Characterization of Lithia-Based Machinable Glass-Ceramic Materials

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.

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 (α = 0.05).

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.

A variety of lithia-based glass-ceramic materials differed substantially across a range of chemical and physical properties.

A range of dental lithia-based glass-ceramic materials exhibited substantial differences in chemical composition, strength, and optical properties of a magnitude expected to influence their clinical performance. The milling of partly crystallized blocks, followed by additional crystallization, almost doubled flexural strength values in comparison to the milling of fully sintered blocks or control materials. At high magnification, machining damage was evident for all materials except for one partially crystallized lithia-based material, which had also exhibited the highest strength.