Effects of polishing and heat treatment on physical and mechanical properties of lithium disilicate glass-ceramic
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Objectives: A partially crystallized lithium disilicate glass-ceramic material (IPS e.max CAD) with various translucency levels has been developed for laboratory and clinic CAD/CAM applications. Variations in heating cycles and polishing procedures may affect its physical and mechanical properties. The purposes of this study are to evaluate the flexural strength, microhardness and microstructure of IPS e.max CAD subjected to various heat treatments and polishing procedures. Materials and methods: Untreated IPS e.max CAD blocks of HT, MO, and LT translucency types were sectioned into 381 bars of 4mm x 2mm x 15mm (127 bars for each type) using a diamond saw. Eight heat treatment scenarios were tested: untreated; standard (IPl), fast (IP3), and superfast (IP5) cycles in Ivoclar Programat furnace; simulated standard (VPl), fast (VP3), and superfast (VP5) cycles in Vita Vacumat furnace; and an additional superfast cycle fired by Ivoclar Vivadent company (C-IP5). Specimens were divided into 24 groups and subjected to assigned heating scenarios. All furnace-fired specimens were further divided into polished and non-polished subgroups. Polishing was done for the said subgroups on one side of the specimen. Flexural strength was detemined using a 10 mm-span three-point-bending test on an Instron machine at a crosshead speed of 0.5 mm/min with a lkN load cell. From each subgroup, speciimens with lowest and highest flexural strengths were selected for microhardness test using a Knoop diamond pyramid indenter at a load of 100g. Specimens were also evaluated under an SEM at their fractured and polished surfaces. Three rectangular specimens each (12.5mm x 14.6mm x 2.0 mm) were prepared from untreated HT, MO, and LT blooks and subjected to standard (IPl), fast (IP3), and super fast (IP5) heat cycles in Ivoclar furnace, respectively. Illuminance readings were obtained using a GretagMacbath color spectrophotometer and a Vita shade scanning device. Statistical analyses were conducted using one-way ANOVA, Tukey post hoc tests at p=0.05, and Weibull analysis. [TRUNCATED]
PLEASE NOTE: This work is protected by copyright. Downloading is restricted to the BU community: please click Download and log in with a valid BU account to access. If you are the author of this work and would like to make it publicly available, please contact firstname.lastname@example.org.Thesis (MSD) --Boston University, Goldman School of Dental Medicine, 2011 (Department of Restorative Sciences and Biomaterials).Includes bibliography: leaves 125-132.
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