Optimization of the microstructure of lithium disilicate glass-ceramics for best fatigue resistance

• Grant number: 17/21889-7
• Support Opportunities: Scholarships abroad - Research Internship - Scientific Initiation
• Start date: January 03, 2018
• End date: April 04, 2018
• Field of knowledge: Engineering - Materials and Metallurgical Engineering - Nonmetallic Materials
• Principal Investigator: Edgar Dutra Zanotto
• Grantee: Anelise Simões Sampaio
• Supervisor: Vincenzo M. Sglavo
• Host Institution: Centro de Ciências Exatas e de Tecnologia (CCET). Universidade Federal de São Carlos (UFSCAR). São Carlos , SP, Brazil
• Institution abroad: Universitá degli Studi di Trento, Italy
• Associated to the scholarship: 16/03836-0 - Study of the flexural strength of the lithium disilicate glass ceramic for use as a dental prosthesis, BP.IC

Abstract

The large increase in interest in aesthetic and functional oral aspects has led many people to switch from metal or metal alloys coated with porcelain to fixed ceramic prostheses. As a consequence, there has been a substantial increase in worldwide research involving dental materials in the past few years. In this scenario, a promising candidate for those applications is glass-ceramic prostheses, especially those based on lithium disilicate (LD), since they allow one to combine mechanical resistance with aesthetics due to their high translucency, which results in a similar effect to natural teeth. One of the most important features for dental materials is the fracture strength, for which the best commercial values are approximately 400 MPa [CLAUSEN JO, TARA MA, KERN M., Dent Mater 2010; 26: 533-538.]. However, it was recently shown that other materials could achieve even higher values, above 700 MPa [HÖLAND, W.; RHEINBERGER, V.; APEL, E.; VAN'T HOEN, J. Eur. Ceram. Soc. 2007, 27, 1521-1526.], which demonstrates that it is still possible to improve the 400 landmark. In a recent work developed in our group at UFSCar, i.e., the PhD thesis of Mariana O.C. Villas Bôas, we developed two types of materials, with several different compositions, one for Injection molding and the other for CAD/CAM (computer-aided design/ computer-aided manufacturing). The properties of these prostheses have been analyzed since her doctorate through various techniques, such as Vickers hardness (presenting values as 6.0 GPa), chemical solubility (being lower than recommended by the commercial standards), translucency (presenting different levels, similar to commercial materials) and cytotoxicity (being inert). Now it is important to investigate in detail the mechanical properties of the materials developed by Dr. Villas-Boas. Therefore, in the initial project (developed at UFSCar) we studied the biaxial flexural strength of our material and how variables such as polishing, annealing, and testing device affect the mechanical properties, using samples designed for CAD/CAM. The results were compared with those for the available commercial material. Among all mechanical parameters, the fatigue behavior is a crucial property, since it is the primary cause of failures for dental restorations. Thus, the main goal of this work is to use the conditions already obtained in the doctorate of Dr. Villas Bôas and measure the fatigue strength of the developed material for CAD/CAM with crystals of 5 µm or smaller grain size, having a higher crystallized volume fraction, to investigate which combination guarantees the maximum fatigue resistance. (AU)