Surface properties of a new lithium disilicate glass-ceramic after grinding

Larissa Natiele Miotto,Mariana De Oliveira Carlos Villas-Bôas,Lígia Antunes Pereira Pinelli,Eduardo Bellini Ferreira,Edgar Dutra Zanotto,Laiza Maria Grassi Fais

doi:10.1007/s10856-021-06592-w

Abstract

This study aimed to evaluate the effect of grinding on some surface properties of two lithium disilicate-based glass-ceramics, one experimental new product denominated LaMaV Press (UFSCar-Brazil) and another commercial known as IPS e-max Press (Ivoclar), in the context of simulated clinical adjustment. Discs (N = 24, 12 mm in diameter) were separated into four groups: LaMaV Press with no grinding (E), LaMaV Press after grinding (EG), IPS e-max Press with no grinding (C), and IPS e-max Press after grinding (CG). A 0.1-mm deep grinding was carried out on EG and CG samples (final thickness of 1.4 mm) using a diamond stone in a low-speed device. The E and C samples had the same thickness. The effect of grinding on the sample surfaces was evaluated by X-ray diffraction, mechanical and optical profilometry, scanning electron microscopy, goniometry, and Vickers hardness. The mean roughness (Ra) was evaluated by Kruskal–Wallis and Student–Newman–Keuls statistics. The surface energy (SE) by the sessile drop method and Vickers hardness (VH) were analyzed using two-way ANOVA. The Ra medians were E = 1.69 µm, EG = 1.57 µm, C = 1.45 µm, and CG = 1.13 µm with p = 0.0284. The SE and VH were similar for all materials and treatments. Grinding smoothed the surfaces and did not significantly alter the hardness and surface energy of both LaMaV Press and IPS e-max Press. These glass-ceramics presented similar surface properties, and clinical adjustments can be implemented without loss of performance of both materials.A grinding standardization device developed that allowed to control the amount of grinding, the speed of rotation speed and the force exerted on the samples.

Highlights

Lithium disilicate (LS2) glass-ceramics were introduced in dentistry 20 years ago [1]
There is no minor crystalline phase for a good approximation besides those values shown, which could impair the results presented below
Even though the main crystalline phase has a lathed shape in both materials, the crystals in the LaMaV Press are larger, randomly oriented, and with a broader size distribution than those in the IPS e-max Press, which are partially aligned

Summary

Introduction

Lithium disilicate (LS2) glass-ceramics were introduced in dentistry 20 years ago [1]. When the parent glass of these materials is conveniently heated, a lithium phosphate nanophase (Li3PO4) precipitates and acts as a catalyst for the heterogeneous nucleation of lithium metasilicate (LS), concurrently with the formation of LS2 crystals [2]. The final microstructure comprises ~70 vol% crystalline phases, being LS2 the primary phase [3,4,5]. These LS2 glass-ceramics are produced by melting a mixture of chemicals and quenching it to form a glass, which is subsequently heat-treated for controlled crystallization [3]. A precursor material consisting of partially crystallized glass is heated to achieve a suitable viscosity and injected into a die in a class of such glass-ceramics formed by injection molding. It is cooled down to some extent, but kept above its glass transition for further crystallization

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