimens exhibited higher Martens hardness values than those of IPS e.max CAD and GC Initial LiSi Block. Firing had the greatest effect on hardness and indentation modulus, with all parameters showing a consistent peak after the first additional firing.