Characterization of Lithia-Based Machinable Glass-Ceramic Materials

Objective: Lithia-based glass ceramics lead the indirect single-unit restoration market, but the underlying evidence is dominated by a single material. New materials have been introduced. The purpose was to investigate the elemental composition, elemental oxide composition, as-fabricated surface morphology, as-fabricated flexural strength, color, contrast ratio, and absolute light transmission for a variety of lithia-based glass ceramics. Materials and Methods: Test and control materials included: Amber Direct, Amber Mill, Cerec Tessera, IPS Emax CAD, Enamic, IPS Empress CAD, Initial Lisi, Supriniy PC, and TriLuxe Forte. Inductively coupled plasma-optical emission spectrometry, X-ray fluorescence, scanning electron microscopy, mechanical testing (n = 10), visible light spectroscopy (n = 4), and transmission testing (n = 4) were used to evaluate the above parameters. Where appropriate, ANOVA and multiple comparisons testing were used to determine which of the materials differed from one another (alpha = 0.05). Results: A range of lithia-based glass ceramics exhibited substantial differences in the above parameters. Differences were of sufficient magnitude to have statistical significance (p < 0.05) and clinical importance. Milling partly crystallized blocks, followed by additional crystallization, almost doubled flexural strength values in comparison to milling fully sintered blocks. Differences in a wide range of color parameters, more than sufficient to be obvious to the eye, were measured even though the materials were all the same nominal shade. Conclusions: A variety of lithia-based glass-ceramic materials differed substantially across a range of chemical and physical properties.