Abstract
In recent years, Zirconia-reinforced Lithium Silicate ceramic (ZLS), combining lithium-silicate and zirconia features, has shown to have excellent mechanical and aesthetic characteristics. Thus, the aim of this study was to compare the fracture strength of ZLS single crowns cemented with two different cementation techniques. Twenty crowns were realised and cemented on teeth replicas achieved from an extracted premolar human tooth. The samples were divided into two groups of 10 specimens each, Glass-ionomeric cement (GIC) group and Self-Adhesive Resin Cement (ARC) group. The mechanical test was performed using a universal testing machine. The specimens were then evaluated with a scanning electron microscope (SEM) to identify for all crowns and related abutments the pattern of fracture after the breaking point. The data obtained were statistically analysed. The mean fracture toughness values and standard deviations (±SD) were 2227 ± 382 N and 3712 ± 319 N respectively for GIC and ARC groups. In fact, t-test showed a statistically significant difference between the two groups (p < 0.001). Moreover, the SEM results demonstrated portions of abutments still attached to the crown fragments in the ARC group, whilst these were not present in the GIC group. Within the limitations of this study, these results suggest the use of adhesive cementation for ZLS crowns, which significantly increase the compressive strength of ZLS restorations compared to GIC.
Highlights
Traditional methods and metal ceramic restorations used for many years have been an acceptable combination of both mechanical and aesthetic characteristics and proven long term of follow-up [1,2], new aesthetic materials have been made available over time, showing increased aestheticMaterials 2020, 13, 2012; doi:10.3390/ma13092012 www.mdpi.com/journal/materialsMaterials 2020, 13, 2012 and mechanical properties [3,4,5]
It is composed of 65 vol% lithium disilicate, small needle-shaped crystals (3–6 μm × 0.8 μm) inserted in a glass matrix, with a 1 vol% porosity [6,7], showing advantageous mechanical characteristics (flexural strength: 350 MPa; fracture toughness (KIC): 3.3 MPa·m1/2 ; heat extrusion temperature: 920 ◦ C
In relation to mechanical characteristics, glass ceramics have basic limitations which discourage their use in some evaluated clinical situations
Summary
Traditional methods and metal ceramic restorations used for many years have been an acceptable combination of both mechanical and aesthetic characteristics and proven long term of follow-up [1,2], new aesthetic materials have been made available over time, showing increased aestheticMaterials 2020, 13, 2012; doi:10.3390/ma13092012 www.mdpi.com/journal/materialsMaterials 2020, 13, 2012 and mechanical properties [3,4,5]. Lithium disilicate represents a good compromise in terms of optical and mechanical characteristics. It is composed of 65 vol% lithium disilicate, small needle-shaped crystals (3–6 μm × 0.8 μm) inserted in a glass matrix, with a 1 vol% porosity [6,7], showing advantageous mechanical characteristics (flexural strength: 350 MPa; fracture toughness (KIC): 3.3 MPa·m1/2 ; heat extrusion temperature: 920 ◦ C and thermal expansion coefficient (CTE): 10.6 + 0.25 ppm/◦ C) [8]. The glass ceramics, due to their inherent translucent characteristics and high optical properties, represent a valid alternative to the polycrystalline ceramic materials [3]. In relation to mechanical characteristics, glass ceramics have basic limitations which discourage their use in some evaluated clinical situations
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