EFFECT OF CRYSTALLINE VOLUME FRACTION AND CRYSTAL SIZE ON THE TRIBOLOGICAL PROPERTIES OF LITHIUM DISILICATE GLASS-CERAMICS

Reference	Presenter	Authors (Institution)	Abstract
10-008	Crislaine Cruz	Cruz, C.(State University of Ponta Grossa); Mathias, I.(State University of Ponta Grossa); SENK, M.V.(Federal Institute of Paraná); Serbena, F.C.(State University of Ponta Grossa); de Souza, G.B.(State University of Ponta Grossa);	Glass-ceramics of lithium disilicate (LS2) are widely used as dental prosthetics and dental restorations. Based LS2 glass-ceramics have hardness and translucency similar to that of natural teeth. They have an excellent aesthetics and can be machined or pressed at the ontological clinic. In this study, LS2 glass was prepared by melting and the glass samples were submitted to a double stage heat treatment for nucleation and growth of crystals. Two groups of samples were prepared with different crystal sizes: 4 and 12 micrometers. Crystalline volume fraction was varied from 32% to 98% for the samples with 4 mm crystal size and from 16% to 100% for the samples with 12 mm. A glass sample was used as reference. Tribological properties were studied using a pin-on-disc tribometer with a tungsten carbide sphere in unlubricated condition. Surface and wear tracks profiles were measured using an instrumented nanoindenter. Scanning electron microscopy was used to analyze the morphology and chemistry of the worn surfaces. The specific wear rate was calculated from data of tribological and profile measurements. For the 12 mm crystal size, the friction coefficient decreased slightly with crystallized volume fraction up to 80%. Increasing further the volume fraction, the friction coefficient increased and the 100% crystallized sample had a friction coefficient similar to the glass sample. On the other hand, a small variation in the friction coefficient were observed for samples with 4 mm crystal size as a function of the crystalline volume fraction. The 64 % crystallized sample presented the highest value of friction coefficient. The specific wear rate increased with crystalline volume fraction for both crystal sizes, except for the 100 % crystallized sample and 12 mm crystal size, where it presented a wear rate equals to the glass sample. Investigations are under way to characterize the different mechanisms affecting wear in this glass-ceramic.
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